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Moisture degradation of masonry walls
Ritchie, T.
https://publications-cnrc.canada.ca/fra/droits
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'
SerTH9,
I
N21d
no. 693
National Research
Conseil national
c. 2
I
*
Council Canada
de recherches Canada
MOISTURE DEGRADATION OF MASONRY WALLS
by
T.
Ritchie//
Reprinted, with permission, from
Proceedings, First Canadian Masonry Symposium held at the University of Calgary, Calgary, Alberta 7 10 June 1976
p. 6 6
-
71DBR Paper No. 693
Division of Building Research
Le but de cette conrmunication est de revoir les mdcanismes responsables de l'humidification de la ma~onnerie. En plus de la pluie qui tombe sur les murs, ces mdcanismes comprennent: la condensation de la vapeur d'eau qui se diffuse 5 travers les matgriaux de maqonnerie et de la vapeur d'eau contenue dans l'air qui traverse les poresde la maqonnerie ou les owertures dans les murs; 11humidit6 dans le sol qui monte dans la maqonmerfe par capillarite et l'eau submergeant la maqonnerie 1 cause d'une dtZfectuosit.5 du rdseau d'dvacuation des eaux pluviales ou des eolins. On discute dgalement des effets de l'humidification de la ma~onnerie sur certains aspects de son comportement et des particularitgs de conception et de construction des murs de ma~onnerie qui provoquent l'humidification.
T.
Ritchie
Division
of BuildingResearch
National
Research Council,
Ottawa, Ontario
INTRODUCTION
Problems r e s u l t i n g from t h e w e t t i n g o f masonry w a l l s a r e common i n Canada. Rain p e n e t r a t i o n o f w a l l s o c c u r s f r e q u e n t l y ; a t b e s t i t i s a n u i s a n c e r e q u i r i n g o n l y t h e mopping up o f t h e w a t e r , b u t a t w o r s t i t may s t a i n t h e i n t e r i o r s u r f a c e s o f w a l l s a s w e l l a s l o o s e n p l a s t e r and f l o o r c o v e r i n g s . The w e t t i n g o f masonry g i v e s r i s e t o problems o f s t a i n i n g and e f f l o r e s c e n c e and i s a n i m p o r t a n t f a c t o r i n t h e o c c u r r e n c e o f
f r o s t damage o f masonry m a t e r i a l s .
The purpose o f t h i s p a p e r i s t o review t h e mechanisms r e s p o n s i b l e f o r w e t t i n g masonry. I n a d d i t i o n t o r a i n f a l l i n g on w a l l s , t h e s e i n c l u d e : c o n d e n s a t i o n o f w a t e r vapour d i f f u s i n g through t h e masonry m a t e r i a l s and o f t h a t c o n t a i n e d i n t h e a i r
p a s s i n g through masonry p o r e s o r w a l l openings, "wicking" o f ground m o i s t u r e i n t o masonry, and f l o o d i n g o f w a t e r o n t o masonry because o f d e f e c t i v e d r a i n s and f l a s h i n g s . The e f f e c t s of t h e w e t t i n g o f masonry on c e r t a i n a s p e c t s o f i t s performance, and t h e d e s i g n and c o n s t r u c t i o n f e a t u r e s o f masonry w a l l s t h a t i n f l u e n c e t h e i r w e t t i n g , a r e a l s o d i s c u s s e d .
