Wolfgang92025 wrote:I put several coat of varnish on my wall.
Used PL adhesive to glue my light to the wall and they came right off.
Used sandpaper to rough up the area were the glue would be and it's been good for 7 years now.
If you mean traditional varnish, then that's why the polyurethane-based PL adhesive didn't work for you; Varnishes are generally made up of five specific ingredients: oil, resin, solvent, dryers and ultra- violet additives, while PL is is a one component, polyurethane based, moisture-curing adhesive, so it attaches more strongly to similar coatings. My trailer was thoroughly coated with the "mix", first, then pure polyurethane, then a solvent-based paint (which was applied so soon afterwards, that the solvents from each coat were still drying), and thus added to an intermix bonding. After that, using PL on top, it found a similar substrate to bond with, so it lasts and holds well. You can see in the picture I posted that the PL adhered so tightly to a total of 5 or 6 coats of "mix", poly, paint (I forget the exact #), that it literally tore plywood away with it when removed. That's a strong bond. My plywood was pre-sanded from Home Depot, and only degreased prior to using the "mix", and never afterwards.