Study of efflorescence in clay bricks

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Study of efflorescence in clay bricks

NATIONAL RESEARCH COUNCIL CANADA

DIVISION O F BUILDING RESEARCH

A STUDY O F E F F L O R E S C E N C E IN CLAY BRICKS by J. I. Davison I n t e r n a l Report. No. 3 1 3 of t h e Division of Building R e s e a r c h OTTAWA J u n e 1965

PREFACE

The appearance of efflorescence on a b r i c k m a s o n r y building i s usually d i s t r e s s i n g t o t h e designer, t h e owner and the manufacturer of t h e bricks. At a minimum it constitutes an a e s t h e t i c f a i l u r e for a s long a s i t p e r s i s t s , but i s a l s o c a u s e for s o m e concern that i t m a y r e f l e c t a situation in which deterioration of t h e m a s o n r y may occur. F o r t h e s e and other r e a s o n s t h e Division h a s had a long-time i n t e r e s t in efflorescence problems. The p r e s e n t study c a r r i e d out at Halifax h a s been b a s e d on l o c a l m a t e r i a l s and h a s provided t h e opportunity t o c o m p a r e l a b o r a t o r y and field experience and t o extend knowledge of t h e efflorescence phenomenon.

The author, a c h e m i s t and a r e s e a r c h officer of t h e Division a t t h e Atlantic Regional Station in Halifax, i s engaged in r e s e a r c h on m a s o n r y m a t e r i a l s with e m p h a s i s on regional problems.

Ottawa June 1965

N. B. Hutcheon A s s i s t a n t D i r e c t o r

A STUDY O F E F F L O F E S C E N C E IN CLAY BRICKS

J. I. Davison

During t h e winter of 1962-63, field o b s e r v a t i o n s i n s e v e r a l locations i n t h e Atlantic a r e a r e v e a l e d a h i g h e r t h a n a v e r a g e o c c u r r e n c e of e f f l o r e s c e n c e on w a l l s of c l a y b r i c k m a s o n r y . T h e s e v e r i t y of t h e e f f l o r e s c e n c e s e e m e d m o r e c l o s e l y r e l a t e d t o s p e c i f i c b r i c k s t h a n t o m o r t a r composition, t y p e of c o n s t r u c t i o n , etc. It w a s s u g g e s t e d that b r i c k s w e r e contributing t o t h e p r o b l e m e i t h e r by providing (a) a s o u r c e of soluble s a l t s , o r (b) s a t i s f a c t o r y m e d i a f o r

e a s y p a s s a g e of s a l t s i n solution f r o m m o r t a r and/or back-up m a t e r i a l t h r o u g h t h e walls. A study w a s , t h e r e f o r e , u n d e r t a k e n t o i n v e s t i g a t e t h e e f f l o r e s c i n g t e n d e n c i e s of c l a y b r i c k s commonly u s e d i n m a s o n r y c o n s t r u c t i o n i n t h e a r e a .

GENERAL

E f f l o r e s c e n c e , defined a s a deposit of w a t e r -soluble s a l t s e i t h e r (a) on t h e s u r f a c e of a m a s o n r y wall, o r (b) behind t h e s u r f a c e , within t h e p o r e s of t h e u n i t s of t h e s t r u c t u r e , h a s been s t u d i e d extensively i n r e c e n t y e a r s (1, 2,

3,

4). E f f l o r e s c i n g s a l t s , unsightly on m a s o n r y w a l l s , f r e q u e n t l y a p p e a r on new buildings and a r e a s o u r c e of c h a g r i n and e m b a r r a s s m e n t t o t h e owner, t h e a r c h i t e c t , and t h e builder. P a r a d o x i c a l l y , although t h e s a l t d e p o s i t s a r e a e s t h e t i c a l l y objectionable, t h e y a r e h a r m l e s s and u s u a l l y d i s a p p e a r during w a r m , d r y w e a t h e r , while s a l t s deposited behind t h e f a c e and within t h e p o r e s of t h e u n i t s of t h e walls, f r e q u e n t l y i g n o r e d b e c a u s e t h e y cannot be s e e n , h a v e b e c o m e r e c o g n i z e d a s a p o t e n t i a l c o n t r i b u t o r t o m a s o n r y d e t e r i o r

-

ation ( 1 ) . The build-up of s a l t s within t h e wall i s accompanied by i n c r e a s i n g p r e s s u r e which c a n eventually r e s u l t i n a s p a l l i n g a w a y of t h e f a c e of ( a ) t h e unit, o r (b) t h e m o r t a r joint. Among t h e f a c t o r s t h a t a r e e s s e n t i a l i n c a u s i n g e f f l o r e s c e n c e a r e : 1, w a t e r

,

2. a s o u r c e of soluble s a l t s , 3, a w a l l s t r u c t u r e conducive t o t h e r e a d y p a s s a g e of w a t e r , and 4, s u i t a b l e w e a t h e r conditions.

No e f f l o r e s c e n c e c a n o c c u r in t h e a b s e n c e of w a t e r . It i s t h e w a t e r that c a r r i e s t h e s a l t s in solution t h r o u g h t h e m a s o n r y , and when i t e v a p o r a t e s , t h e s a l t s r e m a i n e i t h e r on t h e s u r f a c e o r within t h e m a s onr y.