I
CONDENSATION II
I n w i n t e r , t h e a i r w i t h i n b u i l d i n g s h a s a h i g h e r m o s i t u r e c o n t e n t t h a n t h a t I w i t h o u t and t h e r e s u l t i n g d i f f e r e n c e i n w a t e r vapour p r e s s u r e c a u s e s a d i f f u s i o n o fvapour outward through t h e b u i l d i n g e n c l o s u r e . ?he amount o f w a t e r vapour a b l e t o
'
d i f f u s e through t h e w a l l depends on t h e p r e s s u r e d i f f e r e n c e a s w e l l a s on t h ep e r m e a b i l i t y .of t h e m a t e r i a l s through which t h e vapour h a s t o d i f f u s e . A t some p o i n t i n t h e c o u r s e o f i t s p a s s a g e through a m a t e r i a l , t h e v a p o u r l s dew p o i n t t e m p e r a t u r e may b e reached and c o n d e n s a t i o n t a k e s p l a c e , t h u s i n c r e a s i n g t h e m o i s t u r e c o n t e n t o f t h e m a t e r i a l . C a l c u l a t i o n s o f t h e t h e o r e t i c a l amount o f w a t e r condensed i n a b r i c k w a l l by t h e p r o c e s s o f d i f f u s i o n i n d i c a t e t h a t t h e q u a n t i t y i s s m a l l [ I ] ; i t amounts t o 4 . 5 l b o f w a t e r p e r 100 s q f t o f a n u n f i n i s h e d ( u n p l a s t e r e d ) , 1 2 - i n . b r i c k w a l l made o f porous m a t e r i a l s , s u b j e c t t o s e v e r e c o n d i t i o n s f o r 100 d a y s . Because t h i s a r e a o f a 1 2 - i n . w a l l r e p r e s e n t s a b o u t 1848 b r i c k s , t h e amount o f w a t e r condensed, i f e v e n l y d i s t r i b u t e d t h r o u g h o u t t h e b r i c k s , r e p r e s e n t s 0.002 l b p e r b r i c k ; a b r i c k of moderate
p o r o s i t y h a s t h e c a p a c i t y t o a b s o r b a b o u t 0 . 5 l b o f w a t e r .
Condensation o f w a t e r vapour c a n a l s o o c c u r w i t h i n masonry w a l l s by a p r o c e s s t h a t i n v o l v e s t h e outward l e a k a g e o f a i r through o p e n i n g s and c r a c k s i n t h e w a l l s . C o n d e n s a t i o n o c c u r s when t h e a i r c o o l s . A i r l e a k a g e i n b u i l d i n g s may be a p p r e c i a b l e , I a s shown by measurements made on f o u r b u i l d i n g s [ 2 ] . Varying i n h e i g h t from 11 t o
22 s t o r e y s , t h e s e s t r u c t u r e s had l e a k a g e r a t e s between 0.00127 and 0.00244 m 3 / s / m 2 o f w a l l a r e a a t a p r e s s u r e d i f f e r e n c e o f 75 ~ / m ~ . The l a t t e r r a t e produces a d a i l y flow o f a b o u t 210 m 3 o f a i r p e r s q u a r e metre o f w a l l a r e a (689 cu f t / s q f t ) .
C a l c u l a t i o n s o f t h e t h e o r e t i c a l amount o f w a t e r condensed i n a b r i c k w a l l by t h e a i r ' l e a k a g e p r o c e s s [ I ] show t h a t t h e m o i s t u r e c o n t e n t can amount t o 735 l b o f w a t e r p e r 100 s q f t o f t h e 1 2 - i n . b r i c k w a l l d e s c r i b e d p r e v i o u s l y , s u b j e c t t o e x t r e m e c o n d i t i o n s . Because t h i s a r e a o f t h e w a l l r e p r e s e n t s a b o u t 1848 b r i c k s , t h e amount o f w a t e r condensed, i f e v e n l y d i s t r i b u t e d through t h e b r i c k s , r e p r e s e n t s 0 . 4 0 l b p e r b r i c k , which i s a b o u t e q u a l t o t h e amount o f w a t e r t h a t a b r i c k o f moderate p o r o s i t y
can a b s o r b .
INDEX O F RAIN- WETTING
No a r e a o f Canada i s f r e e o f r a i n and t h e r e f o r e a w a l l o f any b u i l d i n g e r e c t e d i n t h i s c o u n t r y w i l l b e w e t t e d by i t p r o v i d e d t h a t t h e r e i s a s u f f i c i e n t l y s t r o n g wind t o blow t h e r a i n d r o p s a g a i n s t t h e w a l l . The d e g r e e o f r a i n - w e t t i n g , however, s h o u l d b e e x p e c t e d t o depend on two f a c t o r s , ( 1 ) t h e amount o f r a i n f a l l , which v a r i e s o v e r t h e wide range o f a few i n c h e s t o more t h a n 100 i n . p e r y e a r and, (2) t h e f o r c e o f t h e wind, which n o t o n l y blows t h e r a i n o n t o a w a l l b u t a p p l i e s a p r e s s u r e t o t h e w a l l s u r f a c e , f o r c i n g t h e r a i n i n t o t h e p o r e s and o p e n i n g s o f t h e masonry.
