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Technical Note (National Research Council of Canada. Division of Building Research), 1963-02-01
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Silicone Masonry Water Repellents
Hutcheon, N. B.
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389
PREPARED BY N. B. Hutcheon CHECKED BY APPROVED BY
DATE February 1963
PREPARED FOR Limited Distribution
SUBJECT
SILICONE MASONRY WATER REPELLENTS
The remarkable materials known as silicones are being used as the basis for a variety of products, one group of which is now being offered for the treatment of exterior masonry to make it water-repellent. Silicone compounds for this purpose are now commonly supplied in a volatile solvent capable of producing water repellency in depth when flooded on clean, dry masonry surfaces and the solvents allowed to evaporate.
Silicone compounds can quite readily be deposited in a thin layer on the surfaces of many common materials. Such layers can be formed not only on the outer visible surface of a material, but also on the walls of the internal pore structure to which the silicone may be carried by the particular vehicle and application method used. It is generally acknowledged that penetrations up to 1/8 inch or even 1/4 inch from the surface into pores to which the vehicle has access can be obtained.
It is known that these silicone layers once deposited are relatively very difficult to remove completely by either physical or chemical means and that the silicone compound itself is chemically very stable. These features justify the claims made for silicone waterproofers that the water-repelling property which they impart to masonry surfaces will be persistent and
relatively durable under conditions of exposure to the weather. It should not be assumed that water-repellency is an absolute property, at least in the context of masonry waterproofing. The term is used to describe an improvement in the resistance of a porous masonry surface to the passage or entry of water.
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-Many common materials have an affinity for watero They are readily wetted by water and a drop of water placed on them will spread and wet a much larger area o In addition, liquid water
at a surface can be drawn by surface tension into any open or connected pores or capillaries, the suction or force producing such entry being in inverse proportion to the diameter of the pore or passage o
These effects can be modified by coating the surface of the solid with a very thin layer of some substance such as silicone or an oil or wax which does not exhibit the same wetting action with watero Silicones are certainly capable of neutralizing the tendency for water to spread and to enter the pores of materials which in their normal state are wetted by watero As a result, a drop of water on a silicone-treated surface does not spread but remains intact0 It is in this sense only that the water is
"repelledu by a siliconed surfaceo Some small positive pressure would be required to make the water enter the treated poreso
Rain falling on a silicone-treated wall can therefore run off without being absorbed by the wallo Any wind or water effects
operating to produce pressures across small gaps, cracks or pores, however, could lead to entry of water regardless of silicone
treatment0 It may be said that a silicone treatment eliminates
the natural tendency for water to be sucked into the pores of a material, making it necessary to have a small positive force to produce water entryo
Silicones therefore offer the possibility of a masonry waterproofing treatment which is colourless and does not discolour with age, is qUite readily applied, and which maintains water-proofing properties for a much longer time than oils or waxeso In addition, since it is not a filler, it allows the possibility of water vapour diffusion through pores, thus it is believed, avoiding some of the difficulties encountered with "non-breathing" types of surface treatments0 It is maintained that masonry surfaces which
have been treated with silicones remain cleaner, and that the formation of efflorescence on the surface of masonry is reduced or preventedo
The evaluation of the efficacy of silicone treatment is an extremely difficult matter since the basic SUbject involved is the action of water within materialso This subject is extremely complex and is only partially understoodo Practical situations involve a large number of variable external factors such as
rainfall, drying conditions, the incidence of freeZing when wet, and the location on the buildingo Also involved is the influence
of water migration within the wall and the salts present in or
and pore structure of the material, as well as of adjacent materials and the incidence of cracks or flaws within materials and at joints are also known to be possible factors in determining the wetting effects and the accompanying degradations which it is desired to avoid. As a consequence any experimentation'with actual bUildings is likely to be complicated by the lack of control over various factors leading to complications in interpretation of results and by the relatively limited number of cases which it may be possible to study. Correspondingly, experiments in the laboratory or with small panels or test walls outdoors are likely to be inconclusive in respect of the performance to be expected under actual full-scale conditions.
As a consequence of these considerations the state of
knowledge regarding silicone waterproofers is far from satisfactory. The proponents can claim quite properly that there is no conclusive evidence that the claims made for them are incorrect, while others holding contrary views may equally correctly maintain that the claims made have not been proven. There are a number of research and technical people concerned primarily with the facts in the situation who may be forced on occasion to pass judgement on these
ｭ｡ｴ･ｲｾ｡ｬｳｯ In so doing they must rely on such evidence as is available, supported by conclusions drawn from the best possible understanding of the phenomena involved. It has been these people largely who have been concerned over possible difficulties which may be created by the general use of silicone waterproofers in accelerating or in promoting certain degradation effects in walls. The present situation is therefore an unsatisfactory one for all concerned, but it is one which is not readily changed.
Those who are concerned over possible difficulties
promoted by the use of silicones are in general influenced by the fact that even though a silicone-treated surface can pass water vapour, it ineVitably will restrict any flow of water outward in the liquid phase through the treated layer. This will thus affect both the manner and the rate at which water which may have entered the material behind the treated face can escape. This reasoning gives rise to two possible points of concern: that water which has entered a wall may be hindered in its escape with consequent
ill effects, and that the free passage of efflorescing salts to the surface may be prevented, also with ill effects.
Anything which can lead to higher moisture contents in an exposed material is likely to increase the risk of freeze-thaw damage which is known to increase in proportion to the degree of saturation at the time of freezing. Claims that the silicone
treatment will reduce rather than increase the possibility of water entry can in part be countered by argument that water can and
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-frequently does enter a wall at one point to escape at another, and that silicones will seldom be effective in reducing water
entry at points of weakness of the kind which are most commonly
involved in serious local leakage into masonry walls. It is conceded by some proponents of silicone treatment that there is an added
risk if walls do become wet, and it is usually recommended that walls be treated only after all obvious defects which might lead to water entry have been corrected. This begs the awkward question of whether all the undesirable defects can be recognized and
remedied and if they can, whether there is then any useful job for the silicone treatment to perform.
The present state of knowledge about silicone masonry water repellents would appear to support the following conclusions: 1. When a portion of exposed masonry wall surface is wetted from within by water which has entered elsewhere to escape by evapora-tion from the exposed surface, the addievapora-tion of a silicone treatment may reduce the rate of escape, leading to increased levels of
moisture content and thus to increased danger of degradation brought about by freeze-thaw action.
2. The use of silicone treatment will not usually be effective in preventing the entry of water into masonry through cracks or very large pores, which are the most common sources of difficulty with rain penetration of walls. Masonry may also be wetted through contact with the ground. Such faults should be corrected before treatment with silicones.
3. Silicone treatment of the face of a wall is not a cure-all for masonry leakage problems and should not be expected to make a poor wall resistant to rain penetration. On the other hand its
use is probably well justified in cases of wetting or dampness arising from entry of water through fine cracks or through the
normal pore structure of the materials forming the" exposed surfaces of the construction.