S i m i l a r l y , soluble s a l t s m u s t be p r e s e n t . A v a r i e t y h a v e b e e n identified, including a l k a l i (Na and K) s u l p h a t e s and c a r b o n a t e s ,

a l k a l i n e e a r t h (Ca, Mg, Al) s u l p h a t e s and, i n s m a l l e r a m o u n t s , c a r b o n a t e s . NaCl h a s b e e n identified in c o a s t a l a r e a s w h e r e unwashed b e a c h s a n d s a r e f r e q u e n t l y used, and C a C l m a y o c c u r ₂ if t h i s m a t e r i a l is u s e d e x c e s s i v e l y a s an additive in t h e m o r t a r . T h e s e s a l t s a r e a l l white i n colour. Vanadium and molybdenum compounds, which a r e o c c a s i o n a l l y found i n e f f l o r e s c e n c e , p r o d u c e a g r e e n colour. T h e s o u r c e s of t h e s e soluble s a l t s in m a s o n r y m a y be: 1. back-up m a t e r i a l s , 2. m o r t a r , 3. b r i c k s , and 4. w a t e r . T h e r e l a t i v e c o n t r i b u t i o n s of back-up m a t e r i a l s and m o r t a r s h a v e been e x t e n s i v e l y studied (5, 6, 7 ) , and it is g e n e r a l l y a g r e e d t h a t

e f f l o r e s c e n c e f r o m t h e s e s o u r c e s i n c r e a s e s with i n c r e a s i n g a l k a l i n e content in t h e m a t e r i a l s . T h e p r e s e n c e of a c i d s and soluble s a l t s i n r a i n w a t e r e n t e r i n g m a s o n r y w a l l s h a s a l s o b e e n e s t a b l i s h e d (1) and should not be discounted.

T h e e x i s t e n c e of s o u r c e m a t e r i a l i n b r i c k s h a s b e e n s i m i l a r l y d e m o n s t r a t e d . A "wick" t e s t h a s b e e n developed t o a s s e s s t h e tendency of b r i c k s t o w a r d e f f l o r e s c e n c e . T h i s i s included in t h e ASTM S t a n d a r d Method of Sampling and T e s t i n g B r i c k s , C-67. In a n e x t e n s i v e s t u d y t h a t included 684 b r i c k s m a n u f a c t u r e d i n t h e United S t a t e s , M c B u r n e y and P a r s o n s (8) found t h a t 8 3 p e r . c e n t did not c o n s t i t u t e a s o u r c e of e f f l o r e s c e n c e . C o r r e s p o n d i n g l y , Bonnell and B u t t e r w o r t h (9) found t h a t l e s s t h a n 1 1 of 175 b r i c k s f r o m p l a n t s in G r e a t B r i t a i n and N o r t h e r n I r e l a n d gave h e a v y or s e r i o u s e f f l o r e s c e n c e . B r o w n e l l ( 3 ) s t a t e s t h a t a c e r a m i c p r o d u c t can contain about 0 . 2% of e x t r e m e l y soluble s a l t b e f o r e e f f l o r e s c e n c e b e c o m e s a p p a r e n t .

It is difficult for w a t e r t o m i g r a t e through a w a l l i f t h e w a l l contains d e n s e i m p e r m e a b l e u n i t s and h a s been c o n s t r u c t e d with s u p e r i o r workmanship. I n f e r i o r w o r k m a n s h i p , however, m a y r e s u l t i n r e a d y p a t h s f o r w a t e r t o t r a v e l along, and even with good w o r k m a n s h i p , i t i s p o s s i b l e t h a t t h e p o r o s i t y of t h e u n i t s m a y be in a r a n g e t h a t w i l l f a c i l i t a t e m o i s t u r e movement. B r o w n e l l ( 3 ) f u r t h e r s t a t e s t h a t a c e r a m i c body with z e r o p e r cent a b s o r p t i o n cannot p r o d u c e e f f l o r e s c e n c e , and t h e r e i s p r o b a b l y s o m e p r a c t i c a l l i m i t between z e r o and s i x p e r c e n t a t which e f f l o r e s c e n c e will not o c c u r .

Weather conditions a1s.o p l a y a n i m p o r t a n t p a r t i n t h e e f f l o r e s c e n c e phenomenon. T h e y d e t e r m i n e , i n f a c t , whether

e f f l o r e s c e n c e will occur on the s u r f a c e or within t h e unit. During t h e l a t e winter months, t h e combination of r e l a t i v e l y low t e m p e r a t u r e s and high h u m i d i t i e s p r o d u c e s a slow r a t e of. evaporation. Throughout

t h i s period, any w a t e r in a s t r u c t u r e r e a c h e s the s u r f a c e b e f o r e evaporation, leaving the u n a t t r a c t i v e s a l t s on t h e wall, T h i s is a s e a s o n of poor drying weather when t h e incidence of unsightly e f f l o r e s c e n c e is a t i t s peak. Upon t h e advent of w a r m , d r y s u m m e r w e a t h e r , however, t h e w a t e r m a y change t o vapour b e f o r e r e a c h i n g t h e s u r f a c e of t h e m a s o n r y , and t h e s a l t s a r e

deposited within t h e wall, hidden, and g e n e r a l l y unsuspected. A s p r e v i o u s l y mentioned, t h e danger in t h i s c a s e i s t h a t s a l t s will a c c u m u l a t e in l a r g e enough amounts t o c r e a t e p r e s s u r e s sufficient t o spa11 t h e s u r f a c e f r o m m o r t a r or m a s o n r y uniis.

EXPERIMENTAL

The method u s e d in t h i s investigation w a s e s s e n t i a l l y t h a t followed by R i t c h i e i n which h e studied e f f l o r e s c e n c e on c e r a m i c wicks embedded in c y l i n d e r s of m a s o n r y m o r t a r s of different composition,

which w e r e a l t e r n a t e l y wetted and d r i e d a f t e r t h e m o r t a r had h a r d e n e d . (5). As t h e p u r p o s e of our study w a s t o a s c e r t a i n t h e influence of t h e b r i c k s in t h e e f f l o r e s c e n c e p r o c e s s , t h e wick w a s t h e v a r i a b l e i n s t e a d of t h e m o r t a r . Wicks w e r e cut f r o m t h e v a r i o u s u n i t s and embedded i n .cylinders of a 1:3 p o r t l a n d cement:sand m o r t a r .

T h e wicks w e r e a p p r o x i m a t e l y 3 in. long by 12 in. wide and 3/16 in. thick. T h e r e w e r e 8 different wicks cut f r o m 7 b r i c k s and a sandstone. Throughout t h i s p a p e r , t h e u s e of t h e g e n e r a l t e r m "bricks" will e n c o m p a s s a l l s a m p l e s , including t h e sandstone. T h e 7 b r i c k s r e p r e s e n t e d 6 v a r i e t i e s . Wicks w e r e cut f r o m one b r i c k a t two distinct l e v e l s of i n i t i a l r a t e of absorption.