An i n d e x o f t h e w i n d - d r i v e n r a i n f o r a p a r t i c u l a r l o c a t i o n , which t a k e s i n t o a c c o u n t t h e amount o f r a i n and t h e wind s p e e d , may be c a l c u l a t e d by t a k i n g t h e
p r o d u c t o f t h e a n n u a l r a i n f a l l and t h e mean wind s p e e d . A d r i v i n g - r a i n map p r e p a r e d from such c a l c u l a t i o n s f o r 141 l o c a t i o r l s i n Canada [ 3 ] i n d i c a t e s t h a t t h e i n d e x o f d r i v i n g - r a i n v a r i e s from l e s s t h a n one s q u a r e metre p e r second t o more t h a n t e n .
Another i n d e x o f t h e r a i n - w e t t i n g o f w a l l s , b a s e d on r a i n s t o r m s o f more t h a n 1 2 h o u r s d u r a t i o n a r ~ d a c o n s t a n t wind d i r e c t i o n , h a s been d e r i v e d from t h e w e a t h e r r e c o r d s o f t e n Canadian c i t i e s [ 4 ] . ' This "wall p e n e t r a t i o n " i n d e x was o b t a i n e d by n l i ~ l t i p l y i n g th e s q u a r e o f t h c a v e r a g e wind s p e e d d u r i n g p r o l o n g e d s t o r m s by t h e d u r a t i o n o f t h e s t o r m s , t h e former f a c t o r t a k i n g i n t o a c c o u n t t h e wind p r e s s u r e .
The w a l l per1ctr;ltiorl i n d e x e s f o r c e r t a i n c i t i e s show i m p o r t a n t d i r e c t i o n a l dc1)entlcncies. I h u s p r o l o n g e d r a i n s t o r m s s h o u l d a f f e c t o n l y e a s t - f a c i n g w a l l s i n Vnr~couver and t h o s e f a c i n g s o u t h - e a s t i n V i c t o r i a , and e a s t and n o r t h - e a s t w a l l s i n b o t h Quebec and H a l i f a x .
D l RECTlONAL WE'T'I'I NC O F MASONRY
Prorlouncctl d i r e c t i o n a l i n f l u e r ~ c e was shown i n t h e r e s u l t s o f a s t u d y i n v o l v i n g t h e e x p o s u r e o f v a r i o u s masonry m a t e r i a l s t o r a i n - w e t t i n g [ S ] . The m a t e r i a l s , e x p o s e d a t t l a l i f a x and Ottawa, i n c l u d e d s e v e r a l d i f f e r e n t b r i c k s a s w e l l a s b r i c k - s h a p e d
o f each m a t e r i a l were exposed t o t h e f o u r d i r e c t i o n s b u t o n l y one v e r t i c a l s u r f a c e c o u l d b e w e t t e d by r a i n . The m o i s t u r e c o n t e n t o f t h e samples was determined by weighing them p e r i o d i c a l l y throughout t h e time o f t h e i r exposure, which s t a r t e d i n O c t o b e r and l a s t e d u n t i l t h e f o l l o w i n g J u n e .
The samples exposed a t b o t h l o c a t i o n s d i f f e r e d s i g n i f i c a n t l y i n m o i s t u r e c o n t e n t depending on t h e d i r e c t i o n o f e x p o s u r e . The Ottawa samples f a c i n g s o u t h and west c o n t a i n e d v e r y l i t t l e m o i s t u r e throughout t h e exposure p e r i o d , whereas t h e samples f a c i n g e a s t had a h i g h m o i s t u r e c o n t e n t , s l i g h t l y g r e a t e r than t h a t o f t h e n o r t h - f a c i n g samples. The d i r e c t i o n a l e f f e c t a t H a l i f a x r e s u l t e d i n h i g h m o i s t u r e c o n t e n t f o r t h e e a s t - f a c i n g samples. The H a l i f a x samples f a c i n g n o r t h had low m o i s t u r e c o n t e n t and t h e south- and w e s t - f a c i n g sanrples were a t i n t e r m e d i a t e m o i s t u r e l e v e l s .
