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The problems of painting over concrete and cement mortar
Tarbouriech, M. A.; National Research Council of Canada. Division of
Building Research
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PREFACE
Numerous problems associated with the p a i n t i n g of concrete have been brought t o the a t t e n t i o n of the Division of Building Research s i n c e i t s e a r l i e s t days. That these problems do occur
l a understandable when one r e c a l l s the broad range of concrete materials a v a i l a b l e f o r various purposes which i n t u r n may be painted w i t h any one of s e v e r a l d i f f e r e n t types of p a i n t .
This t r a n s l a t i o n i s of s p e c i a l i n t e r e s t i n t h i s regard and discusses the e f f e c t t h a t such concrete c h a r a c t e r i s t i c s a s
a l k a l i n i t y , moisture and p o r o s i t y can have on the performance of p a i n t s . The r e s u l t s of work t h a t a r e reported on the use of
form s t r i p p i n g a i d s with various p a i n t s a r e of p a r t i c u l a r b e n e f i t . This t r a n s l a t i o n was prepared by M r . D.A. S i n c l a i r of the
N.R.C. t r a n s l a t i o n s t a f f and the Division i s g r a t e f u l t o him f o r making t h i s information a v a i l a b l e .
Ottawa R.F. Legget
NATIONAL RESEARCH CO UNC IL OF CANADA
Technical T r a n s l a t i o n 1142
T i t l e : The problems of p a i n t i n g over c o n c r e t e and cement mortar ( ~ a r a c t e ' r i s t i q u e s des bdtons e t m o r t i e r s de ciment )
Author : M.A. Tarbouriech
Reference: Annalea de l t I n s t i t u t Technique du ~ 8 t i m e n t e t d e s Travaux Publics, ( 1 9 0 ) : 1054-1062, 1963
THE PROBLEMS OF PAINTING OVER CONCRETE AND CEMENT MORTAR
Summary
The p a i n t e r i s mcre and more f r e q u e n t l y confronted w i t h c o n c r e t e and cement mortar s u r f a c e s t o be covered d i r e c t l y w i t h p a i n t p r o d u c t s . This a p p l i e s both t o i n s i d e and o u t s i d e work, and t o o n - s i t e a s w e l l a s p r e f a b r i c a t e d c o n s t r u c t i o n .
These m a t e r i a l s p r e s e n t problems t o t h e p a i n t e r by reason of t h e i r p o r o s i t y , a l k a l i n i t y , moisture c o n t e n t and s u r f a c e s t a t e .
L a b o r a t o r i e s a r e p a r t i c u l a r l y concerned with v a r i a t i o n s of moisture c o n t e n t and t h e danger t h r e s h o l d s , depending on t h e charac- t e r of t h e p a i n t s . They s t u d y t h e p o s s i b l e e f f e c t of s t r i p p i n g pro- d u c t s on t h e s u r f a c e s t a t e and t h e adhesiveness of p a i n t s .
By t a k i n g i n t o account t h e s p e c i f i c p r o p e r t i e s of t h e s e m a t e r i - a l s and t h e l a b o r a t o r y r e s u l t s supplemented by o n - s i t e i n s p e c t i o n s , v a l i d s o l u t i o n s t o most of t h e s e problems a r e a v a i l a b l e t o t h e
p a i n t e r by s e l e c t i o n from t h e v a r i o u s conunercial. products a v a i l a b l e .
Modern c o n s t r u c t i o n p r a c t i c e s l e a d t o t h e c r e a t i o n of ever l a r g e r s u r f a c e s of c o n c r e t e and cement mortar which must be covered d i r e c t l y with p a i n t . These Include smooth o r s t i p p l e d s t u c c o , t r o w e l l e d o r foamed cement, s t r i p p e d con- c r e t e s u r f a c e s , concrete blocks, p r e f a b r i c a t e d p a r t s , and a s b e s t o s cements.
In t h e n o t too d i s t a n t p a s t t h e use of p a i n t s was r e s t r i c t e d t o e x t e r i o r s t u c c o , and involved a l i m i t e d number of f a m i l i a r products which gave more o r l e s s s a t i s f a c t o r y r e s u l t s , mainly s i l i c a t e p a i n t s and o i l emulsion p a i n t s . In t h e i n t e r i o r s of dwellings, cement masonry f i r s t received a c o a t i n g of conven- t i o n a l p l a s t e r , and t h e r e was no p a r t i c u l a r problem concerning t h e choice of p a i n t s t o be used.
We s h a l l f i r s t s t u d y t h e various p r o p e r t i e s of t h e s e n l a t e r i a l s which t h e p a i n t e r must t a k e i n t o account. A second p a r t of t h e paper w i l l t h e n d e a l w i t h t h e l a b o r a t o r y r e s e a r c h c a r r i e d o u t on t h e a e m a t e r i a l s , and f i n a l l y we s h a l l review t h e main t y p e s of p a i n t s which w i l l s a t i s f y t h e requirements of t h e m a t e r i a l s .
P r o p e r t i e s of Concrete and Cement Mortars
We s h a l l d e a l i n p a r t i c u l a r w i t h t h e i r p o r o s i t y , a l k a l i n i t y , moisture c o n t e n t and s u r f a c e c o n d i t i o n ; i n a d d i t i o n , we s h a l l t a k e up s p e c i a l a p p l i c a - t i o n s , e . g . heated c e i l i n g s , where t h e temperature may have a c o n s i d e r a b l e e f f e c t on t h e p a i n t s .
Poros i t y
A i l t h e s e m a t e r i a l s a r e porous, b u t a s b e s t o s cement h a s a g r e a t e r p o r o s i t y t h a n cer~ient niortars and c o n c r e t e s , b u t n o t a s g r e a t a s c e l l u l a r c o n a r e t e
.
I n a given cement o r c o n c r e t e u n i t t h e p o r o s i t y v a r i e s from p l a c e t o p l a c e , and t h i s may r e s u l t i n p a r t i a l s c a l l n g of t h e p a i n t where subsequent a b s o r p t i o n o f nioisture o c c u r s . T h i s happens i n a s b e s t o s cement p a n e l s even when t h e y a r e p a i n t e d on both s i d e s while t h e u n p r o t e c t e d edges a r e i n c o n t a c t
w i t h o r c l o s e t o s t r u c t u r a l beams l a d e n w i t h m o i s t u r e . The a s b e s t o s f i b r e s e x e r t a w i c k - l i k e e f f e c t and t r a n s p o r t t h e nloisture. Under t h e s e c o n d i t i o n s imperlneable c o a t i n g s cannot be used. The a b s o r p t i o n by t h e m a t e r i a l should be reduced and c o n t r o l l e d w i t h t h e a i d of a s u i t a b l e s e a l e r .
In t h e c a s e of c e l l u l a r c o n c r e t e , s t r u c t u r e n e c e s s i t a t e s t h i c k c o a t i n g
w i t h s p e c i a l cement p a i n t s having a h i g h f i l l e r c o n t e n t . A l k a l i n i t y
-
A l l cement based m a t e r i a l s show a s t r o n g b a s i c r e a c t i o n due t o t h e
p r e s e n c e of f r e e lime. T h e i r a l k a l i n i t i e s on t h e pII s c a l e range froin 7 t o 14.
