These type of "bonding" problems over concrete (it is over concrete?) usually breakdown two ways: one, under the concrete can "wick" different chemicals through it, causing it to loose its adhesion (think painting over dirt or oil)
two, the intense heat (uv rays mostly) breakdown the bonding chemical that holds this type of product together.
Best bet is to pay a seasoned pro concrete guy to come out and either show you how to fix, or give you a bid to fix...
There are "clear" epoxy's/resins out there that can go over your existing, and after you make a "matched" repair
Hope this helps, Mike
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Mike
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