Finishing mahogany

[IgorV]

Being completely new to boatbuilding am wondering if there is a prefered way to finish mahogany - I will use it for transom and centreboard case side pieces in a 14ft dinghy. All pieces are freshly planed and finely sanded.

http://boatinhouse.files.wordpress.com/2010/04/dsc2003.jpg

Since this is a new build all options are open, I am thinking of using oil (tung oil), have really no experience with it. I will be fitting the pieces in app. two months from now so if I have to apply oil on them I could as well do it now to leave enough time to dry. I'm not sure if oil is enough or should I be varnishing the wood on top of the oil once it has completely dried?

http://boatinhouse.files.wordpress.com/2009/09/mahogany.jpg

I tried linseed oil on a small piece of mahogany (on top) and left it outside for two weeks while the wood below has been kept inside of the workshop untreated. Oiled wood looks nice now and has darkened to some extent, I read about linseed oil turning black after a while, that's something I would like to avoid.

[SchoonerRat]

I'd finish with a good quality marine paint or varnish. Paint will be more durable, but mahogany such a pretty wood that it's a shame to cover it.

Mahogany is a very open grain wood. A filler stain under varnish will make for a smoother finish with fewer coats and less sanding.

[Mrleft8]

First coat Zinsser's seal coat de-waxed shellac. sand with 320 and a sanding block. Second coat, same as the first.
3rd coat Benjamin Moore 440 spar varnish. Allow it to dry for 24 hours. Sand with 400 wet paper and a sanding block(The black stuff, use water).
Use a clean cloth dampened with alcohol and wipe the sanding slurry off after it dries. let it dry again, and wipe it clean with a dry cloth. Repeat step 3 two more times. Step 6, apply another coat of Benjamin Moore 440 spar varnish and allow it to dry for 48 hours. Dampen a cloth and dunk it into a bag of rottenstone. Spritz your varnished surfaces with water, and rubbing with the grain, completely muddy up your beautifully varnished surfaces. With a clean cloth wipe off the slurry. If there are shiny spots, repeat until you have an even dull surface. Thouroughly clean and wipe dry your surfaces. Apply a final coat of Benjamin Moore 440 spar varnish.

[Dave Thibodeau]

Mrleft8 has the answer

[Lew Barrett]

Varnish. There are other programs you can employ but Lefty's sounds very deluxe, though it's more and less than I'd do. Mahogany transom on a small boat should be varnished. There's no point debating this with us!

[Canoeyawl]

And repeat every three years!

[paul oman]

reminds me of the man that drank a quart of varnish.

A terrible end, but a beautify finish.

[Thorne]

Mahogany transom on a small boat should be varnished. There's no point debating this with us!

:D and I am unanimous in this! :D

[IgorV]

Thanks, this makes it a very clear answer on what to do and how to do it. Wasn't sure if varnishing was the best solution from a practical point of view, because the wood will be in contact with seawater and was thinking about keeping the inner side of the boat unvarnished so that the wood can dry on one side when the water gets into it from the outside.

[Lew Barrett]

Varnish both sides. All the wood of an open boat needs to be finished. Don't worry about the water! The boat will like it as much as you do. If salt water was bad for varnished wood, we'd all be in trouble! :)

[John P Lebens]

Varnish - no other option should be considered. Consider using a stain under the varnish, though with that beautiful clear wood, I would just - varnish. 10 coats...

[darroch]

Ditto varnish for the transom. And the oars.

[IgorV]

Varnish both sides. All the wood of an open boat needs to be finished. Don't worry about the water! The boat will like it as much as you do. If salt water was bad for varnished wood, we'd all be in trouble! :)

Ok, thanks all, varnished on both sides it will be. Good to know I am not alone in this ;)

[Bob Cleek]

Yes, varnish, but I would add that mahogany is one of the most difficult boatbuilding woods to keep looking good when finished bright. It will weather and stain quickly if moisture gets to it through a break in the coating and, even if kept well coated, will fade to a straw color under UV exposure. The fading isn't a problem, so long as it's even. Once the natural color loses its even coloring, through water staining or otherwise, there is often little that can be done to return the wood to its "just sawn" appearance other than sanding off all the discolored surface or (and sometimes together with) staining it. Wood bleach (oxalic acid) which works miracles on weathered teak, has very little effect on mahogany. Staining darkens the wood, which increases the heat absorbed in the sunlight, and only accellerates the natural degradation of the varnish.

