# concrete block wall question



## cbzdel (May 11, 2010)

i have excavated all the required dirt for the first phase of my concrete block retaining wall. Its going to about 30-36" tall. Once I hit 30" I will decide if I want another row or not.. My blocks are good for up to 36" as well.

my problem is the it lists "6 inch gravel base" for the base and "free draining material" for the rock along the inside of the wall.

My problem is I do not have a truck so I have to get all this rock delivered. I calculated that I will need 1.5 yards for the base and 3.5 yards for the inside drainage rock. My question is can I use the same style rock for both, and if so what should I get (material and size). I am just trying to save money because for every delivery I have its $60  and I am only about 1 mile away from the dirt store. I contemplated renting a truck but that would take ALOT of shoveling and I dont know if I am up for it.


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## Kurtzilla (Jul 12, 2010)

What you need to use is 3/4" fractured stone with fines for your base material and 3/4" clear stone for your drainage column. You don't want to use 3/4" fractured with fines for your drainage column behind the wall, as it will have a tendacy to hold moisture instead of draining free. You should see if your supplier is capable of delivering your stone in super sacks, instead of loose bulk material. That way, they can piggy back the loads together, instead of multiple deliveries. Hope this helps. Always remember, when installing a wall. Start at your lowest elevation first, then build up. Here's a link that might help you with your base design. http://www.goarticles.com/cgi-bin/showa.cgi?C=3087674

:thumbsup:


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## cbzdel (May 11, 2010)

here is another question, do I really need a drainage perf pipe on the backside of the first stone? seems like if its perf, it wont really drain at all, it would just flow though the holes in the pipe to the underside of the footing.


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## bernieb (Mar 20, 2010)

I'm assumming your trying to hold back dirt on a hill .......is that correct? How long is this proposed wall? The way I'm reading your post is that your setting block on gravel and I don't think it'll stay in place with hard freezes. Depending on how many friends willing to pack concrete up the hill for cold beer,you'd be better off with a poured wall with a footer poured all at the same time. Have legs running out into the bank two feet, with poured wall leaning slightly into bank, with re-bar throughout. If you really feel cocky you can put weathered barn boards on the show side inside of form work. Just my opinion..........my own wife tells me I'm nuts.......so there.


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## cbzdel (May 11, 2010)

here is what I am doing...










I just placed the block in place to get a general idea. The sheet of directions that I got specifically said not to use a concrete base, it said only to use compacted gravel.

Its going to be a stepped wall, the first wall will be 30-36" tall and the second will be around 12 to 24 depending on final grade. Once the I am done will all the walls, I will tear out the stairs and redo those as well.


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## concretemasonry (Oct 10, 2006)

The light bulb finally goes on and it hits me!! - You are building segmental block retaining wall instead of a rigid wall with a concrete footing. It is much more DIY friendly than the complicated rigid walls that usually crack or tilt after a few years. Freezing is not a concern if built properly since they have been developed in a cold climate and are used in many countries. The hight your your wall since I have seen 40' high engineered walls without and concrete, mortar, grout or rebar.

You never, never use a concrete footing, but use a compacted gravel base that is LEVEL. That is key to the success and making the rest of the construction easier and better. You probably have a requirement that the toe of the wall is 6-8" below the lower surface. It is not necessary for the bottom of the wall be at the theoretical "frost depth". The height limitation is the height above the lower soil level. - Usually these sytems can go 4-5', but you may be facing some local jurisdiction requirements for one reason or other.

You definitely want a well draining fill in the foot or two behind the walls to minimize the pressure. You are right that the moisture behind the walls can just drain out from the joints. The use of the perforated drain tile is to collect the water and drain it away i8f there is a discharge point. The goal of the perforated pvc is to carry the water away and minimized the draining from the surface because you never know what kind of minerals you have in the soil and many can cause stains, moss, etc. of the wall surface.

I assume you just stacked some units to get an idea of how it might look. In actual construction, the first course shoul be on the LEVEL compacted base and be placed LEVEL, using a LEVEL. After that it is simple. What I saw in the photo was not level enough.

