As a newbie to HVLP, I have encountered the following problem...
I am spraying Minwax (water-based) Polycrylic semi-gloss polyurethane.
Although the spray seems to atomize well, it seems that unless I put on
a fairly heavy coat that it deposits in discrete though very small
droplets resulting in a somewhat rough surface.
i.e. - the spray doesn't seem to coalesce into a uniform coat unless I
spray it on pretty thick. It's almost if some type of surface tension is
causing the spray to coalesce together rather than completely and
uniformly wetting the surface.
When I move the gun slower to let more finish deposit, I do get a
uniform sheen that completely 'wets' the surface (however this only
works when the surface is horizontal because otherwise it would run).
- Is this normal or am I doing something wrong?
- If so what are the likely causes and corrections?
Note: I am using the low cost but surprisingly well reviewed Harbor
Freight #66222 (purple) gun. My 8 gallon compressor seems to have enough
reserve to power the gun since it is able to cycle. on and off and the
pressure never drops below about 70psi.
The surface I am spraying is clean, well-sanded Birch plywood.
I have the inlet pressure set at about 30PSI.
I have made some (non-exhaustive) attempts to:
- Adjust the inlet pressure in the range of 20-40PSI
- Adjust the fluid volume
- Adjust the spray pattern (more round vs. more oval)
- Adjust the distance to the object (from maybe 8 to 16 inches)
- Adjust the speed at which I sweep across the object
While Minwax claims it hasn't tested and hence can't recommend
polycrylic for spraying, others have had good results with it. Also, it
seems to be of fairly high viscosity and hence seems to spray well.