How to Tell if You Have Garage Floor Moisture Before You Seal It

Is garage floor moisture plaguing you? You aren’t alone. Plenty of homeowners deal with it, and it’s one of the main hindrances to successfully applying epoxy coatings without delamination.

If you have moisture anywhere in your home, it’s a problem. But unlike other areas, moisture in your garage might be a little more difficult to diagnose. Is it coming from above or beneath the slab? garage-floor-moisture-seal


It’s an important question to answer, especially before you invest in a garage floor coating, as moisture can have a drastic negative effect on its durability.

Signs of a Moisture Problem

The signs of moisture may be subtler than you expect. It’s easy to notice if a part of your concrete is darker or damp. But have you ever seen powdery residue on the surface of the slab? This is called efflorescence, and it’s a sign of moisture as well. It’s created when water is absorbed into the concrete, condenses and then evaporates. What’s left behind is a calcium hydroxide residue — this white powder that you’re always sweeping up.

Conduct a Moisture Test

If you don’t notice either of those two symptoms, you can test the slab for hidden moisture. Use duct tape to secure a plastic sheet to the garage floor. Let it sit for 24 hours, then check the underside for any signs of condensation. Also look at the garage floor beneath the plastic to see if it’s damp.

Fix the Problem Before You Seal

If you find moisture, you’ll want to know what’s causing it. Ultimately, if your garage floor did not have a vapor barrier installed before the concrete was poured and moisture is originating from beneath, it will be difficult to rectify, apart from laying a vapor barrier over the floor and pouring another slab on top.

Test for the level of moisture or call a professional to help. If you have less than four pounds of moisture flowing per 1,000 square feet every 24 hours, you can safely seal without worrying about future consequences. Talk to your garage coating professional — applying a moisture barrier coating underneath epoxy as a primer could be an effective solution.

It’s important to deal with garage floor moisture before you seal, no matter the amount, because a high water content can cause epoxy to peel and curl away from the concrete. Trust Packman’s Coatings for an in-depth assessment of your concrete before applying a coating — we can find a solution for you.