Well, I decided to take the plunge and give the seam repair a go. Things did not go quite according to plan, but I think I somehow managed to do a decent repair for a first-timer.
I researched as much as I could as far as materials and settled on using Armstrong S-761 seam adhesive with a protective coat of Mannington MCT-20 seam sealer. First delay was I attempted to order S-761 through Lowe's online since they didn't carry it in store and after a week I was informed that they couldn't fulfill the order. Found a vendor online through Amazon and acquired the seam adhesive, seam sealer, and a seam roller (went with Everhard Convertible Silicone Seam Roller).
The seam is in an area with heavy daily foot traffic combined with a fair amount of dog water dripping, so I wanted to try to repair the entire seam. It's likely that if I just fix the seam only at the location where the veneer is starting to peel, I'd likely have to repeat the process in other parts along the seam relatively soon after. My plan was to break the seam starting from the crack along the entire length, re-apply adhesive along the entire length, and finish with a new protective seal coat.
My vinyl flooring has a grey backing layer and a veneer with the printed layer and along the seam there was some separation of the veneer layer from the backing (you can kind of see that difference on the right section of the seam in the picture). It's important to try to get underneath the grey backing layer and pry it up gently from the flooring. I started with the low setting of my Black and Decker heat gun and waved it over a 3" section back and forth quickly about 2" above the floor for about 10 seconds. Using a 1" metal putty knife, I was able to get the corner of the metal blade underneath one side of the vinyl flooring under the backing of the existing crack after careful prodding. I repeated applying about 10 seconds of heat and using the putty knife to pry up the flooring until I could get the whole width blade underneath the flooring. I went slow and did not want to use a lot of pressure as I read it's very possible to tear the vinyl, and the vinyl is 10 years old. I would say after about 3 iterations of heat and putty knife, I was able to get the putty knife to lift up about 1/2" of the flooring on one side. Then I repeated to get the other side lifted with the putty knife.
Once I got the putty blade underneath, I used the heat gun in 3" segments to apply heat and using the putty knife like a scraper gently lift each side of the flooring sideways all along the seam until I reached the two ends. Upon close inspection, I could see the old glossy seam sealer that I had to break through but the heat seemed to make that not a problem. Overall I'd say it took me a little over an hour, half of that was trying to be extra careful getting the putty knife blade fully inserted under the backing without tearing the flooring on both sides. Once you get a small lift with the putty blade, heating the adjacent section and side scraping seemed to make it go pretty easily. Just don't apply too much pressure and let the heat gun do the softening.
The second phase of the process was attempting to apply the Armstrong S-761 seam adhesive to re-glue both ends of the flooring down. My plan after applying the adhesive to the seam, I’d use the seam roller on top of wax paper to roll along the seam to squeeze out any extra adhesive. Then I would need to weigh down the seam along it’s length. In preparation, I collected some block cut scrap pieces of 2x6” that I had and laid out over the floor to cover the entire length. I also collected some heavy garage items and books in totes that I could place on top of the wood to maintain pressure. I also got a couple of shop towels (retired kitchen towels) damp ready to wipe up excess adhesive.
This is the start of when I earned my Dumdum sucker. The S-761 seam adhesive came with a clear nozzle with a small red cap, so I figured I'd just pop off the red cap and start applying the adhesive. I squeezed and didn't notice any adhesive approach the nozzle tip and thought "Man, did I get some bum stuff from amazon?". I opened the cap and everything appeared to be moist enough, so I replaced the clear nozzle and squeezed really hard and saw that a little adhesive came out of the side of the cap. You would have thought I would have figured out the problem by now, but no, I decided well I just need to stir it up with a chop stick because maybe the top is a little less viscous or dried out. I put the cap back on and squeezed really hard and the same thing happened again.
At this point I'm confuzzled and starting to panic and I start trying to use the putty knife and chopstick to apply seam adhesive under the crack and making a huge mess. At this point my wife notices me and wondering what in the world I’m doing. At this point I’ve probably got about like 9” of seam adhesive applied with more on the outside of the seam than the inside. She politely asks me, “Did you poke a hole in the top of the nozzle?”. I raced to the garage to find a small nail to poke a hole in the top because knew I was on the clock. I poked a nail hole in the tip and squeezed pretty hard but still nothing came out. I ran back and got my wire cutter and clipped a small piece off of the plastic tip and finally got a bead of adhesive to come out.
With that, I was able to fit the nozzle under the vinyl floor and proceeded to apply adhesive down the seam. My thought was to take some pieces of wax paper to place it over the seam to minimize the adhesive sticking to the seam roller as I rolled over the seam, and then I'd use a damp shop towel to wipe up any excess adhesive. What ended up happening is that the wax paper was too thin and not waxy enough so when I removed the paper, it tore in pieces around the seam. I used my putty scraper to clean up best I could and wipe away the adhesive. However, I noticed that there were some sections where both of the vinyl flooring that didn't really stay perfectly down. I then put down 2x6" along the seam and placed weight on it and waited till morning to dry.
The next morning, I used the putty knife to gently unstick the 2x6" pieces on the seam and am somewhat disappointed as there were a couple of sections that didn't really stay flat kind of left a gap in the adhesive. Maybe I didn't apply enough pressure? Maybe the vinyl is aged and not as flexible as fresh flooring? I didn't like the small holes and sliver gaps in the seam adhesive, so I use toothpicks and my finger pressure to try to fill in those gaps and press down those sections along the seam. I also got a 3" wide thin piece of wood to try to increase the local pressure on the seam with the same weight. I waited 8 hours or so and it was definitely better, but still had a couple of small slivers in the seam. I re-applied a 3rd time and by this time it was evening the same day.
After the 3rd application, there were no holes or slivers in the seam adhesive. I felt that the seam was protected, but it was rough around the seam from small layers of adhesive that formed on the vinyl side of the flooring. I wanted to clean that up, so I scraped along each side of the seam with the putty knife to remove the adhesive which wasn't too bad. However, it was still rough feeling, so I then scraped over the seam itself using the middle of the putty knife until everything along the seam felt smooth. Overall took 45 minutes of scraping for that length.
Finally I was able to apply the clear protective coating (the Mannington MCT-20) over the seam and got some ventilation going as it was pretty strong odor and let it cure overnight. I waited 24 hours before replacing the trash can and dog bowl per the directions.
Overall I would say that I'm pleased with the repair, though definitely not pro level by any means. There is still a feelable ridge along certain sections of the seam, but doesn't feel rough to the touch, and it's not readily apparent except perhaps to pro vinyl flooring installers. If I were to do it again, I wouldn't use 2x6" scrap wood to keep weight on the seam, but start with a finished 2 or 3" wide strip, and use my body weight standing on it plus the totes for the first 10 minutes while the adhesive is setting to see if I can avoid the mutiple seam adhesive applications for the seam gaps I had to refill.
I know this is a bit long winded, but I'm sure there's someone out there who has an unsightly vinyl flooring seal crack. If your floor is still in decent shape, doing this may help extend the perceived service life another 5-10 years before coming around again. The next time though, I'll probably go ahead and replace the floor all around.