# retaining wall for garden



## JP79ST (May 3, 2008)

Hello everyone,

I want to build a rectangular raised bed for a garden. (Raised about 6 or 8 inches.) I am only starting to consider this project. The area is on a slight, consistent slope of about 20 degrees. I want it to be made of brick or stone and mortar. Although the yard is sloped, I want the bed to be level with the foundation of the house. Of course, I want it to be sturdy and long-lived.

My neighbor had a contractor build something similar for his flowerbeds, which are on level ground. It's only been one year and already the mortar between the stones has cracked in several places. I wonder if they will begin to fall apart. 

My questions are (1) Can such a structure be built on sloped ground? (2) If so, what sort of foundation is required for the wall (width, depth, concrete, sand?) (3) What may have caused my neighbor's retaining wall to begin to fall apart (sloppy workmanship, unsuitable soil conditions?)? 

Thanks in advance...


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## Dr Dave (Jan 1, 2009)

hello, the answer to your questions 
(1) Yes
(2) For a simple brick and mortar wall prepare your site by getting it as level as you can. dig a trench approx 6 to 10" wide and about 8 to 10" deep. then get that trench level, line it with builders plastic and lay out some mesh/reo bar to fit the hole (don't lay it on the ground) u will need to seat the mesh so its off the ground a bit. use general concrete in the pre made bags (just add water) it is much easier than trying to work out ratio's. once that's all in level it off as good as you can. probably too much info for you. sorry
(3) the reason its falling apart can be any. incorrectly mixed ratio of mortar is more than likely the reason. but it could also be not enough .. some dodgy contractors don't get right in the gap with the mortar ... rather just make it look nice on the outside. take your time with it and do it right the first time
let me know if i can help with anything else


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## concretemasonry (Oct 10, 2006)

Use a wall built out of Segmental Retaining Wall units (SWRs) that are built up to 45' high without a concrete footing and do not ever use mortar.

They are designed for the type of situation you have. Look at some of the internet sites for Allan Block, Anchor Wall Systems, Keystone and Versalok. The units are similar and all have great sites. They are available across the U.S. through local manufacturers and in most countries. You will get some good information.

Your walls are not high and can use the smaller units which are set on a compacted soil base. You are probably in error on the slope since a 20% grade is really steep and most people over-estimate the slope. Even if it is 20 degrees, there is no problem.


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## beranbr (Jan 9, 2009)

Not an impossible task, but for someone who has never built something like this it can be very intimidating. Whether you are building it out of block and mortar, brick and mortar, wood, or a concrete retaining wall block the basic rules are basically the same for building a raised planter on this height (less than 12 inches). I would use a concrete retaining wall block because they are easier to install on a slope unless you are an experienced mason.

1. Decide on a design complete with exact dimensions.
2. Lay the design out with spray paint. 
3. Using string and a string level or a laser, find the difference in fall from the highest point to the lowest point. Finding this out is critical because it will determine how tall the tallest wall will be and will determine if you need re-enforcement for the wall. Being this is a planter, it is not a crucial as if it were a true retaining wall.
4. Determine the depth of your trench to be dug. It needs to be deep enough to allow the footer (concrete for block, brick, or stone and mortar or a compacted aggregate base for segmented concrete retaining wall blocks) and one course of wall material or 10% of the total wall height. 
5. Starting at the lowest point start digging the base trench 24 inches wide by the depth figured out in step 4. The bottom of the trench needs to be reasonably level, so to save material you can step the trench up going into the slope. Check out this page on Allan Blocks website. This site will help you build retaining walls and planters.

http://www.allanblock.com/retainingwalls/Installation/Landscape/stepups/stepup.aspx?ta=2&product=rt

Hope this helps.


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## concretemasonry (Oct 10, 2006)

Some good details on instructions plus a better direction on the type of wall to use for this common application.

Allan Block is slighly different than the other products, but they are all designed, and are very commonly used, for this type of installation. Depending where you are you may find one brand more readily available that others because of the proximity to the licensed manufacturers. - I always suggest all of the majors because they are all good and provide good information. Beware of the local "knock-offs" because they have to eliminate some features to avoid losing their business in a law suit and they usually offer little support and technical information.

the advantage of these units is that you do not have to use a concrete footing and they can be used on both straight and curved walls and easily adjust the elevation or grade changes.

Dick


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## beranbr (Jan 9, 2009)

I agree with Dick here. Unless you are trying to match an existing wall I would go with a concrete retaining wall block. If you are in the North East I would highly recommend using either Nicolock, E.P. Henry, or Techo-Bloc. They are the some of the best out there that offer wall blocks and they come in MANY different colors and can be stacked completely vertical without any reinforcement if the wall is 2 feet or less and/or does not have a large surcharge above it. In your application, that would be no issue. Once you get your base course laid, you simply apply a bead of masonry adhesive and stack the next course up and follow this until you reach your desired height. Then most companies offer a cap stone that will finish the wall off nicely. Making the planters square makes it even easier because you don't have to make any cuts if you carefully plan.


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## concretemasonry (Oct 10, 2006)

My good friends and acquaintences that were mentioned in the area may be promoting the type of units that require adhesive they sell. there is really not much benifit in the long run for an adhesive. The onlt place it is needed is a small dab to hold the standard solid cap blocks in place.

A good retaining wall system uses block designed for the purpose and do not need "glue" no matter how high. Most of the good systems go 4' to 5' without an permit, engineering or special approval and are comonly used by many municpalities. You would never see a responsible engineer or contractor using glue for masonry. If you want to go 40' high, you need an engineer that would never allow glue.

I suspect those producers also offer the better units, but prefer to push the "knock-off" types to the DIYer so they can sell some extras.

It is your choice sine your wall is so low.


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## beranbr (Jan 9, 2009)

Using a retaining wall block that steps back as you go up due to a back lip or a front lip in the case of allan block absolutely requires no glue, but in the case where you are building a wall that does not step back and is completely vertical like I mentioned does need glue if you are not using pins(which are more of a hassle to use). I should have been more clear. Because the original poster said it was a square planter and the walls were less than 2 feet tall, I suggested using this type of block because it is more physically appealing and is not really retaining anything other than good rich organic soil which drains well and is held in place by the plants roots in the planter.


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