A s noted previously, t h e m o r t a r contained one p a r t portland cement t o t h r e e p a r t s sand by volume. A pit sand was used along with distilled w a t e r . T h e m o r t a r w a s mixed i n a H o b a r t N-50 m i x e r for 5 min, final flow being a d j u s t e d t o f a l l between 110 and 1 2 5 p e r cent.

Two- by four-in. cylinder m o l d s w e r e used, with a wooden plug i n s e r t e d i n t h e lower p a r t of t h e mold s o that t h e r e s u l t i n g m o r t a r cylinder was 2$ in. high.

T h e m o r t a r w a s placed i n t h e mold i m m e d i a t e l y a f t e r mixing w a s comp1e:t:d and a wick, p r e v i o u s l y wetted i n d i s t i l l e d w a t e r t o i m p r o v e i t s contact, w a s i n s e r t e d t o a depth of 1 in. A deep s c r a t c h had been m a d e on t h e wicks 1 in. f r o m t h e end, and s e r v e d a s a guide in i n s e r t i n g t h e m t o t h e p r o p e r depth i n t h e m o r t a r . L a t e r , t h e s c r a t c h w a s u s e f u l i n facilitating s e p a r a t i o n of wick and m o r t a r by breaking. T h e wick- m o r t a r a s s e m b l a g e w a s r e m o v e d f r o m t h e mold a f t e r 24 h r and s t o r e d i n controlled l a b o r a t o r y a i r (70" F and 50 p e r cent

R.

H. ) for 7 days b e f o r e s t a r t i n g t h e wetting-drying cycles.

F o r wetting and drying, s a m p l e s w e r e p l a c e d i n s m a l l j a r s ( c a p a c i t y about 7 oz. ) and distilled w a t e r w a s added t o b r i n g t h e l e v e l just below t h e top s u r f a c e of t h e m o r t a r . M e t a l c o v e r s , i n which s l o t s w e r e cut t o p e r m i t t h e wicks t o p r o t r u d e , w e r e p l a c e d on t h e j a r s . E v a p o r a t i o n of w a t e r through t h e gap between t h e wick and edges of t h e slot w a s r e d u c e d by placing thin g l a s s p l a t e s on t h e c o v e r a g a i n s t t h e wick. T o s t a r t t h e cycling, s a m p l e s w e r e i m m e r s e d i n w a t e r , a s

d e s c r i b e d , for a 24-hr period. T h e n t h e y w e r e r e m o v e d f r o m t h e w a t e r and allowed t o d r y i n l a b o r a t o r y a i r f o r 7 h r . T h e y w e r e then r e p l a c e d in t h e j a r s , using t h e o r i g i n a l w a t e r , which w a s r e p l e n i s h e d i n o r d e r t o b r i n g t h e l e v e l t o its o r i g i n a l height. After 17 h r i n t h e w a t e r , t h e drying p r o c e d u r e w a s repeated. Thus, in 24 h r , s a m p l e s w e r e wetted for 17 h r and d r i e d f o r 7.

During t h e wetting p e r i o d , w a t e r m i g r a t e d through t h e m o r t a r and into t h e wick, u l t i m a t e l y evaporating f r o m t h e wick s u r f a c e s . During i t s m i g r a t i o n , t h e w a t e r picked up soluble s a l t s f r o m t h e m o r t a r and/or t h e wick, and t h e s e s a l t s w e r e left behind when t h e w a t e r evaporated, e i t h e r on t h e s u r f a c e o r within t h e wick.

After completing 10 wetting-drying c y c l e s , t h e s a m p l e s w e r e s t o r e d f o r 7 days i n c o n t r o l l e d l a b o r a t o r y a i r . A s s e s s m e n t s by v i s u a l

o b s e r v a t i o n w e r e made, and t h e s a m p l e s photographed. Wicks w e r e then c a r e f u l l y b r o k e n away f r o m t h e m o r t a r cylinder (along t h e s c r a t c h line), d r i e d i n an oven f o r 48 h r a t 100" C, cooled and weighed. T h e n t h e y w e r e e x t r a c t e d with distilled w a t e r . E a c h wick w a s p l a c e d i n 50 m l of distilled w a t e r and allowed t o s o a k f o r 24 h r . T h e w a t e r w a s t h e n d r a i n e d f r o m t h e wick and r e p l a c e d with another 50 ml. An hour l a t e r t h e p r o c e d u r e w a s r e p e a t e d , and t h i s continued until t h e wick h a d been washed i n 250 m l of water. T h e w a s h w a t e r w a s l a t e r evaporated, and t h e s a l t s r e c o v e r e d w e r e weighed and r e t a i n e d f o r a n a l y s i s .

After t h e washing t r e a t m e n t , wicks w e r e d r i e d for 48 h r at 100" C, cooled and weighed. T h e d i f f e r e n c e in weight, b e f o r e and a f t e r washing, r e p r e s e n t e d t h e weight of soluble s a l t deposited in t h e wick. Blank r u n s had p r e v i o u s l y been conducted on wicks f r o m a l l of t h e b r i c k s , and soluble s a l t t o t a l s , r e c o v e r e d f r o m wicks i n s e r t e d i n m o r t a r , w e r e c o r r e c t e d accordingly. As the wicks v a r i e d slightly in s i z e , f i n a l r e s u l t s w e r e e x p r e s s e d a s a p e r c e n t a g e of t h e i r d r y weight. All s a m p l e p r e p a r a t i o n , wetting-drying cycling, etc.

,

was conducted i n c o n t r o l l e d l a b o r a t o r y a i r (70" F and 50 p e r cent R.H.).

