Foundation Coating

Foundation coating goes on the outside of a foundation wall while it’s dug out, to keep ground moisture from soaking through. Do it right the first time, because the next chance to reach that wall means digging it out again. For most block and poured walls, a five-gallon pail of non-fibered asphalt coating, rolled on over clean, patched concrete and given a day to dry before backfill, is the job.

What you’re buying

WBC carries two foundation coatings, both meant for the outside of a foundation wall:

WBC foundation coating	Size	Use it for
Non-fibered oil-based foundation coating	5 gallons	Exterior foundation walls, the full run of a dug-out foundation
Premier foundation coating	4-3/4 gallons	Exterior foundation walls

Foundation coatings like these are typically liquid asphalt. Black Jack’s foundation coating, a common example, is made for block walls above or below grade, dries black, and also protects underground wood footings and metal. Clean your tools the way the pail’s label says.

Coatings like these are sold as dampproofing: they keep soil moisture from wicking through the wall. A product sold as a waterproof membrane is a different, heavier system. Liquid Rubber’s foundation sealant, for comparison, builds a rubbery membrane 40 to 50 mils thick in four or five heavy coats, at about 20 square feet per gallon. If your wall has water standing against it, that’s a drainage and membrane question to settle before you buy a pail of dampproofing.

What “non-fibered” means for you

Non-fibered coating is thin and paint-like. It soaks into the surface of the concrete or block and goes on with a roller or brush, the way paint does. Gardner’s non-fibered coating, a typical example, is a light brush grade covering about 70 square feet per gallon. The thin body is the point: it penetrates the wall’s surface and rolls out fast over a long run of foundation. It is not a filler, so it won’t bridge cracks or voids. That’s what the patching is for.

Prepare the wall: crack prep comes first

The coating needs a clean, sound surface free of dirt, rust and loose material. Brush the wall down and knock off anything flaking.

Then deal with the cracks and holes. One maker’s foundation instructions are a good standard to work to: fill cracks, joints and voids an eighth of an inch or wider with concrete patch, make the repairs smooth and flush with the wall, and let the patch cure by its own directions before you coat over it. The same instructions call for new poured concrete to cure 28 days first. Follow your pail’s label where it says otherwise.

A crack is sometimes more than a crack. Foundation cracks can be a sign of structural damage, and around Great Falls, expansive clay is a known foundation problem. If a crack keeps opening, find out why before you seal over it. A coating hides a moving crack; it doesn’t stop it.

Roll it on, give it its day, then backfill

Roll the coating across the whole exterior surface below grade. It only dampproofs where it covers, so don’t leave thin spots or gaps at the corners.

Watch the weather more than the calendar. A non-fibered asphalt coating like Gardner’s calls for surface temperatures between 50°F and 120°F, a clear, warm day with no rain forecast for 24 to 36 hours, and 24 hours of drying before backfill. When it’s 50°F or colder, warm the pail to 70 to 80°F for a day before you open it. Keep pails from freezing in storage.

If you’re coating in Montana’s fall rush to close in before freeze, the nights are already dropping. A warm afternoon doesn’t make a warm night, so plan from the overnight forecast. Before the dirt goes back, hang roofing felt over the dry coating so rocks in the backfill don’t scrape it off.

Water management does as much as the coating. Spring snowmelt keeps Montana ground wet for weeks, so extend the downspouts and slope the grade away from the house.

The Pick

For an exposed exterior foundation wall, buy the five-gallon non-fibered oil-based foundation coating; the Premier 4-3/4-gallon pail does the same wall job. Patch and cure the cracks first, coat the whole buried surface on a dry day, and give it 24 hours before backfill.

Frequently Asked Questions

What is foundation coating used for?

Foundation coating seals the outside of a foundation wall against ground moisture before it’s backfilled. Asphalt coatings like these are made for foundation walls above or below grade and also protect underground wood footings and metal. It works best alongside good drainage: gutters extended and the ground sloped away.

Can foundation coating seal cracks?

No. A thin non-fibered coating doesn’t bridge cracks. Fill cracks and voids first (one maker’s standard is anything an eighth of an inch or wider) with concrete patch, make the repair flush, and let it cure before coating. If a crack keeps opening, have it looked at, because foundation cracks can signal structural damage.

What is the difference between dampproofing and waterproofing a foundation?

Asphalt foundation coatings are sold as dampproofing, to keep soil moisture from soaking through the wall. A product sold as a waterproof membrane is a heavier system; Liquid Rubber’s, for example, builds a 40-to-50-mil rubbery membrane in several heavy coats. If water stands against the wall, fix the drainage and talk through a membrane before relying on dampproofing.

How long before you can backfill a coated foundation?

Follow your pail’s label; a typical non-fibered asphalt coating like Gardner’s calls for 24 hours of drying before backfilling. Hang roofing felt over the coating to protect it from rocks in the fill. A waterproof membrane system can need longer; Liquid Rubber calls for 48 hours.