I tried to repair some creases in a polyester board with epoxy (quality SP-brand stuff). Sanded it with 60, then wiped clean with acetone and laminated one 160 g/m2 (6 oz?) cloth, let it dry for 24 hours, then sanded a little and added some epoxy to have a sanding coat.
As I peeled the mask tapes off I noticed that the laminate hadn’t glued to the board, it peeled off completely by hand in large pieces. The ‘sanding coat’ had didn’t separate from the first epoxy coat, but there was practically no adhesion between the board and the epoxy laminate.
What could have gone wrong?
Is there something in the hotcoat of the board that the epoxy don’t stick with? Should I have sanded more in the first place so that the original hotcoat came off the board?
Can there be a mismatch in between the epoxy and the polyester laminate?
The epoxy was a bit old, it had expired half a year ago. Could it be the reason? (the epoxy layers didn’t separate from each other, however)
So, I’ll have to start all over again, and I’d still like to do it with epoxy (unless someone convinces me not to) because or its strenght and adhesive(?) properties. What could have gone wrong, what’s the trick to do it right this time?
That’s a weird one onshore… some epoxy distributors actually recommend epoxy over poly for various boat repairs like blistering. Supposedly better adhesion to poly than poly itself. Was the 60 grit prep sand out to edge of repair? Did the epoxy seem to fully cure? Maybe you touched it and left some greasy fingerprints? The expired outdate is a possibility but if it fully cured, I don’t know why it wouldn’t have stuck. Have you asked the distributor where you bought it?
The Technical Data Sheet for System 3 SB 112 epoxy claims that polyester hot coats can be applied directly to the epoxy (although I have never tried doing it that way)!
Did it twice. First just roughed the surface and laminated, did not bond. Then sanded to the cloth. Did not bond with the poly at all. Both times cleaned with acetone.
Yesterday I finally laminated it with polyester, which bonded perfectly.
I asked from the distributor of SP 115 epoxy about this and they said that although it’s rare, epoxy doesn’t bond with all types of poly.
Don’t use acetone. If you use acetone on epoxy it makes the epoxy kind of gummy. Maybe it didn’t fully evaporate and kind of messed up the epoxy from underneat.
The last time I tried with epoxy there was 4 hours beetween cleaning with acetone and laminating, so there was plenty of time for the acetone to evaporate.
Dunno, however, if acetone laves some kind of residue after evaporating?
Besides, the epoxy sanding coat bonded perfectly to the epoxy laminate, which was cleaned with acetone.
The last time I tried with epoxy there was 4 hours beetween cleaning with acetone and laminating, so there was plenty of time for the acetone to evaporate.
Dunno, however, if acetone laves some kind of residue after evaporating?
Besides, the epoxy sanding coat bonded perfectly to the epoxy laminate, which was cleaned with acetone.
Do not prep a surface for epoxy adhesion by cleaning with acetone. If you are using epoxy, don’t even break out the acetone container. Use alcohol. Only. For prepping surfaces, and for cleaning tools.
Acetone has a flash point of three degrees F, and evaporates dead clean with no residue. Good general rule would seem to be “use like with like”, per your experience.