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Journal of the Canadian Ceramic Society, 35, pp. 85-92, 1967-07-01
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Study of efflorescence in clay bricks
Davison, J. I.
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A STUDY OF
EFFLORESCENCE
IN
CLAY BRICKS
by
J. I. ~ a v i q s o n
Reprinted from the Journal of the Canadian Ceramic Society, Volume 35, 1966
A
Study
of
Efflorescence
in
(2) as a result of wetting during rain storms, (3) by migration of water vapour into the wall from high-humidity areas within the enclosure.
Clay
Bricks
During the construction process water is deposited in the structure in masonry mortar and plaster, and as the new walls dry out,by
J.
I.
Davison
emorescence often appears. This "initial"emorescence usually disappears after the construction water has evaporated, and if the During the winter of 1962-63 field observa- wall is resistant to rain penetration it prob- tions at several locations in the Atlantic area ably will not reappear.
revealed a higher than average occurrence of I t is inevitable that masonry walls will be efflorescence on walls of clay brick masonry. subject to wetting during rain storms. The Its severity seemed more closely related to amount of water entering the wall will specific bricks than to mortar composition depend on (1) the effectiveness of the design or type of construction. It suggested that details and the degree of workmanship bricks were contributing to the problem obtained during construction, and ( 2 ) the either by providing ( a ) a source of soluble nature of the structure of the masonry salts, o r ( b ) satisfactory media for ea*) materials used.
passage of salts in solution from mortar Among the important considerations at and back-up material through the walls. A the design stage are:
study was therefore undertaken to investigate (1) the type of wall structure,
the efflorescing tendencies of 'lay bricks (2) adequate flashings, particularly around commonly used in masonry construction in
openings, the area.
(3) sills and copings that project sufficiently
Background to throw water clear of the wall necessitating T h e appearance of efflorescence o n brick a properly designed "drip".
masonry buildings is a Source of chagrin to TOO much emphasis cannot be placed o n owners, embarrassment and workmanship. The best procedures f o r ensur- frustration to architects. T h e aesthetically ing a wall with maximum resistance t o rain objectionable salt deposits are the result of penetration must be insisted upon. inferior
the migration of workmanship inevitably results in ready soluble salts from within the the paths for water to enter and travel through surface, with subsequent evaporation of the
masonry
walls, ~ ~ i ~ i ~ lemorescence
mas
be water. During periods of warm; dry weather, by rain falling on partially conl- the transformation from liquid vaPour pleted walls that have not been adequately may occur before the solution reaches the covered at the end of the work, surface, thus leaving the salt deposits within E~~~ if the above precautions have all the wall. Paradoxically, although the s~lrface been observed, the nature of the structure of deposits are of great concern because the bricks and mortar used may promote are unsightly, they are harnlless; deposits efflorescence. Highly porous materials with left within the wall are generally high absorption potentials permit the entry because they are not obvious, but they have of water into the wall and facilitate its become recognized as a potential source of circulation through the interior. Browne]lc:i) masonry deterioration(lJ. As these salt states that a ceranlic body with zero per deposits build UP, they exert gradually in- cent absorption cannot produce efflorescence, creasing Pressures that and there is probably some practical limit great enough to spa11 away the surface between zero and 6 per cent at which the bricks and the mortar. emorescence will not occur.Efflorescence has been extensively studied ~h~ effect of weather conditions on e ~ l o - by many workersc1"'"'-" in recent years. resccnce has been mentioned previously. The factors essential for its Occurrence have After initial efflorescence has disappeared, been established to include: water enters the masonry during rain storms, (1) water, and the final location of the salt deposits o n (2) a wall structure conducive to ready pas- the surface o r within the wall depends upon the weather conditions during the drying
sage of water, period.
(3) a source of soluble salts, A variety of salts have been identified in (4) suitable weather conditions.
water
may enter masonry in several ways: Mr. Davison is research officer, Atlantic Regional Station, Division of Building Research, NationalTABLE I'
Absorption Properties of Wicks
.-
Wick IRA* 24-hr Submersion 5-hr Boiling
No. gm/30 sq in./min Absorption,
%
Absorption, "/, Porosity,X
*IRA values for bricks from which wicks were cut. TABLE I1
Results of Blank Tests on Wicks
-
.-
Salts Recovered, Wick from Brick No. "/, wt, of wick
TABLE 111
Chemical Analysis of Mortar Materials -
--
Wash Water of Portland the Sand (Parts Cement,
%
per Million)efflorescence deposits and are so well known *n.d. = none detected.
that they will not be discussed. ~h~ sources rescence was induced On ceramic wicks
of these salts have been established as: embedded in cylinders of masonry mortars of different composition by subjecting them ,
(I) back-up materials, to wetting and drying cycles after the mortar (2) mortar,
(3) water,
(4) bricks.