The v a r y i n g c a p a c i t i e s o f masonry m a t e r i a l s t o absorb r a i n was a l s o shown i n t h i s s t u d y . P r a c t i c a l l y a l l o f t h e r a i n s t r i k i n g t h e s u r f a c e , o f a h i g h l y porous
m a t e r i a l was absorbed, whereas much o f t h e r a i n r a n o f f t h e s u r f a c e o f o t h e r m a t e r i a l s
w i t h o u t b e i n g absorbed. I
NON-UNI FORMITY OF WETTING
S t u d i e s o f t h e r a i n - w e t t i n g o f w a l l s have shown t h a t t h e r e i s a p p r e c i a b l e non- u n i f o r m i t y o f w e t t i n g . Small cups designed t o c o l l e c t o n l y t h e w a t e r t h a t would s t r i k e t h a t a r e a o f t h e w a l l covered, c o l l e c t e d v a r y i n g amounts o f r a i n w a t e r a t d i f f e r e n t l e v e l s and l o c a t i o n s . For example, a cup l o c a t e d n e a r t h e t o p o f t h e w a l l c o l l e c t e d s e v e r a l times t h e amount o f w a t e r caught i n t h e same s t o r m by a second cup d i r e c t l y below i t n e a r t h e bottom [ 6 ] . Such s t u d i e s confirm what i s o f t e n n o t i c e d when b u i l d i n g s a r e w e t t e d by r a i n , t h a t much more i n t e n s e w e t t i n g u s u a l l y o c c u r s n e a r t h e t o p o f w a l l s than a t lower l e v e l s . D i f f e r e n c e s i n w e t t i n g a r e a t t r i b u t a b l e t o t h e wind-flow p a t t e r n s o v e r t h e w a l l s u r f a c e , which d i r e c t t h e p a t h s o f t h e f a l l i n g r a i n d r o p s [ 7 ] .
I
RAIN PENETRATION1
The r a i n t h a t f a l l s on a masonry w a l l has t h r e e p o s s i b l e p a t h s o f p e n e t r a t i o n : through t h e body o f t h e u n i t ; through t h e body o f t h e mortar; {hrough openings between t h e u n i t and t h e m o r t a r . The amount o f w a t e r t h a t p e n e t r a t e s m o r t a r does n o t c o , ~ t r i b u t e s i g n i f i c a n t l y t o a l e a k a g e problem. The p e r m e a b i l i t y o f c e r t a i n u n i t s , however, may b e s u f f i c i e n t l y h i g h t h a t a s i g n i f i c a n t amount of r a i n may p e n e t r a t e
them. The r e l a t i v e l y open p o r e s t r u c t u r e o f c o n c r e t e b r i c k s and b l o c k s , and of c l a y b r i c k s made by d r y - p r e s s i n g may r e n d e r t h e s e m a t e r i a l s s u f f i c i e n t l y permeable f o r r a i n t o p e n e t r a t e them i n t h e c o u r s e o f prolonged wind-driven r a i n .
Openings a t t h e u n i t - m o r t a r i n t e r f a c e a r e major p a t h s f o r r a i n p e n e t r a t i o n o f masonry w a l l s . Such openings r e s u l t from incomplete c o n t a c t o r bond between u n i t and m o r t a r when masonry i s l a i d up. This c o n d i t i o n may be caused by t h e use o f h i g h s u c t i o n u n i t s t h a t draw w a t e r s o q u i c k l y from t h e f r e s h mortar t h a t i t l o s e s p l a s t i - c i t y b e f o r e a second u n i t c a n b e p l a c e d i n i t .
Although many o f t h e f a c t o r s i n v o l v e d i n w a t e r p e n e t r a t i o n o f masonry a r e under- s t o o d , t h e r e h a s been no development o f t h e combinations o f u n i t s and m o r t a r t h a t w i l l p r o v i d e optimum r e s i s t a n c e . Another s o l u t i o n t h a t h a s come i n t o e x t e n s i v e u s e ,
I however, i s t h e c a v i t y w a l l , a d o u b l e w a l l w i t h a c o n t i n u o u s a i r s p a c e between t h e
I two p a r t s . I t i s assumed t h a t r a i n w i l l p e n e t r a t e t h e o u t e r p a r t , b u t t h e c a v i t y
p r e v e n t s w a t e r from c r o s s i n g t o t h e i n n e r p a r t . The w a t e r t h a t d r a i n s down t h e i n n e r
s u r f a c e o f t h e o u t e r w a l l i s c a u g h t i n a trough formed by a f l a s h i n g a t t h e b a s e o f
t h e o u t e r w a l l and t u r n e d up a g a i n s t t h e i n n e r w a l l . The w a t e r d r a i n s o u t o f t h e
c a v i t y through h o l e s i n m o r t a r j o i n t s a t t h e bottom o f t h e o u t e r w a l l .
