ᐅ Crack in two-component floor coating in garage

Hello
A few weeks ago, I had a professional apply a two-component floor coating in my garage.
Unfortunately, a crack has appeared in the coating.
The crack was already visible and present in the screed (about 15cm thick (6 inches)) before. According to the coating specialist’s statement at the inspection appointment, a crack is not a problem; it would simply be filled, and once the coating is applied, it would no longer be visible. The screed had dried for about one year.

Now the crack has appeared again, and I am unsure how to proceed.

I have already informed the company.

How likely is it that saltwater will penetrate the crack and cause the coating (3 or 4 layers) to peel off again?

Regards, Hans

A crack 15cm (6 inches) wide is no longer just a crack. Are there any pictures of the crack before and after?

What is the cause of the crack?

I would first ask the screed manufacturer (why not concrete?) to address the defect. Ideally, this should be done before applying any coating.

Well, the specification of 15cm (6 inches) was somewhat misinterpreted by "hanghaus."
The 15cm (6 inches) refers to the thickness of the screed.
Now, this brings us to the root cause analysis:
Generally, such a thick screed is not necessary in a garage if it was installed as a bonded screed— which is likely the case— and not above insulation (i.e., a floating screed, which is highly unusual in garages).
Typically, installation thicknesses of around 25mm (1 inch) are sufficient.
The probably existing installation thickness of 150mm (6 inches), however, is the main problem in three ways:
1. It is practically impossible to install such a thick screed in a single layer with the necessary structural compaction,
2. such a thick screed is highly prone to cracking, and
3. it makes no sense at all to use such a thick screed as a load distribution layer. What incredibly high loads would this need to withstand????? (rhetorical question!)
The crack has occurred; the subsequent contractor (the floor coating specialist) noticed the crack beforehand and must therefore address it appropriately to prevent future stresses from affecting their work (the floor coating).
The original screed installer is no longer responsible since the floor coating specialist accepted the substrate as suitable.
Therefore, the coating specialist is now your point of contact.
Do not let yourself be dismissed with pseudo-arguments here!
You did not order the crack, so you are not obliged to accept it.
As I am familiar with common practical tactics:
Be sure to send them a formal defect notice (this must be stated explicitly in the subject line!!) and set a deadline (let’s say five weeks) to have the defect remedied.
How they do this is, from a technical standpoint, clear to me, but it is their trade, so they must figure it out.
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Best of luck: KlaRa

So, as far as I know, the 15cm (6 inches) layer is standard concrete. This was because the slab for the house and garage is a single pour, meaning my garage is integrated into the main building, and there is a full room above the garage.

Inside the house, the floor buildup is 17cm (7 inches), which created a step of 17cm (7 inches) leading to the garage. That’s why the garage floor has a 15cm (6 inches) thick screed.

The coating specialist saw the crack during the inspection and said to just fill it with putty and then apply the coating.

Now he wants to cut open the crack in the coating (about fingernail width) with an angle grinder and fill it with some kind of Sikaflex.

I’m thinking that if there was a crack from the beginning, I might as well not have had the coating applied at all. Especially since this is a spot where the car always drives over and leaks saltwater.

How should the crack have been professionally treated to prevent the coating from cracking?
In the bathroom, we injected resin, made transverse cuts every 10cm (4 inches) with an angle grinder, inserted metal wave plates, and filled it with two-component resin.
Would the same method have been the right choice here, so that if the concrete moves, it moves together?

hans123 schrieb:

So the 15cm (6 inches) layer is regular concrete.

Then you shouldn’t be calling it screed.

hans123 schrieb:

The coating specialist saw the crack during inspection and said they would just fill it and that’s it. Then apply the coating.

You can see from the result what their expertise is. They knew exactly what to do. It would have just taken a bit more time. After all, the defect should have been fixed by the slab contractor beforehand.

hans123 schrieb:

Now he wants to cut open the crack in the coating (about fingernail thickness) with an angle grinder and inject some Sikaflex.

That sounds as likely to succeed as their first idea.

hans123 schrieb:

I’m just thinking I wouldn’t have needed the coating if the crack was there from the start.

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

Do you have any pictures of the garage slab? I’m guessing there’s only a single layer of reinforcement mesh lying on the ground.

hans123 schrieb:

In the bathroom, we injected resin, every 10cm (4 inches) we cut a transverse slit with the angle grinder, inserted metal corrugated plates, and filled it with 2-component resin.
Would that have been the right solution here too, so that if the concrete moves, it stays together?

That already sounds much better than the contractor’s suggestion.

In my opinion, it’s also sufficient to widen the crack with an angle grinder, then clean it thoroughly with compressed air, and inject 2-component resin until it no longer sinks in. That method has lasted over 20 years in my experience.

The only problem is that you can’t force the contractor to follow your preferred crack treatment method. The most you can do is raise concerns.