T h e relative contributions to efflorescence of source materials in back-up units and mortars have been extensively studied("6,;J. It is generally agreed that efflorescence in- creases with increasing alkali content in the source salts. Acids and soluble salts have also been identified in rain water and can enter masonry walls via this medium.
The presence of source salts in bricks has also been established. In an extensive study that included 684 bricks manufactured in the United States, McBurney and Parsons(8) found that 83 per cent did not constitute a source of efflorescence. Similarly, Bonnell and Butterworth(g1 found that less than 11 of 175 bricks from plants in Great Britain and Northern Ireland gave heavy o r serious efflorescence. Brownell(3) indicates that a ceramic product can contain about 0.2 per cent of extremely soluble salts before efflorescence becomes apparent. These studies have resulted in the development of an efflorescence test(l0) to indicate the pres- ence of soluble salts in bricks.
Experimental
T h e method of investigation was essentially that reported by Ritchiec",, in which efflo-
had har&kned. ~ksuits.were assessed on the basis of ( I ) visual observations and photo- graphs of the specimens, and (2) quantitative recovery of soluble salts from the wicks.
In the present study, the wicks were the variable instead of the mortar. Approxi- mately 3 in. long by I?: in. wide and 3/16 in. thick, they were cut from seven bricks and a sandstone. The seven bricks represented six types-two bricks of one type were included t o represent two IRA levels. T h e use of the term "brick" hereafter will cover all types, including the sandstone. All bricks were initially subjected to the efflorescence test previously mentioned. One showed severe salt deposits, one a trace (Figure I ) , while the others were clear. IRA and other absorption properties were determined and are listed in Table I. Blank tests were also conducted o n the wicks to determine the amounts of salts initially present. One of the wicks contained 0.26 per cent; values for the others were all under 0.10 per cent (Table 11). T h e wicks with the high salt content came from the brick that reacted positively t o the efflorescence test.
T h e mortar selected was a 1:3 cement- sand combination containing portland cement, a pit sand and distilled water. Chemical analyses were performed o n the portland cement and on a n aqueous extract of the sand (Table 111).
The rest of the experimental procedure from the mixing of the mortar to the quanti- tative recovery of soluble salts from the wicks was exactly the same as that described by Ritchie(6). As the wicks varied slightly in size, the amount of salts recovered was expressed as a percentage of their dry weight. All work was done in controlled laboratory air ( 7 0 ° F and 50 per cent R H ) .
TABLE IV Salts Recovered from Wicks
After Efflorescence Test
Salts recovered as
%
of wt. of wick -- Wick No. Total Corrected*. -. - - . .
1 0.24 0.22
*Total amount less amount originally present in wicks.
Results
Visual: Visual observations and photographs (Figures 2 to 4 ) revealed fairly heavy deposits o n some wicks, while others were comparatively free of salts. The most pro- nounced efflorescence was observed on wicks No. 3 and 6 , with No. 8 close behind. Wicks No. 1 and 5, on which there was no visible efflorescence, are not shown.
A significant con~parison of results o n the basis of visual observations proved dificult.
Figure 1: Efflorescence test on bricks Nos. 5 and 7. Top: Brick No. 5-Heavy efflorescence on odd- numbered specimens compared w i t h even-num- bered controls. Below: Brick No. 7-Note small salt deposits on upper front corners o f specimen
No. 5.
Specimens were not all observed at the same time. They were evaluated as wetting and drying cycles were terminated on each group of wicks, that is, at intervals of several days. Photographic assessment was com- plicated by the fact that wicks of four dif- ferent colours were used: red, brown, buff, and grey.
Quantitative: The amounts of salt extracted from the wicks a r e recorded in Table IV. The first column indicates total salts re-
Figure 2: Efflorescence on wicks embedded in mortar. Top: Wick No. 2-There is some deposit near top of wicks. Wicks are buff colour making efflorescence less obvious. Below: Wick No. 3.