BLANK TESTS ON MATERIALS

All t h e b r i c k s w e r e subjected t o t h e e f f l o r e s c e n c e t e s t outlined in ASTM C67-60, in which t h e s p e c i m e n s a r e s e t on end i n distilled w a t e r , i m m e r s e d t o a depth of 1 in., and left for 7 days. They w e r e then d r i e d and c o m p a r e d visually with duplicate c o n t r o l s p e c i m e n s . F i v e of the 7 b r i c k s t e s t e d w e r e f r e e of efflorescence. Heavy e f f l o r e s c e n c e o c c u r r e d on one of t h e b r i c k s (No. 5) and t h e r e was a minor o c c u r r e n c e on b r i c k No. 7 , w h e r e a t r a c e of s a l t a p p e a r e d on t h e top f r o n t c o r n e r s of one s a m p l e . R e s u l t s f o r t h e s e two b r i c k s a r e shown i n F i g u r e 1.

Blank r u n s w e r e a l s o conducted t o d e t e r m i n e t h e soluble s a l t content of t h e wicks. The p r o c e d u r e followed i n washing t h e m with distilled w a t e r was outlined previously. The amount of s a l t s r e c o v e r e d is shown in T a b l e I. Seven of t h e eight wicks contained 0. 08 p e r cent

o r l e s s , while wicks f r o m b r i c k No. 5, which exhibited s e v e r e e f f l o r e s c e n c e in t h e t e s t above, contained 0.26 p e r cent.

A c h e m i c a l a n a l y s i s of t h e s a l t r e c o v e r e d f r o m t h i s b r i c k is included in Table IV, and it indicates that the m a j o r constituent i s magnesium sulphate.

C h e m i c a l a n a l y s e s w e r e a l s o c a r r i e d out on t h e m o r t a r constituents, R e s u l t s f o r portland cement and a w a t e r e x t r a c t of t h e sand a r e shown in T a b l e 11. It will be noted that only negligible amounts of s a l t s a r e p r e s e n t i n t h e sand,

SELECTION O F MORTAR MIX

In a p r e l i m i n a r y study, wicks f r o m b r i c k NO, 8 w e r e s e t i n m o r t a r s of v a r i o u s compositions, including a r a n g e of c e m e n t - l i m e combinations and two m a s o n r y c e m e n t s .

R e s u 1 . t ~ w e r e s i m i l a r t b t h o s e of R i t c h i e in establishing g r e a t e s t e f f l o r e s c e n c e with m o r t a r s having highest portland c e m e n t contents (5).

A 1:3 portland cement:sand m o r t a r was, t h e r e f o r e , s e l e c t e d a s t h e m o r t a r in which wicks w e r e t o b e embedded.

RESULTS O F TESTS ON WICKS EMBEDDED IN MORTAR A. Visual

Visual o b s e r v a t i o n s and photographs ( F i g u r e s 2 t o 4)

of wicks f r o m t h e v a r i o u s b r i c k s embedded in m o r t a r c y l i n d e r s indicated f a i r l y heavy deposits on some, while o t h e r s w e r e c o m p a r a t i v e l y f r e e of s a l t s . The m o s t pronounced e f f l o r e s c e n c e was o b s e r v e d on wicks Nos. 3 and

6,

with wick No. 8 c l o s e behind. A c o m p a r i s o n of v i s u a l r e s u l t s proved difficult. Specimens w e r e not a l l s e e n at t h e s a m e t i m e , but w e r e

evaluated a t i n t e r v a l s of s e v e r a l days. It should a l s o b e noted t h a t r e d , brown, buff, and g r e y wicks w e r e used. Thus, 4 different colour b a c k - grounds added another complication t o a difficult problem. P h o t o g r a p h s of wicks Nos. 1 and 5, on which v i s i b l e e f f l o r e s c e n c e w a s negligible, a r e not shown.

B. Quantitative

T h e amounts of s a l t s e x t r a c t e d f r o m t h e wicks a r e

r e c o r d e d in T a b l e 111. The f i r s t column i n d i c a t e s t o t a l s a l t s r e c o v e r e d , and t h e second, t h e c o r r e c t e d amounts (value f o r t o t a l s a l t s l e s s t h e amounts originally p r e s e n t in t h e wicks

-

T a b l e I). L a r g e s t amounts of s a l t s (2. 58 p e r cent) w e r e r e c o v e r e d f r o m wicks Nos. 2 and 5, with 2.37 and 2.27 p e r cent being r e c o v e r e d f r o m wicks Nos. 7 and 8. L e s s than 1 p e r cent was r e c o v e r e d f r o m each of t h e r e m a i n i n g 4 wicks.

T h e c o r r e c t e d t o t a l s indicate a h i g h e r f i g u r e for wick No. 2 than for wick No. 5. T h e significance of t h e c o r r e c t e d t o t a l s m a y not be great. P o s s i b l y t h e 2. 58 p e r cent m a y r e p r e s e n t t h e capacity of t h e wicks t o hold s a l t s . Any additional s a l t could have been "lost" f r o m t h e e x t e r i o r of t h e wick, e i t h e r by m e c h a n i c a l action in i n s e r t i n g and removing t h e wick f r o m t h e slotted c o v e r on t h e j a r s , o r s i m p l y by a "flaking off" of t h e s a l t f r o m t h e s u r f a c e .

Quantitative r e s u l t s thus definitely e s t a b l i s h t h e higher e f f l o r e s c e n c e potential of wicks Nos. 2, 5, 7, and 8.

ANALYSIS O F SALTS

S a l t s r e c o v e r e d f r o m wicks Nos. 2, 5, and 8, f r o m which t h e l a r g e s t amounts w e r e obtained, and f r o m wick No. 6, which r a t e d " s e v e r e 1 ' i n t h e v i s u a l a s s e s s m e n t , w e r e analyzed t o d e t e r m i n e t h e m a j o r constituents, and r e s u l t s a r e shown i n T a b l e IV. A l s o included i n t h i s t a b l e i s an a n a l y s i s of s a l t obtained f r o m b r i c k No. 5 during the blank t e s t on it.

