Crack in 2k floor coating garage

Hello I had a 2k floor coating applied in the garage by a professional a few weeks ago. Unfortunately, a crack has formed in the coating. The crack was already visible and present in the screed (approx. 15cm thick) beforehand. According to the coating specialist during the inspection appointment, a crack is not a problem; it is simply filled in and then you don’t see it anymore once the coating is applied. The screed had dried for about 1 year. Now the crack has appeared again, and I don’t know how to react. I have already informed the company. How great is the risk that saltwater will penetrate the crack and cause the coating (3 or 4-layer) to flake off again? Regards Hans

A crack 15 cm thick is no longer a crack. Are there pictures of the crack before and after?

What is the cause of the crack?

I would first ask the manufacturer of the screed (why no concrete?) to remedy the defect. Naturally better before coating.

Well, the specification of 15cm was somewhat misinterpreted by "hanghaus". The 15cm referred to the thickness of the screed. And now we come to the root cause analysis: Basically, such a thick screed is not necessary in a garage if it was installed as a bonded screed (which is to be assumed) and not above thermal insulation (i.e., floating screed, which is highly unusual in garages). Typically, installation thicknesses of about 25mm are sufficient. However, the probably existing installation thickness of 150mm is the main problem, in three respects. 1. It is impossible to install such a thick screed in a single layer with the necessary structural densification, 2. Such a thick screed is highly prone to cracking, and 3. It makes no sense at all to install such a thick screed as a load distribution layer. What insanely high loads are supposed to be absorbed by it????? (rhetorical question!) The crack has appeared; the subsequent trade (the coating applicator) recognized the crack beforehand and then also has to treat it accordingly so that the stresses do not impact his trade (the floor coating) in the future. The screed installer at the time is out of the picture since the coating applicator has deemed the substrate suitable and accepted it. And thus he is now the focus as your contact person. Do not let yourself be fobbed off here with pseudo-arguments! You did not order the crack; therefore, you do not have to accept it. Since I am familiar with the tricks of the trade: Be sure to write him a defect notice (this must be stated as such in the subject line!!) and request him, with a deadline (let’s say 5 weeks), to remedy the defect. How he does it is technically clear to me personally, but it is his trade, so HE has to consider it. ---------------------------- Regards and success: KlaRa

So the 15cm is already a normal concrete as far as I know, it turned out this way because the floor slab of the house and garage is one cast, i.e. my garage is integrated into the house building, above the garage there is still a fully functional room. Now we had a floor structure of 17cm in the house and therefore this step of 17cm to the garage. That’s why we have a 15cm thick "screed" in the garage.

The coating specialist saw the crack during inspection, said to fill it with putty and that’s it. Then put the coating on.

He now wants to cut open the crack in the coating (about fingernail thickness) with an angle grinder and smear some Sikaflex in it.

I just think I wouldn’t have needed a coating at all if there was a crack from the beginning. Especially at a place where the car always drives over and spills salt water.

How should the crack have been professionally treated so that the coating would not have cracked? In the bathroom we have used resin, every 10cm a cross slit with the angle grinder, inserted metal corrugated plates and poured over with 2k resin. Would this also have been the method of choice here, so that if the concrete moves it always moves together?

So the 15cm is already a normal concrete

Then you shouldn’t call it screed either.

The coating specialist saw the crack during inspection, said to fill it and that’s it. Then apply the coating.

From the result you can see what his expertise is. He knew exactly what to do. It just would have taken a bit more time. Because the defect should have been fixed by the slab installer beforehand.

He now wants to cut open the crack in the coating (about fingernail thickness) with the angle grinder and smear some Sikaflex in.

That sounds to me about as successful as his first idea.

I just think I wouldn’t have needed a coating at all if there was a crack in it from the start.

No, you wouldn’t have needed the coating. A professionally treated crack would have been sufficient. The slab manufacturer should have fixed the crack after notification of the defect (at their expense). I would have invoiced them for the necessary coating afterwards.

Do you have pictures of the slab in the garage? I would guess there is only one reinforcing mesh laid on the ground.

In the bathroom we injected resin, every 10cm a transverse cut with the angle grinder, metal corrugated plate inserted and poured with 2k resin.
Would this have also been the method of choice here, so that if the concrete moves it always moves together?

That already sounds a lot better than the contractor’s suggestion.

In my opinion, it is also sufficient to cut the crack open with the angle grinder, then clean the crack properly with compressed air and then fill it with 2K resin until nothing subsides anymore. This has lasted for me for over 20 years.

Only you have no way to dictate to the contractor how he treats the crack. At most, you can register concerns.