Figure 3: Efflorescence on wicks embedded i n mortar. Top: Wick No. 4. Below: Wick No. 6.
TABLE V
Chemical Analysis of Soluble Salts Obtained from Wicks and Efflorescent Salt Removed from Brick No. 5
Salt from Salt from
Wick Number: (2) (5) (6) (8) Brick No. 5
covered, the second, the corrected amounts are potassium and sulphate, with smaller (value for total salts less the amounts origi- amounts of calcium and carbonate. I t is nally present in the wicks-Table I ) . Largest also interesting to note that magnesium sul- ,.quantities of salts (2.58 per cent) were phate, the major constituent of salts origin- recovered from wicks No. 2 and 5; 2.37 and ally in brick No. 5, becomes potassium 2.27 per cent were recovered from wicks sulphate in the wick after it has been in No. 7 and 8. Less than 1 per cent was re- Contact with the mortar.
covered from each of the remaining four wicks.
The corrected totals indicate a higher figure for wick No. 2 than for wick No. 5. The significance of the corrected totals may not be great. It is possible that 2.58 per cent represents the capacity of the wicks to hold salts, and that any additional salt could havc been "lost" from the exterior of the wick either by mechanical action in inserting and removing the wick from the slotted cover on the jars or simply by a "flaking o f f of the salt from the surface.
Quantitative results thus definitely estab- lish the higher efflorescence potential of wicks No. 2, 5, 7, and 8.
Analysis
of
saltsSalts recovered from wicks No. 2, 5, and 8, from which the largest amounts were obtained, and from wick No. 6, which rated "severe" in the visual assessment, were ana- lysed to determine the major constituents (Table V). Also included in this table is an analysis of salt obtained from brick No. 5 during the blank test on it.
Results indicate that salts obtained from wicks No. 2, 6, and 8 contain potassium carbonate, primarily, and a small amount of sulphate. The main constituents of No. 5
Figure 4: Efflorescence on wicks embedded in mortar. Top: Wick No. 7. Below: Wick No. 8.
TABLE VI
Pore-Size Distribution of Six Bricks (Pore Size,
%)
Brick Total NO. < 0 . 5 ~ 0.5 to 1 . 0 ~ l . O t 0 2 . 5 ~ 2.5 t 0 5 . 0 ~ 5 to l o p > l o p Porosity,%
I 3.96 10.44 1.18 0.24 0.24 0.62 16.7 2 2.37 3.44 7.58 6.92 2.19 1.42 23.9 3 1.83 1.77 0.88 0.54 0.82 3.46 9.3 4 1.75 1.94 1.79 0.33 0.40 0.95 7.2 6 2.05 0.95 1.70 2.45 3.45 0.35 11.1 8 0.74 1.75 3.81 3.00 3.58 3.32 16.2Discussion
Results of visual assessment of efflorescence were inconclusive and did not agree with quantitative results. T h e latter, however, were in good agreement with field observa- tions where the three bricks, from which t$e ;our wicks containing greatest amounts of soluble salts were obtained, are identified with the most severe efflorescence problems. Examples from the field, involving two of the three bricks, are shown in Figure 5.
Chemical analyses of salts from wicks and brick, coupled with the severe efflo- rescence occurring during the blank test on the brick, established the source material for wick No. 5 as magnesium sulphate located in the brick. It is interesting to note that salts recovered in the blank test were 0.26 per cent of the weight of the wick. This substantiates Brownell's assertion that efllore~cence will probably occur when the ceramic product contains in excess of 0.2 per cent of extremely soluble salts(").
T h e source material for the soluble salts
recovered from the remaining wicks is Fiaure 5: Field observations of efflorescence on
assumed to have originated in t h e mortar. masonry buildings containing-Top: Brick No. 5.
N o appreciable quantities of salts were re- Below: Brick No. 2.
covered from blank tests on the wicks,
while the presence of alkaline salts was 3
indicated by a chemical analysis on the portland-cement used in the mortar (Table a
11). As the same mortar combination was 20
used for all specimens, the differences in , 15 the results obtained must reflect differences
$
lo in the properties of the wicks. A comparison 5 of the quantitative results and these proper-2
ties is shown graphically in Figure 6 .There does not appear to be any relation- , 9
ship between salts recovered and IRA. Wick
:
g z
8 No. 2 from a brick with an IRA of 132 ~ :
7 gm/30 sq. in./min had a 2.58 per cent salt_
6 content; wicks No. 7 and 8 from bricks with g2
a much higher and two different IRA values A an?w 4
had lower salt contents. Salt content values
for wicks No. 2 and 3 from bricks with com- 3 70 parable IRA values were also inconsistent.