A l k a l i n i t y i s e s p e c i a l l y dangerous when t h e s u p p o r t ( c o n c r e t e s u b s t r a t e )
i s green and nioiat. Over a c o ~ n p a r a t i v e l y lo n g time, depending on t h e I n d i v i d - u a l c a s e , i t s chemical reactivity d e c r e a s e s . I n p a r t i c u l a r , v e n t i l a t i o n and p o r o s i t y o f t h e m a t e r i a l g r e a t l y f a v o u r t h e c a r b o n a t i o n of t h e f r e e lime, whereas c l o s e s t a c l t i n g i n p o o r l y v e n t i l a t e d p l a c e s i s d e t r i m e n t a l t o t h i s n a t u r a l n e u t r a l i z a t 1 . o n .
Sometimes a d d i t i o n s of a l k a l i n e p r o d u c t s f o r v a r i o u s p u r p o s e s ( a n t i f r e e z e , w o r k a b i l i t y a i d s , e t c . ) i n c r e a s e t h e a l k a l i n i t y of t h e m a t e r i a l and a r e
d e t r i m e n t a l t o i t s n a t u r a l n e u t r a l i z a t i o n . Aobcstos cement, f o r example,
m a i n t a i n s a high and prolonged a l k a l i n e r e a c t i o n , d e s p i t e i t s s m a l l t h i c k n e s s . T h i s a g g r e s s i v e chemical c h a r a c t e r p r o h i b i t s t h e u s e of c e r t a i n p a i n t s , e s p e c i a l l y t h o s e c o n t a i n i n & d r y i n g o i l s t h a t a r e e a s i l y s a p o n i f i e d , e x c e p t on well-aged, very d r y and well-carbonated s u r f a c e s . G e n e r a l l y speaking,
n e u t r a l i z a t i o n should be promoted:
( a ) by a s u i t a b l e a c i d s o l u t i o n followed by c a r e f u l r i n s i n g . T h i s method i s always v e r y dangerous;
( b ) with rna~;nesium o r z i n c f l u o s i l i c a t e s o l u t i o n s of v a r i a b l e s t r e n g t h . It i s p r e f e r a b l e t o u s e a neutralizing s u b s t a n c e wherever t h e r e i s any
doubt about t h e n e u t r a l i t y of t h e m a t e r i a l .
lie s h a l l s e e l a t e r t h a t t h e r e i s a range o f p r o d u c t s rvhich can be used t o p a i n t cement inortarn and c o n c r e t e s w i t h o u t r e ~ a r d t o - t h e i r a l l t a l i n i t y
.
Moisture c o n t e n t
-
The moisture c o n t e n t v a r i e s depending on t h e c h a r a c t e r of t h e a a r e g a t e s , t h e p o r o s i t y of t h e m a t e r i a l and i t s age. It i s t h e moisture c o n t e n t which enhances t h e a l k a l i n i t y of t h e c o n c r e t e s u b s t r a t e and promotes s a p o n i f i c a t i o n of p a i n t s with a o i l b i n d e r base.
In
the s a t u r a t e d s t a t e t h e s e m a t e r i a l s mayhave mol,sture c o n t e n t s normally between 6 and 12$, d i s r e g a r d i n g c e l l u l a r con- c r e t e and a s b e s t o s cement, i n which t h e moisture c o n t e n t may c o n s i d e r a b l y exceed t h e s e f igux'es.
A s i n t h e case of a l l porous m a t e r i a l s , t h e moisture c o n t e n t i s r e s p o n s i - b l e f o r a l a r g e nwnber of p a i n t f a i l u r e s .
Various p i e c e s of equipment based on d i f f e r e n t p r i n c i p l e s enable us t o e s t i m a t e t h e moisture c o n t e n t of porous m a t e r i a l s . T h e i r une i s g e n e r a l l y t h e p r e r o g a t i v e of t h e l a b o r a t o r y t e c h n i c i a n . However, t o some e x t e n t , t h e
experienced p a i n t e r i s a b l e t o d e t e c t an i n s u f f i c i e n t l y d r y s u r f a c e by v a r i o u s r u l e s of thumb ( c o l d t o t h e touch, l a c k of hardness, t h e s u l p h u r match t e s t , where t h e match w i l l l i g h t o n l y on d r y s u r f a c e s , e t c . ) . On cement o r c o n c r e t e no e m p i r i c a l t e s t i s p o s s i b l e , because n o t h i n g outwardly d i s t i n g u i s h e s a dry base from a 1:101st one.
The age of t h e m a t e r i a l i s no l o n g e r important i n t h i s r e s p e c t and we have seen c o n c r e t e s which had been placed e i g h t e e n months and more on which f a i l u r e s occurred with c e r t a i n t y p e s of p a i n t , whereas n o t h i n g would have
happened on p l a s t e r s of t h e same age, f o r t h e simple r e a s o n t h a t t h e c o n c r e t e s i n q u e s t i o n s t i l l showed c o n s i d e r a b l e moisture c o n t e n t on i n s p e c t i o n , Standard p l a s t e r c o a t s i n normal environment a r e p e r f e c t l y d r y l o n g b e f o r e e i g h t e e n months have passed. I n t h i s connection i t should be borne i n nllnd t h a t cured c o n c r e t e s l a b s do n o t l o s e t h e i r moisture by t h e p r o c e s s of c u r i n g , which is
intended only t o a c c e l e r a t e t h e i r s e t t i n g and p e r m i t immediate h a n d l i n g . Surface s t a t e
The adhesion of p a i n t s obviously depends on t h e c o n d i t i o n of t h e s u r f a c e . This may be s t a t e d a s a g e n e r a l r u l e of p a i n t i n g r e g a r d l e s s of t h e m a t e r i a l employed
.
Stuccos and c o n c r e t e s which e x h i b i t a rou@ s u r f a c e g r e a t l y f a v o u r t h e adhesion of c o a t s of p a i n t s , whereas mortars placed i n t o smooth forms (plywood, s h e e t m e t a l ) e x h i b i t very smooth s u r f a c e s , except f o r t h e entrapped a i r voids t h a t cannot be t o t a l l y avoided. These s u r f a c e s a r e very s a t i s f a c t o r y from t h e p o i n t of view of planeness, b u t p a i n t i n g them p r e s e n t s d i f f i c u l t i e s .
Such c a s t u n i t s can a l s o e x h i b l t niore s u p e r f i c i a l l o c a l flaws, due t o a g g r e g a t e s e g r e e a t i o n s and nol-mally porous l a i t a n c e accumu1.a t i o n s
.
These tend t o show a l a c k of cohcslon and powderiness of t h e m a t e r i a l i n q u e s t i o n .S t r i p p i n g compounds c a n a g g r a v a t e t h i s phenomenon, b u t t h e e n t i r e blame cannot be a t t r i b u t e d t o t h e form o i l .
