Rain on Fresh Concrete

Bonnan · Oct 22, 2015

How much rain can freshly poured concrete take? We poured 10 yards this morning and it is now drizzling; about 4 hours later?

Wheatfarmer · Oct 22, 2015

This floor took on a heavy rain just as me finished. Didn't hurt it a bit.

Part Time Pete · Oct 22, 2015

Wet cure is the best way. The slower the cure, the better

Mike M · Oct 22, 2015

It is actually good to keep concrete damp so as to slow down the curing. As long as it does not pock mark it should be ok ? Some cover it in burlap or plastic to protect it.

casenut1 · Oct 22, 2015

Yea, but those tire chains don't do it any good.

farmerwithmutt · Oct 22, 2015

Poured a grain bin foundation in a pouring rain never cracked then did one on a nice day it cracked. Funny one was a new guy on truck decided we didn't have to shovel had a 15 foot length it flowed like water didn't take the forms off for a couple days just in case and it never cracked just make sure it's vibrated down good a guy I know just dumped it in with a skid loader huge holes in it after had to bust that out and start over

Billy NY · Oct 22, 2015

Light drizzle, after its set up, should not be a problem, heavy downpour may damage the top layer/finish, exposing aggregate. Very common to use burlap and sprinklers on bridge decks or other similar flat work, more so when its hot out. Like was said, slow cure is a good thing for this material, and unless you are in a hot climate, spring and fall is a great time to do a slab, having mild temperatures etc. Fresh concrete will actually displace water.

Hay hay hay · Oct 22, 2015

I had then same situation, more of a light rain. It made the surface a bit rougher than normal finish. Plastic over it would have helped...i think.

markct · Oct 22, 2015

Chains won't hurt good concrete, especially on a little tractor like that. Where I work we chain up 20 or so garbage trucks every storm, the concrete floor in the bay we usually chain up in is just fine after a decade of that

farmerwithmutt · Oct 22, 2015

Your right forgot about those cute dimples from the rain drops

dpendzic · Oct 22, 2015

too much water in a mix really affects longevity,strength and durability--the less water the better but you do have to vibrate it more to get in place----water content is measured by the slump test in the field

Richard G. · Oct 22, 2015

Every time I pour concrete, I wet it for days to make it cure slower and not crack.
If you don't have a heavy downpour within a few hours, you should be fine.
Richard in NW SC

big jt · Oct 22, 2015

The best way to cure concrete is put it under water for a month after it is set enough.

Worst thing is to let it freeze.

Had a class in college that one of the Lab's dealt with this. poured a bunch of cores, third were set in a freezer, third were air cured, and a third were put under water. Took samples every week and put them in a press that measured the force to crumble the samples. The difference was VERY significant.

jt

Switchflicker · Oct 22, 2015

When you say not to let it freeze, how soon or later after pouring would freezing not be a problem? I might be facing that problem in a month or so.

dpendzic · Oct 22, 2015

concrete should be kept at 40 degrees or more for 7 days---but should be exposed slowly to freezing temps after that--there is an ACI spec on how many degrees drop per hour

dpendzic · Oct 22, 2015

common misconception is that moisture slows down the curing. Concrete cures by a process called hydration in which it needs moisture to cure, so keeping it wet speeds up the cure which gets it to its design strength quicker and reduces shrinkage which causes cracks

D beatty · Oct 22, 2015

In 1964 Dad pored a slab in front of the four bay workshop in the last week of November and they put an anti freeze of some sort and covered it with straw. It was cold and below 40 degrees at that time of year. It was the best concrete we ever pored and never cracked until years later when dad backed a Case 750 crawler loader on it and it picked up one crack which is still the only crack in the slab today.

JayinNY · Oct 22, 2015

What slump did you pour at? I like 5, most are afraid to pour at 5, if you did 5 the concrete should have been set up and finished by four hours later, a light drizzle will not hurt it, In fact you should keep it moist to help it cure slow and therefore make it stronger.

504 · Oct 22, 2015

They poured the floor for my house and it started raining hard before they got it struck off. The contractor left and I really did not think much about it(it was after 5:00 and I thought a beer and dry clothes they would be back to finish it). The next day you could dig a hole in it with the tip of your boot. After two weeks he asked when I was going to pay him the twenty thousand I owed him. The answer was as soon as you fix that floor. 8 hours with two men, and they ground that floor to solid concrete. The building contractor was happy, the concrete guy got paid, and I had a new house six months later.

big jt · Oct 22, 2015

The class I referred to below this was also discussed. My take away was that while concrete cures all of it's life it was something like 90% or more is done in the first month.

I would say that if the concrete is safe from a hard freeze for a month you should be in good shape.

jt

Switchflicker · Oct 23, 2015

Thanks for all the replies re: freezing.

Doesn't make me feel very good though. Might have to wait 'till spring (insert sad face here)

Bonnan · Oct 23, 2015

Again this forum proves it's worth to me. No where else can I turn to get common sense input and discussion on a problem or issue.
All is well with our job and weather is great today.
Thanks again

Rain on Fresh Concrete

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