Should I Seal My Basement Floor

When I first moved into my home, it had a partially finished basement. The rec room had drywall on its walls, an exposed ceiling, and a bare concrete floor. To expand our living space, we decided to finish the basement properly.

Since my wife doesn’t like the look of carpet, we decided to go with a floating laminate floor instead and to save money I took on the project myself. I knew I needed to have a vapor barrier between the concrete floor and the wooden floor, but I didn’t know if I needed to seal the unfinished concrete as well.

After doing some research online and talking to the experts at my local hardware store, I found out that you should always seal the basement floor with a moisture barrier primer. After a home is built and the concrete floor is laid, the water in the concrete will begin to push it’s way out of the concrete as it starts to dry.

That water will leave hundreds and thousands of little fine pores throughout the concrete no bigger than a piece of hair. Those pores in the concrete will eventually allow moisture and gases to make it’s way up into your home.

Failure to seal your concrete floor before installing a wooden floor, or even carpet, could lead to moisture seeping through the concrete below which will cause the carpet or wood to dampen and eventually rot. This will then lead to mold and mildew issues down the road.

Properly sealing your concrete floor will block off cracks, and holes, trapping the moisture from rising from the ground.

How To Check If You Have Moisture Coming Up Through a Concrete Floor

Before you apply a concrete seal, it is recommended that you first test to see if your floor is damp. To test for moisture, take a square 20-inch by 20-inch sheet of clear plastic and completely tape down all four sides to the floor. Do not put this anywhere that there will be excessive heat or direct sunlight to the plastic.

Wait 24 hours and then peel the plastic off the floor if you see any dark patches of concrete where the plastic sheet was sitting then this would indicate that the concrete is too wet, and you should not apply the seal at this time.

Before you can seal the floor, you will need to dry it out for the seal to work correctly.

How Can I Dry a Damp Concrete Floor?

Before you can seal the floor, you need to make sure that the concrete is dry. Luckily there are a few things that you can do to help speed up the dry time.

One of the best options is to use a dehumidifier along with a floor fan. The dehumidifier will help draw out the water from the concrete while the fan circulates the air and speeds up the evaporation process.  

If you do not have a dehumidifier, a fan working to circulate the air will still do the trick.

Alternatively, you could use a heater to help warm the room, which will help dry the floor. If you do use a heater, you will want to make sure also to use a fan to move the warm air around, and that your room is properly ventilated, so the moist air has a place to escape. Otherwise, once the warm air starts to cool the water vapor will condensate and turn back into a liquid.

Continue to dry the floor until your dryness test using a clear square of plastic taped to the ground remains dry overnight.

How Long Does It Take To Dry a Damp Concrete Floor?

Waiting for concrete to dry is almost as fun as waiting for paint to dry. To determine how long it will take to dry a damp concrete floor depends on a few different things. For example, did the concrete just get poured? Has there been a lot of rain lately? Is the basement humid? How wet was the floor in the first place?

On a newly poured concrete floor, it is said that you should wait for at least one week per cm of thickness up to 4 cm, and two weeks for every additional cm of thickness after that, up to 6 cm. Everything thicker then 6 cm, you should wait at least four weeks or more.

If the floor is at least a couple of months old or more, a fan working and dehumidifier should be able to dry the damp concrete within 24 – 48 hours although this time is not set in stone or at least concrete. Dry times can vary depending on your situation.

How Can I Seal a Damp Concrete Floor?

Sealing a damp concrete floor is relatively easy, and it is something that you can do yourself without having to call a professional.

Step #1 –  Seal Cracks Around The Walls

The first step is to take a look at the floor joists and walls to make sure there are no cracks. Use a high-quality silicone caulking to go around the entire room sealing where the wall meets the floor.

Before you start, check with the manufacturer of the floor sealer that you are using to make sure that the silicone you are going to use will not have an adverse reaction with the sealer.

Once the silicone caulking has been applied, allow significant time before you start to roll out the sealer.

Not all basements will require an application of silicone along the bottom of the walls, so only do this if you notice some cracking or gaps.

Step #2 – Clean and Prepare The Floor

If the floor is a little dirty, you should take a scrub brush with some soap and water and give the surface a good clean. Scrap off anything stuck to the floor such as bubble gum that’s been sitting there for who knows how long. If you have an old painted floor and the paint is peeling, scrub and scrape away that.

Take a look at the base of the walls for any signs of mold growth. Use a fungicide to remove any of that before applying the sealer thoroughly.

Once everything is cleaned, take a broom and give the floor a good sweeping.

Step #3 – Make Sure The Concrete is Dry

Before you can apply the sealer, you will need to make sure that the concrete is dry. To test this, take a square 20-inch by 20-inch sheet of clear plastic and completely tape down all four sides to the floor so no air can get in. Make sure that it is not anywhere that will be exposed to heat or direct sunlight.

After about 24 hours peel back the plastic sheet and look for any water or condensation on the plastic. If you can see any darker spots on the concrete, this will also give you an indication if the floor is wet.

If you do notice any wetness, you will need to make sure that the floor is completely dry before applying the sealer. If everything looks dry, then you can move onto the next step.

Step #4 – Apply The Application

Before you apply the sealer, take a moment and completely read the manufacturers recommendations for applying.  Most sealers require you to apply the application in one go to form a better mechanical seal over the concrete.

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