Do you guys prefer doing overlays on cracked slabs or tearing out and pouring fresh?

I've been putting overlays down for about nine years now and my rule is pretty simple: anything wider than a credit card gets treated like a moving crack, not a static one. I grind the crack out, fill it with a flexible filler, then bridge it with mesh embedded in the base coat before the finish coat goes on. The mesh doesn't stop movement forever but it holds the overlay togehter so a crack telegraphs as a hairline instead of opening up.

Where I've gotten burned is cold joints and old control joints that were never properly placed. Had one driveway overlay about four years back where I treated everything the same, and the old expansion joint came right through within a year becuase the slab was still moving side to side. You can't mesh your way out of lateral movement, only downward shifting.

On tear out, I tell customers straight up what the odds are. If the slab is otherwise solid and the cracks are shrinkage cracks, an overlay is a reasonable gamble and I'll give them a one year workmanship warranty covering separation or delamination, not cracks. If the slab is heaving, tilted, or has crushed edges, I won't touch it and I hand them names of demo guys. I've walked away from two jobs this year doing that and slept fine both times.

The part most people miss is moisture underneath. Overlaying a slab that's absorbing ground water is asking for failure no matter how you prep the cracks. I always tape plastic down overnight before I quote anything.

I come at this from the other end. I stopped promising much on patched cracks years ago after a driveway I did in 2018 came back on me. Filled everything, waited two weeks, put the overlay down, and by the following spring the crack had walked right through the finish coat like it was on a rail. Since then I treat a cracked slab as a slab that wants to move, period. What I do now instead of fighting it is work with it. If the customer won't tear out, I chase the crack, fill it, then come back with a saw and cut a clean control joint directly over where the crack runs, straight through the new overlay. The movement has somewhere predictable to go and the joint looks intentional instead of like a failure. I've had way better luck with that than with mesh, which in my hands just gave me a crack with a wider shoulder. On the warranty question, I tell people up front it's a cosmetic fix, not a structural one, and I put that in writing. Customers respect honesty way more than a phone call two winters later. If the slab is cracked all over and heaving, I just say no and point them toward tear out, even if it costs me the job. One bad review from a failed overlay costs more than walking away does.

Total outsider reading this trying to picture it, but that plastic sheet trick sounds so simple I love it. When I got quotes for my back pad the guy just eyeballed everything for five minutes and wrote a number on a napkin. How do you even tell if the ground under it is still moving years later, like is there a sign the average person coud spot before hiring someone?

That 2018 driveway story matches what I went through on a back porch overlay. Skipped the filler on two hairlines because they looked tight enugh, and both showed up in the finish coat before the first summer was over. Now I chase every crack with a grinder no matter how small it looks, takes an extra twenty minutes but I stopped getting callbacks for it. Also started telling customers upfront the crack will probably ghost back through eventually, just thinner. Once they hear that going in, nobody's mad when it shows up in year three.

I frame it as a money conversation and let them pick. On my own patio last summer the tear out quote was more than double the overlay, so I get why people roll the dice. What I tell them is the overlay buys you looks, not structure, and if the slab moves the pretty surface goes with it. Had a customer pick the overlay knowing that, signed off on it, and two years later it still looks fine because the cracks were just shrinkage. The ones that bite you are always the slabs that moved after they were poured, and no filler on earth predicts that from the surface.

The bonding primer changed everything for me. Used to just dampen the slab and go, kept getting little hollow spots pop up at the edges a year later. Started rolling an acrylic bonding agent down first about six years back and I havent had a single delamination since, even on older slabs I wouldve second-guessed before. One thing I watch for now is downspouts dumping water near the patio. If the soil under one side stays soaked it moves diffrent than the dry side and no crack prep fixes that. I ask customers where the water goes before I quote anything, sounds dumb but it has saved me from a couple bad bets.