Let's begin by answering this question- What is Thixotropic Grain Filler?
Using grain filler is an essential part of the paint/lacquer finishing process on open-pored woods such as ash and mahogany. It performs two functions:
A. It fills the larger areas of the grain, giving a flat surface so that sprayed on finishes do not pool.
B. It fills the pores in the wood, which helps to achieve an even finish.
Crucially, grain filler acts beneath the surface of the wood, in contrast to the paints and lacquers that follow which form a coating on top of the surface of the wood.
What Makes it Thixotropic?
“Thixotropic” refers to how the viscosity of the filler changes when it is stirred and agitated. When it has been left to rest it is thick and hard, but with some stirring transforms into an easily spreadable paste.
How to Apply Grain Filler
• Nitrile gloves should be worn throughout the application process. Always work in a well-ventilated area.
• The wood should be clean and smooth. Sand your surface with 120 grit and progress through the grits up to a maximum 320 grit.
• If the grain filler has been left unused then its components will split. Stir the grain filler well to a smooth uniform paste.
• White Spirit can be added to the grain filler to make it more easily spreadable.
• The filler is quite fast drying so it is best to work in small areas, approximately 4” x 4” at a time.
• Apply a thumb-sized amount of grain filler with a rubber edged grain filler applicator. Applying firm pressure, work the filler in to the wood in the direction
of the grain.
• Now, working across the grain, scrape off all of the excess grain filler. Try to scrape off as much as you can - grain filler is intended to work below the surface
of the wood. The more you scrape off the surface now, the less sanding will be required later on.
• Leave overnight to harden then sand the surface to 320 grit. Repeat this process if required (particularly wide-grained pieces of Ash and Mahogany may require two applications).
• Repeat these steps for all surfaces of your workpiece.
Thixotropic grain filler is suitable for use under most paints and lacquers including nitro, cellulose and pre-cat.
Filled wood can be dyed. After filling and, should you choose, dying the wood, the next step is a sealer or primer.