Concrete or coating failure?

[Quick240]

My parents had this house built in Florida about 2 yrs ago. The coating was added during initial construction, so I'm not sure what product it is. Immediately after they moved in, this started happening. The builder has attempted to "fix it" twice now. The second time, they scuffed the whole floor and recoated the whole thing over (2 coats plus 1 clear). Didn't take long before it started happening again. To me, since the coating isn't actually peeling, but is pulling up chunks of concrete with it, I'd lean toward the concrete being bad, but I wanted to get your opinions.

If it is the concrete, what's the solution here? Will grinding it down (not just scuffing the old coating like they did last time) and recoating work? Or does the whole slab need to be torn out?

 

[LegacyIndustrial]

I can't see the pic but this is unfortunately common in FL.
It is the concrete and not the coating.

The floor would have to be ground very, very aggressively (all the way back to the stones) to get this to stop from happening.

 

[Quick240]

Oops, hopefully you can see the image now, but thank you for the reply!

 

[LegacyIndustrial]

Oops, hopefully you can see the image now, but thank you for the reply!

Yes, that is it. This is called a "weak cap". In some cases a general diamond grind won't even do it, need to grind it 2x and get all the way to the stones or rent a big planetary unit. Either way you will likely pull a bunch of dust off that floor, 50 or 60 lbs!!

 

[The Wolff]

Yes, that is it. This is called a "weak cap". In some cases a general diamond grind won't even do it, need to grind it 2x and get all the way to the stones or rent a big planetary unit. Either way you will likely pull a bunch of dust off that floor, 50 or 60 lbs!!

How would you tell if you have this weak cap concrete before you start coating?

 

[Quick240]

Yes, that is it. This is called a "weak cap". In some cases a general diamond grind won't even do it, need to grind it 2x and get all the way to the stones or rent a big planetary unit. Either way you will likely pull a bunch of dust off that floor, 50 or 60 lbs!!

Not great news, but that at least gives us a direction to go in. Really appreciate the info!

 

[LegacyIndustrial]

How would you tell if you have this weak cap concrete before you start coating?

It's tough to know sometimes because they "butter" the surface pretty well.
Sometimes you see little areas that look like the top flaked off.

If your diamond grinder starts to work like it's the energizer-bunny vs. the tortoise, that is a good indication that somethings up!!

 

[MoonRise]

Like Scotty said, if the coating is pulling up the actual concrete, then the concrete is no good.

Some possible causes of a weak surface layer of concrete, in no particular order:

- the concrete was too wet (too much water in the mix, the entire batch is then weak) Some 'contractors' do this because they either don't know WTF they are doing or don't care and want the 'wet' concrete because it 'flows' easier (water pours easier and spreads easier than rock, that sort of thing)

- the concrete was overworked and too much "cream" (weak wet cement layer with no or minimal aggregate like sand or rock in it) was brought to the surface while troweling it

- surface carbonation caused by fuel-burning heaters (typically) while pouring concrete in 'cold' weather inside a building. Shouldn't be an issue in Florida, but I'm listing it anyway.

- overworking (over-troweling) the surface while the "bleed water" was on it. Again, contractor didn't know or didn't care.

The fix is to remove enough of the 'weak' concrete (might be just the 'surface', or it might be the entire slab) to get to 'good' concrete.

https://www.concreteconstruction.net/how-to/meaning-of-laitance_o

https://www.forconstructionpros.com...57543/avoid-surface-defects-on-exterior-slabs

http://www.concreteisbetter.com/wp-content/uploads/2013/06/Slab-Surface-Prevention-Repair-a.pdf

https://www.nrmca.org/aboutconcrete/cips/01p.pdf

https://www.ccaa.com.au//imis_prod/documents/Library Documents/CCAA Datasheets/DS2005Dusting.pdf

 

[Shea]

https://www.concreteconstruction.net/how-to/meaning-of-laitance_o

https://www.forconstructionpros.com...57543/avoid-surface-defects-on-exterior-slabs

http://www.concreteisbetter.com/wp-content/uploads/2013/06/Slab-Surface-Prevention-Repair-a.pdf

https://www.nrmca.org/aboutconcrete/cips/01p.pdf

https://www.ccaa.com.au//imis_prod/documents/Library Documents/CCAA Datasheets/DS2005Dusting.pdf

Excellent references for people to read, Moonrise.

 

[brownbagg]

its not the coating, its bad concrete