Concrete foundation advice

[tbuff]

Re: Advice taken, and another Q

Boondox,

From a faceless granite state native

Any of the materials mentioned will work.
However, DO NOT PLACE SAND OR CRUSHED PROCESSED GRAVEL (sand, stone mixtures) on top of a gravel (crushed stone) as the sand will run into the stone and you either have voids, expensive processed crushed gravel, or both. Don't use a stone dust product.

the finer the material, means more compaction effort needed --->more water, thinner lifts, and more passes with the compactor. For Sand I would use 4" lifts if a plate compactor is used, for crushed stone 8" lifts

On the last 4" immediatly below the slab, place a layer of 3/4 inch crushed to act as a wicking barrier. A poly vapor barrier above is optional, I have seen poly help and hurt slab installations. For this one item, I suggest you talk to your local building inspector, vapor barrier usage tends to vary by area.

 

[Currmudgeon]

Re: Advice taken, and another Q

</font><font color="blue" class="small">( Well graded crushed gravel = dense= compaction. )</font>

We may be fighting regional differences in terminology, here.

For a load bearing granular material, e.g road base or under slab, I usually specify a well graded, crushed aggregate material, placed in lifts and compacted to at least 95% of maximum density (Modified Proctor). The gradation is usually whatever the local DOT uses.

I suspect the term "gravel" may mean open graded stone or river run, depending on the location. Those materials can be problematic in terms of compaction.


You want crushed material, if you can get it, as the stuff locks together better than round (River run) stones. You want well graded material, because the sand and finer particles fill the voids between the gravel sized particles, resulting in a dense mass.

 

[Egon]

Re: Advice taken, and another Q

I did say crushed did I not?

Egon

 

[Currmudgeon]

Re: Advice taken, and another Q

</font><font color="blue" class="small">( I did say crushed did I not? )</font>

Yep, you did.

I was just trying to sort out the differences between the various forms of advice.

/forums/images/graemlins/smile.gif