You can waterproof most basements yourself in a long weekend or two. Start outside by moving rain water away from the foundation, then figure out whether the water inside is seeping through the concrete or condensing on it. If it is coming through the walls or floor, strip off old paint, clean and dry the concrete, and seal it with a penetrating liquid rubber system such as SANI-TRED. This guide gives you the short version of each step and points you to the detailed guides when you are ready to start.
Step 1: Fix the outside first
Most basement water starts as rain or snow melt that collects against the foundation. These fixes cost little and make every inside repair work better:
- Clean the gutters and check that they slope toward the downspouts.
- Extend downspouts so they empty at least 6 feet from the house.
- Regrade soil so it slopes away from the foundation. A drop of about 6 inches over the first 10 feet is a common target.
- Seal gaps where walks, patios, and driveways meet the house so water doesn’t run down along the wall.
Step 2: Find out where the water comes from
Damp walls can come from water pushing through the concrete or from humid air condensing on a cool wall. Tape a 12 by 12 inch square of plastic or foil tightly to the wall and leave it for two or three days. If the side against the wall is wet, moisture is coming through the concrete. If the outer side is wet, the problem is humidity, and a dehumidifier is the first fix.
Look for other signs too. White, chalky crust (efflorescence), peeling paint, and a damp line along the floor joint all mean water is moving through the concrete. For a full list of causes and how to read them, see SANI-TRED’s guide to waterproofing basement walls.
Step 3: Know when to call a pro
A DIY coating handles seepage, damp walls, leaking cracks, and the wall-floor joint. Call a foundation contractor or structural engineer first if a wall is bowing or leaning, if cracks are wider than about 1/4 inch or keep growing, or if the basement floods during storms. Those problems need structural repair or drainage before any coating goes on.
Step 4: Prep the concrete
Prep decides whether a waterproofing job lasts. Every surface has to be clean, dry, and free of old paint, sealers, and dirt so the first coat can soak into the pores.
- Remove old coatings. Basement paints and masonry sealers block a penetrating product. SANI-TRED’s Off The Wall Coating Remover lifts latex DRYLOK, most paints, and adhesives. Try a test spot first. Then strip the wall with a pressure washer, ideally 3,000 to 3,500 psi with a turbo nozzle. If you don’t plan to pressure wash, skip chemical strippers and use grinding or media blasting instead.
- Etch the floor. Smooth poured concrete floors should be acid etched and neutralized following the product directions.
- Dry it out. If you aren’t sure the concrete is dry, a propane weed torch dries the surface and the concrete just beneath it, and burns off oils.
Step 5: Prime, patch, and topcoat
The SANI-TRED system uses three products. Here is how they go together:
- Prime with PermaFlex. Brush or roll one coat of PermaFlex on every surface you want to waterproof. Concrete block takes two prime coats. PermaFlex soaks into the pores and cures as a tough, flexible rubber that bonds to poured concrete, block, brick, and stone.
- Patch with LRB and TAV. Mix 2 parts Liquid Rubber Base (LRB) with 1 part Thickening Activator (TAV) to make a paste about as thick as caulk. Fill cracks, holes, the wall-floor joint, and gaps around pipes. You can also use it to smooth rough areas.
- Topcoat with PermaFlex. Roll a final coat of PermaFlex over everything. It bonds to the patches and the primer to form one continuous, seamless membrane.
Once activated, LRB has a pot life of about 30 minutes, so mix only what you can use. TCP’s SANI-TRED systems page lists the technical details: PermaFlex is solvent free, non-flammable, and low VOC, and both products stay flexible instead of turning brittle with age. After the topcoat cures, you can paint the walls or frame and finish the room.
Watch the full application on The Concrete Protector’s YouTube channel:
For a materials list, product amounts, and the full walkthrough with photos, use SANI-TRED’s basement waterproofing guide.
Extra benefits: mold and radon
Mold needs moisture, so a dry basement is the best defense against it. See SANI-TRED’s page on mold causes and prevention. A coated floor also stops concrete from dusting and gives you a surface that wipes clean.
The same membrane helps with radon. SANI-TRED products have been tested in the lab and in the field to seal out over 99 percent of radon. The EPA recommends fixing homes at or above 4 pCi/L. In one home SANI-TRED tested, readings dropped from 155.3 pCi/L to 0.2 pCi/L after the coating went on. Test your home before and after any radon work.
Frequently asked questions
Can I waterproof my basement myself?
Yes, for seepage, damp walls, and leaking cracks. SANI-TRED products are made so a homeowner, handyman, or painter can apply them with brushes and rollers. Structural damage and flooding need a professional.
Can I put waterproofing over painted basement walls?
Not with a penetrating system. The old paint blocks the primer from soaking in. Strip it first with a coating remover and pressure washer, or by grinding or blasting.
Is it better to waterproof a basement from the inside or outside?
Outside waterproofing means digging down to the footings, which is expensive. Interior waterproofing costs far less and works well when the coating bonds to the concrete and can hold back water pressure from behind. Fix gutters and grading outside either way.
How do I seal the joint where the basement wall meets the floor?
Prime it with PermaFlex, fill it with a thickened LRB and TAV mix, then topcoat it along with the walls and floor so the joint becomes part of one continuous membrane.
How much does DIY basement waterproofing cost?
It depends on square footage, wall type, and how many cracks you have. SANI-TRED’s basement waterproofing page walks you through figuring material amounts for your space.
Get help before you start
Talk with a SANI-TRED tech at 866-784-3308 or send in the DIY expert advice form. You can buy SANI-TRED products through the TCP store, and learn more on our SANI-TRED systems page. Contractors who want to add waterproofing and decorative coatings to their services can get an overview of SANI-TRED at TCP’s hands-on training in Lima, Ohio, or book a consultation.
Sources: U.S. EPA, “A Citizen’s Guide to Radon”; SANI-TRED product data and test results.