Level chipboard before underlayment?
I have a small area (in an RV) that had laminated wood glued to thin wood strips running perpendicular which were glued and nailed into 1" chipboard substrate on steel joists. One area got a bunch of water on it (ice maker leak) and started to curl. I pulled up a plank right there very easily and decided I'd rip it all up, put down SurePly 1/4" vinyl underlayment board over the chipboard, then vinyl sheet with tape. The area is less than 12', so no seams. Should be easy.
Ha! In the areas not soaked with water the glue the manufacturer used is amazingly strong. I called them, they reccomended using a heat gun to soften the glue. I got a big heat gun from work which did nothing but made the substrate smoke and set off the smoke alarm several times. I stopped that technique before I set fire to the RV with its tanks of propane and diesel fuel.
So I chiseled up all the floor leaving only the chipboard. However due to the excellent glue used, parts of the chipboard tore up as apparently the glue used to stick the chipboard together was of lower quality than the flooring glue.
So now the question. Do I just screw the SurePly over the chipboard with all these 1or 2 chip deep divots on its surface? Or should I first be leveling the chipboard with something like portland cement based Henry #547 UniPro Universal Patch and Skimcoat? Or will that just break up when I drive in all the galvanized screws SurePly
Thanks for your help.