curing my slab - plan - input welcome

[NWOhioChevyGuy]

So I am going to have my slab poured for my 28' x 28' garage on Saturday the 27th.

4" slab with rebar on 24" grid w/ vapor barrier & 2" foam under

slab will be sloped to the overhead doors.

Plan is to flood cure.
a) poly with 2x8's across door ways to seal up the entries (will this seal good enough)
b) flood with water to 4-6"
c) cover with tarp to slow evaporation & keep cooler
d) check levels and keep flooded for 5-7 days

Slab is being poured before the garage is framed - to make it easier for working on the framing. I am doing everything except the concrete work on this project.

Anything you would do differently?

I will be treating the concrete with Ghostshield 4500 & 8510 once properly cured.

 

[bagged89s10]

I don’t have an answer but I’m following as I’ll be getting a 24x32 floor poured in the next few months.

 

[BigGarage]

I also don't have a definitive answer but I can tell you this: I worked in a cement plant lab and one of the ways the compression strength of the cement was tested was to make cubes in molds (2" x 2" I think) and place them in a humidity controlled room and have them completely submerged under water for 1, 3, 7, 28, and 56 days (IIRC). At those times the cubes would be placed in a compression machine and compressed until they shattered. I've never heard of anyone doing it to a slab (submerged) but it's not a bad plan.

Dennis

 

[NWOhioChevyGuy]

With all the talk on this site about the do's and don'ts with concrete, I am shocked that I have not received more feedback.

Here is a great read for you all.

https://www.aboutcivil.org/curing-of-concrete-types-methods.html

Ponding &/or flooding a concrete slab is how you achieve the strongest results from a concrete of any formula / mix. Allows the hydration to act fully and removes heat from the concrete / reaction.

 

[boley]

I have no useful advice, but I am glad you brought up the topic. My 24x26' slab goes in on Monday. Very similar situation to yours, with a few layers of block and brick on footers with a slab going inside. After reading your linked info and some other articles I am shifting from water and plastic curing to ponding.

One potentially semi useful piece of advice. I don't think a poly covered 2x4 is going to seal your doorways. My plan is to use mud/sand/gunk of some sort against a 2x4. Based upon what I have read, the mud is typically enough to hold a few inches of water. So mud backed up by a 2x4 should be plenty strong.

Some additional info I found.
https://gharpedia.com/blog/cure-concrete-ponding-method/
https://www.bobvila.com/articles/curing-concrete/

 

[NWOhioChevyGuy]

Funny thing, I was on both of those sites during my research.

I may pick up a bag or two of bentonite (Clay) this weekend, and use that in front of the 2x6's that I already have for the doorways. We live on a sand hill so dirt/mud that will retain water is not easily found.

 

[ConCretin]

The goal when curing concrete is simply to prevent the premature evaporation of mix water to allow the hydration process to continue until design strength is achieved. The OP's plan will certainly achieve that goal but it's probably overkill for a residential garage slab.

Better curing won't necessarily produce a stronger slab. The minimal level of curing that preserves adequate mix water will allow the concrete to achieve the same strength as the most elaborate curing method. The concrete just needs enough water relative to the amount of cement in the mix. I'm not disparaging the OP here. I applaud his thoroughness.

I'd alway cure a slab to maximize my investment but the reality is that in all but the hottest and/or windiest conditions, most people would never notice the difference between a properly cured slab and one that wasn't.

 

[Marctrees]

It will be very difficult if not impossible for a regular residential flow water line and hoses to keep up with and overcome the leakages, even if only at the door openings.

What will your water bill be if your hose is running wide open for 5-7 Days ?

If you can make a tight seal, it's a great idea.

It may be prudent to have pre planned and setup working 4 sprinklers to not lose any surface dehydration, while trying to seal the opening.

If you succeed in sealing them, all the better.

If you can't, the hoses and sprinklers saved the job.

Marc

 

[Marctrees]

I suppose if your poly came up between concrete and the forming at the doorways, AND your forms ran higher than the screed level... AND you had the bentonite or whatever to berm against the form, maybe it could work.

Marc

 

[NWOhioChevyGuy]

Country living - no water bill & a well that produces 15GPM+

I will have a few sprinklers as a back up, but suspect i can get it sealed up good.
Now just to find where I can buy the bentonite.

 

[NWOhioChevyGuy]

So I ended up going with doing just sprinklers on the slab - on day 3 currently plan is to do 5 days of constant watering then 4-5 of keeping it cool / wetting it down 6-10 times a day.

 

[nitroracer20]

we have been using a roll comprised of two materials for summer curing - the top (sun exposed) is a white plastic, and the bottom is almost like a fabric cloth that retains water. i am amazed how well it works - the white reflects the sun excellent. We have had very hot days and when you peel it back slab is wet.

We tried sprinklers and soaker hoses, but always flooded the adjacent area. Save water, drink beer, use curing blankets.

ill post a spec sheet / check pricing when i get back into the office, but i believe the roll was 10.5' wide X 300' + long for $350. Sell the remaining on let go / craiglist.

No notable surface discoloration like possible with burlap / poly. We have been power troweling.