5
60 A more consistent pattern emerges when 5 50salt contents are compared with the 24-hour immersion absorption values of the wicks, where higher salt content values accompany increasing absorption values. There is a dis-
tinct difference between the high salt con-
2
10tent wicks and the low ones. As the former -
.
W l c l c n o , - - 0 - C 0 -.
- - 0 0 - - o -_
- I I 1 I I o o - - - O.
-- - - - - 0 0 - - - O I 01 - I I 1 . - - - - - ~_.
- - 0 - - - - 0 0 - r 1 o O 1 I I I 0 1 2 3came from bricks known to be susceptible
to efflorescence in the field and the latter S A L T S R E C O V E R E D , % O F W E I G H T O F W I C K from bricks that are not, the observations Figure 6: Comparison of salts recovered and
of Brownell(3) concerning the relation be- properties of wicks.
tween efflorescence and absorption of the line with wicks having 9.4 per cent porosity units are supported. than with those at the 22.0 per cent level. The same general relation exists between This general relation indicating greater the salt contents and apparent porosity, with salt deposits with increasing 24-hour im- larger salt concentrations occurring in the mersion absorption and porosity values, wicks having highest porosities. There is would appear to explain the high salt con- some scatter. Wicks with 17.2 per cent tent value for wick No. 2. This was in line porosity had salt content values more in with values for wicks No. 7 and 8. All three
had comparable 24-hour immersion absorp- tion and porosity values despite the fact that they were obtained from bricks having widely separated I R A values.
The remaining point for discussion con- cerns the conflicting results for wicks No. 3
and 6. Visual observations revealed pro- nounced salt deposits, but amounts of salts recovered quantitatively were considered low. T h e absorption values are low, but the porosity of No. 6 is fairly high at 17.2 per cent and is twice that of No. 3. Neither of the bricks from which the wicks were obtained had been associated with serious efflorescence problems in the field. I t can only be suggested that salt deposits that occurred were the result of the surface tex- ture of the wicks-that is, that the deposits on the wicks were the result of surface capil- larity, facilitated by the surface texture, rather than the movement of an aqueous solution through the body of the wick to its surface.
Effect of pore-size distribution
Some consideration was given t o the relative importance of apparent porosity and pore- size distribution t o the efflorescence process. It was thought that bricks with relatively low porosity, yet having a pore-size distribution in a range conducive to maximum moisture movement, might be more susceptible to efflorescence than those having higher poro- sity values but less favourable pore-size distributions.
At the time of the study, records of the pore-size distributions for six of the eight bricks included were available. The values, obtained with a mercury porosimeter, are recorded in Table VI and are shown graphi- cally in Figure 7. Although these values were f o r samples representative of the bricks included in the study, they were not the specimens used.
Pore sizes in bricks No. 1 and 4 are small; over 80 per cent of those in brick No. 1 were under 1 p and 75 per cent of those in
brick No. 4 were under 2.5 p. Twenty-five per cent of the pores in brick No. 3 were between 1 and 10 p , with the remainder being fairly evenly divided between less than 1 p and more than 10 p.
The remaining three bricks had a large percentage of pores in the 1 to 10 p size range. Almost 70 per cent of the pores in brick No. 2 were between 1 and 10 p . Most
of the remainder were under 1 p . Relatively,
the same distribution occurred in brick NO. 6. Brick No. 8 had over 60 per cent of its pores in the 1 to 10 p range, with the re-
mainder divided between less than 1 p and more than 10 p. It differed from bricks No. 2 and 6 in having a greater percentage of pores over 10 p in size. N o data are available
f o r brick No. 5 or for brick No. 7, although
B r ~ c k n o 1 B r l c k n o 2 P o r - 16 7% lo P o r - 23 9% B r i c k n o . 3 B r i c k n o . 4 P o r . - 9.3%
I:
P o r . - 7.2% B r ~ c k n o . 8 P o r . - 16.2% P O R E S I Z E , ,UFigure 7: Distribution o f pore sizes in bricks.
the latter is considered essentially the same for this purpose as brick No. 8.
