Poly has both benefits and disadvantages. A few, but by no means all,
are listed below.
With poly you are placing concrete against "formwork" instead of
against earth. This requires less clearance for reinforcing.
With poly you greatly reduce moisture migration. Floor coverings will
bond better to a concrete floor with poly under than without the poly.
It will also provide a barrier to water soluble sulphates etc.
Poly will reduce friction between ground and concrete. This may be
either good or bad depending on you want more or less friction.
Poly will keep the "work" out of the mud/dirt. This will keep the
reinforcing clean to improve bond and keep mud/dirt from mixing into the
concrete during placing.
Poly costs money, therefore, don't use it unless it serves a useful
Poly affects initial "set up" time. Floor finishers don't like it for
Regarding sand, I usually don't use sand unless a) I need to use poly,
and b) sharp stones or other surface defects might damage the poly.
Hope this is some help.
H. Daryl Richardson
george simmon wrote:
> Hello Everyboby!
> I am in need of your valuable opinions on supposedly a simple question.
> Do you provide sand/polyethylene under a ground supported concrete floor
> slab, or do you provide compacted subbase material? When should each be
> used? What are the pros and cons of each?
> Thanks a million in advance.
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