In May, we had a surprise rainstorm which inundated Montreal with so much water, manhole covers were shooting off and fountains of sewer and rain water were pouring into the streets. In our neighbourhood, there was very little we could do at the time to prevent flooding; the water poured down driveways that led into basements (like ours), it bubbled up through toilets and overflowed into homes, and, as one of my friends told me, it bubbled up through her concrete basement floor, flooding her entire basement with a solid four inches of water. Four inches of water might not seem like a lot, but take a look at how much stuff you have touching the floor from hockey equipment to tools to cardboard storage boxes. If you have a finished basement it’s even worse with carpets, furniture and electronics potentially affected by flood water.

So even if you get a toilet drain backstop and sewer drain backstop, you might be pulling your hair out wondering how to avoid water from bubbling up through the concrete. I figured there had to be a product out there to stop that, so I contacted Kevin Royce at Eco Building Resource, and sure enough, he recommended RadonSeal. While RadonSeal is made primarily for protecting homes against– you guessed it —  radon gas infiltration, it’s also an excellent product for sealing concrete against water and mold infiltration.

Concrete is porous, which is why, if you’ve ever spilled any liquid on an unsealed concrete slab, the liquid will seep into the slab before you can clean it up. But what goes down through the concrete, can also come up and hence the problems during intense rainstorms.  Because of concrete’s porosity, when there’s enough pressure from the ground below, water will eventually find its way through the concrete — water always takes the path of least resistance.

RadonSeal protects concrete floors and walls by penetrating into the concrete and blocking the porous holes. It prevents radon gas, water and vapor infiltration. According to the website it is non-toxic, zero VOC and penetrates concrete up to 4 inches to seal it. RadonSeal leaves the surface paintable after application.

It is applied with a spray-gun like the type used with a garden hose, it needs two applications over an unpainted or untreated concrete floor — or walls, but it is a permanent application and never needs to be applied again. For concrete slabs over 20 years old, use RadonSeal Plus.

Cost: Order in Canada through Eco Building Resource. $209.99 (CDN) for a 20L pail. Coverage for concrete slab: 1000 square feet @ 2 coats/coverage. For concrete blocks: 500 sq ft, cinder blocks: 400 sq ft.

Radon gas: If you’re wondering about radon gas and its dangers, here is a  link to information on it from Health Canada:

BEC Green

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