Water vapour plays a role
Water also migrates in the form of water vapour as relative humidity (RH). RH is water held in air as a dissolved gas. As water vapour heats up, it contains more water and exerts vapour pressure. A lot of water can be transported through concrete as vapour. The direction of flow travels from high vapour pressure, generally the source, to low vapour pressure by a process of diffusion. The direction of flow can vary depending on environmental conditions.
The direction of vapour flow is critical when applying waterproofing treatment in situations where an unbalanced vapour pressure gradient exists. Some typical examples of this are:
- applying a low vapor permeable membrane such as a traffic deck coating over a damp concrete surface (even if the very top surface is dry) on a warm day results in vapour pressure build-up and can lead to pin-holing or blistering;
- applying a coating or sealant to the outside of a building wall may trap moisture into the wall if the sealant is not sufficiently vapour permeable; and
- applying low vapour permeable flooring over a slab-on-grade where there is high subsurface moisture content may result in delamination of the flooring.
As a rule of thumb, a low vapour permeable sealant or coating should not be placed on the downstream face. This could damage or blister the membrane. Some types of coatings and water permeability reducing admixtures accommodate considerable vapour movement, thus allowing them to be placed successfully on the downstream side.
How crystalline waterproofing works
Crystalline waterproofing improves the waterproofing and durability of concrete by filling and plugging the pores, capillaries, micro-cracks, and other voids with a non-soluble, highly resistant crystalline formation. The waterproofing effect is based on two simple reactions—one chemical and one physical.
Let us start with the basic fact that concrete is chemical in nature. When a cement particle hydrates there is a reaction between water and the cement, which causes it to become a hard, solid mass but there are also chemical byproducts given off that are lying dormant in the concrete.
With crystalline waterproofing, there is a second set of chemicals and when these two groups are brought together (i.e. the byproducts of cement hydration and the crystalline chemicals) in the presence of moisture a chemical reaction takes place and the end product of this reaction is a non‑soluble crystalline structure.
This crystalline structure can only occur where moisture is present and thus will form in the pores, capillary tracts, and shrinkage cracks in concrete. Wherever water goes, crystalline waterproofing will form.
Crystalline waterproofing is unique in that it can be incorporated and integrated into the concrete matrix in multiple ways and achieve similar results. For instance, crystalline waterproofing can be added as an admixture at the time of concrete batching, and thereby be fully integrated throughout the concrete mixture.
It can also be applied to the concrete surface either as a coating for cured concrete or as a dry-shake application to a fresh concrete. In these two application options, a process called chemical diffusion takes place. The theory behind diffusion is that chemicals in a solution of high chemical density will migrate through a solution of lower density until the two equalize.
All information listed in this section was submitted by Xypex Chemical Corp.
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