Buffing Out Two-Part Polyurethane

Hard urethane coats need careful treatment to avoid fine scratches. January 14, 2009

Question
We are currently in the middle of a project involving some ebonized oak tops for an office. The oak is very dark and almost black, therefore just about everything shows up on the surface. We have filled all the grain and have been using a National Detroit inline sander through the process to get a very flat surface.

The problem began when we went to rub and buff the product (Milesi two-part polyurethane) to the final glorious shine we found it almost impossible to get the surface to rub out completely as we worked it.

Our process was to sand the surface with 600 grit on the inline sander with soapy water, move on up to 800 grit, then 1000, and after that using a rubbing compound on a DeWalt buffer, then on to a finer rubbing paste, then polishing paste. We have had fantastic results with this same process, but this is the first time it has been used on a nearly black surface, and we are seeing a considerable amount of our tiny sanding marks left in the final finish.

My conclusion is that maybe the Milesi Polyurethan when cured is too hard to allow any necessary rubbing/buffing to be completed to the extent desired. Is this sound reasoning?

Does anyone have any experience rubbing this stuff? Any help would be greatly appreciated. The customer is waiting for the pieces.

Forum Responses
(Finishing Forum)
From contributor C:
First off you probably are not removing the last grit scratches with the new higher grit. Use a white guide coat. Second I would go much higher with paper before compounding.


From the original questioner:
What do you mean by a white guide coat?


From contributor R:
I like to go to a higher grit also - sometimes 4000 grit. I use the Milesi urethane and it buffs out great. I can get 1500 grit scratches out with 1 coarse compounding. What brand of compounds are you using?

From the original questioner:
I am using the Menzerna four step kit. The stuff works great on our Chemcraft Aqualux acrylic-urethane. What kind of sanders are you using - random orbital? I wonder if my inline sander is too aggressive for this finish.

From contributor R:
I use the Dynabrade orbital sander and prefer 3M microfinishing film for sandpaper and 3M buffing compounds. I use a lamb’s wool pad for the cutting compound and foam pads for the glazing compounds. I used to use the dual pad inline sander and didn't really care for the results. The dynabrade has given me the flattest surface of anything I have tried.

From the original questioner:
Great. Thanks for the info contributor R. I will fire up the Dynabrade and report back.

Thanks everyone for all your help. I simply began with 1500 on a Dynabrade and went up from there, then it buffed out beautifully. I’m pretty sure cutting it with the 600 to begin with was just way too harsh for the Milesi product.

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