I have experienced the same problem that rhyswklein and jmsn reported back in 2020 when spraying 2-Pack Northane Clear.
Refer to: Tiny Bumps in Northane Gloss 2 Pack | Sailing Forums, page 1 (seabreeze.com.au)
My surface also ended up covered in small dimples, like tiny burst bubbles.
Initially I thought this may have been a problem with the fibreglass (polyester) surface, so ensured it was cleaned thoroughly with Acetone, Wax and Grease remover and then finally Northane Spraying Thinner. The extra preparation made no difference.
I then brushed on 3 coats, all of which went on OK.
This year, I once again attempted to spray a top coat onto the rudders with new tins of 2-Pack Northane Clear - 15% Northane Spraying Thinner, only to end up with a similar pock marked surface.
I even tried two different spray guns / nozzle sizes. The smaller nozzle did result in smaller dimples however did not eliminate the problem.
There must be a way of getting a good finish however I won't be attempting to spray 2-Pack Northane Clear again.
I had a similar issue rolling 2 Pack (Wattyl PU2000). I found that if I was too agressive when mixing I was entraping tiny air bubbles. These were not big enought to work their way out of the mix but surfaced once the paint was applied. I got the tiny dimpled effect!
Possibly the brush application is brushing the bubbles out.
I have had a similar thing happen to 2 pack on a hot day, thinning it further helped but it wasn't perfect.
Crusty, you are right on! Your comment got some brain cells remembering.
About 10 years ago I built a new cabin for my 38ft cat. I did an alright job on fairing and high build and bought a petrol compressor so I could spray on the mooring. It was very hard to get everything right but one day I anchored the cat in a private bay to spray the cabin. I put the petrol compressor up the front of the boat. All went well with the spray job but I did see tiny fish eyes. I never got them at home with the electric compressor so I reckon it was little specks of oil in the compressor exhaust.
So I reckon AusTornado, check your compressor line, you are probably getting little drops of oil through the line. You need an oil trap or better filter in the output hose from the compressor. It could be water too I guess, how good are your filters or water traps?
Cheers Phil
For those interested, I recently had great success rolling PolyU 400. The trick was 20 percent L754 thinners and a short nap microfibre roller. Put the Bunnings foam rollers in the bin
havent heard of that one Kankama Poly U400 till now.
I just noted that, like many 2pack Polyueurethanes, it has Isocyanates as catalyst.
If anyone wants to spray it, make sure you have a spare pair lungs, as that stuff isnt to be messed with.
Brushing/rollering wont be as bad,, but even the various 3M normal cartridge masks arent happy to cope with Isocyanate when sprayed..
You need a full face pressure mask, thats air filter fed.
As an alternative, some of the brushing polyeurethenes dont have it, plus its less airborn when rollered.
Ive used the Norglass and Altex mentioned in that thread ok.
