Insulating Masonry Blankets or Not

[Jawgarage]

My urgent question is getting buries in another post so I am calling it out here.....

We are pouring iur 6" 4000#psi slab tomorrow in the 24x32 garage addition. Its on top of 4-6" compacted gravel and we are using 6mil vapor barrier and wire mesh.

QUESTION: the daytime temps will be from low 40's to mid 50's for the next week (started today). Nights will be 28 tomorrow night and low to mid 30's for the next weeks evenings.

So......do I need to put insulated masonry blankets on the slab or not? If I do, I will not be around after Friday afternoon to remove or check on them again until Monday. Do I weight them down with bricks on top of the fresh pour?

Thanks.

 

[matt_i]

If the pour can start early AM and all finishing done before sundown, and you use an accelerant (CaCl2 or NCA) then you can probably get enough strength that it would be OK left bare. The exothermic reaction does help it somewhat although obviously a large surface area from which to remove heat also.

However: you have a lot of money on the line and I wouldn't want to screw up something imporant like that especially because a mess-up also screws all the prep work. So, I would have the blankets available and use them for insurance.

 

[Jawgarage]

If the pour can start early AM and all finishing done before sundown, and you use an accelerant (CaCl2 or NCA) then you can probably get enough strength that it would be OK left bare. The exothermic reaction does help it somewhat although obviously a large surface area from which to remove heat also.

However: you have a lot of money on the line and I wouldn't want to screw up something imporant like that especially because a mess-up also screws all the prep work. So, I would have the blankets available and use them for insurance.

Thanks. At what point do they go on? And is it OK to leave them on for a few days when nobody is there?

 

[rburke65]

When I was in a similar situation..... my temps. were somewhat colder.....I sprayed the pour with Thompson Water seal, which probably isn't the best product for the job....covered the concrete with Visueen and broadcast straw on top to retain the heat. Worked well for me. Is the garage/shop erected? If so, that will help.

 

[ms fowler]

Put them on as soon as the concrete is "finished". If the finishers can walk on it as they run the troweling machines, it will be fine. It should bear weight without leaving marks. Also--if you are having them cut control joints, put the blankets on right after they finish the cuts. Put down the blankets, use at least a foot, if not two feet of overlay. Weight them down with bricks, blocks pieces of rebar.
Leaving them on for a few days will not harm anything.

 

[joes169]

IF it's going to get down to a low of 28 degrees tonight, you need to cover with something, not just to prevent freezing, but to retain some of the heat generated to promote decent curing before the real cold strikes again. I wouldn't use blankets, they're a lot of screwing around and require quite a few do to lapping. Simple plastic sheating, 4 or 6 mil, laid on the slab will be enough to keep fresh concrete warm enough overnight. Much easier to place and remove (if they're sawing the following day) and cheaper/easier to work with.

No matter if you use blankets or plastic, you will get some discoloration (worse if using Calcium Chloride accelerant) from the plastic/blankets not making 100% contact with the surface. If you can live with it (it does slowly get better), then don't sweat it. I not, there's other alternatives, but they obviously are more complicated.............

 

[EOC_Jason]

They've been pouring slabs for homes, driveways, and sidewalks around here with the temps dipping below freezing at night. I've only seen them cover one with visqueen, but I think that was more because of a chance of rain than the temps. The others they never bothered to cover.

I would think visqueen would be sufficient, but I'm no expert.