Prevent an Outdoor Stone Wall from Crumbling

LESLIE: Roger in West Virginia’s got a retaining wall problem. What’s going on?

ROGER: Yes, hi. I’ve got a wall that’s probably about waist high on the backside of the house. And it’s not actually holding any dirt back unless the hillside slid down into it; then it would stop it. But there’s probably about an inch tall concrete cap; this block, like, that goes all the way across the top of it, OK? This thing’s probably, maybe – I don’t know – 50, 60 foot long; something like that. Anyway, I keep noticing that this … these caps are crumbling. And I’m seeing little – oh, goodness – the pieces all falling down along the edge of the wall and I’m not really sure what’s going on or what I should actually do there?

TOM: Well, Roger, the way the retaining wall is constructed is probably leading to that situation. In a perfect world, that block wall would be built up and behind it would be probably a foot of stone. That’s fairly large stones; like one to two inch diameter stones. And on top of that, there would be some black cloth that stops the weeds from coming through. And on top of that, might be some …

LESLIE: Called weed blocker.

TOM: Weed blocker. Sorry, the technical term (laughing) escaped me for a moment. The weed blocker cloth. And on top of that, there could be anything; from nothing to the concrete cap. But it sounds to me like what’s happening here is there’s no drainage behind the wall so the water is getting trapped right behind that concrete cap and, of course, it’s freezing and spawling; spawling meaning a cracking as the water gets in there.

So you will continue to have to replace those, over the years, until that wall is draining properly. The solution on this might involve you excavating out parts of that wall to create those drains so that the water falls down and runs out through the wall, as opposed to over the wall. Or it could even involve regrading the top. Sometimes, if the soil hits behind the wall, as opposed to even with the top of the wall, the water will trap behind the wall and cause more damage. But that’s why it’s happening. The water is getting in there. It’s not draining through the wall like it’s normally supposed to. And that’s going to continue to cause spawling because the wall system is just not designed properly. OK?

ROGER: OK.