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Building Science by Norman Aceron Garcia

Basement waterproofing

by Norman Aceron Garcia

foundationBasements are normally the part of a building most at risk for water damage as they are situated below grade and surrounded by soil. Soil discharges water it has absorbed during rain or snow thawing, and the water can penetrate the basement through cracks or leaks. Water can even migrate through solid concrete walls through capillary action. Liquid spontaneously rises in a constricted space, such as a narrow tube, or via permeable materials. Wet basements can induce problems such as flaking paint, foundation failure, building decay, and lethal mould contamination.

Restraining water from infiltrating the basement by ensuring it is redirected away from the foundation is of most important concern. The most common causes of wet basements are surface runoff and poor roof drainage due to inappropriate site grade and gutter. Fixing these issues will go a long way toward ensuring that water does not seep in the basement.

Swales or shallow ditches should be used in situations where one or more sides of the building face an upward slope. Low spots that may cause water pooling should be levelled out to avoid the risk of standing water close to the foundation. The finish grade must be sloped away from the building for three to five metres. Install and maintain gutters and downspouts so that they direct all rainwater and snow melt away from the building foundation to guarantee that pooling does not take place near the walls. Water and moisture can enter through small holes or cracks in the basement’s interior. The holes or cracks could be the result of a number of factors such as poor workmanship, a build up of water pressure from the exterior, and building settlement. Repairing every hole and crack will help to avoid floods and leaks.

Determine spots where water may be inflowing through holes or cracks by examining for discolouration or leaking. Every square metre of the basement should be inspected, especially in areas where flooding or leaking has not been noticeable, but moisture build-up is readily obvious. A waterproof formula of epoxy and latex cement can be used to effectively fill small hairline holes and cracks. This mixture can help make certain that water and moisture do not go through basement walls.

Cracks larger than about four millimetres must be filled with hydraulic cement or mortar prepared from one part cement and two parts fine sand, and with just adequate water to make a fairly firm mixture. Using a standard trowel, the mortar must be pushed tightly into all parts of the holes and cracks to ensure that no air pockets or bubbles remain. This application procedure will be sufficient if particular care is taken to fill all cracks entirely and that water is not being forced through basement walls due to outside pressure.

However, if water is being forced through external pressure, the surface areas of the walls or floors with cracks must first be chiselled out a bit along its length and at the mouth of the crack. With a chipping chisel and hammer, cut a dovetail groove alongside the mouth of each crack and then apply the mortar thoroughly. The filled dovetail groove should be tough enough to resist the external pressure that was pushing water through the crack.

After all runoff has been thoroughly diverted away from the foundation, and all holes and cracks have been patched, a waterproof sealant should be applied as a finishing procedure. Sodium silicate is a water-based mixture that can penetrate up to 100 mm. Lime in masonry and concrete reacts with sodium silicate to make a hard, crystalline structure that fills in all infinitesimal pores, holes and cracks. Because the masonry and concrete have now become denser and rigid from the sodium silicate, gas or water vapour will not be able to penetrate via capillary action.

By undertaking these procedures, the possibility or risk of water-related issues in basement interiors can be significantly reduced, thereby protecting the home from damage such as peeling paint, mould growth, and foundation rotting. The quality of indoor air will also improve because gasses transmitted from the soil outside will be blocked.

Norman Aceron Garcia is a registered Professional Engineer and a Certified Professional Inspector of Mr. Peg Property Inspections Inc. Please visit for more information on building science and home maintenance.

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