Choosing the Right Viscosity

Knowing the viscosity for a wood coating is the first step in understanding how thick a coating should be to spray it, in this module we’ll determine what is the right thickness to spray the coating.

If you look on a Product Information sheet (the P I sheet) you’ll notice the product viscosity is listed. That is the current viscosity of the material in the can, in the ideal environment of 77 degrees Fahrenheit. Your ideal viscosity is up to you, your equipment, and your shop. The wrong viscosity can cause problems that you can easily avoid by finding your idea spray viscosity.

For example, if your coating is too thick you might have a hard time spraying it through your spray gun at all and if you can get it to leave the nozzle in the most extreme cases it will sputter or drip.

Slightly thinner coatings may spray but could still not aerate into a fine mist. This could leave large clumps of coating on the surface with material pooling more in some areas than others.

When the viscosity is only slightly thicker than the desired thickness, material may appear to go on properly but rather than flow into a smooth surface texture it will appear like the texture of an orange peel with obvious raised hills and valleys that will require extra sanding to flatten.

Slightly too thin and the wood coating will need too many coats to build up a think wood coating and when it’s far too thin, the material will run off the wood like water or sag on vertical surfaces and pool at the bottom.

The perfect viscosity will allow your equipment to turn the wood coating into a fine mist at the lowest air pressure possible to avoid the coating simply bouncing off the surface, and give the resulting coating time to properly flow and level consistently across the wood.

To determine if your current viscosity is too thick, or too thin, spray out a sample as you would on a final product and determine if you’re happy with the result. Next, we’ll look at how to adjust the coating viscosity.