We have a sheet vinyl floor in our kitchen that has been down about 15 years. Due to settlement, we have a small separation in one of the seams. What product should we use to re-seal the seam?
Fifteen years is a long time for vinyl to last, so your floor might be due for replacement. You can attempt to reseal it, though - assuming no fragments have broken off or gone missing.
Start by pressing down the loose edges to make sure they'll match up if resealed. If they do, thoroughly vacuum out any dirt or debris that's gotten under it. Scrape away any loose, old adhesive, as well. Next use a putty knife to apply a multipurpose vinyl adhesive beneath the elevated sections, pulling them back a bit and applying the adhesive as far beanth as you can get it without lifting off more of the vinyl.
Rub down the seam and tape the seam, temporarily, to keep it in place while the glue adheres. It never hurts to place something heavy on top of it, as well. The next day, after it's had time to dry, apply a seam sealant - it's available in gloss and satin, so make sure the type you buy matches your floor's sheen.
Hopefully this fix gets you a few more years out of your vinyl. Good luck - and if it works, post before and after pics on the Money Pit Facebook page!