Using wood filler as primer

[woodartist]

I have been working on planking a single layer hull that will be painted. The wood supplied by Billings had a rough finish and even after course and then fine sanding there was a noticeable grain that was visible and tactile. I was trying to figure out how to cure the problem, in the process, I,  for the first time actually read the instructions on Bert's Goodfilla wood filler. It suggested that if you mix the filler with 20 percent warm water it could be used as primer. I have been using this brand since my first boat build, I know it is expensive, about $12 for 8 oz. but it comes in multiple wood colors, dries quickly, and has an ultra fine grit that fits into minute cracks.

So I mixed up a batch to try it. The water when thoroughly mixed with the filler becomes a soup with a little body and can be applied with a paint brush, I used a 1/2" brush. I let it dry and sanded it with 320 grit sandpaper. The sanding dust is super fine!! It left a glass smooth finish. Even though most of the filler was not visible on the plank, the grain was no longer tactile. In the bigger gaps where the filler was clearly visible the filler was like glass as well. So if you have the same problem I recommend giving it a try.

[wefalck]

I don't know anything about USAmerican products, however, for me a wood-filler is a primer. Unlike on metal, one normally does not need to 'prime', unless it is a very resinous wood.

 

For decades I have used a German product that is marketed as 'Fast-sanding Ground'. It is essentially, a nitrocellulose varnish filled with pumice and talcum. I know, in some countries they now frown upon organic-solvent based varnishes/lacquers/paints, but water-based acrylics don't really beat them, when it comes to penetration.

 

I gather your wood-filler needs dilution, because the acrylics suspension has been formulated with a too high viscosity, not allowing good penetration. Adding water reduces the viscosity. It may be worthwhile trying some alcohol. Some acrylic suspensions can also be diluted with alcohol without breaking down. That should improve penetration as 'primer' even further.

 

[paul ron]

we (my cub scouts) used elmers wood filler (white tubs) for projects to completely cover over inferior wood (pine wood derby cars). i sanded the filler using a fine grit paper till it was as smoothe as a baby's bottom. the spray acrilic came out glass smooth in just 2 coats. i still have the cars, 35 years, and the finish is still beautiful as the day we painted em.