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I have stone-and-cement retaining walls on two sides of my sloped driveway; they're new, and have cement caps. There's a long wall on the side of the driveway that's sloped about 1:20, and at the bottom end is a shorter wall that is sloped at about 1:40. The walls slope towards their mutual corner.

Water runs down the driveway towards both walls. The long wall is protected from water by a granite curb, but that just directs the water over the short wall. The water pours over the top of the wall and runs down the face and through the stones. I'm worried that this will harm the wall, especially with all the freeze cycles we endure in New England.

I want to add a second curb that protects the shorter wall from water, but which ends about 2' from the corner. Water would be directed through this gap, and somehow be brought away from the wall so it doesn't run down the face.

I can figure out how to choose and fasten the new curb (or I'll post a separate question): for the moment I'm looking for ideas on keeping the water away from the wall. An example would be to take some heavy rubber sheeting, glue it to the top of the wall, and drape it down the back of the wall, with the bottom edge ending in a trough to take the water away. But, I doubt the glue joint would last more than a season or two.

So, any ideas on how to protect the wall from water? (I'm also interested in comments on whether my worry is valid; it's a well-built wall, and perhaps it will just shrug off the water.)

Here are some pictures. First, from the driveway side; note the curb down the wall on the right:

Driveway side of walls

Second, from the back of the shorter end wall. I'd want to have water coming over the corner at the left, but protect the wall from the water:

Back side of shorter wall

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Honestly, I would imagine your walls will be just fine with a little water running over them. The stone walls all over the Irish countryside have been standing for a year or two and seem to cope with the wet, cold North Sea coastal weather pretty well, and most of those aren't even set in mortar. ;-)

What I definitely would do is consider what kind of footing the wall is built on. If there's a chance of water running down the wall and digging a trough at the base that undermines the wall, you might beef up the footing and/or build in some drainage.

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  • Thanks, but do note that the walls shown aren't retaining walls, and so don't need to hold back any force. – Daniel Griscom Jul 14 '15 at 11:20
  • @DanielGriscom Sure, but if water does dig a channel under the wall it could still fall down. – Craig Jul 14 '15 at 15:44
  • Sorry, wasn't clear: the walls shown in the Iris countryside aren't retaining walls, and perhaps don't need to be as strong as those holding up my driveway, and so perhaps don't need to fear water pouring over them as mine. – Daniel Griscom Jul 14 '15 at 19:19
  • @DanielGriscom, oh, I see. By "the walls shown" you didn't mean the ones you showed. ;-) So...I still wouldn't worry too much about water on the walls themselves, but I would look seriously at the foundation of the walls and make sure you have good drainage so water isn't pooling. These aren't exactly holding up your whole drive, in the same way that a dam isn't actually holding back all the cumulative pressure of all the water in a reservoir, but rather holding back just the pressure of the water column in contact with the dam. – Craig Jul 14 '15 at 19:33
  • Of course driving or parking heavy cars very near the retaining wall might increase the pressure on the wall. But I really think the place water might be your enemy is at the base of the wall, as it has the potential to wash away your foundation and undermine the wall. If you didn't build it with a good foundation with good drainage, you could probably find an expert who knows how to help do that after the fact. – Craig Jul 14 '15 at 19:35

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