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What are the pros and cons of using crack filler like Sikaflex Polyurethane Sealant or its self-leveling type versus concrete patch like Quikrete Concrete Patch Repair?

My understanding is that if cracks (not control joints) are large enough to use either option, the concrete patch will be superior in strength and does not introduce a very different material (although it has polymer additives).

More specifically, I am thinking of cracks on driveway as well as small hairline cracks on pool decks (at the four corners), if these special situations change any consideration.

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If the cracks are due only to an initial settling, and the slab is now stable, patching with concrete definitely does have the benefit of being the same material and can be stronger. However, this makes the whole slab one block again.

The advantage of the flexible sealants is that if the cracks are due to seasonal movement of the slab, they allow the slab to still move a bit while still being sealed (like a control joint). If a concrete-patched slab needs to bend or adjust a bit, it will just crack itself again.

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    I think there should be emphasis on the fact that if you use concrete patch on slab cracks: "it will just crack... again". – Jimmy Fix-it Dec 26 '20 at 21:23
  • For concrete paving with control joints, wouldn't the control joints take care of seasonal motion? It is probably easy for stress cracks to form with initial settling, especially around corners -- do these tend to occur seasonally as well? – P. B. Dec 28 '20 at 21:31
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    @P.B. - That is the idea of control joints, but sometimes there are not enough / the ground just moves. The seasonal link would be if the cracks tend to grow or shrink throughout the year. May not be visible to the unaided eye, though. Hairline cracks around an inground pool sound like an initial settling, not a seasonal occurrence. If the cracks have not changed in appearance over a few years you could try with the concrete patch, and if it reoccurs next year use something flexible. Driveway could be seasonal settling if it's regularly getting heavy vehicles driven over it. – IronEagle Dec 29 '20 at 6:34
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I've used both types and each has unique benefits depending on the situation. If the crack is shallow and narrow the self leveling caulking works very well at filling it completely.

For wider larger gaps the thicker less fluid caulking and a putty knife works well. I've also used the self leveling type caulking to fill larger cracks ,but after pushing in a backer rod to prevent the caulking from sinking away.

On pool decks the self leveling is the better product to use. It fills the crack fully and if you duct tape the cracks two edges, it looks neater.

Urethane caulking, once it dries, is a tough, durable yet resilient compound. It's paintable and is made in several colors to match it's surroundings.

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