1. Sand any saw marks, heavy texture, or roughness from surface to be primed. Use 120 grit sandpaper.
2. For deep cuts or abrasions, pre-treat by spot priming with FSC-88 WB (link), or in extreme cases FSC-360 WB (link) knife grade filler. Allow to dry and lightly sand before continuing. To make FSC-88 WB a thicker consistency for use as putty, pour a small quantity on cardboard and let set until desired thickness occurs.
3. Apply liberal coat of FSC-88 WB by brush, roller, or spray gun. When applying by brush or roller, scrub in the first coat to wet out the cells. Allow to dry to tack free – about 15 minutes, recoat as soon as surface changes from gloss to flat matte. Spraying results in faster drying because of the higher solvent content and spray atomization. See FSC-88 WB Product Data Sheet for spraying details. Do not sand between coats.
4. Apply a second medium heavy coat of FSC-88 WB by brush, roller, or spray gun. Do not allow it to run. Allow to dry to tack free – about 15 minutes. When a totally smooth surface is not required, skip step 5 and go on to step 6. Do not sand second coat if proceeding to third coat.
5. If required, apply a third medium heavy coat of FSC-88 WB. Remember: All sanding must take place in the filler before getting back to the original Precision Board surface. Since Precision Board HDU is made of millions of tiny cells it is impossible to sand it smooth.
6. In areas of detail, i.e., relief cuts, vertical sides, and other hard to reach surfaces, allow the FSC-88 WB to dry a little longer. Use a brush wet with water to gently smooth out the filler. With a little practice you can use this technique to eliminate all sanding of these hard to reach areas. Let dry overnight.
7. Sand smooth with 120 grit sandpaper or 120 grit Drywall & Plaster sanding screens.
8. Lightly sand with 220 grit sandpaper. FSC-88 WB is totally dry when no balling up occurs on sandpaper. If it does, let dry until it does not occur.
9. For complete drying use a larger shop fan to blow across surface. Do not place item in direct sunlight as the FSC-88 WB might dry to quickly causing blistering in the primer.
10. Wipe with tack rag and proceed with top coat system.
LINK (Priming Tips from the Experts)
LINK (DYK: Priming HDU)
LINK (ten tips)
LINK (FSC-88 How to on YouTube)