Slab on Grade Road Base

[tumbleleaves]

Does anyone see any problems with using road base for a garage slab? Instead of sand or gravel.

The only issue that comes to mind, is the capillary break would be reduced.

 

[Ron]

No problem other than what you mentioned and the fact that it probably isn't necessary.

 

[tumbleleaves]

Thanks for the response Ron. This is for a small single car garage, where the owner will also need to construct some sidewalk and driveway as part of the project.

They have to use road base for the drive and walk: so wouldn't it be easier to just deal with one material? Does seem trivial, but most of the stuff big or tiny typically does (in my limited experience).

I just figured forgo the sand forgo the gravel, use a vapor retarder if you want. Wam bam done.

 

[Ron]

I don't see the need to use road base for any of it unless you have a very poor subgrade. The loads are not high and unless you have a very high water stable and unstable soils, no need to do anything other than place concrete on compacted subgrade.

 

[cvg]

hard to answer this question without any idea what type of soil / subgrade conditions you have. But I do think it is always a good idea to place road base under a driveway. Sidewalk is probably not necessary. Garage slab, wouldn't hurt.

 

[tumbleleaves]

Road base for walk and drive is the Local Agency standard--their walk their way. I'm satisfied with the structural section. This job is a freebie I'm doing for a relative.

Personally my feelings about the "capillary" action is that it's generally false. Unless you have an extremely high GWT there won't be enough moisture where capillary action will have any effect. The purpose of the granular material is to get the top and bottom surface of the concrete to "dry" (I don't mean cure) about the same, so that the slab cures symmetrically and thus curls less; and also to allow the concrete to move a little more easily in the case of sand, to reduce shrinkage cracking; and lastly to provide base/foundation to the slab. My reasoning is that the water in the soil will condense on any impermeable barrier on top of the soil, it is water in a vapor state, not a liquid.

Say if I place two pieces of glass 2'x2' in the yard one with a layer of sand underneath the other directly on the earth. The supposition of the "capillary" theory is that the one placed on sand will not have water condense on it? Has anyone tried this?

Thanks all for the comments, and let me know if I'm mistaken or my reasoning went off kilter.