Dust spots in the finish

Q: Some shoddy workmen applied high gloss polyurethane to my sanded oak (80 years old, at least) LR and DR floors, without clearing the dust from the rooms! The next workman, trying to correct this, sanded with a fine grade grit (120?). While the floor FEELS SMOOTH, you can still see the dust spots as if they were still there. Also, the floor still looks shiny on parts of the grain.

Should the grit have been coarser, 60 or 80, such as was used for the first sanding? And do you think the next sanding would eliminate the sight of the dust in floor finish? Lastly, what sheen do you have on the floors in your advertising picture? It looks like satin to me. I had such a hard time trying to get my questions answered between my 2nd workman, and the guys at the home improvement center, and with the stress of getting the sander back on time (which I will now have to rent again)!

A: Cleaning and prep before applying coatings can’t be overstated. Vacuum and wipe the floor down with a micro weave mop or similar. The finishes used must also be kept clean. I work with gallon cans and after I coat a floor I pour the finish back into the can through a strainer in case I picked up some debris.

With inter coat abrasion I try to use the finest grit which will de-gloss the previous coating and scratch the finish without leaving heavy scratch marks that will likely show through the next coat as swirl marks. 3M and Norton have developed abrasive pads that can achieve this. If the coating has cured too long or is too tough to knock down then one needs to go to a more aggressive screen. If 220 grit won’t work, go to 180 or 150. If neither of those work 120 is the next one down. It is best to try to avoid using coarse screens which, as I mentioned, tend to leave visible scratches. If one had to use such an aggressive approach, I would suggest buffing a second time with a much finer abrasive, such as one of the abrasive pads I mentioned at the start.

If there are defects a lower sheen will help to hide them and is for the most part, much more pleasing to the eye than a very shiny coating. Satin is good. There are also finishes with a lower shine level: matte and another new one called natural matte. Semi gloss, gloss and hi gloss are much more unforgiving.