I did my own mastic. Of course my concrete and coping was messed up so I couldn't mess it up any worse really.

Go here to buy it, http://www.poolcenter.com/service_supplies_pool_caulking_supplies.htm.

I used the Vulkem but I didn't want mine to over-self level because the concrete was a mess. You just have backer rod in the seam and you add sand on top of that so you don't use up all the mastic. You apply the mastic and after it levels to where you want, you put sand on top. You don't have to do the sand on top, but thats the look I like.

The only FYI I can think of is the stuff runs all over the place so it can make a mess if you are not careful and well planned out.

One other comment- the foam strip runs the full depth of the joint but should be perforated. You don't want to remove the entire foam strip, just the top section. When you pull on it, it should tear at the perforations. The mastic joint should only be about 1/2" deep.

Thanks for the advice! One question that comes to mind: if have the foam strip, do I need to get backer rod or something else to ensure that the mastic doesn't drip down?

If they installed the type with the perforations then you won't need backer rod. Once you remove the top portion of the strip then the lower portion remains in place and performs the same as backer rod would. Here's a picture of the perforated type of filler:

{{!gwi}}

Oh - that's good news. I checked and I do have the perforated foam. The foam looks narrower than the gap - maybe by 1/8 inch on each side. Is that ok or should I fill in with sand or something similar?

I was thinking of using Sikaflex 1A to do this. Is that the right kind or should I use something else?

Thanks!

Have you inquired as to how much it would cost to have it done by a pro? I'm a big DIY but this is a very visible part of the pool and I'm very happy that I didn't even attempt this. On my pool, two men came out, cleaned out the joint, let me have a choice of about 50 colors, custom mixed the color, and applied the product. I believe they used a 2 part polyurethane. My pool has about 150 linear feet and I was charged $300. It seemed like money well spent.