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I am building a wall that is 10.5' long and 28" high. There will also be side walls sloping down from both corners to enclose a patio. I would like to use blocks that are 15" wide, 5" tall and 8" deep, but there is no lip and it is concerning. There is about 6' of soil between my house and where the gravel backfill would begin and there is a very slight slope. Would construction adhesive between the blocks be sufficient for support along with the proper backfill and drainage?

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Those feel rather small for a wall of that height. But I'm not an engineer, either. –  DA01 Apr 26 '13 at 2:35
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Without the lip, your retaining wall may not retain anything. I don't know anything about forces and pressures exerted by soil/water, but I have seen improperly built retaining walls fail. One option might be to build a proper retaining wall, then a false wall in front of it to make it pretty. –  Tester101 Apr 26 '13 at 12:21
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2 Answers 2

If i understand the question, you want to use these blocks to create a retaining wall for your patio? the patio will be enclosed by these walls?

A 28" wall made from solid block is fairly heavy and might settle if not built on a footing or well compacted gravel base. You didn't mention what part of the country you are in. If you are in an area with ground frost, a footing becomes even more important. Seasonal movement can be substantial.

At 6 blocks tall, I would not recommend masonry adhesive. I think you should consider using mortar instead. Adhesive is fine for caps or just a couple of courses, but six interlocking courses should have mortar and possibly vertical re-bar if you want it to last more than a season or two.

Another consideration is the drop off height. 28 inches is a substantial drop. You should design some sort of railing or barrier so you or your guests don't step off a 3 foot drop to a broken leg or neck during a festive BBQ. Since I always cook with beer, it would be a concern to me!!!!

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I live in central Indiana and there is plenty of frost and snow throughout the winter. I planned on using 6" of crushed stone for the base. I also have plans for a large stone step at the top which I want to tie back to the ground level with rebar. This should add some stability to the center of the wall. I am fine with the mortar, but still wonder if the lack of a lip is a deal breaker. –  Erik Schamel Apr 27 '13 at 11:08
    
@Eric: Can you explain what you are referring to as a lip? I am not really sure what you are talking about. May be just a difference in vocabulary. Are you referring to interlocking lips on the paving stones? –  shirlock homes Apr 27 '13 at 11:19
    
Most retaining wall blocks have a small lip on the back underside of the block that catches the backside of the block it sits on. Some blocks that claim to be retaining wall blocks don't have the lip and require more reinforcement. The stones I want to use are decorative stones used for freestanding walls, but I've seen plenty of walls all across town with these types of blocks. –  Erik Schamel Apr 28 '13 at 19:13
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First the blocks you are describing seem plenty big enough for a 28" wall. You are talking about 7 blocks high. I would personally use a taller block but I like making the install go easy. Smaller blocks I believe are more work.

I have used LIQUID NAILS® Landscape Block, Stone & Timber Adhesive

However I only glue the caps (top layer to the second to top layer). The other layers shouldn't need it. Either way the glue will last only a few years if you are in a temperate climate.

I also would not install blocks without a lip for any area that will be walked on that is that high. Having a lip or not really matters with the amount of frost your region has and the amount of traffic in the area.

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