Polyurethane and contaminants


Coastyboy

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I have made a communion table for the church I attend and am so close to delivering it except for my final topcoat. I'm spraying the poly in my garage and because it's so slow drying I keep getting some dust particles on the top of the table. I used to spray lacquer and that was so easy compared to this, on hot days it would be dry in a few minutes, oh well. I have sprayed two coats of sealer, and now I must have 5 coats of the poly on, even used some vm&p naphtha 50/50 with the poly so it would dry faster which it did but, still some small particles lying there. I just sanded the top with 1000 grit and was going to shoot another coat but am wondering if I could just use some paste wax and be done with it. Would the wax cover 1000 grit lines? I'm afraid if I shoot it again I will still be feeling some blemishes.

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Try brown paper, like the kind from a grocery bag. Rub the finish down with that and then apply paste was and buff. It should give you a very buttery smooth to the touch finish.

3m also makes finishing pads in varying smoothness levels. Their smoothest one, white I believe, may do the trick too.

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ended up shooting another coat yesterday afternoon while it was raining out, figure there would be no dust blowing around and no bugs flying in the rain, well low and behold after a minute or so I looked back at the table and the was a mosquito standing up in the wet finish and I also must have shed a arm hair in it too. :angry: A friend from church owns a quality body shop here in town and told me yesterday that I could come over Friday night after they are through for the day and shoot it in their booth and leave it for the night in there. I'm going to do that 

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Curious why you are spraying poly?  Waterbase or lacquer, as your point out, have a quicker dry time.   Also, there are ways to speed up the drying of poly.  You can buy a quick drying poly (I know minwax makes one) or add a small amount of japan dryer.   I have never done that, but a little google searching should give you good results.

 

It is kind of a myth that naptha makes poly dry faster.  Yes, it does evaporate quicker but you are thinning the finish, as a result you need more coats.  Naptha does nothing to speed up curing time.

 

I like to rub finishes with an abralon pad on my ROS.  For oil based poly you do need a long cure time before rubbing out, at least a couple of weeks.  I typically use a 500 then 1000 grit abralon pad with a just a touch of water.  Basically I wipe the piece with a damp/dry cloth, then hit it with abralon pads. You can fix most surface defects that way.

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Something to consider. I see you are at 5 coats of poly. Possibly more now. You might check the can for thickness limits. I spray lacquer and 2k poly. I don't go over 4 dry mils with lacquer and 8 with poly. You risk cracking the finish.

I don't know what poly you are spraying or what time frame you have, but I would think after 5 coats you could let it cure a couple weeks and it would rub out amazing.

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