OT: Concrete Question

I'm getting a driveway poured today, guessing around 11AM. We are suppose to get thunderstorms tonight, probably after 8PM. Do I need to worry about tarping the driveway to protect it? It's a large area, so would rather not, but don't want to have something happen to an expensive project. Would this be something the concrete contractor should take responsibility for? Thanks for your opinions

I think you are gonna be just fine.

The drive will have taken a set by then and the rain might even help to slow down the cure a bit, which is a good thing.

Tell 'em to get 'er laid. :>)

Allan

The answer is: It Depends

It depends on the temperature and humidity of your area and it depends on how much moisture is in the concrete mix, how thick the slab is, and other factors too. Those can have a big effect on how fast your concrete sets up.

If it is in place by 11, you ought to be OK by 8pm like Allan says. But if they just get there by 11 and don't get it poured until later in the afternoon, it could get dicey.

I've put in concrete that we had to bust our butts to get a finish on before it set up, and I've had some that we sat around for hours waiting for it to "go". You never know.

If it was me, I'd have some plastic available to throw over it, especially if you expect a hard, driving rain. Better to have it and not need it than to need it and not have it.

Good insurance to have that large roll of poly enough to cover that driveway, real good insurance, if you can't stop the pour today.

Contractors liability, your talking an expensive material here, what does you contract read ? If you give the go ahead and the contractor documents your directive to proceed, you own it if it rains and it's not set enough to withstand the damage. Contractor will always try to transfer risk, and justifiably so.

11:00 a.m. at this time of year ??? A large pour should start no later than 7:00 A.M. heck I'd want it at 5:30 a.m. if I could get it without paying O.T. at the plant or for the drivers. Your weather forecast should have reinforced that, you may very well have green areas that will sustain finish damage by this heavy rain, hail and all that, I'd be the first one to tell you to call it off, t-storms are too violent, too much rain at once. After it's set up, if you use what is done on bridge decks for example, they use sprinkler hose and burlap to cover it, to obtain a slow cure, not allowing the concrete to hydrate (cure) too quickly, especially in hot weather conditions. A nice soaking slow rain would duplicate this, thunderstorm could wash the finish right off and expose aggregate if it's too green because they got a late start, always pour as early as you can on something like this. Even with poly covering it, the weight and impact of the water can have an effect. The concrete has to be of correct mix design as it's placed, finishers need to screed and finish it off in time to get the right finish on top, no time to waste there, any variances here and you don't get the benefit of the doubt there, + heavy rains you may not be happy. Lot of variables in concrete work, every pour and batch is a little different.

Don't mean to sound harsh, but I'd want an early pour with enough time for it to cure before rain, in the next few days, sprinkle and soak it all you want to keep it from drying out to quickly, but right after it's set, heavy rains, hail and all the rest that goes with thunderstorms, not happening on my job that is for sure.

I would call it off if you don't have something to cover it handy.
I poured a 30 X 50 floor several years back early morning with thunder storm predicted for night. We were up on it with power trowels before lunch time. Looked up and saw a dark cloud on the horizon. Didn't have a square inch of plastic to roll out over it. We never stopped the trowels and the down pour only lasted a few minutes but we watched the surface run off the forms with the rain as we troweled.

if the guys pouring the concrete ask you what you want to do put it off. there is no guarantee if it will even rain but the more sun the faster it will flash over and then it will withstand rain dry ground will help it set too but I think getting some plastic on hand for insurance would be advisable then if you don't need it take it back. or try to pour it in smaller pours that way it can be covered easily and quickly

I worked with my uncle when i was teenager he was very perticular about his concrete he would feel the truck and if it to hot he would the load back. One day the guy was real late and the truck was quite warm he sent the load back boy were they mad I think the driver got fired.

Ask the contractor to do a slump test if he doesn't know what it is get another contractor.

Walt

There's actually a meter for the concrete barrel on the truck, according to American Concrete Institute (ACI) not supposed to rotate more than 300 revolutions.

Slump is important for many reasons, one thing is for sure, the design mix's water/cementitious ratio if changed ( adding more water to the design mix on site than called for in the actual mix design ) can substantially reduce the compressive strength of the concrete.

For residential contractors, say using a 3000-4000 psi mix design, a seasoned contractor would know already what mix design to use with a slump that works best without adding more water, enough to weaken the mix. That experienced contractor will know the suppliers and what to order. If the ready mix truck does show up and it's too stiff, yet the batch plant having been calibrated correctly to provide the correct lbs of materials including correct amount of water, it is not advisable to allow the contractor to arbitrarily add water as they see fit to loosen the mix and increase the slump, increasing the water to cementitious material ratio will definitely weaken the material. It happens and materials are subject to rejection, it needs to be workable and allow time to place, without altering the mix design

Residential applications are not monitored like large commercial jobs, it is imperative to have an experienced concrete contractor in the residential sector, one that can be trusted and knows this material and how to deal with reputable suppliers.

Your uncle was definitely onto something there, concrete creates heat, usually noticed after it's placed when you touch the form, like on a wall, but in the barrel, never heard of that, but can assume he knew that if the barrel was warm, the concrete has started the hydration process, been in the truck too long and won't be able to be placed, finished in time, as well as it failing prematurely.

Concrete suppliers are well aware of punctuality for the most part, if you are doing any kind of pour in NYC, you don't want those trucks caught in traffic, even for some small sidewalk jobs, controlled inspections are required, engineer is sent to the plant to inspect/monitor the batching plant, and an inspector is on site taking test cylinders usually 4 per so many cubic yards placed, kind of forget how many per cu yd now, as well as performing inspections of reinforcing and placing the concrete, each pour requirtes a licensed P.E. to sign and stamp, on large jobs at the end, these reports are all reviewed by a city plan examiner prior to approval for certificate of occupancy on building jobs. Much of what is done on these large jobs can be scaled down and applied to the smallest of jobs like what is common on residential work. The right contractor is key to this on residential work as it's only them and a homeowner, neither may know much about the material from what I have seen and things can go wrong quickly, absolutely correct, get another contractor at the first sign of incompetence or lack of knowledge, can be very costly.

I investigated a claim recently, they just ommitted the reinforcing in a slab, and it was required on approved drawings, now it cannot be approved by the municipality for C of O, they now have to hammer it all out and do it over, had a superintendent type or inspector been on the job, it could have easily been avoided, even if you ate the cost of one or 2 trucks, was as strip mall, quite a large slab, stop work order would have prevented a large claim here.

A few years ago, I had a ramp poured in front of my garage for the kids to play basketball on. The day it was poured, the weather was just fine, but that night we had a terrible thunderstorm. I had not tarped or covered the ramp in any way. The contractor had not thought it was necessary.

I sure wish I had, at least in the area where there was a drip from the garage roof. Now the surface of the ramp is spalling off real bad, mostly in very thin flakes.

What looked real good to begin with is now an eyesore. I am looking into resurfacing it with something else, like epoxy.

I would sure cover it if it was mine. Good luck!