Fix a Cracking Outdoor Retaining Wall
LESLIE: Roger in West Virginia’s up next and you’ve got a retaining wall that’s falling apart. Tell us what’s going on.
ROGER: Hi, folks. Hey.
LESLIE: Hi there.
ROGER: Hey, I need your help with this – one wall is not a retaining wall, OK? It’s a concrete block but it’s more like a fence than anything else. It doesn’t hold back dirt.
TOM: It just holds back the neighbors. (laughter)
ROGER: Yeah. Yeah.
LESLIE: Sometimes they’re worse than dirt. (laughter)
ROGER: The top of it is disintegrating and I’m sure it’s because of water being in it. A couple of the caps have fallen to pieces and I’ve replaced a couple of them but I’m going to have to do more. This is what I want to know with that particular wall. Which would be better? To seal the wall in with concrete or to drill holes in the back of it to let the water out and how far apart would you have to do that?
TOM: You know, the thing is, the concrete wall or the block wall is pretty hydroscopic. So I think the water’s going to get out one way or the other. I don’t necessarily feel like you have to drill holes in it. Because it is an exposed block wall, it’s going to be subject to frost heave. You’re going to get moisture in there and it’s going to get cold, it’s going to crack and deteriorate. So the most important thing is that cap. So any improvement you can make to the cap would be the smart thing to do. I don’t feel it’s necessary at all to fill the whole thing with concrete.
If you see water being trapped inside of it and you wanted to put some weep holes in it, I see, also, no problem doing that. I just don’t think it’s necessarily required. If you’re trying to paint the wall and you get it very wet, the paint’s not going to stick and the holes could let the water kind of weep out, perhaps a little quicker.
But I think the key to keeping this intact is to make sure the cap is in good shape. So I would concentrate your maintenance work on that cap and not so much on the walls because if the cap is intact, the water’s not going to get in there and the wall’s going to stand up.
ROGER: Is there some kind of a sealer coat that I should put on the top of it?
TOM: Well, first of all, structurally, make sure you’re using the right products. And then, secondly, you can put a masonry sealer on there but make sure you choose one that’s vapor permeable; that’s very, very important and it’ll say so on the sealer that you buy. Because if it’s not vapor permeable, what happens is the moisture gets in but it can’t get out. Even though it’s a sealer, there will be some moisture that will eventually weep in and if that happens, you want to make sure it can get out because, if not, it stays in there and then it freezes and cracks.
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