How Do I Drain Behind a Retaining Wall?
Q: "My retaining wall doesn't have weep holes, and water builds up behind it. How do I fix it?"
I have a poured-concrete retaining wall in my backyard that is about 3 feet high and 85 feet long. Unfortunately, the builder never put weep holes in the wall, and water tends to build up behind it. So I drilled weep holes every 8 feet along the base of the wall, but I still can't get any paint or stucco to stick to it. Now I'm thinking about facing the wall with ceramic tiles. Would that be a way to fix this problem?
— Lou, Hollywood Hills, CA
Roger Cook replies: I'm not a tile expert, but the moisture that's pushing the paint off the concrete will probably cause problems for the tile too. I think you should first tackle the source of the problem — the water buildup behind the wall. Then you have a shot at keeping paint, or tile, on the surface.
Ideally, you'd dig out behind the entire length of the wall, put some sort of waterproofing membrane against it, and then backfill the area with drainage stone. That would encourage water to drain out the weep holes. But I'm guessing that making an 85-foot trench is not your idea of fun.
Here's another suggestion: Dig a series of holes behind the wall that run down to the level of your weep holes. You can use a posthole digger if you're fit, or a power auger if the ground's not too rocky. (Before you dig, call your local one-call center to determine the location of any utility lines; you wouldn't want to accidentally slice through a power line or gas pipe.)
Line each hole with filter fabric and then fill it in with ¾-inch washed stone. This should help drain the surrounding soil and encourage the water to flow to the weep holes. (Just keep them free of debris.) Also, if possible, grade the surrounding soil into gentle swales that direct surface water away from the wall.
If the wall is still too wet, don't despair. You may just need to drill more weep holes and dig more drainage holes. I'd suggest spacing them 4 feet apart. Once the wall is dry, you should be able to cover it any way you want.