New concrete question

[HELLSUNICORN]

I have a couple of questions about the new concrete I poured about a week and a half ago. The concrete was poured for an addition to my garage. Here are the specs of what I have. 23x20 foot slab, 5.25 inch thick pour. 6 inch gravel base. 3 inches of foam on top of that. It has pex in it as all has a full covering of remesh with rebar in certain areas. 4000psi mix with a hand trowel finish.

I did the prep work and paid a concrete finisher to finish it for me. I am not very happy with the trowel finish I ended up with. I asked for a power trowel finish and that isn't what I was given. That is another story.

My original plan was to build a garage addition on top on it ASAP but as usual life is getting in the way and I haven't been able to start construction.

The day it was poured it was 70 degrees and got down to about 50 that night. The weather has been in the 50s during the day and about 38 at night since then. I never got any cold weather care tips from the finisher so I have not done anything with it. It has sat uncovered since it was poured.

Fast forward to today. I get a text saying a had better cover the concrete with plywood or layers of plastic or the top trowel finish will "pop". This is the first I am hearing of this.

Now I am worried that I am going to come out one morning and it am going to have spalling all over.

Do I need to cover it? Am I to late and the damage done already? I am basically looking for cold weather care tips for new concrete. I plan to start building in a couple of weeks but that may not happen until the spring. Thanks

 

[BlackTalon]

After a week and a half? Covering it at this point should not make a difference unless temps are in the freezing range. But as far as ensuring proper curing initially, how was it covered the first week? (or at least the first few days?) Did you moisten it and keep it covered so wind, etc. would not dry out the surface?

 

[HELLSUNICORN]

It was not covered the first few days because it never got below 45 at night. It is just starting to get into the mid 30s the next couple days. I did not moisten it but it was very slow to dry because it was overcast and temps were at about 50 that week. Also it rained 2 days after it was poured.

I poured my apron years ago and I never covered it when it got cold. I had my driveway poured last year at the end of oct and I never covered it and it turned out fine.

I am wondering why all of the sudden he is insisting I cover it? I would assume after almost 2 weeks the chance of it being damaged by the cold would be minimal.

 

[BlackTalon]

Well, plywood won't do anything, and covering it in plastic could actually result in the escaping moisture condensing on the plastic, and possibly causing damage to the concrete surface if it get much below freezing. So whatever he was telling you was questionable. Insulated blankets are the best thing, but after almost two weeks it should not be an issue.

 

[kenwood327]

You should be ok at this point. 6,000 psi concrete should be used for a floor. 4,000 psi would be for a footer.

 

[HELLSUNICORN]

6000psi? Im not sure about that. For what I am using it for 4000psi with all the steel I have in it and 5.25 inches is overkill. That is not what I am worried about. I am worried about the top spalling in the cold.

 

[NZ0J]

The 6000 psi thing is just plain bad info. I manage a ready mix plant for a living, we use 4000 99% of the time for floors, and 3000 or 3500 for footings.

The reasons he's wanting you to cover it is because of the type of finish he put on it. I know you said you asked for a power troweled finish, but didn't receive it, I'd like to know what he actually did. Typically, a smooth troweled finish shouldn't be left out in the elements with freeze and thaw cycles. Smooth troweled floors are typically poured with low, or no air entrainment in the concrete. Even if the concrete did have air in it, troweling the surface would most likely remove any air in the surface, still leaving it susceptible to freeze thaw cycles. I would try to locate some concrete blankets and cover your slab with those, or, get to building and get it covered.