# Knee Wall Questions



## hortman (Nov 8, 2010)

*Knee Wall questions*

Hello sheaka. Ken here with The Home Depot in the Chicago area. It sounds like
you’re on the right track. Mortar what is going to hold back soil and patio. As long
as nobody is going to use the knee wall as a seat your can dry stack it. Make sure
it is stable. If stability is a problem, then glue everything up higher. Don’t use mortar
in the joints. Use landscape adhesive instead. You use it on block to block surfaces gluing
top to bottom. That way it looks dry stacked but it isn’t.
I hope this helps. Take care.


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## user1007 (Sep 23, 2009)

hortman said:


> Hello sheaka. Ken here with The Home Depot in the Chicago area. It sounds like
> you’re on the right track. Mortar what is going to hold back soil and patio. As long
> as nobody is going to use the knee wall as a seat your can dry stack it. Make sure
> it is stable. If stability is a problem, then glue everything up higher. Don’t use mortar
> ...


You must be kidding right:laughing:? Mortar is what keeps soils and other lateral forces like patios, flood waters and so forth from collapsing a retaining wall? Mortar seals the joints of the material being used. It has essentially no structural properties at all. Nor does landscape adhesive. If stability is an issue from, in this case lateral forces and gravity? You just build the retaining wall higher? And you build a knee wall in your landscape and expect some force like a gorgeous, size 2 blonde astrophysicist not to sit on it with you? If you had such fantasies, then filling it with concrete or rebar would be justified? Otherwise, in case endentulous 500 bound mother in law came to rest a spell you would leave it hollow? 

Bubba, people sit on landscape knee walls. It is a timeless fact of life. 

Anyhow what the poster needs to do first is establish first the real slope involved here. It may look like a foot or so but I just bet you it is more. You will need a couple of tree stakes six to eight feet tall, a good string line, and a line level. I guess I don't care if you buy them at a HD but it will take you an hour to find someone that knows what a line level is and whether the store stocks one. They are like $5 at a place like HD I suspect.

Anyhow, if you think the slope is minor and we are only talking a foot? Pound the stakes in at high ground where you slope starts, reasonably square to the ground. Use a framing level if you want to be more accurate. Then at the bottom where you plan to build the wall. Stretch the string line from the stakes. Plunk the line level on the string and raise it until level. Was I wrong? You have a bit more than a foot to hold back with the knee wall? The triangle created from the level line across with the string level, the reasonably upright stakes create the three sides of a triangle. The last one is the lay of your land and its actual degree slope. 

You can also accomplish this in a few seconds renting a laser survery thingie. Trust me, HD rental does not have them or the targets they need to work. Plug it in at low ground with targets on high ground and aim it as best you can so it doesn't spend all day searching. It will find the first target, do the math and tell you your slope. It will then assume proximity and find the others. 

Anyhow, back to basics, No hollow concrete block retaining wall is going to retain even a 1 foot slope that stretches back more than a few feet or inches. You should plan on filling yours and maybe adding some steel rebar. 

I wish HD would have the courage to keep people off this site if they have no idea where they are coming from.


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## HomeInsulation (May 25, 2011)

*Concrete Block Retaining Wall*

Well said sdsester!

Throwing a few concrete blocks on the ground will not hold back 16" of earth.

Building a patio on a slope is not that hard, you just need to consider what you're trying to do. Holding back tons of soil that expands and contracts as it swells with water and dries out requires a strong wall.

I built this wall 5 years ago by pouring a concrete footer reinforced with rebar. Then stacked 8in concrete block on top of one another and filling the holes with rebar and concrete.

To keep water from accumulating and freezing in the winter, I cut holes in the block and installed 2in PVC pipes for drainage behind the wall.

The wall has been there for 5 years and doesn't have a single crack. I live in the North East where it rains, snows and freezes all the time.

Here's the link to the photos:
http://www.flickr.com/photos/howtohomeinsulation/sets/72157626842238220/


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## user1007 (Sep 23, 2009)

Hey Home Insulation. Nice looking retaining wall. It will move with the forces against it eventually as all walls do but not in your lifetime. At least with the rebar and filling you will have time to notice major shifts and changes and if anything it will warp a bit on you before all else happens. 

The HD person just suggesting the OP just stack hollow blocks or even the suggestion you can hold that much tonnage of soil with mortared solid block kind of scared me.


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## 99altrade (Nov 18, 2010)

*CMU Footing*

I noticed on the site from link you mention a 12" footer (or something like that). Was the footing not dug down 3' or so, etc. to frost line? I'm new at CMU wall/footer construction, is that sort of deep footing not needed in this setup? 



HomeInsulation said:


> Well said sdsester!
> 
> Throwing a few concrete blocks on the ground will not hold back 16" of earth.
> 
> ...


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## mustangmike3789 (Apr 10, 2011)

sdsester said:


> You must be kidding right:laughing:? Mortar is what keeps soils and other lateral forces like patios, flood waters and so forth from collapsing a retaining wall? Mortar seals the joints of the material being used. It has essentially no structural properties at all. Nor does landscape adhesive. If stability is an issue from, in this case lateral forces and gravity? You just build the retaining wall higher? And you build a knee wall in your landscape and expect some force like a gorgeous, size 2 blonde astrophysicist not to sit on it with you? If you had such fantasies, then filling it with concrete or rebar would be justified? Otherwise, in case endentulous 500 bound mother in law came to rest a spell you would leave it hollow?
> 
> Bubba, people sit on landscape knee walls. It is a timeless fact of life.
> 
> ...


 i think if you call the glue company, they will deliver a truck with a few yards glue mixed and ready to pour in the footers. that should do it.


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