Is it sealer or matex? I also heard that after using sealer, its very hard to apply colours to the wall as the sealer cause the wall to be "water-proof". the fact is, after apply sealer, then you will more easy to apply color coat. If there is a mark on the wall, the new coat will not able to cover it if there is no sealer. If you have false ceiling, the screw use to faster the ceiling board, silicon use to sealing the edge,The area will start to turn yellow after 2 years, dun believe, ask your friend who live in condo to check their kitchen or bathroom. Why? they didnt use sealer (price for sealer is 3 time more then matex) Hope you understand by now.