Thread: Does Polyester Car filler work with epoxy ok?

Howdy,

Basically the criteria for fillets that work without glass taping over is that the powder be a fibre rather than something round. Means that any crack has to travel a long way to get to the other side as it has to weave around all the fibres.

If the powder is rounded then the crack will not be deviated much.

So long thin fibres like pulverised glass, pulverised cotton fibres (floss), colloidal silica etc are ideal and fill the requirement for fillets .. meaning you can use the standard rules of thumb for fillet size and they will work. - the radius is three times the thinner ply thickness up to 9mm ply. After that the fillet has to be pretty big and it becomes more economical to have a small fillet and use double bias glass tape.

Using the rule of thumb plus the right powder will mean the plywood will break off before the filleted join breaks. With a low stress boat like a canoe you can probably get away with lots of things you can't get away with in boats subject to sailing or motoring loads.

Often you only get to know just how well something works after using it for a few years on different boats and different situations and see how it goes over the really long term with different users and different environments.

Easy sanding mixes of epoxy are usually the more rounded grain powders, as it takes less energy to break them out of the surface.

If you glass over the fillet, it probably doesn't matter too much what you use as the glass will tie everything together ... so long as the glass will stick to it of course!

Also there can be problems if the material in the epoxy can swell significantly and the boat is kept in the water.

Best wishes

MIK

back to the original question.
im not a huge fan of the polyester car bog on epoxy sheathed or wooden boats.
so for the small holes, i think it would be ok,
but for the larger wider area i wouldnt. best stick with the epoxy for better adhesion, especially where the filler will feather out.
if it is underwater, hell no. poly on epoxy will let go, not straight away, but carbogs all absorb water and will let go eventually