What is this material on my patio?

Question

I have a cobblestone patio (see photo below). Between the stones is a black material that looks like grout. However, in some areas it's peeling up easily, definitely not a hard stone material like grout. More like rubber. Where it has peeled up, weeds are growing through. What is this material? How do a re-apply it?

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Answer 1

It appears to be the vinyl seam/crack filler thats sold at Home Depot or Lowes in the concrete section of the store . It comes in a quart size bottle with a tapered nozzle, just shake well and squeeze it out  . Hope this helps!  

Answer 2

It looks like someone has used an indoor tile grout on your stones.You need to remove it all,and put a proper outdoor cementing grout down.

Answer 3

It may be a butyl compound that is rubbery and meant to seal out water.  I have used it on gutters but never heard of it on paving. Its never going to stick well to stones even when it seems to when first applied.  It does stay flexible but when it pulls away from the bricks weed seeds will get in and grow.  You can replace it and just spray for weeds but the spray may damage your grass.  Butyl comes in a tube like caulk and is easy to apply.

Answer 4

It is actually roofing tar that comes in a tube..I can notice and tell by how grainy it is unlike butyl or caulking compounds which will have a smoother surface