: I've used Durham's water-based wood putty, in equal parts with sanding dust
: from my hull sanding (50-grit), to fill some small gaps and dings in my
: hull, prior to 'glassing.

: I let the filler dry for around a day, temperature is in the 70's.

: Problem is when I sand the filled hull, much of the putty in the cracks pulls
: out of the recesses, it doesn't seem to want to "stick". When I
: looked through the archives, it seemed as if Durham's/wood flour mix is
: the consensus for the appropriate filler. So what's the secret for having
: it stay in the cracks?

: Is 50-grit sanding dust a good approximation of wood flour?

: (I note that some references suggest using microballoons in the mix, since I
: don't have any, I haven't tried this. Would microballoons add to the
: adhesion? I thought this was just a thickener to add body).

: If anyone has any advice or thoughts I'd really appreciate it. Thanks in
: advance.

Hi Les

Moisture!!! When you added the filler ( saw dust ) it probably took all the moisture out of the mix. You have to have the moisture in the mix in order to get a good bond. Something like concrete. You can mix the rocks and sand and cement powder and water. The more sand or cement poweder you add, the more water you need to add. It keeps the mix wet enough to hold together and also to shape it in the scratches and also it helps the glue soak into the wood and get a good bite. I don't know about Durhams as I've never used it, but what I use ( on furniture projects ) is oil based and they have a solvent that works with it. When you use something to thicken it, you need to put a few drops of the thinner as well, to loosen it back up and get it to stick. Hope that helps.

Rehd