Adjusting Viscosity for a Wood Coating

Now that we know the viscosity of our wood coating, and we’ve seen the results of spraying at that thickness, we can adjust to find the perfect viscosity. Don’t worry, you won’t have to do this every time you spray a wood coating, just when you are problem-solving or working with a new product.

If your material is too thick, unable to spray, or has an orange peel appearance we can add a thinner to the wood coating to lower its viscosity. For solvent-borne coatings, a thinner is a combination of solvents designed to work with the resins in a coating. In the case of waterborne coatings, distilled water can be used to thin the coating.

Determine how much thinner you’d like to add, if you’re not sure start with a low number such as 5% and see the result before progressing to a higher amount. Add the thinner to the coating, mix it in until the material is completely mixed, then measure the viscosity again.

Now, respray the coating and see the results. If the coating is too thick, repeat the process until you are happy with the coatings flow and levelling. If it’s too thin, remix the coating to a higher viscosity until you are happy with the final result. Each step of the way, be sure to keep accurate records of the amount of thinners you’re using, the viscosity, temperature, and results so that next time you can easily adjust the material to your ideal viscosity.

For example, if you’re using a pre-catalyzed product that has a viscosity of 33 seconds in a seventy-degree shop but your shop is only sixty-five degrees, you may need to add a reducer to lower the viscosity of the coating. If you determine your spray equipment worked best at a viscosity of 25 seconds, and it took a 5 percent reducer to lower your viscosity, that will be a good starting point for similar situations to get the best results possible in the future.

So what is viscosity and why does it matter?

Viscosity is the thickness of a wood coating and understanding how thick a wood coating is will help you to predict how efficiently it will spray through your spray equipment.

Coatings that are too thick (or high in viscosity) will not spray, or will not aerate properly resulting in a bumpy surface. Coatings that are too thin (or low in viscosity) will run and sag on surfaces.