On t h e o t h e r hand, t h e t e c h n i q u e o f smoothing c o n c r e t e s u r f a c e s by means of a wash, o r cement g r o u t , 1 . e . cement mixed w i t h an e x c e s s o f w a t e r , r e s u l t s
I n phenomena s i m i l a r t o t h e f o r e g o i n g .
These powdery p a r t s , without any c o n s i s t e n c y whatsoever, a r e g e n e r a l l y l i f t e d by t h e p a i n t s a p p l i e d t o them, and it i s wrong t o speak of removal o f t h e s u r f a c e m a t e r i a l , because t h e f l a k e s of p a i n t t a k e cement ponder, sand o r f i n e a g g r e g a t e s w i t h them.
The p a i n t e r should e l i m i n a t e t h e s e powdery elements, n o t w i t h a w i r e brush, a s i s most o f t e n done, b u t r a t h e r w i t h a wet sponge, which w i l l a t t h e same time remove any form o i l from t h e s u r f a c e .
S p e c i a l a p p l i c a t i o n s : heated c e l l i n
Concrete s l a b s c o n t a i n i n & h o t w a t e r c o i l s c o n s t i t u t e a s t r u c t u r a l u n i t p o s s e s s i n g t h e f a c t o r of " h e a t " I n a d d i t i o n t o t h e u s u a l c h a r a c t e r i s t i c s . Heat enhances t h e a l k a l i n i t y of moist m a t e r i a l and produces t r a n s f e r s of mass.
I n o t h e r words, w a t e r , i n i t s l i q u i d and vapour p h a s e s , m i g r a t e s away from t h e warmer s e c t i o n s t o t h e c o l d e r o n e s . These t r a n s f e r s of mass may c a u s e b l i s t e r i n g and detachment of t h e s u r f a c e p a i n t . A t t h e same t i n e t e m p e r a t u r e d i f f e r e n c e s i n s p a c e and t i m e , owing t o t h e expansions and c o n t r a c t i o n s t h u s brought a b o u t , s e t up f a t i g u e and a g i n g s t r e s s e s which t e n d t o l i f t t h e p a i n t . These phenomena can be of c o n s i d e r a b l e magnitude i f t h e c o i l s a r e p o o r l y
placed i n t h e s l a b , and i f c e r t a i n elements, because of t h i s , a r e v e r y c l o s e t o t h e s u r f a c e . I n some c a s e s i t i s p r a c t i c a l l y i m p o s s i b l e t o p a i n t w i t h o u t f i r s t a p p l y i n g a t h i c k s u r f a c e p l a s t e r .
Laboratory Experiments
I n view of t h e p o s s i b l e f a i l u r e s n o t e d , we wished t o c h a r a c t e r i z e t h e adhesion of v a r i o u s p a i n t i n g systems a s a f u n c t i o n of t h e f a c t o r s which a p p e a r t o u s t o be most important a t t h e p r e s e n t t i m e , namely m o i s t u r e c o n t e n t and s u r f a c e c o n d i t i o n .
Adhesion i s a tenuous, almost I n t u i t i v e concept which i s g e n e r a l l y determined by chequering on a non-porous, e . g . m e t a l l i c , s u r f a c e s . By s c r a t c h i n g a g r i d down t o t h e s u b s t r a t e , we produce s m a l l s q u a r e s of p a i n t which f l a k e o f f more o r l e s s , dependin2 on t h e t e n a c i t y of t h e c o a t i n s . The a d h e s i o n I s s a i d t o be good when t h e paLnt does n o t f l a k e o f f a t a l l , even when we t r y t o remove t h e s m a l l p a i n t s q u a r e s e i t h e r w i t h t h e r"ingcrna1ls o r by a p p l y i n g Scotch t a p e t o t h e g r i d . T h i s method, which Is o n l y q u a l i t a t i v e
and depends e s s e n t i a l l y on t h e s c r a t c h i n g instrument and t o some e x t e n t on a p e r s o n a l f a c t o r , f a i l s completely i n t h e c a s e of porous s u b s t r a t e s , r e g a r d - l e s s of t h e i r compactness.
We a r e a t p r e s e n t developing a more o b J e c t i v e , q u a n t i t a t i v e method I n
t h e l a b o r a t o r y . Thio may be described a s f o l l o w s ( ~ i g . 1):
A c i r c u l a r m e t a l p e l l e t i s glued w i t h a s u i t a b l e a d h e s i v e t o t h e f i l m of p a i n t t o be t e s t e d . The choice of an a d h e s i v e , of course, i s v e r y important, because a t a l l c o s t s t h e p a i n t must not be a f f e c t e d , 1 . e . t h e a d h e s i v e must n o t r e a c t w i t h t h e p a i n t . We g e t s a t i s f a c t o r y r e s u l t s by 11sing epoxy r e s i n
g l u e s without a s o l v e n t . The g l u e and i t s c a t a l y s t s a r e mixed a t t h e time o f application and t h e p e l l e t i s glued t o t h e c o a t i n g by means of t h i s mix- t u r e . The s u r f a c e t h u s glued i s detached from t h e surrounding p a r t s by means of a sharp n a i l . A dynamometer i s f i t t e d t o t h e p e l l e t by means of a threaded r o d . The glued c o a t i n g i s t h e n s t r e s s e d by p u l l i n g f o r c e s normal t o t h e
s u r f a c e . The dynamometer n e e d l e shows t h e f o r c e i n kilograms as i t develops up t o t h e tlLi;~c of r u p t u r e . The h i g h e s t f i g u r e o b t a i n e d a t t h e i n s t a n t of r u p t u r e i s recorded. The r e s u l t can be converted t o :kg/cm2, and i n t h i s way c h a r a c t e r i z e s t h e adhesion of t h e p a i n t t o t h e s u p p o r t .
Experience shows t h a t t h i s f i g u r e , which i s v a r i a b l e , i s p r a c t i c a l l y always g r e a t e r t h a n 1 kg/cm2 when t h e adhesion of t h e p a i n t t o t h e s u b s t r a t e
i s sat:Lsfastory. The t e s t s , of course, a r e always r e p e a t e d a t l e a s t t h r e e times, and a n average r e s u l t i s r e c o r d e d . It l o a l s o p o s s i b l e by t h i s method t o determine whether t h e r u p t u r e t a k e s p l a c e between d i f f e r e n t l a y e r s of t h e c o a t i n g , o r I f t h e l a t t e r i s detached from t h e s u b s t r a t e without modifying i t , o r if t h e f o r c e s of adhesion of t h e c o a t i n g exceed t h e m a t e r i a l t o which t h e p a i n t i s a p p l i e d , which sometimes b r e a k s w i t h i n t h e f i l m . We have
obaerved r u p t u r e s w i t h i n a s b e s t o s cement, f o r example, i n c a s e s where t h e p a i n t could not be detached from t h e s u p p o r t .
F i r s t experiment
-
on form o i l sSome small s l a b s of c o n c r e t e measuring 20 cm x 20 cm x 2 cm were poured
from a mortar made up as follows:
S e i n e c h i p p i n g s
5
t o 10 ...87 0 kg Sand 0 t o 5...910 kg Cement C . P . A . C . . . 3 0 kg...