Plan ahead to how to build the corner for each level since it changes slightly because of the small batter of the wall. You may have to chip, slit or saw some corner units, so plan to the cut ends are burried in the wall and not. The international licensors have great web sites regarding details (installation and corners) for their particular units I am guessing those block are either Anchor Wall Systems, Keystone or Versalok. Were they made by Mutual Materials?

Dick


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## Kurtzilla (Jul 12, 2010)

You should do complete demo on your stairs aswell, instead of waiting until you get your walls done. This will make for installation of your stairs and walls that much easier. You can also wrap your walls into the sides of your steps, thus creating cheek walls that go up with your steps. As for retaining walls, you can build a gravity free wall up to four feet in height without any soil reinforcement behind the wall, that is if it's level behind the wall and in front of the wall. The drainage column and perf pipe is just additional insurance for proper drainage. If you see water weeping through the face of the wall, thats good. The system is working. On top of your leveling pad, you can incorperate what is called a choke course of either limestone screens or torpedo sand. This is a thin layer of material that will help in leveling your first course of block. Always make sure that you level your block from front to back and side to side.


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## cbzdel (May 11, 2010)

I cant decide on what to do with stairs, I know it will be 10x easier with removing the stairs but my problem is.. even if I had all the materials in place and ready to go it would take me a few days to do the whole project, then I dont know how to get up into my yard for that few day period without stairs, and what to do about the mail.


I really like the idea of pulling out the stairs and doing it all at once, it just takes my somewhat simple projects and turns it into a massive landscaping project. 

Any input?


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## bernieb (Mar 20, 2010)

Thanks for the picture. The last poster is right about the footer for that type of wall by the way, but I'd run a straight wall back inline with your neighbors rock wall and work something out with that tall corner fence post if you can. Maybe just put gravel or concrete when you do the steps in that 18 inch area. Yes a flowered terrace there would look nice, and it will go with the house. good luck


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## cbzdel (May 11, 2010)

I can not go inline with the neighbors rock wall because of my natural gas line, its slopes down the hill, I have to be out almost 12" in the very middle of the wall..


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## Kurtzilla (Jul 12, 2010)

What you do is pre-plan for the removal of your steps at a later date. By doing so, there are several manufactures that make larger slab steps that can accomidate your demensions. So plan your layout for your walls to accomidate your step demensions for later install.


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## cbzdel (May 11, 2010)

new question.. so finally got around to starting my project and making progress.. I set 8"-12" of a compacted gravel base then set the stones on that. I used a 8" long level for each stone to check square front to back, side to side, and diagonals. Then used a 48" long level to check each stone in relation to the stones next to it. This base was 100% level in EVERY possible way! I was so excited, I then set the second layer of the wall. I used a chisel to removed all the extra material on the base of each stone to make them as flat as possible (some of the edges had lager aggregates sticking out so I would remove them). So the second layer was all said and done took a step back and it was not 100% level, I took my level out and none of the stone were prefect anymore, it was more of a front to back issue to. 

Thoughts on what the problem could be, just low qualify blocks I guess....??? Maybe I should of spent more, these were $3 a block..


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## concretemasonry (Oct 10, 2006)

Those block usually have a molded lip or use pins to provide a small set-back or "batter" to the wall and increase the wall strength.

The block could be "knock-off" copies of the units that are common around the world. If they were made by a good manufacturer, they could steer you to the installation instructions on line that are very complete. If they were made by someone like Mutual Materials, they can provide instruction for the one of the 4 major products (Allan Block, Anchor Wall Systems, Keystone and Verslok) commonly produced. The installation suggestions are a bout the same and there are just minor differences in the actual units. Do not get carried away on the leveling of the rest of the courses, because the wall is designed to move or flex to conform to the compacted base and the properly set first course over time - that is why they perform so well in severe climates or for 40' high engineered walls with no concrete footings allowed.

You just have to have a good compacted stable base and get the first course level and the rest is simple unless you have corners that may require some chipping or sawing depending on the angle of the corner.

Dick


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