New Retaining Wall Clarification


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Old 03-29-21, 10:17 AM
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Question New Retaining Wall Clarification

Long-time lurker, but this is my first post. I am mid-project in a DIY yard project. I have subbed out a large retaining wall to a civil / wall contractor. It's 220 feet long, between 2-5' in height, and makes 2 90-degree turns. It's built to code with CMU blocks and has an overkill of rebar in it and through the 26" wide and 14" deep footer. i'm in Southern California, so it's a dry climate. I plan to have the face of the wall stuccoed.

The wall just went up this weekend, but hasn't been filled with concrete, yet. That is coming this weekend. Before he comes back on Saturday morning I wanted to get a few things cleared up for my own knowledge and to know what to ask for to make this wall last. The wall has a lot of room behind it now, but will be backfilled with 12" of 3/4 gravel and then compacted and graded soil. No landscape fabric.

When reading on the Internet, the topic of sealing the back, "positive" side of the wall has come up quite a few times. People on the Internet say both you should *NEVER* seal a retaining wall and others say you should *ALWAYS* seal a retaining wall. The never crowd says that hydrostatic pressure will build behind the waterproofing and lead to a wall failure. The always crowd says that letting water into the blocks will lead to the blocks deteriorating and the stucco peeling off of the front face in a few years. Some places even seem to have local building codes that either require it or require you not to do it. My local building code does not even mention sealing the backside of retaining walls either way. What is reality - should you seal the back like a below-ground foundation or not seal it at all?

Secondly, my contractor brought in 4" corrugated pipe with holes on all sides to act as the drain tile at the base of the backside of the wall. I don't see sock material. I was under the impression that you only wanted the holes on top of a strong PVC pipe so water could easily enter the pipe, but then the continuous bottom of the pipe could run the water out to drainage holes. Is it OK for him to use the pipe with holes on all sides or will the water just go in the pipe and run through it and sit below it?

Thanks in advance for your help!
 

Last edited by pennstump; 03-29-21 at 11:00 AM. Reason: Added local code info.
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Old 03-29-21, 11:00 AM
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The clean crushed stone and drainage pipe on the wet side of the wall is to remove the hydrostatic pressure. The drainage pipe is installed with the holes facing downwards so water can enter. If they faced up water would only get into the pipe after it was over 4" deep. Remember it's not a pressurized water pipe. It's a path of least resistance for the water to drain away.

I would damp/waterproof the back/water side of the retaining wall. If you have moisture penetration it could cause trouble for your decorative stucco face.
 
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Old 03-29-21, 12:00 PM
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Thanks, Pilot Dane. Would you use an Asphalt Emulsion Sealer or something else to dampproof / waterproof the back side of the wall?
 
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Old 03-29-21, 02:12 PM
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I would use a basement/foundation damp proofer. It doesn't have to be 100%. The crushed stone and drainage pipe should take care of the liquid water. You just want to stack the deck in your favor to keep water out of the wall which can cause efflorescence in the block which isn't good for stucco staying in place.
 
 

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