Water added t o t h e d r y m a t e r i a l s 205 kg
So f a r t e n products have been used t o l u b r i c a t e t h e m e t a l moulds, f i v e of them being non-emulsioned o i l s and t h e o t h e r f i v e having t h e form of aqueous emulsions, i n some c a s e s mixed a t t h e time of u s e . Three t y p e s of
specimens were produced. One s e r i e s was obtained without l u b r i c a t i n g t h e moulds, another by l u b r i c a t i n g t h e moulds according t o t h e d i r e c t i o n s of t h e manufacturer, and a t h i r d s e r i e s by u s i n g twice t h e amount of l u b r i c a n t recommended by t h e manufacturer.
A f t e r s t r i p p i n g , t h e specimens were l e f t t o stand i n t h e a i r f o r a mini- mum of one month, a f t e r which t h e exposed f a c e received two c o a t s of p a i n t without priming o f :
-
a g l o s s y g l y c e r o p h t h a l i c p a i n t ; o r-
a g l o s s y isomerised rubber base p a i n t ; o r-
a P l i o l i t e p a i n t ; o r-
a f l a t c h l o r i n a t e d rubber base p a i n t ; o r-
an o i l base emulsion p a i n t ; o r-
a polyvinyl a c e t a t e emulsion p a i n t .A l l t h e painted specimens were l e f t t o s t a n d f o r about two months i n t h e a i r before being t e s t e d .
The following o b s e r v a t i o n s were made:
-
no spontaneous l i f t i n g of t h e p a i n t s was observed;-
t h e r e s u l t s of t h e s t r e s s t e s t s a s known so f a r a r e a l l very s a t i s - f a c t o r y .The following i s a n example of t h e r e s u l t s obtained w i t h one of t h e s e o i l s :
I n t h e m a j o r i t y of c a s e s t h e p a i n t t o r e o u t s u r f a c e elements from t h e c o n c r e t e .
Incomplete a s t h e y a r e , t h e s e r e s u l t s a r e r a t h e r s p e c t a c u l a r and show t h a t t h e good q u a l i t y p a i n t s normally employed i n c o n s t r u c t i o n work have n o t merely s a t i s f a c t o r y adhesions on cement mortars, but exceed t h e v a l u e s t h a t might have been expected a p r i o r i . I t may a l s o be noted t h a t t h e v a r i a t i o n i n breaking l o a d s bore no r e l a t i o n t o t h e presence o r absence of form o i l .
The experiment i s being continued and t h e complete r e s u l t s w i l l be r e p o r t e d a t a l a t e r d a t e .
P a i n t s used
Glossy g l y c e r o p h t h a l i c
Glossy isomerised rubber base ~ l i o l i t e F l a t c h l o r i n a t e d rubber base O i l base emulsion Polyvinyl a c e t a t e emulsion 'labs poured without Om o i l
9
kg/cm2 1 4 . 5 kg/cm2 12.5 kg/cm2 12 kp;/cm2 8 . 5 kg/crn not measured S l a b s poured w i t h double a p p l i c a t i o r : ~ of form o i l13
kg/cm 11 kg/cm2 11 kg/cm 11 kg/cm 8 . 5 k g / c m 2 16 kg/cm2Second experiment
-
on t h e e f f e c t of m o i s t u r e c o n t e n t-
The t e s t s were conducted a s f o l l o w s :The small c o n c r e t e s l a b s were poured, without t h e u s e of s t r i p p i n & : compounds, from a mortar made up a s f o l l o w s :
i
Seine sand 0 t o 5 : t h r e e p a r t s by weightA mortar 1-3 cement C . P . A . C . : one p a r t by weight r a t i o of water t o cement : 0,64
The dimensions of t h e s l a b s were approximately t h e same a s t h o s e used i n t h e f o r e g o i n g experiment. They were kept s a t u r a t e d w i t h m o i s t u r e f o r two t o t h r e e weeks.
The f a c e s and edges were p a i n t e d , a f t e r which t h e specimens were d r i e d c a r e f u l l y t o t h e " d e s i r e d " m o i s t u r e c o n t e n t . A c t u a l l y , i n one s e r i e s of t e s t s t h e specimens a r e p a i n t e d i n t h e s a t u r a t e d s t a t e , while t h e o t h e r s a r e brought t o p r o g r e s s i v e l y lower d e g r e e s of m o i s t u r e c o n t e n t i n o r d e r t o determine t h e c r i t i c a l p o i n t s below which p a i n t s c u r r e n t l y i n u s e i n t h e c o n s t r u c t i o n i n d u s t r y a r e no l o n g e r s u b j e c t t o f a i l u r e . One c o a t of primer and two c o a t s of p a i n t were a p p l i e d .
The f o l l o w i n g t y p e s of primer a r e employed:
-
adhesive primer;-
primer w i t h a v i n y l emulsion binder;-
primer w i t h a g l y c e r o p h t h a l i c v a r n i s h binder; Five p a i n t s were t e s t e d :-
a g l o s s y g l y c e r o p h t h a l i c p a i n t ;-
a f l a t g l y c e r o p h t h a l i c p a i n t ;-
a g l o s s y i s o ~ n e r i s e d r u b b e r base p a i n t ;-
a f l a t isomerised r u b b e r base p a i n t ;-
a v i n y l emulsion p a i n t .A p r e l i m i n a r y experiment was c a r r i e d o u t on specimens kept a t s a t u r a t i o n ( i n t h e p r e s e n t c a s e 10.6%) and on e n t i r e l y d r y specimens.
I n t h i s i n s t a n c e w e d i d not apply a primer, b u t p a i n t e d t h e specimens d i r e c t l y over t h e mortar, 1 . e . on t h e smooth s t r i p p e d f a c e , w i t h two c o a t s of g l o s s y g l y c e r o p h t h a l i c p a i n t . For t h e f i r s t specimens a bed of wet sand enabled u s t o m a i n t a i n t h e moisture c o n t e n t d u r i n g t h e p a i n t i n g o p e r a t i o n and o n l y t h e f a c e i n c o n t a c t w i t h t h e sand remained u n p a i n t e d .
We found f i r s t of a l l t h a t on t h e wet specimens t h e p a i n t hardened v e r y p o o r l y , while i t s adhesion remained p r e c a r i o u s and t o o s l i g h t f o r measurement by t h e t e a r i n g o f f t e s t s . However, i n t h e c a s e of t h e d r y specimens t h e P a i n t s hardened normally and a p p a r e n t l y gave s a t i s f a c t o r y adhesion, a l t h o u g h we d i d n o t a c t u a l l y measure t h e breaking s t r e s s a t t h i s t i m e .
The two s e r i e s of specimens were exposed under i n f r a r e d lamps I n such a way a s t o o b t a i n a s u r f a c e temperature of 35 t o 40". A f t e r 24 hours1 exposure no f a i l u r e was noted. Water was t h e n d e p o s i t e d on t h e s u r f a c e s exposed t o t h e lamps and caused t h e p a i n t t o c u r l and s w e l l only on t h e wet specimens; nothing happens on a d r y specimen. The experiment i s completed by supplying water a g a i n t o t h e d r y specimens, which a r e a l s o moistened on t h e s u r f a c e , and t h e p a i n t c u r l s and s w e l l s a s i n t h e c a s e of t h e specimens kept c o n t i n u - o u s l y m o i s t .
