Garage slab ?

[Denray]

This crack runs all the way across this 9-2014 built home garage floor. No displacement. Is it a problem?

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[kurt]

No.

[Marc]

No. The concrete is just curing, shrinking and cracking as it goes. The steel mesh embedded within it keeps the cracks narrow and on the level.

Marc

[Denray]

Thanks guys. Just seemed kind of big for a new house.

My son did a big slab patio in his back yard a while back. He's an engineer. Put a bunch of rebar in it. No cracks, no cracks, no cracks, then I saw them starting the other day. So sad.

[Nolan Kienitz]

See it all the time here in Texas. Typically not a concern.

[mlparham]

Concrete gets hard and cracks. As long as you cannot stick you pencil in the crack and there is no vertical displacement I would not worry about it.

[Jim Katen]

Thanks guys. Just seemed kind of big for a new house.

My son did a big slab patio in his back yard a while back. He's an engineer. Put a bunch of rebar in it. No cracks, no cracks, no cracks, then I saw them starting the other day. So sad.

Rebar and steel mesh do nothing to prevent cracks, although they can hold that cracked sections together.

If you want to make a slab with no cracks, you've got to prepare an excellent sub base, use a very dry concrete mix with very little slump, and cure it carefully and slowly.

I've done it and, after doing a few, I came to really like the look of cracks. . .

[ghentjr]

I bought my present home in 1978. It has a 1/4" crack in floor of a garage addition built in the early part of 1970. It extends full length and into the garage apron on the exterior. It has not moved, expanded, leaked, or otherwise caused any problems in all these years. It has filled itself with dust and dirt over the years. It has been on my Honeydo list and I will fill it when I get a "roundtuit".

[mjr6550]

I agree that it is a typical shrinkage crack. You should not be surprised that the crack extend the full length of the slab. That is common for shrinkage cracks.

Based on the location of the crack I am guessing that the slab continues under the wall at the right side of the garage and extends a significant distance.

[Denray]

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[Nolan Kienitz]

Sidebar comment follows:

While at a 3-day seminar put on by the Post Tensioning Institute several years ago the first moments of the class were great.

Room of 30+ inspectors, coffee cups filled (some donuts still being munched on) and the PTI engineer/instructor walks in with his cup of coffee and begins class.

He starts off with the "first rule of slabs". "Set the forms, pour the cement, it dries ... it cracks." That's it, class is over, that's all you need ... have a great day!"

He picked up his coffee cup and walked out of the room. Now a room of inspectors quite taken aback and a bit stunned. Then after only a minute or two he returned and repeated what he said. That is the fundamental baseline for slabs ... keep that in mind and now the details.

That began an intense 3-day class on the PTI foundations.

Damn good class and I'll likely never forget the PTI engineers opening comments.

So very true !!

[Marc]

Sidebar comment follows:

While at a 3-day seminar put on by the Post Tensioning Institute several years ago the first moments of the class were great.

Room of 30+ inspectors, coffee cups filled (some donuts still being munched on) and the PTI engineer/instructor walks in with his cup of coffee and begins class.

He starts off with the "first rule of slabs". "Set the forms, pour the cement, it dries ... it cracks." That's it, class is over, that's all you need ... have a great day!"

He picked up his coffee cup and walked out of the room. Now a room of inspectors quite taken aback and a bit stunned. Then after only a minute or two he returned and repeated what he said. That is the fundamental baseline for slabs ... keep that in mind and now the details.

That began an intense 3-day class on the PTI foundations.

Damn good class and I'll likely never forget the PTI engineers opening comments.

So very true !!

Could post-tensioned cables have saved Denray's 3 1/2" thick garage floor?

Marc

[mjr6550]

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Rule of thumb for a slab is to install control joints if the ratio of the length to width exceeds 1.5/1. It is pretty common to see a crack across the slab if the ratio is about 2/1 or greater.

[kurt]

Ratios sound good, but don't mean much without a spec on the mix. We do about 8' centers; those at least crack in the control joints.

[Nolan Kienitz]

Sidebar comment follows:

While at a 3-day seminar put on by the Post Tensioning Institute several years ago the first moments of the class were great.

Room of 30+ inspectors, coffee cups filled (some donuts still being munched on) and the PTI engineer/instructor walks in with his cup of coffee and begins class.

He starts off with the "first rule of slabs". "Set the forms, pour the cement, it dries ... it cracks." That's it, class is over, that's all you need ... have a great day!"

He picked up his coffee cup and walked out of the room. Now a room of inspectors quite taken aback and a bit stunned. Then after only a minute or two he returned and repeated what he said. That is the fundamental baseline for slabs ... keep that in mind and now the details.

That began an intense 3-day class on the PTI foundations.

Damn good class and I'll likely never forget the PTI engineers opening comments.

So very true !!

Could post-tensioned cables have saved Denray's 3 1/2" thick garage floor?

Marc

Not likely. Comments I shared were from an engineer with PTI ... the company who administers the PT slab design, etc..

See cracks all the time in PT Slabs ... that is the bulk of what we have in Texas. Some cracks are just more than others.

Most often the thickness of the slab in the garage area is less than what is set for the living/occupied area. Go figure that one with cars weighing a few pounds more than a few of us humans.

Huge factor is the site prep from proper soils for area (seldom is ever done), proper compacting (sheeps foot, etc.. ... never see it done save for an owner with their own piece of dirt and being knowledgeable about such), proper setup of the PT cables in the trenches and terminated properly at live and dead ends and on and on.

See hiccups all the time and seldom will builder correct before the pour.

I did a phase job on a custom property at Possum Kingdom Lake (West of Fort Worth) several years ago. The engineer for the company who did the foundation had to sign off before the pour. I chatted with him at the site and he left after about 30-minutes having left a one page report with the builder.

Problem being is that he missed two PT cables that had not yet been installed (were still coiled up next to project), several of the cables were rolled over and twisted like a pretzel and several of the live and dead end connections were terribly messed up.

I gave my report to the client and builder and the foundation worker was there trying to get ready for the pour and I went over all my findings with him and the builder and they said they would get it all corrected and were amazed that the PT engineer signed off on it.

Well, when I came back for a framing inspection the two PT cables were still coiled up, but now in the trash pile and the live/dead ends were still messed up. I will only hazard a guess that the pretzel twisted cables are still twisted.

Can only bang one's head into the wall so many times. I shrugged my shoulders and moved on. I did make note of my findings, but to no avail.

[Marc]

Dang engineers.

Marc

[mjr6550]

Ratios sound good, but don't mean much without a spec on the mix. We do about 8' centers; those at least crack in the control joints.

You are correct. Of course, around here with residential jobs the specs don't mean much. The contractor will just add water on-site so that concrete places itself.