: 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.

When I built my strip canoe I used Durham's Water Putty as instructed in Gil Gilpatrick's book "Building a Strip Canoe". I discovered it is a very pale yellow color and it did not match the dark cedar I used to strip the canoe. So I used aniline dyes to color the Durham's which worked quite well. Aniline dyes are a water-soluble powdered dye available at wood working supply houses. It took very little dye to color the putty, 1/8 teaspoon per 4 heaping tablespoons of putty. Dissolve the dye in a little water before adding it to the putty or color streaks will appear. I smeared the whole hull with the putty using a green scrub pad and then after it set I sanded back down to the wood. It filled every staple hole and gap, however, it did take a lot of sanding to get back down to the wood. I did not add any wood dust to the Durham's. I suspect the wood dust you are adding is interfering with the bond. Most builders use wood dust for filler with epoxy to color it and to thicken it so it will fill gaps with out running or sagging. Since Durham's is already a thick putty I would not mix wood dust with it.