From t h i s p r e l i m i n a r y experiment i t may be concluded t h a t i n t e r n a l moisture i n t h e c o n c r e t e i s d e t r i m e n t a l t o t h e good adhesion of p a i n t s , and moreover a t t a c k s them and p r e v e n t s t h e i r hardening; b l i s t e r i n g does n o t occur, however, u n l e s s condensations permit t h e formation of a bubble by plugging t h e c a p i l l a r i e s i n t h e p a i n t . A s f a r a s p a i n t a p p l i e d t o d r y mortar i s con- cerned, i t i s s t i l l s e n s i t i v e t o a b s o r p t i o n s of water by t h e m a t e r i a l and w i l l b l i s t e r a s b e f o r e when t h e c a p i l l a r i e s a r e plugged.
Remarks
When we c o n s i d e r t h e s e p r e l i m i n a r y t e s t s t o g e t h e r w i t h f a i l u r e s t h a t have occurred on s i t e , we can a l r e a d y f o r m u l a t e t h e f o l l o w i n g o b s e r v a t i o n s :
( a ) The s t r i p p i n g products normally used have no a p p r e c i a b l e e f f e c t on t h e adhesion of p a i n t s , even when double q u a n t i t i e s a r e a p p l i e d , provided t h e p r e f a b r i c a t e d u n i t s , whether k i l n d r i e d o r n o t , a r e c o r r e c t l y made up; t h e specimens poured i n t h e l a b o r a t o r y prove t h i s , b u t t h e s e a r e i d e a l c o n d i t i o n s r a r e l y r e a l i z e d on t h e J o b . I f s e p a r a t i o n s occur w i t h l a r g e l a i t a n c e o u t - croppings ( l a i t a n c e fomned by cement and e n t r a i n e d by water i s v e r y porous and mechanically weak, and i t s formation can never be completely p r e v e n t e d ) ,
i t s mechanical s t r e n g t h i s s t i l l f u r t h e r diminlshed by t h e presence of form o i l on t h e s u r f a c e .
L a i t a n c e a l o n e i s a poor enough support f o r t h e p a i n t , but when i t i s
accompanied by form o i l i t i s f a t a l . The p a i n t f l a k e s o f f l o c a l l y and t a k e s powdery m a t t e r w i t h i t .
Form o i l s , even when used i n double o r normal p r o p o r t i o n , do not appear dangerous t o well-made u n i t s , but i t may be assumed t h a t w i t h v e r y l a r g e q u a n t i t i e s t h e adhesion of p a i n t s might be s e r i o u s l y reduced.
( b ) Moisture a c t s mechanically t o oppose p e n e t r a t i o n by t h e p a i n t and chemically by modifying i t s b i n d e r , mainly i n t h e c a s e of o i l e s t e r s , by s a p o n i f i c a t i o n o r h y d r o l y s i s . Glossy p a i n t s , g e n e r a l l y , a r e l e s s permeable t o water and w i l l be s u b j e c t t o b l i s t e r i n g , c u r l i n g and s w e l l i n g on s u r f a c e s f r e q u e n t l y s u b j e c t e d t o condensation i n poorly v e n t i l a t e d k i t c h e n s and
Concrete w a l l s w i l l r e t a i n moisture f o r e i g h t e e n months and more; It Is t h e r e f o r e a b s o l u t e l y necessary t o u s e permeable systerns w i t h s l i g h t l y saponi- f i a b l e b i n d e r s , o r e l s e t o u s e a primer c o a t a t l e a s t some t e n t h s of a m i l l l - metre i n t h i c k n e s s , not a simple s u r f a c e f i n i s h , i n which g r e a t t h i c k n e s s v a r i a t i o n s of some m i l l i m e t r e s a t r i g h t a n g l e s t o s l a b j o i n t s of a few t e n s of microns, s e t up heterogeneous s u r f a c e s t a t e s which a r e g e n e r a l l y d e t r i - mental t o t h e adhesion of p a i n t s and superimposed t h e i r e f f e c t s on t h o s e of m o i s t u r e .
On-site i n s p e c t i o n s have shown t h a t c e r t a i n f i n i s h e s comprising f u l l primer c o a t s covered w i t h t h r e e c o a t s of p a i n t , even g l o s s y p a i n t , may be s a t i s f a c t o r y when a p p l i e d t o c o n c r e t e s s t i l l c o n t a i n i n g 55 f r e e w a t e r . Apparently a proper primer t o g e t h e r with t h e i n t e r m e d i a t e c o a t s of p a i n t c o n s t i t u t e s a b a r r i e r o r a brake f o r t h e water beneath, and perhaps a l s o f o r t h e lime i n t h e w a t e r . The danger comes p r i n c i p a l l y from t h e s i n g l e g l o s s y c o a t on a c o n c r e t e which has merely been scraped by t h e p a i n t e r . For p a i n t systems which a r e s e n s i t i v e t o moisture we a r e unable t o g i v e a d e f i n i t e f i g u r e , but t h e t o l e r a b l e minimum of moisture c o n t e n t would appear t o be l e s s than 4$. C e r t a i n a u t h o r s g i v e
37:.
Before concluding t h e p r e s e n t s e c t i o n i t may be h e l p f u l t o r e c a l l t h e a p p a r a t u s which can a s s i s t t h e p a i n t e r i n r e c o g n i z i n g t h e q u a l i t y of t h e
s u b s t r a t e .
P a r a d o x i c a l l y , it i s p r a c t i c a l l y u s e l e s s t o mention t h e u s e of l i t m u s papers o r p e n c i l s , because we can always expect h i g h pH v a l u e s i n cement mortars o r c o n c r e t e , and p a i n t s must be s e l e c t e d a c c o r d i n g l y .
R e s i s t a n c e t y p e moisture meters o r c o n s t a n t d i e l e c t r i c a p p a r a t u s used f o r measuring t h e moisture c o n t e n t of p l a s t e r s can be a p p l i e d h e r e a s w e l l .
P a i n t s t o be Used on Concrete and Cement Mortar
The p a i n t e r has c o n s i d e r a b l e choice of p a i n t s f o r a l l t h e s e m a t e r i a l s , but a s u s u a l it i s wise t o d i s t i n g u i s h between e x t e r i o r and i n t e r i o r work and f i n a l l y c e r t a i n s p e c i a l caseo where t h e s u r f a c e s a r e n o t s u b j e c t e d t o excessive weathering, but which must show a c e r t a i n d u r a b i l i t y , f o r example s t a i r - w e l l s , p u b l i c c o r r i d o r s and passages, and f i n a l l y f l o o r s , which a r e exposed t o p a r t i c u l a r l y heavy wear.
