Mahogany for repairing dry rot....

[DLL]

Hard to say this in a small subject line.

I have 2 places left with dry rot. My repairman says the 4x8x 1/8th inch thick Mahogany is fine for doing it. He proposed to make a cardboard template, then put layers of this wood in the bad area. It looks like it would take as many as 4layers. The wood is at Lowe's and only about $9 a sheet.

1. Does the wood sound ok? It will be covered by wall paper.

2. What kind of glue for this -- interior only.

3. In the aft head we will be pulling both black water tank indicators off, then put a sheet of this mahogany over that section of the cabinet, cut a hole for only one tank indicator and gluing the wood on, then covering it with wall paper.

IS THIS AN ACCEPTABLE WAY TO DO IT? Do you see any problem with this? Thanks, any suggestions appreciated.

 

[Radioactive]

I'm not going to give a decisive response, due to lack of fine detail inthe question. However i -do- have come questions/concerns:

I'm not real sure that what is being offered at lowe's is actually mahogany. I believe that it is plywood, with very thin outer veneers of mahonany, covering an interior ply of a wood that neither of s have ever heard of. I could be wrong. I happen to have several sheets of "1/8" mahogany plywood" in my shop and I' not betting $0.02 that the structural ply is actually mahagany. ( It, also, was in the $9/sheet price range )

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It is almost certainly rated as an "interior" plywood. While there is no difference in the glue between exterior ply and marine ply, in some cases interior graded ply does not nave a water resistant glue. Yes, this is an interior application, but it is also on a boat. Water water everywhere. If it stays dry, it may serve you well. If not, expect a mess. It is going to look like those layered brown and serve rolls you get at Thanksgiving...

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Let us think nice thoughts about the glue on the interior of the plywood. In that case, what you use to glue up several sheets face to face should at least make some effort toward water resistance. Since this is a) dry and b) interior i would suggest Titebond II (2) or Titebond III (3). ( I'm nuts and might use epoxy, but even I admit that that is way overboard ). The Titebond II is a water resistant PVA adhesive. It is relatively inexpensive, and has an easy water clean up. Working time and characteristics are quite good. Use a 4" foam roller to apply it ( They also make a short nap roller in 4" that works ). The Titebond III is also inexpensive, has a water cleanup,but it's working characteristics are not as nice ( still good/easy ). It is classed as "water proof" but not suitable for immersion or prolonged wetness.

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Using a single sheet of 1/8" plywood structurally gives me the shivers. I recently did a test/prototype which required that I gently bend the 1/8"ply. It shattered the same way Corelle plates shatter when hit with a full pot of hot water ( don't ask. It was a mess ). Covering a small area ( 4" x 4" ) with a single thickness sheet may work; covering a larger area exceeds my "jitter threshold".

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I have tons of questions, but will leave most unasked. Did you consider using 1/4" "luan"? In my experience this might offer a stronger result. ( I have -no idea- how large the area involved actually is. And it is important data in order to give good answers... ) It bending involved? How is it supported? How large an area? You get the idea.

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Ok, so you skipped all of that. Here is the quick answer:

Sounds acceptable, if not necessarily optimal. Make sure that the layers alternate the grain of the wood. Use Titebond III. Fasten ( nail, staple, clamp ) each new layer about every foot, in every direction till the glue sets. Not doing this will result in a glue join failure. Try to use an odd number of thicknesses of the plywood. That is, a 3 layer glue up has 1) vertical 2) horizontal 3) vertical. Using an even number of layers may induce warping. ( Weird, huh )

Have fun!

 

[Ghost]

I'm not sure I could improve on Bill's response. He's right though, the "mahogany" isn't. It's Luan most likely, which can be beautiful, but is relatively soft for a hardwood and is not a true mahogany. Of course, that's pretty much a rediculous statement because I'm describing as Bill notes, just the outer veneer. Who knows what is under that. I'm trying to visualize what it is "repairing" and whether it is really structural or not. It "might" be plenty strong, or might not. I do know that the teak Tolly used was pretty good stuff to begin with. My instinct says that this material is not what it could be.