 

[danpik]

We flood cured my brothers several years ago. For the openings, we simply pulled the vapor barrier up high enough in front of the openings and backed it up with blocking to support it. Worked fine that way. This was the first time I have ever done this and all I can say is that it really made the concrete hard to drill when we wanted to put up a partition wall a couple months after the garage was done

 

[brianpgriset]

Quick question - pouring slab tomorrow for my shop. How soon after finishing can i start spraying water?

 

[NWOhioChevyGuy]

Fine mist can be done pretty quick - think n I started at about 2 hours after finish.

 

[brianpgriset]

Cool, thanks! How long till i can get the sprinklers out?

 

[NWOhioChevyGuy]

Was around 4 hours for me - poured in July w/ temps in the 90’s

 

[brianpgriset]

Ok one more question i promise! I'm also getting a driveway poured that is pretty long. I was planning on only watering the shop portion. Any issues with only watering one section of the poured concrete? Am i setting myself up for big issues at the edge of the water since part will be wet and the other side dry? Thinking like differential expansion...

 

[ConCretin]

All slabs should ideally be cured to help ensure the concrete reaches design strength and the surface is as durable as possible. It doesn't affect thermal expansion but the curing method might affect appearance if different methods are used. Moist curing is the best method but a spray on curing compound is reasonably effective might be a better solution for your driveway or all of the new concrete.

 

[brianpgriset]

Alright today was pour. Things went well but a couple things i thought worth mentioning that may help some other first timers like me with concrete curing. My plan was sprinklers and most cure for about a week. Well here are the words of wisdom.

1. Test your watering rig in advance of pour! I went to walmart and got the cheapest sprinklers they had and of course one of them didnt work. Also it got pretty windy today and stiff enough that i couldnt really reach all parts of the slab and driveway anyways after all that, especially not down a sprinkler. So give it a good test run.

2. Buy poly sheeting even if you dont plan to use it. This saved my *** big time. At 6am i got nervous nd ran to HD and bought 3 rolls of the 6 mil clear poly sheeting just incase i needed to cover the slab. I honestly bought for rain cause around here its 20% chance of rain almost every day in the summer and fall so i went aheaf and bought it as insurance. Well after the sprinkler debacle i just tried hand watering it myself, NOT a CHANCE. It was hot and breezy and it looked like a few places were getting away from me so i had my wife wetting slab real good then id roll the sheeting over right after and put stuff to hold it in place. Worked great. And ill use the sheeting for finishing the interior too anyways so nothing is lost. Worst case you dont use it and just return it later. So just get the sheeting.

That all said, over all went pretty good and finish looked good. Didn't get a great chance to look since i was scrambling with the sheeting but it should do the job.

 

[brianpgriset]

Btw this was about 2300 sqft total pour shop and driveway.

 

[ConCretin]

Nice job!

 

[Marctrees]

Actually flooding and pooling a slab is a great idea, but very difficult and requires major attention to detail, and probably is still not gonna happen.

Been there, done that.

A common residential garden hose only puts out ? X gallons/ hour.

Even if the underslab poly is brought up in a vertical wall on the ENTIRE perimeter, which would be the MINIMUM mandated detail there are still seams like every 12' or whatever on the poly that will easily pass on a typical 1200 ft sq slab MORE than the water supply of the common hose.

The bentonite or similar can help i hear. I don't know, never tried that.

Meaning, pooling the slab is usually impossible unless much smaller slab or non standard special high volume hose setup.

So now we go to sprinklers w good PRE TESTED FULL coverage, or poly blankets of whatever sort.

Or a sealer spray applied in a TIMELY MANNER "they say" may be sufficient to "lock in" the original mix moisture to allow sufficient curing hydration, I dunno.

I would feel best w CONSTANT wetting of the surface at least by sprinkling, rather than a sealer spray, MY opinion.

If one studies commercial practices, the spray sealer sealing the residual water in a TIMELY MANNER MAY be sufficient.... I "assume" that because commercial jobs are done in that way rather than pooling.


That is the reality, VERY difficult if not impossible to pool w a normal water supply unless a tiny garden shed AND with poly brought up to make containment walls.



Marc

 

[brianpgriset]

Ok maximum paranoia setting in. It isnt a big deal having those buckets and such on my new concrete rifht? I mean they only weigh like 30 lbs. I did walk on it to wet it and such too but surely a bit of minor foot traffic aint a big deal? I know the old rule of thumb is 24 hours.

 

[Marctrees]

"24" hours is WAY more than needed.

Don't know where you got that, it's more like 6 hours or less.

brain - You are fine at this point NO problem.

Edit - Brian

Just be aware anytime poly sheet, straw, buckets or whatever is set there may be minor printiong on the slab shading darkness colorwise, but that is what's commonly done.

You sound like you are worrying about 3d imprints like dents... No, you are past that... just shading differences possible.

Marc

Marc

 

[brianpgriset]

Thanks Marc. No problems with the printing, the shop portion will be covered. I don't expect issues with the driveway portion; the broom finish doesn't allow continues contact with the sheeting anyways.

 

[Marctrees]

So, for an ultimate job, YOUR job is to keep it wet for a week or so + depending on your attention to detail.

others will comment, but 7-10 days wet will be a good job.

Leaving it covered wet w the poly for a few weeks more is even better, but w diminishing returns.

Marc

 

[Marctrees]

In Beaumont, You are also automatically benefiting from the weather this time of year.

MUCH better than pouring 2 months ago.

Makes your job easier.

Marc