Concrete Questions

[CurlyDave]

I've probably worked on building 50 homes. zero kept the slab or driveway wet. If we were ready to frame many times we started framing the next day after the pour. I've seen a few building kept covered but it gets real expensive to stop construction to keep a slab wet.

How many of those homes have you come back to 4 or 5 years later and inspected for concrete cracks? I bet that number is very low, approaching zero.

My point is that even though "everybody does it this way" and you have done it 50 times this way, that doesn't mean it isn't important to keep the concrete wet.

On my new house, the "professional" concrete guys did 90% of the flat work. Less than a year later there are way too many cracks for my liking. I did one slab, and I did three things differently.

1. more rebar.
2. I used a concrete vibrator (stinger).
3. I put a piece of sheet plastic over the slab after the pour and flooded the slab under the plastic twice a day for two weeks.

My slab has no cracks at all.

The average contractor would be out of business in a hurry if he took the care I did, but the result speaks for itself. Any owner-builder can do a better job on concrete by taking the extra time.

I did hire a professional finisher, which is well worth the cost.

[NuBota]

Will probably catch flak - but I agree with Pat g in terms of doing it all in increments - especially for your application.

In my first house when I was young and poor, I poured my 12x24 @ 4" patio by hand. Had a boss that would let me bring left over material home from our jobs. So at the end of each day I would shovel left over sand, gravel into my little S-10. Extra bags of portland I could take as well. After a few months I had enough material (had to buy a few bags of portland) - and an old 17cf mortar box and mixing hoe

Anyway, poured two slabs 12x12 a week apart - each took about hours - had my old man helping. Good solid base (had the area framed and prepped for months), 6mil plastic and wire mesh. Was in the house 13 more years with it - cold joint never opened up - no cracks. This was my first time ever doing it - I didn't lay mud on the job until AFTER I did this project. Was in the old neighborhood few months ago and it still looks the same - no cracks or shifting - 20+ years now.

Used a 12' 2x4 to screed/tamp and then just hand mag float and finish
trowel. Did a glass finish (just to see if I could) before brushing

I am doing the same thing as N80 - gonna build the barn with dirt floor - then decide how to handle floor later. Am thinking about doing it the same way since I don't like the pressure of getting it done fast with the truck on site. Buddy of mine got lime poisoning doing the footing for his garage - was rushing to keep up and mud went down in his boots - boy could barely walk for weeks.

Not negating all the good advice here - if I was building a garage or house - I would have the pros do it - I just need a level area to change implements. Over time could extend into a complete floor useing Pat's advice

[RobJ]

Originally Posted by CurlyDave

I've probably worked on building 50 homes. zero kept the slab or driveway wet. If we were ready to frame many times we started framing the next day after the pour. I've seen a few building kept covered but it gets real expensive to stop construction to keep a slab wet.

How many of those homes have you come back to 4 or 5 years later and inspected for concrete cracks? I bet that number is very low, approaching zero.

My point is that even though "everybody does it this way" and you have done it 50 times this way, that doesn't mean it isn't important to keep the concrete wet.

On my new house, the "professional" concrete guys did 90% of the flat work. Less than a year later there are way too many cracks for my liking. I did one slab, and I did three things differently.

1. more rebar.
2. I used a concrete vibrator (stinger).
3. I put a piece of sheet plastic over the slab after the pour and flooded the slab under the plastic twice a day for two weeks.

My slab has no cracks at all.

The average contractor would be out of business in a hurry if he took the care I did, but the result speaks for itself. Any owner-builder can do a better job on concrete by taking the extra time.

I did hire a professional finisher, which is well worth the cost.

Dave I didn't do any of the concrete work, I was a teen and worked on a framing crew. This was just my observation. I'm sure there are some cracks in that concrete by now. But a small hairline crack doesn't mean the concrete failed because it wasn't done properly. You'll see cracks in concrete in a highway, thick concrete, 1/2" rebar on a 12" grid. I doubt if more rebar or bigger rebar would help much. Concrete just cracks!

The only way to be sure your concrete in your house slab isn't cracked is to pull up the carpet, wood, tile and see.

[tessiers]

I work for a large construction company (100 men) and we place probably 4 to 5 thousand yards per year. All concrete slabs over about 15 feet square crack. The steel keeps the cracks from opening and moving but they are still there. We use wire in most slabs although we do use rebar in some of the heavy use slabs. Cutting control joints where you want the cracks will help. We cut them into squares between 10 and 15 feet in each direction.

[Dargo]

Well, according to "ConcreteNetwork", I got really lucky with the approx 4 to 5 days of constant rain after my concrete was poured. Check out this link: Allow Proper Time to Water Cure - Increase the Strength of Concrete Slabs - The Concrete Network

That seems to backup what my concrete company said about keeping the slab wet after it's initial curing. It says "Concrete which is moist cured for 7 days is about 50% stronger than uncured concrete."

This water curing was purely by accident (luck?). I guess I'll see if it holds up better than other outside concrete I have that wasn't cured. I used a cure and seal product on all inside concrete poured as soon as I could walk on it without creating any damage. Most of my outside jobs were just way too big for me to do that. Maybe mother nature helped by water curing this last pour for me. Anyway, maybe this info and link may help someone with future pours. I'd not ever heard of water curing, but it does seem to be well documented online now that I've taken the time to look.