Ask the Expert: Spraying Latex House Paint with HLVP

Q: I want to use a Graco 4900, 4 stage turbine HVLP to spray latex paint. I know that I may have to thin the latex to a viscosity that is compatible with the HVLP unit.

I am concerned that the paint manufacturers that I have spoken with cannot provide any information on thinning their product to the proper viscosity.

The HVLP manufacturers that I have spoken with provide little or no information on the subject either.

I have read that latex should be thinned by 20%. I have also heard that you should dip a mixing stick in the paint, pull it out, hold it at forty five degrees and count the seconds it takes the paint to run off the stick before it starts to drip. This method does not seem like a very accurate one to me. I want repeatable results so I need a method that will provide me with more quantitative results.

I have been looking into using a viscosity cup but none of the paint manufacturers or spray manufactures can provide any concrete procedures for using viscosity cups with their product. None of the outlet stores I have
been in contact with even carry a viscosity cup as part of their inventory.

Without expert advice from the manufacturers, it looks like spraying latex with an HVLP machine will require a lengthy trial and error learning curve.

Can you shed any light on the subject?

A: If the viscosity of the latex paint is too high for your HVLP spray gun then I do not suggest that you add excessive water to thin it. If the paint vendor suggests that you do not add more than 20% water, then I suggest that you treat that as the max. When you over thin the paint you can change its properties to your disadvantage.

Using a mixing stick to meassure paint viscosity is not much more cedible than sailor stories. You cannot, I repeat cannot measure the viscosity of a waterborne latex with a mixing stick.