Refinishing coamings--the fine points

[seandwyer]

Thanks--good to know epoxy is such a panacea for these issues. I had been trying to think of a way to pin the crack back together and all sorts of things that I knew weren't going to work, including carpenters glue.

KC--you are saying that I should apply the epoxy before stripping. Will the heat gun harm the epoxy that I have worked down into the crack, or is there a good rule of thumb in terms of distance to keep away from epoxy and outside of that boundary no harm will come? I'll try to work it in, let it set and then when stripping, carefully use only a sander over that area, but heat gun and sander over the rest.

Greenlake--is the system three epoxy thinner than most before setting up? That may be just the consistency I need to get in in the the cracks with a spatula. I've got a really thin metal cake spatula for this that my wife does not know I am thinking about!

As for the thwarts and structure. I do understand--they really should be seated well into place, and that's what concerns me. What is the correct thing to do: try to pull the boat back closer together and then re-install the thwarts? They won't be able to withstand that sort of stress if the hull is really flexing against them, so that would mean cutting the hull or centerboard trunk somewhere, realigning and then re-installing the thwarts. I like your suggestion more, KC, of measuring the difference and making up for it with mahogany blocks epoxied onto the thwart ends, but IS THE BOAT OK BEING SPREAD OUT THAT LITTLE BIT MORE than it was originally? Of course, I suppose it could have been just like it is now when it was new, but I have a hard time believing anyone would have been happy with the fit and finish if that were the case. And besides, that wouldn't explain the bent screws. I have this fantasy of removing the screws and seeing the boat spring back into alignment--that the bent screws were what held it out of whack We are, after all, only talking about a total of about 7/16", both sides included

Does anyone recommend replacing the thwarts with some other temporary support while I have them out of the boat? They aren't in that bad of shape compared to the combings, but I'd like everything to match.

Thanks!

[GreenLake]

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.

[K.C. Walker]

Sean,

Green Lake covered the epoxy stuff well.

I don't think you're going to be able to pull your boat in to fill those gaps at the thwarts. If your boat is that flexible, then you've got other problems. If indeed you boat has hogged enough to cause those gaps it probably happened over time sitting on the trailer, and basically has taken a set in this new configuration. It's probably minor and not much to worry about. Even if the bottom is distorted, you'd probably be better off leaving things where they are and fairing the bottom with filler.

The main purpose of the thwarts is not to hold the boat together but to keep the centerboard trunk from flexing side to side. There's a great deal of strain put on the centerboard trunk by the centerboard and by the main sheet when close hauled. An uncontrolled gybe can put a serious shock load on the trunk, as well, especially if your midboom sheeting. When I did the overhaul on my boat I fixed a lot of cracks around the centerboard trunk where it attaches to the hull.

It's an interesting thought about whether to have temporary thwarts. When I was overhauling the bottom of my boat I supported it under the gunwale and transom. I was doing major work to a very soft bottom and weakened it even further during the work. Therefore, I was not worried about this. I think if you did notice spreading you should consider looking at how your trailer supports your boat.

[GreenLake]

I thought I'd post some more info that I've stumbled across on the net recently and give some more precise experience report.

Here are two sets of instructions on using varnish over epoxy.

West System

SystemThree (Brochure)

The Achilles heel of both methods (and of varnish in general) is UV exposure. UV attacks epoxy, which therefore relies on varnish with UV blockers for protection. The varnish has UV blockers because it also eventually deteriorates (although cracking comes usually first if applied on non-sealed wood). If you can limit the UV exposure, by use of a boom tent or tarp cover, then the epoxy method gives a clear win. It limits the deterioration due to moisture cycling (which the cover, not being a heated garage, can't prevent) and allows the varnish to live until the other aging factors catch up with it (usually residual UV).

If you catch damage to the varnish (or PU) cover, it should be possible to repair that by sanding back the outer layers and adding fresh ones.

That should extend the period between times that you'd need to take the whole thing back to bare wood. (Which is somewhat painful with epoxy). I'm going on four years now with PU over epoxy for the coamings and thwarts and they still look like new (work done in May, 2009). I had used a Satin for the PU, but have since learned that gloss gives better UV protection (by reflection). Overly glossy looks aren't my favorite, normally, but this could be a reason to choose the glossy variant next time.

The WR-LPU with cross linker from SystemThree is so resistant to abrasion that I have not managed to visibly scratch it on the thwarts, despite not only sitting but stepping on them.

[My notes say I used three coats, first coat, RotFix (the thin stuff) and two coats of ClearCoat for the coamings, and some other (not specified) stuff for the thwarts. Probably laminating epoxy because the notes say "done in conjunction with another project"). The laminating epoxy builds faster, so two coats should be equivalent to three of the ClearCoat.]

[seandwyer]

Interesting--and when you say that removing epoxy is a "painful" process, Greenlake, how do you remove epoxy anyway? Could you use a heat gun, or is it a sanding job exclusively? I started removing the varnish today with a heat gun, and so far its a breeze!

[GreenLake]

I suspect that softening and scraping will work for epoxy, but haven't ever tried it. With the wood not exposed year round it seems to hold up well and I'm kind of predicting at this point that the point where I will need to know that technique is comfortably off in the future. So far, the epoxy sealing has lasted longer than any earlier attempts to varnish, multiple times as long in fact.

