# CMU Filling



## gladiatorxx (Aug 12, 2008)

I had a quikrete salerep talking to me about using the "core fill fine grout" product, instead of regular concrete with 3/8" aggregate.


Thoughts on this?


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## concretemasonry (Dec 1, 2006)

3/8" could be too coarse, depending on the block size and the amount of reinforcement.

Grout is always much wetter (8" - 11" slump) than concrete, which has a slump of 3" - 4".

Grout is fine and wet to make sure the voids are completely filled. High strengths are really not needed and the maximum strength may even be limited for some designs. The grout is intended to fill completely and create a good connection between the block and rebar. It is very rarely used to increase the vertical compressive strength, since block usually have far more vertical strength that you can put on a wall. If the normal block are not stringer an engineer will just specify a higher strength.


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## gladiatorxx (Aug 12, 2008)

In this particular job we we looking for strength against high backfill. It is 9ft high , and we used knockout block with rebar. Maybe we will give the grout a go


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## tkle (Apr 15, 2006)

Retainer walls are usually over engineered anyways. If it's costing extra money it's a waste. If it's not what the engineer specified you're assuming the risk.


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## gladiatorxx (Aug 12, 2008)

understood, this is a repair to a converted guest house, partially set back into a hill. 

How are the benefits in filling core against the backfill surge, vertical is not an issue


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## tkle (Apr 15, 2006)

You need solid grout to tie in the steel if that's what you're asking. CM can better answer your question.


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## Tscarborough (Feb 25, 2006)

He already did. Grout is used to fill the space around rebar in the core. The most important criteria is to assure a lack of voids. Large aggregate and dry mix will make this much harder to achieve. The strength of the grout does not have to be any stronger than the strength of the CMU, and this is easily achievable with a small aggregate, high slump grout mix.

If your engineer relied upon the columnar effect of the grouted cells to withstand the horizontal pressures, he does not know what he is doing.


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## concretemasonry (Dec 1, 2006)

TS -

Amen!!


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