We had a 400sqft patio poured three months ago and in at least two spots there are hairline cracks (1/32 of an inch by 4-5 feet). The contractor was aware that cracking was a big concern and was supposed to do everything he could to avoid it. He used a stone bed, rebar, a gray portland air-entrained mix, and saw cut the patio into 10x10 quarters.

Surrounding the patio is a courtyard wall, roughly 4-5' ft high with 12" wide filled concrete block. The block was laid on a 2' wide by 3' deep footing. There is a tar expansion joint between the wall and patio slab, but I think part of the footing may extend under the slab (since the footing was poured wider than the block).

He has been doing concrete for a long time and I believe he knows his stuff-- still, I am left with cracks in a patio that will only get worse. The previous patio was 50 years old and had NO CRACKS (it had to be dug up for sewer work). Our front porch is old concrete and again, no cracking. I need this work to outlast my mortgage (30 years) and in 3 months I'm not impressed.

This is the same contractor who did the blotchy parge coat on the block walls. I posted about that a few weeks ago. Something else I'm not happy with. Now there's a big white efforvencse area coming through on that.

What's the best way to handle this with a contractor? I want to make sure I'm being reasonable. Any thoughts? I know the contractor will say I'm being too picky. I don't want to end up in court.

 

Unfortunately, although the cracking is not acceptable to you, it would likely be acceptable in any legal venue. The American Concrete Institute, by which almost all concrete specs are written, has addressed the issue in ACI 302.1R-04. In part, it states that "even with the best floor designs and proper construction, it is unrealistic to expect crack-free and curl-free floors. Consequently, every owner should be advised by both the designer and contractor that it is normal to expect some amount of cracking and curling on every project, and that such occurrence does not necessarily reflect adversely on either the adequacy of the floor's design or the quality of its construction."
Now, concerning your joints and the contractor doing "everything he could" to prevent cracking: the joints should have been either tooled into the slab before it set up, or sawed into the hardened concrete as soon as possible (usually within 12 to 18 hours or sooner). If later, the slab may have already cracked due to shrinkage. FYI, I've seen unjointed basement slabs crack from shrinkage while the finishers were still trowelling them! This was due to them pouring the concrete much too wet, which allows for more shrinkage when the slab dries.
In addition to proper spacing, the joints should be of a proper depth (1/4 as deep as the slab is thick). Therefore, for a 4 inch thick slab the joints should be at least 1 inch deep. If not, the crack could jump out of the joint and travel transversely across the slab. Sometimes contractors use shallower groovers because either
1) they don't know any better
2) their 1 inch deep groover has been worn down significantly and they haven't bought a new one
3) The rebar or wire reinforcement is too close to the surface and the joint can't be cut deeper
From the details you gave, the joint depth and slump of the concrete are two factors the contractor may not have considered. You should check joint depth and the concrete batch ticket (available from the ready-mix concrete supplier) to find out how wet the concrete was ordered and placed.
Even if all was perfect, the slab could still have cracked as noted by ACI.

 

Concrete cracks. If cracks are unacceptable, you should choose a surface like pavers that have all the cracks pre-engineered in.

 

I don't think it is reasonable to think a 20X20 concrete slab absolutely won't crack. Who told you it wouldn't? It certainly didn't come from your contractor did it? If he did he's in over his head. I always guaranteed customers that it would crack. That takes care of that misconception right out of the starting gate . Of course we always took the precautions Pecos spoke of.

Besides that maybe the court would rule the landowner is responsible. After all, you obviously owned the property, you hired a contractor and must have said something like I'd like you to put a concrete slab in and put it right there. If the reason for the crack did not come from shoddy workmanship perhaps soil bearing capabilities or earth movement were to blame. Who's fault could that be?

Sorry about your problem but wait a second, for now we know not if this check in your patio is going anywhere. From your description the crack is miniscule at best. We will have to give it some time. It sounds as though your contractor took precautions to minimize a check.

I know it is frustrating but it can be for both sides. Good luck resolving this issue.

bs5

 

The guy who poured my shop flooring guaranteed it would crack. BUT it would crack where he told it to crack, along the cut lines he criss crossed it with. 12 years and it may have cracked, but it would have to be in the joints, as the main floor is perfect. I had HIM prepare the soil, underlayment, etc. Keeping that part to my self would have reversed the liability to me regardless of whether it cracked or not.

 

I shouldn't have mentioned the court angle. It was out of frustration.

Regarding the points mentioned: The contractor used a low-water mixture and didn't add any after it was delivered (I watched for that). He came back within 12 hours to cut the joints. I think the cuts are about 1 1/2" - 2" deep. I saw some sparks so I assume rebar got cut during the process. He used WB Dress & Seal (?) for curing so I wouldn't have to spray it down as it dried.

Our main worry is longevity of the slab. Given that there's tiny cracking within 3 months, what can we expect 5-10 years down the road after many freeze-thaw cycles? This is the beginning of the end of our patio. I talked to a few homeowners who said the same thing-- it shouldn't crack this soon and to expect problems down the road.

I know there are some high-solids sealers out there. Can I apply any of these to fill the gaps and keep the water out?

Should I fill the grooves that were cut with a silicone rubber? They don't drain in any way so water just sits in there. Also, they are not cut wall-to-wall. They stop a few inches short on each side because the saw blade couldn't get any closer. There's also some minor chipping along side those sawcuts.

 

It sounds like your contractor did everything in his power. The other homeowners' comments are worthless. They are looking at it from your angle (homeowner) and probably have no knowledge as to whether or not it "should crack". No one who pays a concrete contractor wants it to crack or thinks it should.
A high solids sealer will not fill the cracks, but epoxy injection would. The sealer will simply seep all the way through the crack and into the stone base. Yes, the crack goes all the way through the slab. It doesn't magically stop halfway through. Caulk might help if it can be forced into the narrow cracks.
Filling all the joints with caulk can help prevent damage from water freezing in the joints.
My saw cuts go all the way to the wall because after I saw, I then continue the joint with a 4" angle grinder equipped with a diamond blade.
The chipping at the joint edges is called ravelling and happens sometimes. This can be a good indicator that the concrete was still "green" enough for the saw cuts to be effective as crack control joints. The joints can later be cosmetically touched up by using a grinder equipped with a crack chasing blade. It's a v-shaped diamond blade that widens the top of the joint a bit. The extra width at the top usually eliminates the chips. It also helps protect against freezing damage in the joints by angling the joint walls, like the way ice cube trays are angled to make it easier getting the ice out. Sorry for the confusing explanation, I just couldn't think of a better way to say it.
In conclusion, it sounds like you got a very structurally sound job with some cosmetic defects. Unfortunately, it happens.