So, if you want to varnish mahogany, be sure to keep it up very well. Bright finished mahogany serves far better for indoor fine furniture than it does for outdoor brightwork. Problem is, mahogany is just so beautiful it practically demands varnish! LOL A mahogany transom is small enough, and easy enough to sand and varnish, that one can justify the burden of keeping it freshly varnished at all times.

[John P Lebens]

Yes, varnish, but I would add that mahogany is one of the most difficult boatbuilding woods to keep looking good when finished bright. It will weather and stain quickly if moisture gets to it through a break in the coating and, even if kept well coated, will fade to a straw color under UV exposure. The fading isn't a problem, so long as it's even. Once the natural color loses its even coloring, through water staining or otherwise, there is often little that can be done to return the wood to its "just sawn" appearance other than sanding off all the discolored surface or (and sometimes together with) staining it. Wood bleach (oxalic acid) which works miracles on weathered teak, has very little effect on mahogany. Staining darkens the wood, which increases the heat absorbed in the sunlight, and only accellerates the natural degradation of the varnish.

So, if you want to varnish mahogany, be sure to keep it up very well. Bright finished mahogany serves far better for indoor fine furniture than it does for outdoor brightwork. Problem is, mahogany is just so beautiful it practically demands varnish! LOL A mahogany transom is small enough, and easy enough to sand and varnish, that one can justify the burden of keeping it freshly varnished at all times.

Based on this winter's experience refinishing a lot of 60 year old mahogany, everything you say is true!

[IgorV]

Yes, varnish, but I would add that mahogany is one of the most difficult boatbuilding woods to keep looking good when finished bright. It will weather and stain quickly if moisture gets to it through a break in the coating and, even if kept well coated, will fade to a straw color under UV exposure. The fading isn't a problem, so long as it's even. Once the natural color loses its even coloring, through water staining or otherwise, there is often little that can be done to return the wood to its "just sawn" appearance other than sanding off all the discolored surface or (and sometimes together with) staining it. Wood bleach (oxalic acid) which works miracles on weathered teak, has very little effect on mahogany. Staining darkens the wood, which increases the heat absorbed in the sunlight, and only accellerates the natural degradation of the varnish.

So, if you want to varnish mahogany, be sure to keep it up very well. Bright finished mahogany serves far better for indoor fine furniture than it does for outdoor brightwork. Problem is, mahogany is just so beautiful it practically demands varnish! LOL A mahogany transom is small enough, and easy enough to sand and varnish, that one can justify the burden of keeping it freshly varnished at all times.

I guess there is no single, perfect solution. Any wood coating will deteriorate after a while when exposed to sun and seawater, sooner or later varnish will begin to crystallize and will become brittle. I think there's no way around taking care of (maintaining a nice coat on) the wood regularly, be it varnish or oil that is protecting it. I've seen many expensive deckings that turned gray after a year of negligence, you couldn't tell ipe from teak, teak from larch, they all looked the same. Oil still seems like an easier solution, maybe not so nice looking on mahogany?

[Bob Cleek]

Oil is NEVER a solution to finishing wood that will be exposed to the elements, unless, of course, you are prepared to continually reapply it and live with the fact that it will collect dirt and discolor to black in no time. Sailors in the olden days weren't called "tars" for nuttin! They were literally covered with the stuff. If you want to oil finish a fine piece of furniture that lives indoors, that's great. Outdoors, oil is simply a short-lived protective finish that offers no long lasting visual advantage whatsoever, unless you want that "workboat look" of blackend wood (and a blackened butt when you're done rowing.)

[RodB]

For added protection you could apply a couple of coats of System Three clear coat epoxy before varnishing. This will significantly increase the moisture barrier and form a great base for the varnish. Just sand to satin finish before applying varnish. Of course, epoxy also needs protection from UV so you will definitely need to keep up the maintenance on the varnishing.