R e s u l t s i n d i c a t e that s a l t s obtained f r o m wicks Nos. 2, 6, and 8, contain p r i m a r i l y p o t a s s i u m carbonate, with a s m a l l amount of sulphate. The m a i n constituents of No. 5 a r e p o t a s s i u m and sulphate, with s m a l l e r amounts of c a l c i u m and carbonate. It is a l s o i n t e r e s t i n g t o note that m a g n e s i u m sulphate, t h e m a j o r constituent of s a l t s o r i g i n a l l y i n b r i c k No. 5, becomes potassium sulphate i n t h e wick, a f t e r it h a s been i n contact with t h e m o r t a r .

DISCUSSION

R e s u l t s of v i s u a l a s s e s s m e n t of e f f l o r e s c e n c e on wicks w e r e inconclusive and did not a g r e e with quantitative r e s u l t s obtained when soluble s a l t s w e r e e x t r a c t e d f r o m t h e wicks. T h e l a t t e r r e s u l t s w e r e in good a g r e e m e n t with field o b s e r v a t i o n s w h e r e t h e 3 b r i c k s , f r o m which t h e wicks containing g r e a t e s t a m o u n t s of soluble s a l t s w e r e obtained, a r e identified with t h e m o s t s e v e r e e f f l o r e s c e n c e p r o b l e m s . E x a m p l e s f r o m t h e field involving 2 of t h e 3 b r i c k s a r e shown in F i g u r e 5.

C h e m i c a l a n a l y s e s of s a l t s f r o m wicks and b r i c k , coupled with t h e s e v e r e e f f l o r e s c e n c e o c c u r r i n g during t h e blank t e s t on t h e b r i c k , e s t a b l i s h t h e s o u r c e m a t e r i a l for wick No. 5 as magnesium sulphate

located in t h e brick. It is i n t e r e s t i n g t o note that s a l t s r e c o v e r e d i n t h e blank t e s t w e r e 0, 26 p e r cent of t h e weight of t h e wick. T h i s s u b s t a n t i a t e s Brownell's a s s e r t i o n that e f f l o r e s c e n c e i s likely t o occur when t h e c e r a m i c product contains in e x c e s s of 0. 2 p e r cent of e x t r e m e l y soluble s a l t s ( 3 ) .

T h e s o u r c e m a t e r i a l f o r t h e soluble s a l t s r e c o v e r e d f r o m t h e r e m a i n i n g wicks is a s s u m e d t o h a v e o r i g i n a t e d in t h e m o r t a r . No a p p r e c i a b l e amounts of s a l t s w e r e r e c o v e r e d f r o m blank t e s t s on t h e wicks, while t h e p r e s e n c e of a l k a l i n e s a l t s w a s indicated by a c h e m i c a l a n a l y s i s on t h e portland c e m e n t u s e d i n t h e m o r t a r ( T a b l e 11). The s a m e m o r t a r combination w a s u s e d for a l l s p e c i m e n s , however, and d i f f e r e n c e s i n t h e r e s u l t s , both visual and quantitative, obtained with t h e v a r i o u s wicks, m u s t r e f l e c t d i f f e r e n c e s i n t h e i r p r o p e r t i e s .

Initial r a t e s of absorpt"ion for the b r i c k s , and a b s o r p t i o n p r o p e r t i e s of wicks cut f r o m t h e b r i c k s and u s e d i n t h e study, having p r e v i o u s l y been d e t e r m i n e d , a r e l i s t e d in T a b l e V. A c o m p a r i s o n w a s m a d e between t h e quantitative r e s u l t s and t h e s e p r o p e r t i e s , and is shown g r a p h i c a l l y in F i g u r e

6.

T h e r e i s no c o n c r e t e evidence of a d i r e c t r e l a t i o n s h i p between IRA of t h e b r i c k s and t h e a m o u n t s of s a l t s r e c o v e r e d f r o m t h e wicks, although t h e r e i s a t r e n d indicating l a r g e r amounts of s a l t s a s IRA v a l u e s i n c r e a s e . T h i s t r e n d is c o n t r a d i c t e d by r e s u l t s f o r b r i c k No. 2, with a n R A of 13 gm/30 sq in. /min f r o m which 2.58 p e r cent soluble s a l t s was r e c o v e r e d , while b r i c k s Nos. 7 and 8, with much higher and quite different IRA values, had lower s a l t contents. Again, b r i c k No. 3, with a n LRA value c l o s e t o t h e value for b r i c k No. 2, h a d a much lower s a l t content.

A c o m p a r i s o n of 24-hr i m m e r s i o n and 5-hr boiling a b s o r p t i o n values with s a l t s r e c o v e r e d , s u g g e s t s a m o r e definite relationship. T h e r e s u l t s in F i g u r e

6

indicate a distinct difference between t h e high s a l t content wicks and t h e low ones. T h e s e l i m i t e d r e s u l t s a r e in a c c o r d with t h e second of B r o w n e l l s s conclusions mentioned p r e v i o u s l y

-

t h a t a c e r a m i c body with z e r o p e r cent

a b s o r p t i o n cannot produce e f f l o r e s c e n c e , and t h e r e i s p r o b a b l y s o m e p r a c t i c a l l i m i t between z e r o and s i x p e r cent at which e f f l o r e s c e n c e will not o c c u r ( 3 ) . .

T h e r e i s a l s o a g e n e r a l r e l a t i o n s h i p between s o l u b l e s a l t contents and a p p a r e n t p o r o s i t y with l a r g e r s a l t c o n c e n t r a t i o n s o c c u r r i n g in wicks with g r e a t e s t p o r o s i t i e s . A s in t h e c a s e of t h e LRA c o m p a r i s o n , t h e r e a r e s o m e c o n f l i c ~ i n g r e s u l t s t o t h i s t r e n d . Wicks with 17. 2 p e r cent p o r o s i t y had soluble s a l t contents m o r e i n l i n e with

9.

