Finishing advice, Please

[GymBob]

I am applying varnish (Interlux, Goldspar one part polyurethane) for the first time and cannot seem to get a smooth surface. I am using a foam roller and tipping with a foam brush. I have applied 6 coats with sanding between each coat with 320 grit on the last 2 coats. When the varnish has dried it always seems to have small raised bumps like pieces of dust/sand have settled on the surface. I am working in a closed room that is very clean when I apply the finish and I sand in different building. I wipe down the surface with solvent to remove any surface dirt before applying. I am using every precaution to keep a clean working area.

Am I doing something wrong? Should I be doing something else?
Any advice from someone with varnishing experience would be a great help. Thanks.

[alan white]

Make sure the solvent isn't causing a reaction. Try vaccuuming and tack-clothing rather than using solvent. Do a side-by-side comparison. Many solvents can remain in the wood even if the surface appears dry.

Alan

[PAR]

Place a cover over the work after you apply the last coats. This will prevent dust in the air from settling on the freshly applied surfaces. You don't have to see the dust for it to show up in the finial coats.

Also tip lightly with a reasonably dry brush. Hold the tipping brush almost straight up and down, not leaned over like when you are applying finish. You may be putting air into the finish as you roll or tip, so work carefully with little pressure.

[rwatson]

I found the west systems advise usefull - clean up with paper towels, and only use the one side. They suggest washing down with water rather than solvent, as solvent dries really quickly, and then the paper is too dry to pick up all the particles.
The other trick for a truly dust free environment is to hang a wet sheet somewhere - the dust in the room is caught and trapped. Wet newspaper or cloth on the ground is also very usefull.