What Is The White Powdery Substance On My Basement Wall?

White powder basment wallIn a word, it’s called efflorescence. When people see it on their basement walls, they often refer to it as the white powdery stuff, white mold, or white mildew.

The white stuff you have on your basement walls, officially called efflorescence, is actually a deposit left behind by water. You may have noticed it on the outside of your house walls too (hopefully below the damp course, that is). The stuff is normally harmless, although you’re still advised to wear hand and face protection when you brush it off, just in case.

The big question is “why is there water there in the first place?” Walls are supposed to be dry. Having damp walls is a bad idea because the moisture could eventually cause the structure to begin to break down.

To answer the question we need to take a trip underground to the dynamic, natural world. Water – the source of life they say – is constantly on the move filtering through the earth and stone. As it travels, it picks up natural minerals and salts that it transports along and finally deposits someplace else. It’s almost as if sand and stone were made for the job!

Our homes certainly are. They are built from natural materials in the form of sand, cement and stone. Water passes naturally though these too, which is why we go to the trouble of baking bricks and painting outside walls with expensive waterproofing paint. We also add damp courses, roofs, gutters, downpipes and overhangs like eaves.


We do everything “upstairs” to keep the water away from our walls. Down in the basement it’s often a different story. When it rains the earth around the foundation becomes saturated. Many basements we’ve encountered are little better than “leaky buckets” rammed into the ground.

In a sense, efflorescence on an inside basement wall is like a friendly sentry-guard. It’s telling us that moisture is penetrating through our basement walls and leaving its customary calling-card behind. It’s likely to be historic evidence left behind as the moisture evaporated, which is why it’s normally more evident in dryer summer months.

This makes it the friend of home buyers too, especially when viewing the basement of a home in summer that’s subject to intrusive damp during winter time. The seller can try their hardest to brush it off, but there’ll always be a stain when you know where to look for it.

This is the biggest single reason to track down the cause of efflorescence if you have it in your basement, and to get rid of it before it starts working down the value of your home. It’s a sign that moisture is making it’s way inside your basement, and with that dampness often comes mold.

Not sure if you have efflorescence or not on your basement wall?  Contact us here for a free in-home inspection of your basement.



The following two tabs change content below.
NuSite Group is a Toronto based basement waterproofing and foundation repair company that specializes in Basement Waterproofing, Basement Lowering, and Foundation Repairs. Call us today at 416-622-7000 or 905-731-1228 for a free in-home estimate and inspection.

Leave a reply

Why choose nusite for your next waterproofing project





Customer Testimonials

Interested in working with us? Check out some of our customer testimonials below and find more on Homestars. We are one of the highest rated basement waterproofing companies in Toronto

Mark Lipton - Homestars Review

Basement Waterproofing

Our basement leaked! Of course . . . we bought a 100 year old house! But my office needed to be in the basement permanently. I interviewed 10 different companies until we decided on the Steinbergs and their crew at Nu-Site! They are professional, reliable, courteous, honest, and they really make an effort to communicate with the client about every step of the process.

Sara Jack - Homestars Review

Foundation and Waterproofing Repairs

After several years of chronic leaks, we decided to have our basement waterproofed once and for all. The team over at Nusite was professional, answered my questions during the project and stayed within their quoted price....which is always a concern for me when working with contractors. Great job overall

Joshua Persaud - Yellowpages Review

Basement Waterproofing

Had several cracks in my basement wall and they would leak whenever we had a heavy rain. It started about a year and a half ago and seems to have gotten worse over the past 6 months. I tried having my neighbor seal it, but it started leaking again within a few weeks. Called several waterproofing companies and got several quotes. Finally went with Nusite contractors for the job. They gave a reasonable quote and I liked the guy that came by for the estimate. They stayed within budget and cleaned up before they left. It's been almost 3 months now and it seems to be working great.