E x t e r n a l s t r u c t u r e s
Usually t h e s e involve rough c o n c r e t e o r s t u c c o . One i n i t i a l o b s e r v a t i o n : c r a c k s g r e a t e r t h a n 100 t o 150 microns cannot be f i l l e d by p a i n t systems, but r e q u i r e t h i c k compounds, p r e f e r a b l y r e i n f o r c e d , capable of a t t a i n i n g 300 t o
The c o a t i n g should n o t be expected t o waterproof porous masonry s u r f a c e s . The p a i n t c a n r e t a r d t h e p e n e t r a t i o n of w a t e r t o a c e r t a i n e x t e n t , b u t c a n n o t c o m p l e t e l y p r e v e n t t h e p a s s a g e of r a i n w a t e r i f t h e masonry i s a v e r i t a b l e s i e v e . Let u s now c o n s i d e r t h e c h o i c e of p a i n t s .
On g r e e n o r new c o n c r e t e , s i l i c a t e p a i n t s c o r r e c t l y a p p l i e d can p r o v i d e a d u r a b l e c o a t , b u t i t must be emphasized t h a t t h e p a i n t e r should make h i s own t r i a l s and u s e t h e p r o d u c t s c a r e f u l l y ; any c a r e l e s s n e s s i n t h i s r e s p e c t c a n l e a d t o d i s a s t r o u s r e s u l t s i n t h e form of premature l i f t i n g o r c r a c k i n g . The r e p a i r of t h i s t y p e of p a i n t p o s e s d e l i c a t e problems f o r t h e p a i n t e r i f he w i s h e s t o r e p a i n t w i t h n d i f f e r e n t t y p e of p r o d u c t . P o l y v i n y l a c e t a t e
p a i n t s , o r b e t t e r a c r y l i c r e s i n p a i n t s , a r e recommended w i t h d i f f e r i n g r e s u l t s . A c t u a l l y , each c a s e i s d i f f e r e n t and something that i s s u c c e s s f u l one t i m e may f a i l on a n o t h e r o c c a s i o n .
On cement o r c o n c r e t e s u r f a c e s t h a t have aged s e v e r a l months emulsion p a i n t s a r e c u r r e n t l y b e i n g a p p l i e d w i t h b i n d e r s r a n g i n g from d r y i n g o i l s t h r o u g h g l y c e r o p h t h a l i c r e s i n s , p l a s t i c i z e d v i n y l r e s i n s t o a c r y l i c r e s i n s . These p a i n t s w i l l l a s t s a t i s f a c t o r i l y on e x t e r i o r s u r f a c e s f o r s e v e r a l y e a r s , provided t h e p r o p o r t i o n of b i n d e r i s a d e q u a t e . 133' way of i n d i c a t i o n o n l y , s i n c e t h i s depends t o a c e r t a i n e x t e n t on t h e f o r m u l a t i o n , t h e d r y weight of t h e b i n d e r should g e n e r a l l y be a t l e a s t 20%. Under t h e s e c o n d i t i o n s , t h e p a i n t s i n q u e s t i o n a r e n o t f l a t , b u t s a t i n . It should be k e p t i n mind t h a t t h e s u b s t r a t e must n o t be powdery. It must be f i r m and c a r e f u l l y f i l l e d w i t h t h e f l u i d i z e d p a i n t , w i t h w a t e r , o r b e t t e r , primed w i t h a d i l u t e r e s i n emul- s i o n . Powdering i s f a t a l t o t h e s e p a i n t s , and t h e more powdery t h e s u r f a c e , o r t h e e a r l i e r powdering o c c u r s , t h e q u i c k e r t h e i r d e s t r u c t i o n . I f t h e s u r - f a c e s a r e c l e a n and t h e p a i n t s a r e of good q u a l i t y t h e a d h e s i o n f o r c e s may r e a c h v a l u e s t h a t a r e r a r e l y l e s s t h a n 10 k{Jcm2.
F l a k i n g i s due p r i m a r i l y t o d e f e c t s i n t h e s u r f a c e s o r t o poor formula- t i o n of t h e p a i n t ( i n s u f f i c i e n t b i n d e r ) .
Among s o l v e n t p a i n t s we must s i n g l e o u t t h e " P l i o l i t e s " . These b i n d e r s have a s t y r e n e - b u t a d i e n e b a s e , d i s s o l v e d i n w h i t e s p i r i t . It i s p e r h a p s t o o soon f o r a f i n a l e s t i m a t e of t h e i r q u a l i t y , but even now t h e y a p p e a r t o p o s s e s s a somewhat g r e a t e r d u r a b i l i t y t h a n t h e emulsion p a i n t s . They a r e p r a c t i c a l l y u n s a p o n i f i a b l e , which i s n o t always t r u e of t h e l a t t e r . F i n a l l y t h e y a r e s a i d t o be c a p a b l e of c o n s o l i d a t i n g d e f e c t i v e s u r f a c e s .
Also among s o l v e n t p a i n t s we should mention t h o s e c o n t a i n i n g o i l v a r n i s h b i n d e r s modified w i t h a r t i f i c i a l r e s i n s , e . g . o i l s o l u b l e p h e n o l s , which were w i d e l y used u n t i l q u i t e r e c e n t l y . These p a i n t s a r e s u b j e c t t o l i t t l e s a p o n i - f i c a t i o n and have t h e g r e a t v i r t u e t h a t t h e y wet t h e s u b s t r a t e s t h o r o u g h l y and a r e v e r y weather r e s i s t a n t . They should r e c e i v e g r e a t e r u s e .
We should a l s o mention, a l t h o u g h t h e y a r e s t i l l not very common, c e r t a i n semi-thick complexes t h a t can be a p p l i e d by t h e p a i n t e r . We r e f e r t o t h e m u l t i - c o a t systems t h a t can a t t a i n t h i c k n e s s e s of 500 microns and more. These
a r e products g e n e r a l l y with a n aqueous emulsion b i n d e r and which c o n t a i n n o t only mineral powders, but a l s o e i t h e r m i n e r a l o r o r g a n i c f i b r e s . The c o a t i n g produces a t r u e s t i p p l e which i s very weather r e s i s t a n t and which can e f f e c -
t i v e l y s e a l c r a c k s .
By a d i f f e r e n t t e c h n i q u e , a semi-thick c o a t i n g can be achieved by d i p p i n g a f i b r e g l a s s s c r e e n , o r b e t t e r a p l a s t i c f a b r i c i n a p l a s t e r , which i s t h e n covered w i t h one o r two c o a t s of an emulsion p a i n t . T h i s method, which i s
a p p l i c a b l e t o o l d s u r f a c e s of mediocre q u a l i t y , can a l s o be used on new cement s u r f a c e s which show f l a w s . The p a i n t e d c o a t i n g can t h e n be regarded a s a n o r g a n i c r e i n f o r c e d microconcrete. The weather r e s i s t a n c e i s c o n s i d e r a b l y i n c r e a s e d by t h e t h i c k n e s s , and maintenance i s l i m i t e d t o t h e r e p a i r i n g of t h e o u t s i d e c o a t s , s i n c e t h e permanent base i s t h e r e i n f o r c e d p l a s t e r . These t e c h n i q u e s , however l a b o r i o u s t h e y may appear a t f i r s t g l a n c e , a r e w e l l r e p a i d by t h e d u r a b i l i t y t h u s a c h i e v e d .
