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How to Seal Concrete

Sealer protects concrete from the elements and makes it easier to clean off deicing salts, oil or grease. But you need to apply it properly. Follow these step-by-step instructions for the perfect application.

Man in garage with concrete floor

Tools & Materials

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When Should You Apply It?

If your concrete is new, you'll need to let it cure -- wait at least one month before applying sealer. Before applying, check the weather. Sealer needs to be applied in dry conditions because it won't adhere to damp concrete. The temperature also needs to stay above 50°F during application and drying time (up to three days). 

Prep the Surface

Clean the Concrete

Step 1

First, thoroughly sweep the surface of all dirt and debris.

Step 2

Remove any grease, oil, mastic or paint, choosing your cleaner based on the stains that you have. For instance, a degreaser is used to remove grease or oil. If you've pulled up carpet or tile, any residual mastic needs to be removed; use a putty knife and a stiff brush to scrape off as much as you can, then apply a citrus-based cleaner, such as orange blossom, to remove the mastic.

Apply your selected cleaner and follow the manufacturer's instructions.

 

Caution

It's important to remove stains during this step -- if your floor isn't cleaned properly, they will show through your new sealer.

Step 3

After the stains have been removed, mop with floor cleaner and water. Use a shop vacuum to clean up any remaining water and debris. Allow it to dry for 24 hours.

Step 4

Any cracks or pitting will need to be filled in before applying the sealer. Apply the concrete repair sealant to the affected area and smooth over with a putty knife. Follow the manufacturer's directions regarding dry time.

Removing Old Sealer

Step 1

If sealer was previously applied to your concrete, you'll need to remove it before applying the new sealer. Not sure if sealer was used? Try this quick test: Pour a large cup of water onto the concrete. If the water beads up and stays on the surface, it's been previously sealed. If it soaks into the concrete quickly, it hasn't been sealed.

There are a couple of different removal methods. Sandblasting is an option, but unless you're experienced with using the equipment, it's not recommended. If used incorrectly, you can damage the concrete. The most effective way for the average DIYer to tackle this project is with a chemical stripper. Chemical strippers are acid-based and caution should be used when applying. Make sure to wear protective clothing, gloves and eyewear.

Good to Know

There are also less toxic and environmentally friendly products made from soy or citrus that will break down the existing sealer. It's a safer alternative to the harsh chemical strippers, but they take longer to work.

Step 2

Using a 1-inch nap roller or handheld airless paint sprayer, evenly spread a thick coat of the stripper onto the concrete. Product times vary, so read the manufacturer's directions to determine how long the stripper should be on the concrete before removing.

Step 3

You should see bubbles or crinkled areas that have formed on top. Use a long-handled scraper to remove the sludge and discard it. Contact your local waste center for the correct disposal method in your area.

Step 4

Scrub the floor with trisodium phosphate (TSP) and water. Then collect the remaining water with a shop vacuum. Let it dry for at least 24 hours before applying the new sealer.

Apply the Sealant

Now that you've cleaned the surface and removed any old sealer, it's time to apply the new sealer. Depending on how porous your concrete is, a gallon of sealer will cover 250-500 square feet.

Instructions

Step 1

Apply two thin coats to ensure a smooth and even finish. Apply the first coat and wait at least two hours before applying the second. Check your sealant can for specific drying times.

Good to Know

If you're sealing an interior concrete floor, make sure that you have plenty of ventilation.

Step 2

For consistent coverage, paint the second coat at right angles to your first coat.

Step 3

Make sure that you don't step on or drive over your new sealant until it's completely dry. Check the sealant can for specific drying times. Drying can take as long as three days.