Efflorescence on a basement floor due to moisture

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This article was published 15/04/2023 (883 days ago), so information in it may no longer be current.

Question: I am experiencing a white powder coming up through the basement tiles in my 40-year-old Charleswood home. Can you recommend a cure? Possibly, a sealer that I can purchase and apply myself.

Thanks, Gary D.

Answer: The cure to efflorescence on a basement floor is to find the source of moisture causing it and eliminate it. That may require evaluation of your exterior grading and water management, sump pumps, plumbing supply, fixtures, drains and any other mechanical systems that may potentially leak.

Yours is a very common question that I receive; what is the white powder I see in my basement and how do I get rid of it? As described several times in previous columns, the white powder is known as efflorescence and is simply minerals that leach out from concrete in the form of a salty powder. This typically occurs after the concrete becomes wet and then dries, or from water sitting on many types of masonry products. The water will draw the minerals to the surface of the cement-based materials and leave behind the white, powdery residue when it evaporates. It is essentially harmless, but does provide good evidence that excessive moisture is present, or has been, in the building material it is found on.

There is no way to seal, paint, or waterproof your basement floor to prevent this from occurring, unless the water is coming from a source inside the home and leaking onto the floor. In that instance, the efflorescence should not be your concern, but the item that is actively leaking. In your case, there may have been some mechanical or plumbing component that has been dripping onto the floor. That moisture may have seeped through the gaps between your floor tiles, wet the concrete floor slab below, and caused the salts to rise up beneath the tiles. Once the amount of efflorescence becomes large enough, it will push its way up through the same gaps the water leaking into. Then, the tiles will likely come loose and replacement or securing them is likely.

The first place to look for water leakage may be your plumbing system. Go through the basement and look for any slow dripping plumbing pipes. This could be your supply pipes, likely copper in a house your age, and may also be due to condensation on the pipes. That may occur on cold water supply piping that is too close to a heat source, during humid summer weather, or on hot water supply pipes that may be too close to a source of cold air.

If that is suspected, simply installing inexpensive foam insulation pipe wraps around the offending sections may stop the problem, completely.

That also commonly occurs on the refrigerant lines that enter the furnace plenum from the air conditioner condenser. If they are not well sealed at the junction, or have deteriorated insulation, they will sweat and drip. Either cause may be eliminated by proper insulation and sealing, using easy to install foam pipe wraps and aluminum tape, or other sealants.

While air conditioner pipes may sweat, other items in that system, and high-efficiency furnaces, frequently leak in basements due to their condensate systems. Both the heating and cooling systems will produce large amounts of water during their regular cycles. This water has to be properly drained to a floor drain, condensate pump, plumbing drain, or sump to prevent it from winding up on the basement floor.

This can be inspected by watching the condensate drains while those two systems are operating. If you see water draining properly through the clear, plastic tubing attached, that should be a positive sign. Once the water leaves that hose, it should be immediately directed into a condensate pump beside the furnace, or other proper drain. If there is water on the basement floor in that location, or wet concrete, then something is leaking. Replacing the plastic tubing if it is clogged, cleaning the pump, or securing the end of the hose inside the floor drain may be required to stop the leaking. If it is severe enough, the water may flow to the area under your floor tiles, leading to the issues already discussed.

In addition to the heating system, water heaters and washers are notorious basement components that frequently leak. Water heaters may slowly leak when their TPR valves are damaged or are physically contacted. Storage right beside the tank may cause an inadvertent compressing of the valve release lever. If excessive rust stains are seen near the bottom of the tank, or small drops of water on the floor, call a plumber for immediate replacement, before a larger breach occurs.

For washers, leakage may be caused by loose or damaged hoses at the supply valves, a poorly secured drain hose, one improperly draining into the floor drain, or an amateurishly installed plumbing drain. Older washers may also leak from the inside, which will require a swift replacement with a newer model.

The dryer should also not be neglected in your evaluation, as a poor quality or improperly connected dryer vent can also be a source of significant water vapour. If you have a flexible plastic or aluminum vent, it is easily damaged and may allow warm, humid air from the dryer to leak into the basement. If that air hits a cold window, water pipe, concrete wall, or basement floor, condensation is almost a certainty. Replacing the vent with a solid metal, duct-taped pipe will prevent blockage, damage, and also help your clothes dry quicker.

The final piece of the puzzle may be moisture leaking into your basement through the foundation walls, or from wet soil under the floor slab. Ensuring you have good grading around the house and ensuring rain and snow runoff are directed well away from the foundation walls will help prevent those two things from occurring.

Stopping white, powdery efflorescence from bleeding up from beneath your basement floor tiles will require investigation as to the moisture source behind it. Ensuring none of the plumbing or mechanical systems in your home are leaking, and that water is not seeping into the foundation from outside, are the two keys to stopping the nuisance salts from being present.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com