4 p e r cent p o r o s i t y wicks than with t h o s e at t h e 2 2 . 0 p e r cent level. T h u s , t h e r e is a g e n e r a l indication of i n c r e a s i n g s a l t content with i n c r e a s i n g a b s o r p t i o n values f o r t h e wicks u s e d in t h e study, but l i m i t e d , and s o m e conflicting r e s u l t s , m a k e definite conclusions difficult,

C o n s i d e r a t i o n w a s a l s o given t o t h e effect of t h e n a t u r e of t h e s t r u c t u r e on t h e e f f l o r e s c e n c e p r o c e s s . C l e a r l y , a b r i c k

containing a l a r g e p e r c e n t a g e of p o r e s running through t h e unit would be m o r e s u s c e p t i b l e t o e f f l o r e s c e n c e than a unit containing a l a r g e p e r c e n t a g e of closed o r "dead-end" p o r e s . S i m i l a r l y , it i s r e a s o n a b l e t o a s s u m e t h a t t h e r e m u s t b e a c e r t a i n r a n g e of p o r e s i z e s t h a t w i l l f a c i l i t a t e m a x i m u m m o i s t u r e m i g r a t i o n and t h u s p r o m o t e e f f l o r e s c e n c e .

R e c o r d s of p o r e - s i z e d i s t r i b u t i o n s f o r 6 of t h e 8 b r i c k s included in t h e study, obtained with a m e r c u r y p o r o s i m e t e r , a r e r e c o r d e d in T a b l e VI and shown g r a p h i c a l l y in F i g u r e 7. T h e s e r e s u l t s a r e f o r

s a m p l e s r e p r e s e n t a t i v e of the t y p e s of b r i c k s u s e d in t h e study, but a r e not a c t u a l l y r e s u l t s f o r t h e p a r t i c u l a r s p e c i m e n s used. In s o m e i n s t a n c e s t h e r e i s a c o n s i d e r a b l e d i f f e r e n c e between t h e p o r o s i t y v a l u e s in T a b l e VI

and t h e v a l u e s l i s t e d f o r t h e c o r r e s p o n d i n g wicks in T a b l e V, F o r t h e p u r p o s e of t h i s d i s c u s s i o n , however, t h e v a l u e s in T a b l e VI w i l l b e

c o n s i d e r e d r e p r e s e n t a t i v e f o r t h e different wicks u s e d in t h e study. P o r e s i z e s in b r i c k s Nos. 1 and 4 a r e s m a l l ; o v e r 80 p e r cent of t h o s e in b r i c k No. 1 w e r e u n d e r 1 p a n d 75 p e r c e n t of t h o s e in b r i c k No, 4 w e r e under 2. 5 p . Twenty-five p e r cent of t h e p o r e s i n b r i c k No. 3 w e r e between 1 znd 10 p , with t h e r e m a i n d e r being f a i r l y evenly divided between u n d e r 1 p and over 10 p

.

T h e r e m a i n i n g 3 b r i c k s had a l a r g e p e r c e n t a g e of p o r e s in t h e 1 t o 10 p s i z e range. A l m o s t 70 p e r cent of t h e p o r e s i n b r i c k No. 2 w e r e between 1 and 10 p, Most of t h e r e m a i n d e r w e r e under 1 p . Relatively, t h e s a m e d i s t r i b u t i o n o c c u r r e d i n b r i c k No. 6. B r i c k No. 8 had o v e r 60 p e r cent of i t s p o r e s in t h e 1 t o 10 p r a n g e , with t h e r e m a i n d e r

divided between under 1 p and over 10 LL

.

It differed f r o m b r i c k s Nos. 2 and

6

in having a g r e a t e r p e r c e n t a g e of p o r e s over 10 p i n s i z e . No d a t a a r e a v a i l a b l e f o r b r i c k No. 5, nor for b r i c k No. 7, although t h e l a t t e r i s c o n s i d e r e d e s s e n t i a l l y t h e s a m e f o r t h i s p u r p o s e a s b r i c k No. 8.

Thus, two of t h e b r i c k s with h i s t o r i e s of r a t h e r s e v e r e e f f l o r e s c e n c e in t h e field, and which yielded l a r g e soluble s a l t contents during wick t e s t s d e s p i t e low s a l t c o n c e n t r a t i o n s e s t a b l i s h e d during blank t e s t s , h a v e p o r e s i z e s p r e d o m i n a n t l y i n t h e 1 t o 10 p r a n g e . T h r e e of t h e four r e m a i n i n g b r i c k s f o r which p o r e - s i z e data a r e available, had

d i s t r i b u t i o n s p r e d o m i n a n t l y below 1 p and o v e r 10 p. T h e f o u r t h b r i c k , No. 6, had a p o r e - s i z e distribution s i m i l a r t o t h a t i n t h e two u n i t s with an e f f l o r e s c e n c e h i s t o r y , but i t i s not a s s o c i a t e d with s e r i o u s e f f l o r e s c e n c e i n t h e field, nor w e r e l a r g e a m o u n t s of soluble s a l t s r e c o v e r e d f r o m i t s wicks. B r i c k No. 6 was t h e s a n d s t o n e ; t h e o t h e r s w e r e f i r e d c l a y b r i c k s . P e r h a p s i t s different behaviour m a y r e s u l t f r o m d i f f e r e n c e s i n p o r e s h a p e s and s t r u c t u r e , r a t h e r than s i z e . T h i s b r i e f study u s i n g p o r e - s i z e d i s t r i b u t i o n s of r e p r e s e n t a t i v e s a m p l e s of u n i t s u s e d i n t h e e x p e r i m e n t a l w o r k s u g g e s t s a n i n t e r e s t i n g a r e a f o r f u t u r e i n v e s t i g a t i o n s of t h e e f f l o r e s c e n c e phenomenon.

