I have built many laminate tops and I never sealed the seam. A good double cut with the router and I never had a problem.what do you guys use to seal the seam in laminate counter tops? The horizontal seams where sheets come together are what I am concerned about...even the 45 degree cuts where joining off the shelf mitered postformed tops.
I never liked using plywood for laminate work. I find it moves to much. Have had much better luck with HDPBgood point on seam placement. I'm switching to using ply for the base material after redoing my countertop made of plywood and seeing how good the condition was at the seams. I've installed postformed miters and the supplied glue (w/ bolts) indicates it keeps out water...not sure how that would work at the to of the seam unless perfect.
would you mind posting a picture of your jig?