Garage floor coating

[DiverDn]

Later this week we have a contractor coming in to coat our garage floor.

 

They are going to use a product by Rock Tred and it's a polymer epoxy.

 

There are areas of the concrete where the surface is coming loose. You can tap on it with a hammer and can tell by the sound that it is loose or hollow underneath. Some areas much worse than others.

 

I have broken out the worse areas and question how far to go with breaking out the areas that sound a little hollow, but seem to be pretty solid.

 

They said that they will fill these areas in with a quick drying epoxy, then go over them with the coating.

 

My question is, how far do I go breaking out the old stuff?

 

Anyone have any experience with this type of repair?

 

Thanks John