There are some local code around here (Mason Co. WA) that call for vapor
barrior under concrete slabs. And if the space is to be heated, they require
2" of foam insulation under the slab or insulate the overhead or walls. (in
other words, so many 'R's of insulation for energy efficiency.)
My carport slab area wasn't large enough to require a permit and I wasn't
going to heat the open area. However I did put a 6 mil vapor barrier under
the slab. Thought it might help keep the the concrete from sweating..
I think that might have been a mistake.. When I toweled and finished the
surface, I had problems getting the cement/sand to the surface and now,
after full cure, the surface is stull soft and I can scratch it with my
finger nail or if I drop anything on it, it chips or leaves a mark.
I have heard that a local cement finisher won't take a job if there is going
to be vapor barrior under the slab. I don't know his reasoning..
I'm not sure of the mechanics/chemistry in cement finishing but I have done
a few jobs in the past and never experienced anything like this..
BTW. the humidity this time of year is around 100% but I'm pouring under a
I mixed my own cement in a 3.5 cu/ft mixer and it was 1 cement, 2 sand and 3
rock (5/8"). I'll admit my mixes were fairly wet (not sloppy wet) since I
was working by myself and didn't want it to set to fast.
I did four seperate pours for my 240 sq/ft carport and all four have the
Anyone have any ideas on what is going wrong here.. ??
I have now poured 240 sq/ft of a 1100 sq/ft total slab area. (yah! I know, I
should call in a redi-mix for an area that large, but I'm working alone. I
got plenty of time).