The remaining point f o r discussion concerns t h e conflicting evidence of visual hnd quantitative r e s u l t s f o r wicks Nos. 3 and

6,

f r o m which comparatively s m a l l amounts of s a l t s w e r e r e c o v e r e d despite pronounced deposits observed visually. It i s suggested that t h i s was t h e r e s u l t of different s u r f a c e t e x t u r e s for t h e s e wicks; that s a l t deposits w e r e left when water moved up the s u r f a c e of the wick by c a p i l l a r y attraction, and then evaporated. Smoother t e x t u r e of the other wicks did not

facilitate s u r f a c e capillarity, and s a l t s recovered f r o m them w e r e

introduced a s water p a s s e d through the p o r e s of the wicks and evaporated. COMPARISON OF SULPHATE AND CARBONATE EFFLORESCENCE

Field observations have indicated a m o r e s e v e r e and somewhat different mappearing efflorescence on m a s o n r y containing b r i c k No. 5, than on m a s o n r y containing b r i c k s Nos. 2 or 8. The f o r m e r h a s the appearance of a loose, fluffy powder and o c c u r s in l a r g e r amounts than the l a t t e r , which a p p e a r s a s a fine, clinging powder. Although

chemical analysis was not done on s a l t s observed in the field, a visual comparison was made with l a b o r a t o r y e f f l o r e s c e n c e c r e a t e d by i m m e r s i n g b r i c k s in solutions of equal s t r e n g t h of potassium sulphate and potassium

carbonate. T h r e e s a m p l e s of b r i c k No, 7 w e r e i m m e r s e d end-wise t o a depth of 1 in. in a 5 p e r cent solution of potassium sulphate. An equal number of s a m p l e s w e r e i m m e r s e d in a s i m i l a r manner in a 5 p e r cent

solution of potassium carbonate, and l e f t f o r 7 days. A heavy efflorescence appeared on the b r i c k s i m m e r s e d in the potassium sulphate solution s h o r t l y after the s t a r t of t h e t e s t , but only a minor showing o c c u r r e d on t h e b r i c k s in the potassium carbonate solution. At the end of the 7 days, the bricks w e r e removed f r o m the solutions and allowed t o dry. Drying resulted in a much m o r e pronounced showing on both bricks. T h i s i s c l e a r l y shown in F i g u r e 8, where a heavier deposit with a different appearance o c c u r s on the b r i c k s that w e r e i m m e r s e d in the sulphate.

Significantly, the efflorescence noted in the top photograph of F i g u r e 8 i s quite s i m i l a r t o that seen in the top photograph of Figure 5, while t h e r e i s a corresponding s i m i l a r i t y between t h e bottom p i c t u r e s in F i g u r e s 5 and 8.

C ONC LUSIONS

1. Blank efflorescence t e s t s on b r i c k s f r o m which wicks w e r e cut w e r e negative in a l l but one instance. Heavy efflorescence o c c u r r e d on b r i c k No. 5. Chemical analysis revealed the major constituent of t h e efflorescent s a l t to be magnesium sulphate.

2. Blank t e s t s on wicks iridicated l e s s than 0 . 1 p e r cent soluble s a l t contents f o r a l l but No. 5, which contained 0. 26 p e r cent. T h e l a t t e r wicks w e r e cut f r o m t h e b r i c k r e f e r r e d t o i n t h e p r e v i o u s p a r a g r a p h .

3. T e s t s on wicks cut f r o m different b r i c k s and embedded i n 1:3 p o r t l a n d cement:sand m o r t a r w e r e u n s u c c e s s f u l i n r e p r o d u c i n g

e f f l o r e s c e n c e s i m i l a r t o t h a t o b s e r v e d i n t h e field.

4. Soluble s a l t t o t a l s , obtained by washing wicks a t t h e conclusion of t h e e f f l o r e s c e n c e t e s t s , r e v e a l e d highest c o n c e n t r a t i o n s i n 4 wicks cut f r o m b r i c k s found t o b e p a r t i c u l a r l y s u s c e p t i b l e t o

e f f l o r e s c e n c e in t h e field.

5. C h e m i c a l a n a l y s e s of s a l t s r e c o v e r e d f r o m wicks embedded i n m o r t a r indicated p o t a s s i u m c a r b o n a t e t o b e t h e m a i n

constituent in all but wick No. 5, w h e r e p o t a s s i u m s u l p h a t e predominated.

6.

Soluble s a l t s o c c u r r i n g in wick No. 5 originated with s a l t s o r i g i n a l l y found i n t h e b r i c k itself, while f o r a l l o t h e r s p e c i m e n s , t h e s o u r c e m a t e r i a l a p p e a r s t o have been a l k a l i s a l t s in the p o r t l a n d c e m e n t u s e d in t h e m o r t a r .

7. A c o m p a r i s o n of t h e a b s o r p t i o n p r o p e r t i e s of t h e wicks and t h e i r soluble s a l t contents i n d i c a t e s a gener a1 r e l a t i o n s h i p with i n c r e a s i n g s a l t contents a s a b s o r p t i o n values r o s e .

8. Examination of p o r e - s i z e d i s t r i b u t i o n s f o r t y p i c a l s p e c i m e n s of

6

of t h e 8 b r i c k s included in t h e study r e v e a l e d p o r e

s i z e s in t h e 1 t o 10 p r a n g e f o r wicks having l a r g e s t soluble s a l t contents, while wicks with lower s a l t contents had p o r e s in t h e r a n g e of under 1 p and over 10 p. An exception was t h e sandstone, which had low s a l t concentration and a p o r e - s i z e distribution in t h e 1 t o 10 p range. An i n t e r e s t i n g a r e a f o r f u t u r e e f f l o r e s c e n c e s t u d i e s i s indicated.

ACKNOWLEDGEMENTS

T h e author w i s h e s t o thank h i s colleague, T , Ritchie, of t h e Inorganic M a t e r i a l s Section, who c a r r i e d out t h e d e t e r m i n a t i o n s of p o r e - s i z e distribution. He i s a l s o indebted t o t h e Division of

Applied C h e m i s t r y and e s p e c i a l l y t o G. R. Duval, A. Mykytiuk, and E. C. Goodhue, who conducted t h e c h e m i c a l a n a l y s e s .

R E F E R E N C E S

1. A n d e r egg, F. 0. E f f l o r e s c e n c e . ASTM B u l l e t i n No. 195, O c t o b e r 1952.

2. B u t t e r w o r t h , B. E f f l o r e s c e n c e a n d S t a i n i n g of B r i c k w o r k . T h e B r i c k Bulletin, Vol. 3, No. 5, 1961.

