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Old 08-03-2010, 06:27 PM   #1
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Dry-stack concrete block retaining wall?


I want to build a small retaining wall maybe two or three blocks high (16-24 inches). It seems to me that I could just stack regular gray blocks and fill them with concrete to keep the whole assembly together. The wall would have two 90-degree bends with about 30 feet in between, so the concrete should be strong enough to prevent tipping at the center of the wall, no?

Anybody ever try to do something like this?

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Old 08-03-2010, 06:32 PM   #2
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Dry-stack concrete block retaining wall?


Where are you located ?

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Old 08-03-2010, 07:21 PM   #3
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Dry-stack concrete block retaining wall?


No mortar? Only for college dorm bookshelves.

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Old 08-03-2010, 07:25 PM   #4
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Dry-stack concrete block retaining wall?


If you use unit masonry blocks designed for walls, you can build up to four feet high with no mortar, provided you use appropriate granular backfill and make sure you have a drain pipe at approximately footing level. You can get away with ordinary concrete block, however they typically have more issues with drainage, and you have to be more careful about installation since they lack an index point that automatically sets the angle of the block slightly less than vertical.
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Old 08-03-2010, 07:26 PM   #5
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Dry-stack concrete block retaining wall?


Gonna need a footing.
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Old 08-03-2010, 10:44 PM   #6
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Dry-stack concrete block retaining wall?


look into segmental retaining wall block. Anchor diamond pro is a good 8" block. Till you pay for the block and concrete, they wont be much more. They'll save some labor and mess as well. At 30' (+ whatever distance on the other side of the 90s) you only need 60-90 linear feet. Talk to a local landscaper that does that sort of thing. They're likely to have a bunch of partial pallets they'd be glad to sell you at a discount. Regardless, make sure you install proper drainage behind he wall if you want it to last.
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Old 08-03-2010, 11:38 PM   #7
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Dry-stack concrete block retaining wall?


Do not put a use mortar or a concrete footing under a segmental retaining wall system. They can go 40' high with no concrete footing because of the concept and unit design. A concrete footing severely limits the wall strength.

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Old 08-04-2010, 11:03 AM   #8
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Dry-stack concrete block retaining wall?


Quote:
Originally Posted by Scuba_Dave View Post
Where are you located ?
Sorry about that. I've added my location (North Carolina) to my profile.

Seems to be a difference of opinion about the need for a footer. I'm planning to use regular 8x8x16 hollow blocks, but I figured I'd use solid 4x8x16 caps at the base so that the concrete (or morter/grout) fill can bond to that and the hollow blocks above. I realize a vertical stack with no gradual set-back will put some lateral force on the wall, but I only plan to have a maximum of 24 inches of crusher-run behind this wall. For most of the wall, it will be 16 inches or less.

Good point about the need for drainage. Slotted septic drain line should do fine here. I think I'll also drop some #4 rebar into the holes for good measure.
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Old 08-04-2010, 11:15 AM   #9
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Dry-stack concrete block retaining wall?


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Gonna need a footing.
and some re-bar...
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Old 08-04-2010, 12:04 PM   #10
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Dry-stack concrete block retaining wall?


Since you are building a rigid retaining wall, you will need to have a footing.

A rigid wall and a segmented wall are two different animals. Mortar, grout and rebars are needed to try and prevent cracks or uncontrolled leakage. A segmented wall is designed to move slightly and then return as the weather cycles and usually has a textured architectural face. One requires some skill with concrete and mortar, while the other requires a compacted soil base and a level first course and can be straight or curved.

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Old 08-04-2010, 12:08 PM   #11
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Dry-stack concrete block retaining wall?


Make sure that they are concrete blocks. Do not use hadite. Hadite will not last if it is in contact with dirt.
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Old 08-04-2010, 01:29 PM   #12
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Make sure that they are concrete blocks. Do not use hadite. Hadite will not last if it is in contact with dirt.
Haydite is used in the more expensive lightweight blocks, right? I recall that my local Lowes store used to have a lightweight concrete blocks at a higher cost, but now they just have what they call standard gray block.

When I was a kid, we used to call everything "cinder blocks". Anyone care to educate us on what's what?
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Old 08-04-2010, 04:38 PM   #13
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Dry-stack concrete block retaining wall?


BRO & Rusty -

If the block are referred to as "cinder block" you either have to be older than me or from the eastern U.S. (PA, NJ or near a train line) where cinders were a variable waste product from the inefficient eastern coal-burning plants that were given away or cost money to dispose of. The slag (dross) from steel mills was a decent product that was sold for a better price. The term cinder block is a short term description of block in some places or a term used for "junk" block in other areas depending on the person's local lore.

Haydite is a manufactured aggregate that is produced for applications such as better insulation and fire resistance. It cost more than the typical heavier aggregates used in all types of concrete because of the value and manufacturing costs. This is similar to other brands of lightweight aggregate that can acheive very high strengths Some are also used for highway bridge decks or fireproofing of taller steel structures or just where a higher fire resistance is used to separate spaces in schools, hospitals, etc. that are closely specified.

Some block produce unknown quality block and give them the label of "Haydite" when the may not use the real aggregate but a cheap substitute such as bottom ash from power plants or other waste unrefined or processed waste materials. - It is just a short catch-all term for block that are lighter than normal weight block.

Lightweight aggregates used in block can create many advantages but few people are willing to pay the extra cost ($0.10 - $0.20 per unit) for the benefits, so the producer supplies cheaper normal weight aggregates.

Retailers, like Lowes sell on price and generally are not concerned with quality or properties or particular products because the floor space dictates the amount of selection/inventory (or knowledge) the buyer may have about what he is shopping for.

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Old 08-04-2010, 06:15 PM   #14
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Dry-stack concrete block retaining wall?


We had a plant here that made hadite blocks. They had signs up and on their receipts, it said they were not to be used as foundation or anywhere they would have direct contact with soil. When asked why, they said the blocks would deteriorate if in direct contact with soil.
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Old 08-04-2010, 07:32 PM   #15
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Dry-stack concrete block retaining wall?


You want a substantial footing, preferably below the frost line. Trust me grasshopper.

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