Exterior 2-part filler with long working time?

[strangerep]

I need to fill a lot of cracks, some wide, some tiny, in about
100 blackbutt ballusters for exterior use. They'll eventually
be painted, so I don't need to make the filler look pretty.
It just needs to be paintable and stable in full exterior exposure.
There's also some shallow depressions in the timber, and I've
that ordinary 1-part fillers don't adhere to the surface well
enough for this.

In the past, I've got best results by pre-painting with oil-based
undercoat (2 coats, with several days drying time between each).
Then I'd use the standard "builder's bog" 2-part filler, allow it
cure thoroughly, then sand and do 2 more oil-based undercoats,
before 2-3 topcoats of acryllic weathershield.

This is fine -- except that standard "builder's bog" 2-part filler
can be a pest when you're working on a large amount of fiddly
imperfections -- because it sets too fast. I always end up wasting
a lot of epoxy. And re-mixing tiny quantities a hundreds of times
is a pain in itself.

So I'm wondering about other solutions, such as epoxy resins
with filler added. Eg., West Systems, or International's "HT9000"
series of products.

I have some questions to which I couldn't find answers on their
websites. Can anyone here help?

1) Are these products ok for filling timber or are they likely to
come loose as the timber expands and shrinks? (Someone
once warned me that ordinary fibre glass resins can lift off
timber over time.)

2) Will these products accept an oil-based undercoat on top?
If not, what intermediate coat could I use so that I can put
acryllic weathershield as the top coat successfully and durably?

TIA for any advice/experience/suggestions.

Cheers.

[Master Splinter]

The marine epoxies are fine for filling timber. They are mostly used to hold wooden boats together (as the sole fastening technique), and unlike polyester based resins, they grip timber very tenaciously.

The West Epoxy pumps will let you measure out small amounts without having to actually measure (just one pump from each and you have the correct ratio) so you can go along mixing small batches. You can also use slow hardener, which will give you longer working time.

Cheap ($2 for 50) disposable plastic shot glasses are handy small mix containers - discard after each few mixes to avoid the setting resin speeding up the set of the next mix.

Larger cracks can be filled with an epoxy and sawdust mix to reduce the amount of epoxy required - but paint the inside of the crack with unthickened epoxy first for maximum adhesion to the timber.

Epoxy paints just fine after sanding (http://www.westsystem.com/ss/testing-house-paint-primers/).