STAINING AND EFFLORESCENCE
S t a i n i n g and e f f l o r e s c e n c e on masonry w a l l s r e f l e c t t h e p a t t e r n s o f t h e w e t t i n g
and t h e manner i n which r a i n w a t e r r u n s o v e r and o f f t h e w a l l s u r f a c e . Although t h e
d e p o s i t s o f a i r - b o r n e d i r t p a r t i c l e s on w a l l s a r e i n f l u e n c e d by a i r flow p a t t e r n s
around b u i l d i n g s , i t i s mainly t h e flow o f w a t e r o v e r t h e w a l l s u r f a c e t h a t c a u s e s
s t a i n i n g . The w a t e r r e d i s t r i b u t e s t h e d i r t , washes i t away from some a r e a s and
c o n c e n t r a t e s i t e l s e w h e r e . The w a t e r flow p a t t e r n s may a l s o produce s t a i n s and
s t r e a k s by e r o d i n g t h e masonry m a t e r i a l , t h e r e s u l t i n g d i f f e r e n c e s i n t e x t u r e a n d c o l o u r g i v i n g an a p p e a r a n c e o f v e r t i c a l s t r e a k s on t h e w a l l s u r f a c e . S t i l l a n o t h e r
cause o f s t a i n i n g i s t h e r u n - o u t from masonry o f w a t e r t h a t h a s e n t e r e d i t e l s e w h e r e ,
s a l t d e p o s i t s marking t h e w a t e r ' s p o i n t o f e x i t . The o c c u r r e n c e of s t a i n i n g a s a r e s u l t o f t h e r a i n - w e t t i n g o f w a l l s and t h e r u n - o f f o f w a t e r h a s been d i s c u s s e d i n d e t a i l i n r e l a t i o n t o c e r t a i n f e a t u r e s o f t h e d e s i g n o f b u i l d i n g s [ 7 ] .
E f f l o r e s c e n c e i s c a u s e d by t h e a b s o r p t i o n o f w a t e r by masonry m a t e r i a l s . The
w a t e r d i s s o l v e s s a l t s i n t h e masonry, forming s o l u t i o n s t h a t s u b s e q u e n t l y move t o t h e s u r f a c e where t h e w a t e r e v a p o r a t e s , d e p o s i t i n g t h e s a l t s . The s a l t s may have
o r i g i n a t e d w i t h i n t h e masonry u n i t s o r t h e m o r t a r , b u t t h e l a t t e r i s a p a r t i c u l a r l y
i m p o r t a n t s o u r c e .
There a r e i n t e r e s t i n g s e a s o n a l i n f l u e n c e s on t h e o c c u r r e n c e o f e f f l o r e s c e n c e . Masonry c o n s t r u c t e d i n t h e f a l l f r e q u e n t l y shows e f f l o r e s c e n c e i n e a r l y w i n t e r , p r o b a b l y because much o f t h e w a t e r used i n c o n s t r u c t i o n ( t h e w a t e r i n t h e wet m o r t a r
t h a t i s a b s o r b e d by t h e u n i t s when t h e y a r e l a i d ) remains and e v a p o r a t e s s l o w l y from
t h e w a l l s u r f a c e d u r i n g t h e c o l d w i n t e r d a y s . E f f l o r e s c e n c e f r e q u e n t l y d i s a p p e a r s
frorn a w a l l i n t h e sualslcr b u t r e c u r s i r 1 t h e w i n t e r , a s i t u a t i o n b e l i e v e d t o be due t o
ttic se:lsorl;l l c l i f f'cl-crice i l l t h e r a t e o f ev;lpor;ltion fro111 t h e masonry. When t h e w a l l
i s wctttatl i n tlic S L I I I I I I I C \ I . i t rc;lbsorbs t h e s;ll t s , b u t b e c a u s e t h c masonry d r i e s v e r y
r a p i d l y tlic p1;111c 01' ~ V L I I ) O ~ : I ti011 l i e s wi tliin t h c t ~ r t i t s , th u s t h e s a l t s do n o t form on
t h e sur.f;lce. In w i n t e r , howcvcr, t h e p l a n e o f e v a p o r a t i o n i s on t h e w a l l s u r f a c e and
thu s n l t s n r c dcposi t c d t h c r - c . E f f l o r e s c c r i c e f r e q u c r l t l y r e f l e c t s t h e d i r e c t i o n a l r a i n - w e t t i n g o f w a l l s ; i n Ottawa a b u i l d i n g n~:tr.ked by e f f l o r e s c e n c e u s u a l l y d i s p l a y s i t on t h e e a s t - f a c i n g w a l l , w i t t i t h e o t h e r w a l l s much l e s s a f f e c t e d , i f n o t e n t i r e l y f r e e o f i t . E f f l o r e s - cencc a l s o r e f l e c t s d i f f e r e n c e s i n t h e amount o f w e t t i n g r e c e i v e d by a w a l l ; i t o f t e n appc;lrs a t t h e t o p o f t h e w a l l b u t n o t a t t h e b o t t o m .
