How Can I Reduce Moisture on My Concrete Garage Floor?
LESLIE: Heading out to Minnesota where Gordon has a question about garage moisture. What’s going on, Gordon?
GORDON: I’m in St. Cloud, Minnesota. I’ve got a two-stall garage. It’s divided. It’s a tuck-under garage. The house is a walk-out, so the back side of the garage is below-grade and it kind – it ramps up from the front to the back.
In the springtime, for a couple – first couple of months in the spring, the garage floor is wet and it’s – I believe that it’s wicking up or coming up from under the floor. I don’t believe it’s just condensation forming on the top.
My question is: is there any kind of a sealer or anything that I can do, short of knocking out the whole floor? I know that now you should have a moisture barrier, some kind of poly under the floor before you pour it, if you wanted to put an epoxy coat or something on there.
TOM: There’s two ways to address a moisture problem in a concrete structure like that. One is to try to make it float, which is not going to happen. And by that, I mean when you put all sorts of sealers and caulks and so on on these floors or on the walls, yeah, you’re never going to block out 100 percent of that moisture.
But the more effective thing to do is to reduce the volume of moisture that’s getting there to begin with. And I think I can explain why you’re seeing that moisture on the floor in the spring. Because concrete is very hydroscopic; it’s like a sponge. Imagine if you stuck the end of a sponge in some water, how quickly that entire sponge fills up with moisture. That’s what happens with concrete.
So the first thing I want you to address is the sources of moisture. And they’re very likely to be the spring rains and the drainage control at the foundation perimeter. It happens to almost everybody. So, the walls that surround that below-grade space, we want to make sure that there’s gutters on that, covering that side of the roof, that are not only there, they’re sized properly, which means you have at least 1 downspout for every 600 to 800 square feet of roof surface and that the downspouts are extended well away from the foundation. We’re talking 4 to 6 feet.
The second thing to do is to make sure that the soil slopes away and there’s nothing trapping moisture against the house, like landscaping. If you do those two things, you will dramatically reduce the amount of moisture that’s getting up against that concrete. And that will stop the moisture that’s – from pulling up onto the floor and perhaps even through the walls.
Now, as for a sealant, what I would recommend you do, because this is a garage floor, is to simply paint the garage floor with an epoxy paint.
These epoxy finishes now are terrific. They’re pretty easy to use. They’re a two-part mix. Usually, when you buy the epoxy kit, you’ll have a gallon that’s about three-quarters filled with product and then a quart can that’s the hardener. You mix the two together and you basically paint the floor. And sometimes, there’s color chips that you can drop in the paint that help hide dirt. And when it dries, it’s a chemical reaction that’s really hard and it really adheres well to the floor. And I think that will stop some of the residual moisture that’s left.
But try to control as much moisture as you can before you take that step. And between the two, I think you’ll be good to go.
GORDON: OK, yeah. That’s kind of what I was thinking.
As far as that epoxy, everything that I’ve seen says to not apply it to a floor that gets damp. There’s a plastic test and you tape a piece of plastic down and if moisture forms …
TOM: Yeah. Personally, I think that’s a really silly test but people seem to like it.
Look, all concrete floors are going to contain some level of moisture. As long as it’s not excessively wet, then I think you’ll be OK. Now, there usually is an etching material, like an etching wash, that you use first. So I would do that, just to make sure the floor is ready to accept it. But if you pick a nice, dry day, I think you’ll be fine.
GORDON: OK. Well, I thank you for the insight. Appreciate your time.