I finished my cockpit grating. I used mahogany 3/4" joined by half-lap joints. It's epoxy-glued together. My question is how to finish it. It will het a lot of wear, and be wet a lot so encapsulating in epoxy makes sense, but I'm already dreading the thought of roughing up the epoxy in the dozens of spaces between the mahogany runners prior to varnishing. Any ideas on how to best finish the piece?
Dave
Grates and slats are best left natural or oiled. Epoxy coating these will just make you cuss a lot more then usual, as there's no way to really protect something with so many edges, that will see so much traffic (edges are where the damage and wear will be worst). This is also why teak and pitch pine are common for slats or grating stock. They wear well, are naturally rot resistant and weather the elements well, with or without an oil finish. Hard cedar (like Spanish) is also a common species, but doesn't wear as well, nor take as much abuse.
Since you've gone ahead and epoxied the pieces, you're married to a hard clear coat or paint finish. Naturally you'll have to maintain the finish to protect the mahogany. This will be a fair bit more effort then slapping on some oil every so often, but it'll probably look a lot better. I'd recommend a clear LPU finish. It will be costly, but it's the toughest of the clear finishes, which is what you're going to need on a grate. Oiling an epoxied surface, will not protect it very well and it will remain slippery for a long time too.
Paul: I just used epoxy glue at the joints. The wood is unfinished! I think I'll just sand and use oil/ Linseed or tung oil?
Dave
Okay, I misunderstood. Linseed will darken the wood to gray black in several years, use tung oil, which also darkens the wood, but much more slowly.
The old fashion way of applying a tung oil finish is to thin the first several coats with a 50/50 mixture of mineral spirits and oil. Soak the wood, once an hour with this stuff for the first day. The next day switch to a 25/75 mix (mostly oil) and soak the wood twice. The following day move to a slightly thinned mix, maybe 10% at most and soak it twice. For the next 5 days soak it once each day with a straight oil coating. Then continue doing this once a week for a few weeks.
This seems excessive, but it's not really if you think about what is happening. The very thin initial soakings, gets the oil deep into the wood, then the solvents flash off, leaving oil in the cells. Continued applications gradually fill the cells of the wood, until the wood can take no more oil. For rot to cause trouble, it needs a place to life, which is inside the cells of the wood. If they're filled with oil, the rot has no place to live and the wood stays healthy.
On the very last two coats, mix in a couple of percent (per batch) oil and Japan Drier, which will speed up drying time and make a hard (ish) surface on the wood.
Once the wood is "treated" this way, you just need to maintenance the oil, every so often (every other month or sooner down here, maybe 2 or three times a year up in Maine). The maintenance coats are a rag soaked in oil, wiped across the surface. Let this sit for an hour then wipe up the excess. If you let it go too long between maintenance coats, you'll need to saturate the wood again with multiple coats of oil.
This is the traditional method of applying a long lasting oil finish. The old saying of "once an hour for the first day, once a day for the first week, once week for the first month and once a month there after", is very accurate description if you want the best protection from an oil finish.
Oil finishes don't offer a lot of UV protection for very long. This is because the oils on the surface wear off or are rubbed off or evaporate pretty quickly (which is why the wood has to be saturated with oil) and you lose the protection. Teak and some other traditional "weather" woods can take this "up and down" treatment fairly well, I'm not so sure about mahogany. This is why you have to keep up an oil finish or the wood will dry out and you have to start over, after you fix the UV damage.
Newb Question here, ok mahogany is fairly rot and weather proof wood tough right? so would it be more of a forgiving wood for such an application?
Also How would it be to acctually soak the wood In the oil, and just let it soak freely for a while , then do some exterior coats to finnish it off?
dont mind me, just thinking again lol.
Brian.
Actually, the mahogany's commonly used in these boats isn't especially rot resistant. It's got lots of nice qualities, but is usually selected for it's looks and hardness.
Yes, you could soak the wood, but it wouldn't work any faster, then my recommended method and it would probably be slower and less complete a saturation. The wood can only take so much, so fast. The only way to rush this is under pressure. So, if you happen to have a boat sized autoclave at your disposal, let me know, we can work out a beer for "cooker" time sort of arrangement. Other wise, you have the "leach" the oil into the wood with solvents.
I have used a pressure cooker on a few occasions and I've also used vacuum and under water pressure to force stuff into wood. Most folks don't have access to any of this stuff. Trust men guys, unless you are substantially bigger then your other half, you don't want to use her pressure cooker, hit a yard sale.
Thanks, Paul. Very helpful information. Tung oil it is!
Dave