I read your article in a recent issue of Sunday homes. You mentioned efflourescence briefly, but did not give a detailed description of a lasting remedy, or how to treat it best. I have it in my basement in 3 places making up areas about 1 square meter. The largest is in an area where the floor is heaving quite badly. Is there a neutralizer one can use? I repaired the one area once but it came back after 3 -4 years. Funny thing is that I have no moisture in my basement, except a single crack in the wall facing the driveway, where a little bit of water comes in when it rains very heavy. But this water does not run near the spots that show efflourescence. Can you elaborate on how to fix it with some permanent results?
Water or moisture in basements is the most common complaint of homeowners according to several studies and many articles I have read. Your description of the moisture in your basement is often one I hear from homeowners during Pre-purchase Home Inspections. “We have never had any water in the basement, except the time….”.
In your situation the efflourescence on the basement floor slab itself poses very little concern, but the cause of the white powdery substance is. This powder is salt and minerals that are leaching out of the concrete, due to dampness in the concrete.
Efflourescence is only seen when there is a source of excess moisture on or in concrete, in this case your foundation walls and basement floor. The moisture may be coming from the soil outside the home or beneath the floor or may be caused by a source of moisture in the home. If this is from water spilled directly on the floor or another interior source it may easily be solved. Poorly vented bathroom exhaust fans or dryer vents in the basement may be the first place to look. Often these have inexpensive corrugated plastic ducts that easily develop holes that can allow moisture to escape into the basement and condense when they hit the cool concrete. Hanging clothes to dry in the basement will raise the Relative Humidity and may drip on the concrete. Leaking furnace humidifiers or air conditioner condensate drains are also a big cause of moisture in basements. These items should all be checked first, before looking for exterior causes of your problem.
Because you have heaving in your concrete basement floor slab, it is likely that the source of the moisture that is causing the efflourescence is coming from the soil beneath the floor. This is most commonly due to blocked or damaged weeping tile beneath the floor and poor drainage on the outside of the home. We will look at ways of improving this, but there may be one other common cause to check first.
Quite often, in the past, a shortcut was taken when central air conditioning was installed in homes that did not have it initially. The inside components, normally installed in the plenum just above the furnace, contain a tray or pan to catch the condensation produced by the coil inside the ducting. This condensate is drained from the pan by a pipe connected to a hose, which is normally a transparent flexible plastic so that the condensate can be seen to flow though. The condensate is water vapour that forms on the coil as the air conditioner operates. This hose normally terminates in or just above the basement floor drain catch basin or in a plumbing stack in the basement, which allows the water to drain into the main plumbing drains. The shortcut is often taken when the floor drain or plumbing drain pipes are too far from the furnace to allow easy installation of the condensate drain hose. Some installers simply drill a small hole in the concrete floor slab near the furnace and stick the end of the condensate line inside.
The volume of condensate produced by the air conditioner on a hot day may be several litres, and in the improper floor slab installation method, will drain into the soil under the floor. If this continues for many years, the soil in this area may erode or simply become saturated. If the soil is saturated, the moisture in the soil may force its way up through the cracks in your basement floor and may be a partial cause of the heaving you described. This can also occur if the condensate line is properly draining into the floor drain, but has worn away the concrete at the bottom of the catch basin, due to many years of use. This is even more common if the clothes washer is draining directly into the floor drain, as well. If this has occurred it is easily fixed by repairing the damaged concrete with concrete patching material.
If all these interior items are checked and are found not to be the source of the problem, then look outside the home. Eavestroughs must have extensions on the downspouts that channel the water well away from the foundation. They must be cleaned out a couple of times a year, especially if there are trees nearby. The soil around the foundation must slope gradually away from the home, and may have to be built up. The crack where the driveway meets the foundation should be caulked or the driveway replaced, if it slopes toward the home. The water getting into the soil around the home from heavy rainwater or snow melt may find its way into the basement through the cracks in your floor or walls. Reducing the amount of this water next to the house may solve the problem. The efflourescence itself is harmless, but may be a nuisance, and can be easily cleaned up once the source of the moisture causing it is dealt with.