I have a question about refinishing hardwood floors. I have recieved a few estimates to sand, make some patches, and poly with gloss. Half the estimates say they are going to sand, apply a sealer, then two coats of poly. Another guy just sands and applies poly, no sealer. Is the sealer a must? The guy who doesnt do it is a guy how comes recommended but I wanted to find out what the deal with sealers are? Do you really need to samd it? The are existing floors from the 50's.