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 shed roof.
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 same result.
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).