You could also appy CPES as a sealer and tie coat to the clean mahogany and get a terrific bond for your varnish in addition to added protection from moisture. Another expensive but effective choice.

RodB

[IgorV]

For added protection you could apply a couple of coats of System Three clear coat epoxy before varnishing. This will significantly increase the moisture barrier and form a great base for the varnish. Just sand to satin finish before applying varnish. Of course, epoxy also needs protection from UV so you will definitely need to keep up the maintenance on the varnishing.

You could also appy CPES as a sealer and tie coat to the clean mahogany and get a terrific bond for your varnish in addition to added protection from moisture. Another expensive but effective choice.

RodB

That could maybe work especially well on the inside faces of the centreboard case, hopefully I'm not going to see them again...

[IgorV]

Oil is NEVER a solution to finishing wood that will be exposed to the elements, unless, of course, you are prepared to continually reapply it and live with the fact that it will collect dirt and discolor to black in no time. Sailors in the olden days weren't called "tars" for nuttin! They were literally covered with the stuff. If you want to oil finish a fine piece of furniture that lives indoors, that's great. Outdoors, oil is simply a short-lived protective finish that offers no long lasting visual advantage whatsoever, unless you want that "workboat look" of blackend wood (and a blackened butt when you're done rowing.)

Was an idea,, I called a guy who is selling tung oil in my area and he tried to convince me that (his) oil was the ultimate solution and absolutely no varnish was needed.
After all feedback received here it's clear for me to varnish.

[Todd D]

I would never consider anything except varnish. However, I would do it very differently than MrLeft. My approach is straight forward. For anything that will see the sun, I suggest staining with Petit red mahogany stain. This keeps the wood from turning that nasty yellow that happens with mahogany exposed to the sun. Well it greatly slows the transition. Next had sand with the grain to 320 grit. They apply a coat of Epiphanes gloss varnish thined 50% with mineral spitits or epiphanes thinner. Let that dry overnight then sand smooth with 320 grit (I use norton XXX paper). Then start the real varnishing using unthinned epiphanes gloss varnish. Allow each coat to dry at least 16 hours and sand between coats with 320 grit. Continue coating until you are sanding only varnish. then put your last coat for the season on. I find that a decent varnish job from bare mahogany generally takes 8-10 coats.

Once you have your first seasons varnish on the wood, apply at least two coats every year to maintain the finish. If you get a ding through the varnish, scrape the varnish off that spot, feather sand around the spot to taper into the good finish and start from scratch on the spot applying 8-10 coats to the damaged spot BEFORE you put your two maintenance coats on the entire piece.

[Vinny&Shawn]

I think the only thing I wood add to this treatment of Mahogany, wood be to apply a grain filler after staining. This greatly reduces the appearance of the open grain. It makes the final coats flow and level much better. I do believe in a couple of sealer coats of shellac.

[IgorV]

I think the only thing I wood add to this treatment of Mahogany, wood be to apply a grain filler after staining. This greatly reduces the appearance of the open grain. It makes the final coats flow and level much better. I do believe in a couple of sealer coats of shellac.

Interesting combination, shellac and varnish, the wood is indeed quite porous. What kind of varnish do you normally use? I will probably be using an alkyd-based varnish because it's commonly available.

[Mrleft8]

If you use shellac, make sure you use only dewaxed shellac. I like the Benjamin Moore 440 Spar Varnish because it builds faster than any other spar varnish that I've tried, and it holds up very well. Epifanes is awful stuff that takes forever to dry, and is so thin it needs 8 coats. I used it on one project, and I had to wait 4-5 days between coats for it to cure properly.

[IgorV]

If you use shellac, make sure you use only dewaxed shellac. I like the Benjamin Moore 440 Spar Varnish because it builds faster than any other spar varnish that I've tried, and it holds up very well. Epifanes is awful stuff that takes forever to dry, and is so thin it needs 8 coats. I used it on one project, and I had to wait 4-5 days between coats for it to cure properly.

Thanks for pointing that out, I'll keep that in mind if I use shellac as filler, some of the varnish types mentioned are not available here or too expensive to ship from the US, it's not the case with Epifanes though, it's available nearby :)
Regards,
Igor