3. B r o w n e l l , W. E. F u n d a m e n t a l F a c t o r s Influencing E f f l o r e s c e n c e of C l a y P r o d u c t s . J o u r n a l of t h e A m e r i c a n C e r a m i c Society, Vol. 32, No. 12, 1949. 4. R i t c h i e , T. Study of E f f l o r e s c e n c e on E x p e r i m e n t a l B r i c k w o r k P i e r s . J o u r n a l of t h e A m e r i c a n C e r a m i c Society, Vol. 38, No. 10, 1955. 5. R i t c h i e , T. S t u d y of E f f l o r e s c e n c e P r o d u c e d on C e r a m i c Wicks by M a s o n r y M o r t a r s . J o u r n a l of t h e A m e r i c a n C e r a m i c S o c i e t y , Vol, 38, No. 10, 1955. 6 . _{R o g e r s ,} P. L. A Method of T e s t f o r P o t e n t i a l E f f l o r e s c e n c e of M a s o n r y M o r t a r . ASTM B u l l e t i n , J a n u a r y 1959. 7. Young, J a m e s E. Backup M a t e r i a l s a s a S o u r c e of E f f l o r e s c e n c e . J o u r n a l of t h e A m e r i c a n C e r a m i c S o c i e t y , Vol. 40, No. 7, J u l y 1957. 8. M c B u r n e y , J. W. and D. E, P a r s o n s , T h e Wick T e s t f o r E f f l o r e s c e n c e of Building B r i c k . ASTM P r o c e e d i n g s , Vol. 37,

1937, p. 332.

9. Bonnell, D. G. R. a n d B. B u t t e r w o r t h , C l a y Building B r i c k s of t h e United Kingdom. HM S t a t i o n e r y Office, 1950.

T A B L E I

R E S U L T S O F BLANK T E S T S ON WICKS

S a l t s R e c o v e r e d , Wick f r o m B r i c k No.

70

wt. of w i c k

T A B L E I1

CHEMICAL ANALYSIS O F MORTAR MATERIALS

P o r t l a n d C e m e n t .

yo

Wash W a t e r of t h e S a n d ( P a r t s

p e r

Million) nn. d.

=

n o n e d e t e c t e d

T A B L E I11

SALTS RECOVERED FROM WICKS AuFTER E F F L O R E S C E N C E T E S T

Wick No. S a l t s R e c o v e r e d , O/o wt. of wick T ot a1 C o r r e c t e d * 1 0, 2 4 0. 22 2 2. 58 2. 52 3 0 . 9 4 0 - 9 3 4 0.90 0.86 5 2. 58 2. 3 1 6 0. 78 0.71 7 2. 27 2. 2 4 8 2. 37 2. 29

'k T o t a l amount l e s s amount o r i g i n a l l y p r e s e n t i n wicks.

T A B L E IV

CHEMICAL ANALYSIS O F SOLUBLE SALTS 0 UTAINED FROM WICKS AND E F F L O R E S C E N T

SALT REMOVED FROM BRICK NO, 5

S a l t f r o m S a l t f r o m

Wick N u m b e r : (2) (5) (6) (8) B r i c k No. 5

40.68 1. 36 35.32 38.96 1.06

T A B L E VI

B r i c k No.

PORE-SIZE DISTRIBUTION O F SIX

BRICKS

( P o r e Size,

70)

T o t a l > l o

CI

P o r o s i t y ,

70

Figure i Efflorescence test on bricks N o s . 5 and '7,

T O P

-

Brick No. 5. H e a v y efflorescence on odd- numbered specimens compared with even-numbered controls.

BOTTOM

-

B r i c k

No,

7 - N o t e small salt deposits

Figure 2 EffEoseacenee on wicks embedded in mortar.

T O P

-

Wick No. 2. There is some deposit near t o p 0% wicks. W i c k s a r e huff csPour making

efflorescence l e s s obvious.

F i g u r e 3 Efflorescence on wicks e m b e d d e d in mortar.

TOP

- W i c k No. 4. BOTTOM

-

W i c k N o .

6.

F i g u r e 4 E f f l o r e s c e n c e on wicks embedded in mortar. T O P

-

W i c k No. 7 .

Figure 5 Field observations of efflorescence of masonry buildings containing:

'TOP

-

B r i c k

No.

5 .

-

-

=

W i c k

no.

5

- -

0

- 0 0

-

- 0

-

0 -

-

0 0

-

-

-

I

I

I

0

0

-

-

-

O

-

-

-

-

-

-

_{0 0}

-

-

0

-

01

I

I

-

o 1

-

-

-

-

-

-

-

-

₀

-

-

-

-

0 0

-

0

001

S A L T S R E C O V E R E D ,

96

O F W E I G H T

O F

W I C K

F I G U R E 6

C O M P A R I

S O N

O F

S A L T S R E C O V E R E D A N D

P R O P E R T I E S O F W I C K S

OR 3 3 7 7 - 1

B r i c k n o .

3

P o r .

-

9.

3%

B r i c k n o .

1

P o r .

-

1 6 .

7%

-

--

B r i c k n o .

4

P o r ,

-

7 . 2 %

--lo

B r i c k n o . 2

--

P o r .

-

2 3 . 9 %

--

8

- -

6

-

4

B r i c k n o .

8

P o r .

-

1 6 . 2 %

--

2

-

I

P O R E S I Z E ,

U

,

B r i c k n o . 6

- - l o

P o r .

-

1 1 . 1 %

--

_-

₈

-

-

6

-

--

4

F I G U R E 7

-

--

2

-

--

D I S T R I B U T I O N O F P O R E S I Z E S I N B R I C K S

AR 3 3 77-2 - ( ~ o ~ 1 ~ 0 ~ ~ ~ '

1

~ ~ (

lcon5 1

2 ~0 . 5 - ~

1

~1.0- 2.5 5

1

2.5- ~5.0 ~

1

5.0-

10.O1

~ ~ >

1

1 0

Figure 8 C o ~ p a r i s o n of sulphate and carbonate after

Brick

No.

9

w a s immersed on end to a depth of 1 in.

TOP

-

5

per cent sokrltion of K ₂

SO

4'

BOTTOM

-

5

per cent solution of

K G O