Radon Foundation Cracks: Does Sealing Them Lower Your Radon?

Does sealing cracks reduce radon?

Not enough to rely on. The EPA’s radon reduction guide says it does not recommend sealing alone to reduce radon (opens in a new tab) because, by itself, sealing hasn’t been shown to lower radon levels significantly or consistently.

The same guide gives two reasons. It’s hard to find and permanently seal every place radon comes in, and normal settling of the house opens new entry routes and reopens old ones.

Sealing still has a job. The EPA calls sealing cracks and other openings a basic part of most radon reduction approaches, because it limits the flow of radon into the house and makes the other techniques more effective and cost-efficient.

Where does radon get into a basement?

Through anything that connects the inside of your house to the soil. The EPA’s Citizen’s Guide lists the radon entry points (opens in a new tab): cracks in solid floors, construction joints, cracks in walls, gaps in suspended floors, gaps around service pipes, cavities inside walls and the water supply.

Radon isn’t pushed in so much as pulled in. The EPA explains that air pressure inside a house is usually lower than in the soil around the foundation, so the house acts like a vacuum, drawing radon in through foundation cracks (opens in a new tab) and other openings.

Any house can have it. The EPA says that new and old homes, well-sealed and drafty homes, and homes with or without basements can all have a radon problem.

How do you test for radon?

Use a short-term test kit in the lowest lived-in level of your home, then confirm a high result before you decide. The EPA says nearly 1 in 15 homes is estimated to have a high radon level, and the only way to know (opens in a new tab) whether yours does is to test.

The EPA’s Citizen’s Guide lays out these steps:

1. Take a short-term test

   Place the kit in the lowest lived-in level: the basement if you use it often, otherwise the first floor. Not in a kitchen or bathroom. Put it at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls.

2. Keep the house closed

   For a test of 2 to 3 days, close windows and outside doors at least 12 hours before you start. Don’t run fans or other machines that bring in outside air, and avoid testing during unusually severe storms or high winds.

3. Follow up a result of 4 pCi/L or higher

   Take a long-term test or a second short-term test. If the first result was more than twice 4 pCi/L, take the second short-term test right away.

4. Decide whether to fix

   The EPA says to fix your home if a long-term test shows 4 pCi/L or more, or if the average of two short-term tests is 4 pCi/L or more.

Short-term tests run 2 to 90 days and long-term tests run more than 90 days, per the EPA. Your state radon office (opens in a new tab) can tell you where to get a kit or a qualified tester.

What fixes high radon in a house?

A vent pipe and fan that pull radon from the soil under the house and send it outside. The EPA’s radon reduction guide calls active subslab suction, also called subslab depressurization, the most common and usually the most reliable (opens in a new tab) radon reduction method.

Here’s how the EPA’s typical reductions compare for basement homes. Sealing is the one row without a number:

EPA, Consumer's Guide to Radon Reduction

A good mitigator tests how air moves under your slab before choosing a method. The EPA describes contractors using chemical smoke to find where air moves into holes, drains, sumps and cracks, which is also how they find the openings worth sealing.

The fan has to keep running. The EPA says it must run continuously for the system to work, and that you should retest after it’s installed.

Where do crack sealers fit in a radon plan?

In three places: as the sealing step of a mitigation plan, in a home that tested below 4 pCi/L, and before you finish a basement. In each case, a sealed crack is one less opening; it isn’t a radon fix on its own, so test again afterward.

If a mitigator is installing a system, ask which cracks and openings they plan to seal and which they’d like you to handle. The EPA notes that proper materials and installation are required, so let the mitigator’s plan decide.

For a crack in a poured concrete basement wall, polyurethane foam injection fills the crack through the wall’s full thickness rather than just covering the face. The foam kit is made for non-structural cracks in poured walls, not hollow block. The injection guide walks through the job, and the basement wall crack repair guide helps you pick a method.

For cracks in the basement floor, the indoor slab kit fills the crack with urethane and dry silica sand; it has no polyurea top, cures tan and needs a dry crack. The basement floor crack repair guide has the steps, and the indoor slab crack kit is the product it uses.

A penetrating sealer on the floor or walls isn’t a radon barrier. PS110’s data sheet says it preserves the concrete’s natural breathing, which is the point of a breathable sealer, and the sealing hub covers where sealers do help.

Can you fix radon yourself?

You can test yourself and seal cracks yourself, but a radon reduction system is a job for a trained contractor. The EPA’s Citizen’s Guide says lowering high radon levels requires technical knowledge and special skills (opens in a new tab), and that if you plan to fix it yourself, you should first contact your state radon office.

Many states require radon professionals to be licensed, certified or registered, according to the EPA. Check your state’s rules before you hire.

Block walls are harder than poured walls. Their hollow cores connect to the soil, the EPA lists cavities inside walls as an entry route, and a crack kit made for solid poured walls can’t seal a hollow block wall from inside.

Should you test before finishing a basement?

Yes. The EPA says that before converting an unfinished basement into living space, it’s especially important to test the area for radon (opens in a new tab) before you begin. If the test finds a problem, it says radon-resistant techniques can be added inexpensively as part of the renovation.

Cracks are easier to reach now, too. Once framing, drywall or flooring goes in, the floor cracks and wall cracks are covered. The before new flooring guide covers fixing floor cracks before the floor is closed in.

Test again when the work is done, because the EPA says major renovations can change radon levels. If you already have a radon system, the EPA’s radon reduction guide says to ask your radon contractor whether the changes could void any warranties.

Who should you call about radon and foundation cracks?

It depends on what you found:

• High radon test result. A qualified radon mitigator. The EPA’s page on finding a qualified radon service provider (opens in a new tab) points to your state radon contact and to the two private credentialing programs, the National Radon Proficiency Program and the National Radon Safety Board.
• A crack that looks structural. A structural engineer, before anyone seals it. That means a horizontal basement wall crack, a bowing wall, a wall crack wider than 1/4 inch, a crack with offset edges, or a stair-step crack in a block wall.
• A crack that leaks water. Fix the water first; the leaking crack guide covers it. White powder along it is efflorescence, explained in the efflorescence guide.

For every other crack, the foundation cracks hub and the basement floor cracks hub help you identify it.