As far as I can gather, normal guitars don’t use expoxy to seal the fret-markers… they just use fret markers about 3mm thick, then sand them down.
I’m attempting to use materials that can be laser-cut though – and that means thinner paua/abalone in laser-etched holes, which means I need to make a dome of epoxy over each one, then scrape/sand them down until they’re the same height as the fretboard. This has taken a fair bit of trialing and erroring (mainly erroring) so I thought I’d best write down what works
1) epoxy doming resin (in picture)
2) two little plastic shot-glasses. You can get these 50 at at time at “everything for $1 shops”
3) little scales, as used by small time drug-dealers. Also in picture. Get them from your local head-shop.
4) a little plastic stirring rod.
5) a little tray/bowl of boiling water
1) in each of the cups, weigh out exactly a 1:2 ratio of the resin and the catalyst. Get this wrong and it will never dry. It doesn’t take much to fill the fret-marker holes… I go for about 2g – which is way too much, but it makes mixing easier.
2) put each in the little cups into the hot water. Hold them under for 1 minute. This makes the liquids easier to pour
3) pour one into the other… and stir slowly for 30 seconds, keeping it in the hot water. The hot water makes mixing easier, and gets rid of bubbles
4) transfer the whole lot to the other cup. This makes the ratios more accurate, and leaves you with two cups you can use again. If you don’t do this one cup will stay sticky forever. Stir for another 30 seconds, keeping it in the hot water.
5) using the stirring rod (or a matchstick etc), drip blobs of epoxy onto the fret markers… push the epoxy right to the edges of the holes, keep dripping until the expoxy meniscus is above the wood. It’s useful to have a bright light / window behind the fretboard) as in photo – makes it easier to see what you’re doing.
6) leave for 3 days. Keep the stirring stick somewhere handy… you can test the dryness by touching the stick rather than your markers. If there are bubbles, you can get rid of them (5 mins after the epoxy is poured) by using one of those little pen-sized blow torches… lightly brushing the epoxy with the flame. If there’s likely to be dust, make a cover to put over it. A long bit of cardboard will do.
After 3 days it’ll be cured. Hotter climates mean faster curing time… but it’s winter here right now, so 3 days it is. I scrape the surface using a razor… as shown here, then use fine sandpaper, then a dremel polishing wheel (very light touches). I’ve found that using a power-sander totally screws up the epoxy. It’s almost like it melts it.
Anyway – there it is.