[jdoorly]

I built a 'stitch and glue' kayak 10 years ago. It is encapsulated in fiberglass and epoxy. The deck is varnished wood and the sides and bottom have extra layers of epoxy mixed with graphite making them black. After a few years and hearing so much controversy about graphite I wanted to evaluate the effect of graphite. So I sanded off the epoxy-graphite layers, did some speed testing, then re-applied a couple graphite layers, prep'd the surface, and tested. The kayak was never stored in the sun and the varnished deck still looks brand new after 10 years.

Now I was sanding down to the level just above the fiberglass (though I went too far in a few places due to impatience) and it is possible to gauge your depth by how the fiberglass underneath looks, and in my case when I got past the black stuff. Also, when I sand epoxy or other coating off wood it is pretty easy to tell when to stop sanding. But the problem with sanding is fumes and dust so you'll want to wear protection (I think getting epoxy dust on your skin is the fastest way to develop sensitivities to epoxy ((these days I get hives just thinking about sanding epoxy!)). Sorry, I haven't tried any chemical strippers on epoxy,but I hope to hear, in this thread, that they are great!

[K.C. Walker]

jdoorly,

Don't leave me hanging… I want to know the conclusion to the speed tests! When I overhauled the bottom of my boat last, I did an epoxy barrier coat, and you guessed it, it was graphite epoxy. I do know that it slips off the bunks on my trailer really well. But I have no idea how it might do in a speed test. I figured make it smooth and fair and it should be good to go. So… What did you find out.

Okay, back on topic. I totally agree with being careful not to get sensitized to epoxy. Heat does make it loosen up, so I think stripping it with a heat gun would work pretty effectively. However, the fumes could easily cause problems for an allergic reaction. Of course, fumes from heated varnish are pretty darned toxic, as well.

[GreenLake]

Why don't we start a new thread for bottom / speed questions?

[seandwyer]

Hi Guys,

Well, I have a quick question concerning this project. I've got everything stripped down (used a heat gun) and now sanded. I'm about to address the cracks in the coamings, but first, I wonder if you guys could give me a consensus about the thwarts. As I illustrated with the photos on the previous page, there are some gaps between the ends of my thwarts and where the fiberglass starts--either at the centerboard trunk or the bench seats. Now that I have them off, I can see that if I push the curved end of the thwarts fully into the "sockets" on the seats, I have just about a half inch gap on the opposite side between the end of the thwart and the centerboard trunk. As a few have already said, there really shouldn't be that much gap, so I am about to trim a few strips of wood to account for this gap and epoxy them on to the flat ends of the thwarts, then re-drill the screw holes. My question is--should there really be NO gap at all? Not even say 1/16" or so--just in case it needs to flex a little? Do I run the risk of jamming the thwarts through the centerboard trunk or the bench? Now--when I say NO gap, I don't mean so tight that I need to beat them into place with a hammer, but snug, as in they fall into place, but fit like a glove etc. I CAN do this since all I need to do is epoxy the blocks in place and then take my time sanding them into the perfect size.

One more quick question--I have a long piece of ash and that's what I'm going to use as the blocks on the ends of the thwarts. I'd intended to use oak, but can't find any to size and I am NOT buying an 8 foot section of mahogany from the wood store for this. Any reason why ash would not be a good choice once epoxied in place and stained to match the color as best I can?

Thanks!

[GreenLake]

I don't believe that there's need to leave room for play. But you don't have to try to go for "press-fit". Making the parts fit snugly without the need to force them into position is what I might aim for (allowing for a generous coating of epoxy or varnish on the inner surface after sanding).

Ash could be fine - you'll probably be able to see the shim, but glued well (and epoxy encapsulated to keep the wood from working with moisture) I don't see why it shouldn't last for your tenure of the boat.

As an aside, aak comes in two kinds, red and white. Only one of it is reasonably rot resistant. While epoxy coating can't overcome all deficiencies (real or imagined) of your choice of wood, it could go a long way to equalizing the chances for the less rot-resistant woods, I would think.

[seandwyer]

OK--good to know. I guess I am just concerned that since the space is there, the hull must have relaxed, spread, hogged, whatever you call it and I worry that it might somehow spring back at some point, in which case the extra space of a half inch on each side won't be there anymore. But, that's silly. If anything, it might relax more.

[GreenLake]

The thwarts are much stronger on compression than on tension, because at under tension they would rely entirely on the screws, not on bracing. You wrote that your screws had ripped out, which makes me think that the same thing would happen again if you put the shorter thwarts back in. (Especially in light of what KC wrote). If you widen them according to your plan and if putting the boat on the water somehow makes the hull want to be narrower, I'd expect the thwarts to handle those loads more easily, by bracing against CB and the notch in the seat. If you do see some evidence of too much compression, you could always cut some off later. Given that, I'd suggest you stick with your plan.

[K.C. Walker]

+1 on what Green Lake said regarding the fit of the thwarts. I made mine with a very slight pressfit, including epoxy and finish. I've seen no problems since. I used 3M 4200 on the seat tank end when I screwed it back down. I didn't want any water to get behind their or into the seat tank. For that matter, I used 4200 as caulking around the edge of my comings, as well.

[GreenLake]

I used some outdoor foam strips between coamings and deck, after going with "nothing" for several years. Doesn't seem to make a huge difference. Unless you sail a bit on the "wet" side, there's just not that much water that gets there. But then, I don't get to sail in chop as much as some people here.