by GreenLake » Sat Mar 09, 2013 3:00 pm
Sean, the best sequence depends on how you want to do the finish of the coamings. If your plan is to take them down to bare wood and then proceed with epoxy coating the wood, then you would take care of the crack at that point, that is after you've stripped/sanded everything down to bare wood.
If, on the other hand, you are planning to use oil or varnish on bare wood, you need to make sure that none of the epoxy you use to fix the crack gets on the face of the coamings. If some does, you'd have to not only wipe it off, but probably sand the area bit to make sure that there's no place where the epoxy ended up "sealing" the wood. Those spots would then be visible later, as they would interfere with the way the wood takes up your oil or varnish. If, in that case, you make the repair first, the remaining old varnish will form a barrier and since you'll do some sanding anyway, you'll be fine.
Different epoxy formulations have different viscosity. I exclusively use the SystemThree line because I'm used to it and it's stocked widely locally, even in non-marine hardware stores. SystemThree makes a non-sagging glue (GelMagic) which is the highest viscosity of all of their liquid epoxies. Next in line would be their laminating epoxy, which is like honey and formulated for its ability to wet out laminate. ClearCoat is intended for applications like epoxy sealing wood, so it's thinner and can be applied more easily to surfaces. Finally, they make an almost watery epoxy called RotFix, which is great if you are trying to soak wood that has seen some decay, but retains a lot of firmness. (One of their products that I haven't tried is MirrorCoat, which is self-leveling for use on table tops).
So, in short, yes, you can get epoxies that are thinner and thicker (and to get really "thick" epoxies you can further add fillers, or buy products that have fillers already mixed in - I didn't mention any of those because they don't figure in your type of project).
To some extent, these epoxies can be used outside their "ideal" purpose. GelMagic will wet out laminate well enough that if I need to both glue and laminate something small, I tend to use it for both. Laminating epoxy (SilverTip) and ClearCoat can both be used to coat wood, in fact I've used both on my thwarts, because I used what I had available. RotFix could be used as a first coat - it will soak into the wood wherever it's a bit porous or has a tiny crack, but it's too thin to fill wider cracks.
The crack in your case looks like it is narrow enough that you don't need a special non-sagging formulation for it, so whatever you are using as a coating (laminating epoxy or ClearCoat) would do. You could try to gently spread each crack open, pour some epoxy and use a thin blade (thin sheet of stiff plastic, for example) to spread the epoxy everywhere, then letting the crack collapse to trap it.
If you are epoxy coating as next step, you can just continue, if you are not going to coat the whole piece, wipe as much epoxy off the piece as possible and then use tape to contain the rest in the crack until its cured. In that case, you'd need to sand the faces to make sure the wood can take up the oil or varnish everywhere.
Other vendors formulate their epoxies differently, but laminating epoxies are broadly similar in properties across manufacturers, and should be thin enough for coating.
~ green ~ lake ~ ~