Thus, two of the bricks with histories of rather severe efflorescence in the field, and which yielded large soluble salt contents during wick tests, have pore sizes predomi- nantly in the 1 to 10 p range. Three of the four remaining bricks for which pore-size data are available had distributions pre- dominantly less than 1 p and more than 10 p. The fourth brick, No. 6, had a pore-
size distribution similar to that in the two units with an efflorescence history, but it is not associated with serious efflorescence in the field, nor were large amounts of soluble salts recovered from its wicks. Brick No. 6 was sandstone; the others were fired clay bricks. Perhaps its different behaviour may result from differences in pore shapes and structure rather than from size.
This brief study of pore-size distributions in representative samples of bricks used in the experimental work suggests an interesting area for future investigations of the efflores- cence phenomenon.
Conclusions
1. Blank efflorescence tests on bricks from which wicks were cut were negative in all but one instance. Heavy efflorescence oc- curred o n brick No. 5. Chemical analysis revealed the major constituent of the efflo- rescent salt to be magnesium sulphate.
2. Blank tests on wicks indicated less than 0.1 per cent soluble salt contents for all but No. 5, which contained 0.26 per cent. The
latter wicks were cut from the brick referred to in the previous paragraph.
3. Tests on wicks cut from different bricks and embedded in 1:3 portland cement:sand mortar were unsuccessful in reproducing efflorescence similar t o that observed in the field.
4. Soluble salt recoveries, obtained by wash- ing wicks at the conclusion of the efflores- cence tests, revealed highest concentrations in four wicks cut from bricks found to be particularly susceptible to efflorescence in the field.
5. Chemical analyses of salts recovered from wicks embedded in mortar indicated potas- sium carbonate to be the main constituent in all but wick No. 5, where potassium sul- phate predominated.
6. Soluble salts occurring in wick No. 5 originated with salts originally found in the brick itself; for all other specimens the source material appears to have been alkali salts in the portland cement used in the mortar.
7. A comparison of the absorption properties of the wicks and their soluble salt contents indicates a general relation with increasing salt contents as 24-hour immersion absorp- tion and porosity values rose. There was no relation between salt content and IRA.
8. Examination of pore-size distributions for typical specimens of six of the eight bricks included in the study revealed pore sizes in the 1 to 10 p range for wicks having largest
-
soluble salt contents; wicks with lower salt contents had pores in the range of less than 1 p and more than 10 p. An exception was the sandstone, which had low salt concen-tration and a pore-size distribution in the 1 t o 10 P range. An interesting area for future efflorescence studies is indicated.
Acknowledgments
T h e author is indebted to G . R. Duval, A. Mykytiuk, and E. C. Goodhue, of the Division of Applied Chemistry, National Research Council for the chemical analyses reported here, and t o R. Lacroix of the Division of Building Research for the pore- size determinations.
This paper is a contribution from the Division of Building Research, National Research Council, Canada, and is published with the approval of the Director of the Division.
References
1. Anderegg, F. 0. Emorescence. ASTM Bulletin No. 195 October 1952.
2. Buttcr~;orth. B. Emorescence and Staining of Brickwork. The Brick Bulletin, Vol. 3, No. 5, 1961.
3. Brownell, W. E. Fundamental Factors Influencing Efflorescence of Clay Products. Journal of the American Ceramic Society Vol. 32 No. 12 1949 4. Ritchie, T. Study of Efflorescen;e on ~ r p e r i :
mental Brickwork Piers. Journal of the Ameri- can Ceramic Society, Vol. 38, No. 10, 1955. 5. Ritchie, T . Study of Efflorescence Produced on
Ceramic Wicks by Masonry Mortars. Journal of the American Ceramic Society, Vol. 38, No. 10,
1955
6. Rogers, P. L. A Method of Tcst for Potential Elllorescence of Masonry Mortar. ASTM Bulletin, Tanuarv 1959.
Young; James E. Backup hlaterials as a Source of Emorescence. Journal of the American Ceramic Society, Vol. 40, NO. 7, uly 1957.
McBurney J. W. and D. E. Parsons. T h e Wick ~ e s ; for Eflorescence of Buildins Br~ck. ASTM Proceedings Vol. 37 1937 p. 332.
Bonnell D. G.
d.
and B' Butierworth Clay Buildin; Bricks of the ~ n j t e d ~ i n s d o m ' . HM Stationery Office, 1950.10. ASTM C67-62 Standard Method of SamplinS and T e s t ~ n g Brick.
