It's just about impossible to get a plug truly flush with the surrounding wood without sanding it flush, which of course damages the finish around the plug. I've tried taping carefully around a plug hole and then carefully sanding the plug down without sanding through the tape, but then the plug is proud of the surrounding surface by the thickness of the tape which can be surprisingly obvious.
The common way to get a plug close to the surface is to use a VERY sharp chisel and mallet, angle the chisel a bit up from the surface, and give it a whack with the mallet. And ALWAYS cut in the direction of the grain in the top of the plug, never across it. Cutting across almost guarantees the plug will break off with part of the top below the surface of the wood its in, which means you either have to live with with the "ding" or remove the plug and try again. Cutting with the grain minimizes this possibility although it can still happen, particularly if you try to get super-flush with the chisel. The chisel is just a way to cut most of the excess plug off. You still need to sandpaper it flush.
The risk here is that if the wood in your boat is old, or has faded due to light, sanding the surface, even a bit, will reveal the unexposed or unfaded wood cells underneath and you won't get a match unless you refinish the whole piece. The wood you sand will generally come out darker than the rest.
Very tricky thing, I've found, dealing with already finished wood and trying to get a match in finish. We have almost always simply opted to refinish any wood trim or components we end up having to remove.
We were advised to secure plugs with Tightbond II wood glue (now Tightbond III which is more water resistant). So that's what we use on all plugs, in the deck, on exterior trim, in the interior, wherever.
When we removed all the teak trim in our aft head/shower so we could repaint the walls, we rebedded the trim in Dolfinite. This is available in "natural" (tan) or white. We used natural since it blends to the wood trim fairly well. We did this to prevent moisture from getting trapped behind the trim. However Dolfinite is not an adhesive so if or when the day comes we have to remove the trim again for some reason, it will be easy to take down. Lucky for us, American Marine did not use plugs in the wood trim strips that cover all the wall-to-ceiling and wall-to-wall joints in the heads, so we didn't have to deal with plugs.
We do not use adhesive sealant on things like exterior or interior trim pieces, exterior window frames, etc.. If a piece needs to be bedded to prevent moisture getting behind them we use Dolfinite. But all the popular sealant/adhesive compounds--- 3M 4200, Sikaflex, Life Caulk, etc.--- are available in black if you want to use a material like that. Just don't use 3M 5200 or silicone....
-- Edited by Marin on Tuesday 19th of January 2010 09:56:57 PM