So I'm covering a wing with Polyspan (my first time using it) and despite my best efforts I managed to apply a couple of wing panels with the rough side out. 
I didn't notice it until I applied the first coat of Polyurethane Minwax. Instead of being all smooth and shiny it is kind of dull and rough. The polyspan was attached with thinned Balsarite which holds it very firmly in place.
I guess my question is can the rough Polyspan be filled by several coats of Minwax to the point where it will look ok with an opaque painted surface or should I try to remove the effected panels and try again?

Thanks, John

BTW I am very happy with the Polyspan where it was put on correctly.   

Mark's suggestion sounds good.  A few coats of Duplicolor Filler/Primer (sanding after a coat or two) might give you a smooth surface, if you can use that kind of paint.

I have a new "Top Hat" that is unfinished for a few years only due to priorities. It is covered with polyspan, and yes I did the same thing, Minwax and all.

 Without using names, a good friend who is one of the best finishers that I know, said to shoot autoprimer and the fuzz can be made to disappear. I still have to try it so I can't tell how much to sand off, but I would guess that just like other filling, you might have to prime some areas a second time. Done correctly it shouldn't add any weight.

This sounds feasible, but I haven't tried it yet.

Oh BTW, Polyspan has a shiny side that is the smooth side to be up. This is also the side on the outside of the roll.

John,
Which Minwax Polyurethane are you using? I see several types listed on their website (not including Polycrylic).  Did it have any effect on the tightness of the polyspan?  Once you have recovered it right side up, will you be using any other type of paint on top of the Polyurethane?  I'm interested in nondope finishes for open bays that are fuelproof and flexible enough not to crack.  Thanks.

John,
Which Minwax Polyurethane are you using? I see several types listed on their website (not including Polycrylic).  Did it have any effect on the tightness of the polyspan?  Once you have recovered it right side up, will you be using any other type of paint on top of the Polyurethane?  I'm interested in nondope finishes for open bays that are fuel proof and flexible enough not to crack.  Thanks.

I am using the Minwax water based Polycrylic in the picture which I purchased at Wal-Mart. In this case it is an electric model (an old time Playboy r/c) so I am not concerned with fuel proofing; I will deffer to the experts here on that. The minwax seems to shrink a very slight amount when dry, most of the shrinking is done with heat before or after applying the Minwax.  I will finish the model with Krylon spray paint or if I'm brave I have been experimenting with adding water based food dyes to the Minwax for a transparent finish. We will see.

BTW, John, I thought I remembered you saying that you were steering clear of dopes, and other smelly paints, which is why I said "if you can use it" referring to the Duplicolor Primer/filler, but if you ever need to do something like that again, and you can use it, the "Filler/Primer" will get the job done.

Definitely something I will keep in mind for the future.


John