Hi. I was reading different sites on the internet, and found differing
opinions. One site actually recommends to follow I guess what I will call a
sandwich method. They recommend to place plastic on top of the soil, then
sand, then another layer of plastic, then crushed gravel. Is this a normal
practice or overkill?

Hi. I was reading different sites on the internet, and found differing
opinions.

Interior (like bsmt/crawlspace floor) or exterior like parking pad or patio
?

Exterior slab.

"Rudy" wrote in message
news:70TPe.316536$s54.32300@pd7tw2no...
Hi. I was reading different sites on the internet, and found differing
opinions.

Interior (like bsmt/crawlspace floor) or exterior like parking pad or
patio ?

They recommend to place plastic on top of the soil, then
sand, then another layer of plastic, then crushed gravel.

Exterior slab.

If this exterior slab is for a patio or something similar, you should be
able to pour the concrete directly on the ground.

The plastic sheet is a vapor barrier to keep ground moisture from coming up
through the slab. For exterior use, I don't see the need, as it'll be
exposed to rain and other moisture anyway. I also don't see a reason why
you would need two layers of plastic?

When we built our garage, I laid 6 mil plastic sheeting directly on the
ground (overlapping rows by at least 12"). Our soil drains well and didn't
have any rocks or sticks that could puncture the plastic. So, I opted not
to use a sand layer. I then covered that with a layer of gravel, and rented
a plate compactor to get everything nice and level. It worked out great,
and I haven't seen any moisture coming through the slab. (tape down a sheet
of plastic for a couple of days, then see if you have moisture underneath
it when you remove it).

For our sheds and whatnot, I just laid the plastic on the ground, and
poured the concrete directly on top. It's not worth the trouble and expense
of adding a gravel layer. It takes a bit more concrete to fill in the dips
and whatnot, but that's very minor.

For our sidewalks, I just poured the concrete directly on the ground.

Anthony

Exterior slab.

If this exterior slab is for a patio or something similar, you should be
able to pour the concrete directly on the ground.

as long as your soil has good drainage like the reply poster.

For my driveway and patio, I dug out several inches of impermeable 'clay
like' soil, put down "3/4 minus" road base gravel then used a plate
compactor on that, then formed, added rebar & poured. Came out good.