Your gun will most likely come with a viscosity cup. Its a cup with a hole
in the bottom. You fill the cup with coating and time how long it takes to
drain. For example, I know that tap water takes 15 seconds. Your gun with
then say what needle and nossle to use for each viscosity rating.
I talked to Benjamin Moore, who makes the enamel I used, and they said I
could think up to 10 or 15%. I forget which. I actually thinned about 25%.
The viscosity was still quite thick, but I used a large nossel and needle
and it worked. You gun will probably come with some guidelines about how
much you can thin different types of materials. Also the manufacturors will
usually give you some guildelines also. I sprayed some anti graffiti paint
that was really nasty stuff. The manufacturor even published which nossle
size to use with HVLP. (BTW, the paint came out great and it really works,
you can clean off graffiti with paint thinner and the original paint still
Worse case, if you have all the different sized tips, then if it isn't
spraying like you want, then you change to tip up or down.
One thing I noticed is that the manufacturors tech sheets say don't thin. I
call BM and asked about that, and they said its due to air quality
guidelines regarding VOCs. For liablity reasons they say don't thin, but off
the record, everybody thins.
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