The difference between cracks in concrete

[Tammy B]

Looking for explanation and guidance on understanding cracks in concrete and what needs filled and what doesn’t need filled before having a full broadcast chip flake system installed. Have talked to 4 different contractors and get different answers.
I have a 750 sq ft garage built 5 years ago and builder used a zip strip system for controlled cracking. Some flooring contractors say this needs to be filled and others say to leave that alone. I also have minor hairline cracks around where the hot tub sits on outside patio. Some say to fill and others say they’ll determine after they do diamond grinding. The 4 different contractors are either using polyurea as base and polyaspartic as top coat, or polyaspartic as base and top. I just don’t understand why some make it a big deal to fill the zip strip cracks while others do not. So any explanation would be much appreciated!

 

[Rusted Nut]

Some epoxy floor systems have a control joint filler material, sometimes applied before epoxy, sometimes after; depends on manufacturer’s system. Ask the manufacturer.

As for hairline cracks, polish it then access.

 

[wssix99]

I just don’t understand why some make it a big deal to fill the zip strip cracks while others do not.

Its purely aesthetics. You don't want to park your new Ferrari on a floor that has a checker board of gutters on it...

That being said, this is not easy to do. You won't have a good experience by telling a contractor with no experience to fill your joints. A non-shrinking, industrial-grade grout is needed. You need someone who can get the right material, work with it and give you a good finish.

My epoxy floor had this done on the control joints and expansion joints. The control joints look great but you can see (if you look hard) where the expansion joints are. (The expansion joints are harder to do because they are wider and the slab is free to move a little more. So you could get some very fine hairline cracking after its all over. This is just a nature of the beast.)

Another reason why your contractors may be avoiding this is because they might have to carve out some of your zip strips in order to grout them up. (This is a PITA.) I would probably do it with a heat knife and sled. Not a big deal because I have one - but this may be something that your contractors are not equiped for.

What look do you want? Can you post a picture of what your zip strips look like?