1
Although c f f l o r e s c e r i c e i s u s u a l l y c o n s i d e r e d t o be a problem o n l y i n r e g a r d t ot h e clppearartce o f masonry, t h c s a l t s t h a t c a u s e i t may a l s o l e a d t o decay. I f t h e i r
c r y s t x l l i z:lt ion t a k c s p l a c e w i t h i n t h e masonry i n s t e a d o f on i t s s u r f a c e , d i s r u p t i v e s t r c s s c . ; way be s e t up.
FROST DAMAGE
Decay due t o f r e e z i n g
i s
a s e r i o u s c o n s e q u e n c e o f t h e w e t t i n g o f masonry.E x p e r i m e n t s h a v e shown t h a t damage done t o masonry m a t e r i a l s by f r e e z i n g depends i n
l a r g e measure on t h e i r m o i s t u r e c o n t e n t when t h e m a t e r i a l s a r e f r o z e n [8]
.
Thed e t e r i o r a t i o n o f masonry m a t e r i a l s b e c a u s e o f f r o s t a c t i o n i s more r a p i d a n d i n t e n -
s i v e , t h e r e f o r e , i n t h o s e w a l l a r e a s where e x c e s s i v e w e t t i n g o f masonry o c c u r s , f o r
example, a t t h e t o p o f a w a l l .
TREATMENT OF MOISTURE PROBLEMS
Because t h e r e a r e many c a u s e s o f e x c e s s i v e dampness i n masonry, i n c l u d i n g r a i n p e n e t r a t i o n , c o n d e n s a t i o n o f w a t e r v a p o u r , d e f e c t i v e d r a i n s and p i p e s , d e f e c t i v e
f l a s h i n g s o r a l a c k o f f l a s h i n g s , i n c o m p l e t e c a u l k i n g a r o u n d o p e n i n g s , a n d t h e "wicking" o f g r o u n d m o i s t u r e i n t o masonry, v a r i o u s m e a s u r e s must b e c o n s i d e r e d t o
c o r r e c t a p a r t i c u l a r s o u r c e o f w e t t i n g . To t a k e a c c o u n t o f t h e p o s s i b i l i t y o f c o n d e n s a t i o n , f o r example, t h e e x f i l t r a t i o n o f a i r must b e p r e v e n t e d by t h e p r o v i s i o n o f an a i r s e a l n e a r t h e i n n e r p a r t o f t h e w a l l a n d v a p o u r d i f f u s i o n m u s t b e c o n t r o l l e d by means o f a v a p o u r b a r r i e r . Once i t h a s b e e n e s t a b l i s h e d t h a t r a i n p e n e t r a t i o n o f masonry h a s o c c u r r e d , a n a s s e s s m e n t o f t h e p e r m e a b i l i t y o f t h e u n i t s i s r e q u i r e d b e c a u s e t h e p a t h o f l e a k a g e may b e t h r o u g h t h e u n i t s a s w e l l a s a t t h e u n i t - m o r t a r i n t e r f a c e . I f t h e w a t e r p e r m e a b i l i t y o f t h e u n i t s i s j u d g e d t o b e i n s i g n i f i c a n t t h e p a t h o f l e a k a g e i s a t t h e u n i t - m o r t a r i n t e r f a c e where o p e n i n g s must b e s e a l e d e i t h e r by c u t t i n g o u t a b o u t 1 / 2 i n . o f m o r t a r from t h e j o i n t s and r e p l a c i n g i t w i t h f r e s h m o r t a r , w e l l p a c k e d i n p l a c e , o r by b r u s h i n g a cement p a s t e i n t o t h e m o r t a r j o i n t s t o f i l l t h e o p e n i n g s a t t h e u n i t - r n o r t a r i n t e r f a c e . Where r a i n p e n e t r a t i o n i n v o l v e s i n t e r f a c e l e a k a g e a s w e l l a s l e a k a g e t h r o u g h t h e u n i t s , t h e l a r g e p o r e s a n d o p e n i n g s o f t h e u n i t s must b e p l u g g e d . Because o f t h e