The v i n y l cement p a i n t s o f f e r a s i m p l i f i e d form of t h e semi-thick c o a t i n g t e c h n i q u e . These p r o d u c t s come i n two p a r t s , a m i n e r a l powder com- p r i s i n g cement, mineral pigments, and dyes, which a r e mixed one-half hour b e f o r e u s e w i t h a n emulsion b i n d e r . Two t h i c k c o a t s a r e a p p l i e d t o cover t h e cement o r c o n c r e t e s u r f a c e . Fine f i n i s h i n g i s not p o s s i b l e , but t h e d u r a b i l - i t y a t t a i n e d a t moderate c o s t r e n d e r s them a t t r a c t i v e . A c o a t i n g of t h i s t y p e was used t o cover t h e o u t s i d e of t h e v a u l t of t h e CNIT b u i l d i n g .
One f u r t h e r word on t h e p a i n t i n g of p r e c a s t c o n c r e t e u n i t s .
Asbestos-cement boards a r e used a s f a s a d e p a n e l s and l a r g e d e c o r a t i v e u n i t s . Generally speaking they do n o t come w i t h i n t h e purview of t h e p a i n t e r , but a r e coated i n t h e shop sometimes w i t h opaque coloured p o l y e s t e r s , some- t i m e s w i t h i s o c y a n a t e ( p o l y u r e t h a n e ) p a i n t s , sometimes w i t h epoxy r e s i n p a i n t s , a f t e r which t h e y a r e k i l n d r i e d o r a i r d r i e d . I t should be kept I n mind t h a t t h e s e p a n e l s must not merely h i d e a s u r f a c e , but must p r o t e c t i t and t h e edges s o a s t o prevent t h e a b s o r p t i o n of m o i s t u r e o r t h e occurrence of i n t e r n a l condensation which would r e s u l t i n t h e l i f t i n g of t h e v e n e e r .
We conclude t h i s s e c t i o n by warning c o n t r a c t o r s a g a i n s t t h e a t t r a c t i v e but dangerous polychrome p r o d u c t s , by reason of t h e chemical r e a c t i v i t y of t h e cement which i f superimposed on weather e f f e c t s t e n d s t o d e n a t u r e t h e pigment combinations sometimes very q u i c k l y . We must remain b l i n d t o c e r t a i n hues which charm u s , j u s t a s Ulysses had t o c l o s e h i s e a r s t o t h e s i r e n s , and r e s i g n o u r s e l v e s t o t o n e s which a r e o f t e n l e s s l u x u r i o u s , but more d u r a b l e .
I n t e r i o r s t r u c t u r e s
F i r s t of a l l I beg i n d u l g e n c e f o r a d i g r e s s i o n which i s n o t w i t h o u t importance.
T h e o r e t i c a l l y , p r e c a s t c o n c r e t e s l a b s used i n w a l l s and c e l l i n g s a r e smooth enough t o r e q u i r e no p r e p a r a t o r y c o a t s . The t r u t h , however, i s o t h e r - wise; some a i r v o i d s a r e unavoidable, and t h e i n e v i t a b l e d e p a r t u r e s from f l a t n e s s a t t h e j o i n t s between s l a b s cannot be n e g l e c t e d w i t h o u t d e t r a c t i n g from t h e o v e r a l l appearance. The same a p p l i e s t o poured c o n c r e t e s t r u c t u r e s , which w i l l show r i d g e s a t t h e J o i n t s between forms, which t h e p a i n t e r cannot remove. T h a t i s t h e way t h i n g s a r e , n o t t h e way we want them t o b e . For t h e s e v a r i o u s r e a s o n s a s o - c a l l e d " r a k i n g " c o a t i s u s u a l l y a p p l i e d which t o some e x t e n t w i l l f i l l up t h e v o i d s and t o some e x t e n t mask t h e j o i n t s . How- e v e r , a p l a s t e r f o r f i l l i n g never h a s t h e same p r o p e r t i e s a s one used f o r c o v e r i n g ; i t i s formulated e i t h e r f o r t h e one purpose o r t h e o t h e r and w i l l
t h e n be a poor c o v e r i n g i f i t i s a good f i l l e r o r v i c e v e r s a . T h i s Is n o t t o o s e r i o u s a m a t t e r i n w a i t i n g rooms and anti-rooms on unheated w a l l s and c e i l i n g s , and l i f t i n g of t h e p a i n t i s u n l i k e l y . However, i n rooms where
c o n d e n s a t i o n s occur and on heated c e i l i n g s t h e r e i s always a r i s k of t h i s , i n one c a s e l e a v i n g t h e i n t e r i o r s u r f a c e of t h e s l a b i n t a c t , w h i l e f l a k i n g w i l l
o c c u r a t t h e J o i n t s , and i n t h e o t h e r c a s e t h e b l e m i s h e s w i l l be r e v e r s e d , b u t s t a r t i n g always from a p o i n t of i n t e r m e d i a t e t h i c k n e s s of t h e c o a t and s p r e a d i n g o u t towards v e r y t h i n o r v e r y t h i c k p a r t s . Under t h e s e c o n d i t i o n s two g e n e r a l s o l u t i o n s a r e p o s s i b l e : ( 1 ) d i r e c t a p p l i c a t i o n of p a i n t t o t h e c o n c r e t e , w i t h a s a c r i f i c e of appearance
-
a l i t t l e l a t e r we s h a l l s e e t h a t t h i s s o l u t i o n cannot be r e j e c t e d o u t of hand; ( 2 ) a p p l i c a t i o n of a f i l l i n g p l a s t e r by t r o w e l o r by s p r a y t o a d e p t h of a t l e a s t 5-
1 0 mm, c a r e f l l l l y f o l l o w i n g t h e d i r e c t i o n of t h e s u p p l i e r .Having s a i d t h i s , we s h a l l a g a i n f i n d a goodly nunber of p r o d u c t s t h a t have a l r e a d y been mentioned. G e n e r a l l y s p e a k i n g , t h e s i l i c a t e s a r e n o t a c c e p t a b l e f o r t h e s e purposes because of t h e i r u n a t t r a c t i v e f i n i s h . R i g h t l y o r wrongly t h e emulsion p a i n t s , and e s p e c i a l l y t h e v i n y l , w i l l t a k e t h e l o i n ' s s h a r e . T h e i r main advantages a r e e a s e of a p p l i c a t i o n , quiclc d r y i n g , r i c h n e s s and f r e s h n e s s of c o l o u r , and t h e absence of any u n p l e a s a n t odour. T h e i r d i s - advantages i n c l u d e s u s c e p t i b i l i t y t o s o i l i n g and poor w a s h a b i l i t y . Apart from t h e s e c o n s i d e r a t i o n s t h e y a r e p e r f e c t l y s u i t a b l e f o r w a i t i n g rooms and a n t i - rooms, and a l l p l a c e s u n l i k e l y t o be s u b j e c t t o c o n d e n s a t i o n . !Jith c e r t a i n r e s e r v a t i o n s , however, t h e y can a l s o be used i n k i t c h e n s and bathrooms. It
i s p o s s i b l e , of c o u r s e , t o u s e l e a n e r formulae t h a n f o r o u t s i d e p a i n t i n g , b u t t h i s should n o t be c a r r i e d t o t h e p o i n t of producing something l i k e a s i z i n g
wash. These a r e cheap b u t more l a b o r i o u s t o apply t h a n c e i l i n g w h i t e , t o which they a r e i n no way s u p e r i o r .
