Ask the Expert Question-and-Answer Archive

by Ron Joseph

July, 2005

Orange Peel with Water Borne Paint

Q. I emailed you on friday and gave you some info on what type of paint I am using. I also got to looking at some of the info that you printed on your breifing and saw something else that may be a problem. I recently purchased a compressor from Sears and I noticed that the cfm is not as high as you reccommend. My compressor is a 7.0 HP with a SCFM @ 40 psig is 12.4 and at SCFM @ 90 psig is only 10.2. Is this enough air to use a HVLP gun or am I going to have to use a conventional one? Here again I wold appreciate some help, please.

A. When you apply a water borne paint you might find it difficult to eliminate orange peel because some of these paints have built-in thixotropy. The best method of eliminating orange peel is to use a high atomizing air pressure and low fluid flowrate. With HVLP spray guns you are legally limited to no more than 10 psig atomizing air pressure, and to get this you need to deliver approximately 50 psig to the handle of the spray gun. Of-course this upper inlet pressure (such as 50 psig) depends on the make of the HVLP gun, the size of the cap, needle and orifice assembly. The spray gun manufacturer states the maximum legal inlet air pressure on the body of the gun, somewhere on the cap or orifice, and/or in the written literature that is shipped with the spray gun.

Best wishes,

Ron Joseph