e f f e c t o f s u c h t r e a t m e n t on c o l o u r and t e x t u r e o f masonry, e x t e n s i v e u s e i s made o f
c o l o u r l e s s " w a t e r p r o o f e r s " and " w a t e r r e p e l l e n t s " . I n r e c e n t y e a r s s i l i c o n e w a t e r
r e p e l l e n t s h a v e b e e n much u s e d , b u t t h e p r o b l e m o f j u d g i n g when s u c h a t r e a t m e n t s h o u l d b e employed, a n d o f a s s e s s i n g i t s p e r f o r m a n c e a n d p o s s i b l e a d v e r s e
" s i d e e f f e c t s " h a s n o t b e e n r e s o l v e d [9].
CONCLUSIONS
Masonry w a l l s may b e w e t t e d i n v a r i o u s ways, two o f which have b e e n d i s c u s s e d i n
t h i s p a p e r : c o n d e n s a t i o n o f w a t e r v a p o u r , a n d w e t t i n g b y r a i n .
Where l e a k a g e o f a i r t a k e s p l a c e t h r o u g h o p e n i n g s i n w a l l s , c a l c u l a t i o n s i n d i c a t e
t h a t s i g n i f i c a n t amounts o f m o i s t u r e can c o n d e n s e i n t h e masonry. A s y e t , however,
no s t u d i e s o f t h e m o i s t u r e c o n t e n t o f masonry s u b j e c t e d t o a i r l e a k a g e a n d o p e r a t i n g
llndcr a tcrnjlcrnture g r ; ~ d i e n t h a v e b e e n made, ei t h e r t o c o n f i r m t h e t h e o r y o r t o
d c t c r ~ n i ~ l c t h e t l c g r e e o f w c t t i n g 1 ) o s s i b l e .
V : ~ r i o u s : ~ s p e c t s o f t h e r a i n w e t t i n g o f masonry w a l l s h a v e b e e n s t u d i e d , i n c l u d i n g
t h e c f f c c t s o f a b u i l d i n g ' s g e o m e t r y . R a i n - w e t t i n g i n d e x e s d e r i v e d from r e c o r d s o f
s t u d i e s have b e e n made o f t h e m o i s t u r e c o n t e n t o f masonry m a t e r i a l s .
I n a d d i t i o n t o s i m p l e l e a k a g e through w a l l s , problems r e s u l t i n g from w e t t i n g o f
masonry i n c l u d e e f f l o r e s c e n c e , s t a i n i n g and f r o s t damage. In some o f t h e s e c a s e s i t
i s o f t e n d i f f i c u l t t o d e t e r m i n e t h e c a u s e o f w e t t i n g , s o t h a t remedial a c t i o n i s
a c c o r d i n g l y d i f f i c u l t . Much more s t u d y i s r e q u i r e d b e f o r e t h e mechanisms i n v o l v e d i n
t h e w e t t i n g o f masonry and i t s c o n t r o l can be a d e q u a t e l y d e f i n e d and t h e a s s o c i a t e d
prob 1 ems c o r r e c t e d
.
APPENDIX I . - REFERENCES
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B u i l d i n g R e s e a r c h , N a t i o n a l Research Council o f Canada, Ottawa, May, 1 9 6 3 .
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3 . R i t c h i e , T . , "Freeze-Thaw A c t i o n on B r i c k , " J o u r n a l o f t h e Canadian Ceramic
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Ottawa, ( J u n e ) , 1974.
5 . R i t c h i e , T . , and Davison, J . I . , "Moisture Content a n d Freeze-Thaw C y c l e s o f
Masonry M a t e r i a l s , " ASTM J o u r n a l o f M a t e r i a l s , .- Vol. 3 , No. 3 ,
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