I'm going to be rebuilding my concrete block retaining walls. How do I estimate how much mortar I will need?

 

Since they failed the first time, why would you want to do it again? Use segmental retaining wall units and be done with it.

(3 bags of masonry cement per 100CMU)

 

They failed because of improper drainage. It will also allow me to veneer them in brick when I have more money to make them look nice.

 

No, they failed because that is not what they are designed to do.

 

Really? How so? They seem to hold back soil when part of a house foundation.

 

Because they have a house sitting on top of them?

 

A basement has lateral support at the top from the first floor and framing system. This distributes the loads differently.

A "rigid" retaining wall (reinforced block or concrete) is cantilever and all loads (vertical, lateral and bending is concentrated at the base. The type of soil, height and footings are the critical items.

You never did say how high the wall was and it there was an upard slope behind it.

Your footing may have failed and rotated a little also.

A segmental wall, like Tscarborough mentioned, could be more reliable, cheaper and easier for a DIYer. Segmental walls are not required and cannot be built directly on a concrete footing, but a base of an existing footing may be acceptable if there is enough separation - Use compacted base material to create a soil base. Up to 4' with no engineering and then up to 45' with engineering, so they have the flexibility can built from straight walls or walls with inside and outside curves. No mortar is used.

Look at the sites of the major segmental retaining wall licensors (Allan Block, Anchor Wall Systems, Keystone and Versalok have great information and installation directions. They are available internationally and probably made near you also.

Dick

 

The walls are holding back about 3'-3 1/2' of soil. The one side has minimal rise in elevation behind it. Perhaps one foot.

I priced out the materials for a segmented block wall to be over $2,000 dollars. The concrete block wall will be less than $500.

 

It looks like a "no-brainer " decision if the footing is good and you can build a proper cantilever reinforced block retaining wall that will look good enough. You will need to provide good aggregate and drainage for behind the wall. The 4X price differnce does not make sense if all materials (mortar, sand, mixer, rebar, etc.) are considered.

Usually, a gravity architectural segmental wall is cheaper because the labor is free and few people can design and build a good cantilever retaining wall. That is the reason most street widening and along new/replacement sidewalks use SRWs and they have standard design plates for crews and contractors. - that is why they are the most common walls in the world for 3-5' high walls since they do not need a good footing and withstand cold weather.

Dick

 

I've decided against the concrete block wall. You were right about it costing a lot when built properly. I'm going with a stacked concrete block wall by EP Henry. Here's how I will be building the wall:

6" of QP for base. I'm not sure what QP stands for but it's stone and dust mixed together.

My blocks are 3" tall so I will have two courses below grade at one end of the wall and more at the other end.

I will be using filter fabric behind the wall with 3/4" clean stone for drainage, and a drainage pipe at the bottom.

I will be using pins and adhesive.

My questions are:

My wall will be a total of 39" tall including the below grade courses. Do I need the base to be 6" thick or can I get away with less?

Do I run the fabric against the backside of the wall or just on the bottom, soil side, and top?

How much adhesive should I be using? A couple dabs or should I run two long beads along the length of the block?