Gravel Base Under Basement Slab

Old 02-25-15, 09:06 AM
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Gravel Base Under Basement Slab

In western PA, would PA 2A be the best gravel for a base under a basement slab? This gravel will both compact and drain. I was planning on a 2 inch base. Thanks
Old 02-25-15, 11:03 AM
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Not sure what grade your 2a is, but gravel doesn't compact. It does drain. 2" doesn't seem to be a substantial enough base for a concrete pour. Our concrete specialists will be along to give better advice, I am sure. So keep checking back.
Old 02-25-15, 11:11 AM
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Standard practice for new homes in Canada is 4 inches of crushed rock (3/4" - 2") under basement slabs. The main thing is to make sure whatever you use drains well. You will want to add a layer of poly or rigid foam insulation over that gravel for moisture control.
Old 02-25-15, 12:21 PM
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You might want to check local building department. 2" doesn't sound right. Normally 4" as Keith said. The gravel or rock can be, and needs to be compacted (tamped).
Old 02-25-15, 02:19 PM
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"Gravel" is a generic term that may not show up in codes or any standards. It varies depending on local habits and use.

Here (MN) usually gravel is the material that is used for road bases and can be compacted for strength and stability and may not have any high permeability in the very short term, but will drain moisture 24/7/365.

Clean stone or crushed rock will drain very well and quickly, but the fines (silt and clay) of the surrounding soils can be eroded into the voids from the water being drained and then ultimately plug the drainage over time. - That is why filter fabric is used in different ways to filter out the fines.

Old 02-25-15, 03:03 PM
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PennDOT 2A material would work for what you want but I would not put down any less than 4".

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