Glycerophthalic p a i n t s , e i t h e r by themselves o r w i t h an undercoat of another t y p e (emulsion f o r example). These come i n f l a t , s a t i n o r g l o s s y f i n i s h e s according t o requirements and t a s t e . I n k i t c h e n s and bathrooms on s u r f a c e s t h a t a r e s t i l l m o i s t , i t would be wise t o u s e t h e d u l l f i n i s h e a . Glossy f i n i s h e s a r e sometimes p o s s i b l e i f a proven technique i s followed, f o r example:
-
a f u l l p l a s t e r , not a f i l l e r ;-
f i n e spraying;-
a c o a t of f l a t g l y c e r o p h t h a l i c p a i n t ;-
and a f i n i s h i n g c o a t of g l o s s y g l y c e r o p h t h a l i c p a i n t . Isomerized o r c y c l i z e d rubber p a i n t s i n f l a t , s a t i n o r g l o s s y f i n i s h . The same q u a l i f i c a t i o n s a s above a r e a p p l i c a b l e t o t h e g l o s s y f i n i s h e s . Theae p a i n t s a r e not much used i n r e s i d e n t i a l rooms, but a r e u s e f u l i n s p e c i a la p p l i c a t i o n s , e.g. l a b o r a t o r i e s s u b j e c t e d t o c o r r o s i v e chemicals such a s a c i d vapours o r ferments ( b r e w e r i e s , d a i r i e s , e t c . ) .
Chlorinated rubber base p a i n t s a r e similar i n t h e i r a p p l i c a t i o n s t o t h e above, except t h a t they a r e sometimes used i n r e s i d e n c e s a s vapour b a r r i e r s o r as i n s u l a t o r s , t h u s making i t p o s s i b l e t o a p p l y o u t e r c o a t s of o i l base p a i n t s .
S p e c i a l s t r u c t u r e s
Concrete f l o o r s a r e o f t e n g i v e n c o a t s of very hard and e a s i l y washable p a i n t s , f o r example epoxy r e s i n o r i s o c y a n a t e p a i n t s . These t y p e s have two components which a r e mixed a t t h e time of u s e . Sometimes hard wearing powders, e . g . corundum, a r e added t o them. The same p a i n t s can be advantageously
employed i n s t a i r - w e l l s , p u b l i c c o r r i d o r s , classroom w a l l s , e t c . For t h e s e products i t i s important f o r t h e s u r f a c e t o be very d r y , o t h e r w i s e t h e p a i n t
w i l l l i f t o f f immediately.
C e r t a i n emulsion p a i n t s , sometitnes c o n t a i n i n g coloured p l a s t i c f i b r e s , a r e a p p l i e d i n t h i c k c o a t s t o h i d e s u r f a c e i r r e g u l a r i t i e s by t h e i r t e x t u r e , and show remarkable r e s i s t a n c e t o shoclcs, a b r a s i o n and v a r i o u s k i n d s of
s o i l i n g , and a t t h e same time t h e y a r e d e c o r a t i v e . Whether p l a i n o r i n t i n t s , t h e s e p a i n t s depend l i t t l e on t h e dryness of t h e cement.
We conclude t h i s s e c t i o n by touching on t h e q u e s t i o n of swimming p o o l s , r e s e r v o i r s , water c o o l e r s and s i l o s . Any such c o n s t r u c t i o n i n c o n c r e t e can be coated w i t h p a i n t s having bases of epoxy r e s i n , c h l o r i n a t e d rubber, poly- v i n y l c h l o r i d e
-
v i n y l a c e t a t e i n s o l u t i o n o r b u t y l rubber i n s o l u t i o n .epoxy r e s i n s i n s o l u t i o n , o r emulsified p i t c h o r bituminous p r o d u c t s , can meet t h e same requirements. A l l t h e s e p r o d u c t s must be very c a r e f u l l y a p p l i e d i n o r d e r t o ensure s a t i s f a c t o r i l y impermeability.
Conclusion
To sum up, t h e problems posed by t h e a p p l i c a t i o n of p a i n t s t o c o n c r e t e and cement mortar come down t o t h e f o l l o w i n g .
( 1 ) Moisture c o n t e n t
This determines i n l a r g e measure t h e choice of p a i n t s e s p e c i a l l y f o r i n t e r i o r work. The f i g u r e s given below a r e not d e f i n i t i v e , but s e r v e a s guides which may be r e v i s e d i n t h e l i g h t of e x p e r i e n c e .
Above
5%
f r e e water content i n t h e m a t e r i a l , only permeable systems, 1 . e . f l a t f i n i s h i n g p a i n t s , can be c o n s i d e r e d .Between 3% and
57;
penneable systems a r e s t i l l p r e f e r a b l e . Glossy f i n i s h e s should be r e j e c t e d i n most c a s e s , except f o r c e r t a i n s p e c i a l l y designed complexes. Below 3% e i t h e r permeable o r impermeable systems a r ea p p l i c a b l e .
( 2 ) S u r f a c e c o n d i t i o n
T h i s determines whether a p l a s t e r must be u s e d .
F i l l i n g . T h i s i s n o t a d v i s a b l e because of s u r f a c e i r r e g u l a r i t i e s a t r i g h t a n g l e s t o panel j o i n t s , e s p e c i a l l y i n k i t c h e n s , bathrooms and unheated c e i l i n g s .
Priminp;. T h i s i s recommended provided i t i s a p p l i e d everywhere and t h i c k l y (500 microns, f o r example).
Veneering p a i n t s . They can r e p l a c e t h e p r e p a r a t o r y c o a t ; t h e y a r e a p p l i e d d i r e c t l y i n s e v e r a l c o a t s , and i n most c a s e s t h e i r g e n e r a l l y f i b r o u s appear- ance w i l l h i d e any s u r f a c e f l a w s .
( 3 ) The use of form o i l s
I f t h e c o n c r e t e s a r e c o r r e c t l y made up t h e r e i s no danger, provided no more than twice t h e q u a n t i t y recommended by t h e manufacturer i s u s e d . It i s wise, however, t o c l e a n powdery o r d o u b t f u l s u r f a c e s w i t h a wet sponge.
We have reviewed most of t h e problems posed by c o n c r e t e s and cement mortars and have attempted t o r e s o l v e them. It would be presumptuous t o claim t h a t we have succeeded e n t i r e l y , but we may hope t h a t e i t h e r new o r o l d products used i n t h e proper way can be of a s s i s t a n c e t o t h e p a i n t e r and enable him t o s u s t a i n h i s fondness f o r and p r i d e i n h i s work.