 

[DLL]

You are right about the wood. All I am going by is what Lowe's calls it. No bending involved anywhere. The repair is under the port, aft window...about 2 ft long. A foot or so high. The guy doing the work did a lot of measuring and said he thinks 2 pieces will be a little too thick. I thought it would take 3 pieces anyway. The window frame sticks out about 1/4 to 3/8 inches from what I remember. I don't have ANY idea what kind of glue they used on the mahogany. Anyones guess. And you are right, if you "bend" this stuff it really comes apart, leaving a mess.

I understand what you are saying about this being a boat. Sooner or later everything seems to get water on it. Maybe after it is installed, we should put a coating of something like clear Thompson's water seal on it. What else can a person do to water proof it? Put water seal on both sides of the 1/8 wood? If we seal the wood, will the glue work well enough??? The original wood didn't do too well either.

We have a West Marine down by the boat, if he does not have his own favorite glue, I guess I could run get a can of Titebond II, IF they have it. Epoxy would be better in my opinion, but I am not doing the actual work. Thanks for the suggestion on the 4" roller for application. Titebond II sounds like the best. Think Lowe's carries that?

Using a single sheet of 1/8" plywood structurally gives me the shivers. I recently did a test/prototype which required that I gently bend the 1/8"ply. It shattered the same way Corelle plates shatter when hit with a full pot of hot water ( don't ask. It was a mess ). Covering a small area ( 4" x 4" ) with a single thickness sheet may work; covering a larger area exceeds my "jitter threshold".

I have never heard of "luan". This area is about 2 ft on the bottom then goes up about 8 inches, then towards the rear about 14 inches, up about 10 inches and towards the rear
another 10 inches.

The forward head still has the de-lam wood in place. I was thinking about buying epoxy, drilling down in the wood, then mix the epoxy and put it down in the hole. We did this on another spot and it seems to have worked quite well. That was before I got hurt in the car wreck and was put on the heavy pain meds. Maybe we drilled several holes, then put the epoxy in all of them. Sorry, morphine has a way of messing up your memory.

MY ANSWERS ARE IN ALL CAPS BELOW.
"Sounds acceptable, if not necessarily optimal. Make sure that the layers alternate the grain of the wood." GOOD IDEA. "Use Titebond III. Fasten ( nail, staple, clamp ) each new layer about every foot, in every direction till the glue sets." WE CAN OPEN THE AFT WINDOW AND GET A CLAMP ON SOME PLACES, BUT NOT ALL OF THEM. THE BACKING IS FIBERGLAS, SO NO NAILS, STAPLES THERE I GUESS. WE MIGHT GET A COUPLE OF LARGE CLAMPS SET UP, THEN PUT A PIECE OF ANGLE IRON OR SOMETHING BETWEEN THE CLAMP AND THE NEW WOOD. "Not doing this will result in a glue join failure. Try to use an odd number of thicknesses of the plywood. That is, a 3 layer glue up has 1) vertical 2) horizontal 3) vertical. Using an even number of layers may induce warping. ( Weird, huh )" THAT IS WEIRD, 2 LAYERS WARPING. AS I SAID, THE GUY IS THINKING 2 LAYERS MAY BE TOO THICK. WE WILL SEE. I CAN'T BE AROUND FUMES ANY MORE, SOMETHING ELSE WRONG IN ME. SO I CAN DISCUSS IT WITH HIM, THEN LEAVE THE BOAT WHILE HE DOES IT. I HAVE A PAINTER'S RESPIRATORY MASK I COULD WEAR I GUESS. I USE 3M 2091 FILTERS.

This repair has nothing to do with structural integrity. It is totally cosmetic. We plan on putting wall paper over it. This "mahogany" is very soft. What do you think about putting water sealant on it first?

 

[Radioactive]

Get the Titebond II or III at any hardware or Lowe's/Hd etc. very common woodworker's glue ( most popular, I think ) It workks great on wood, but likely will -not- work at all on a wood/fiberglass join.

No fumes. It is nice stuff.

BTW: the "1/4" plywood at the big box stores is rarely actually 1/4" anymore. it is 6mm ( or less ) thick...

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I would not seal it. Likely would not be very useful even if you did.

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If it really is a dry area, you might consider some thin hardboard/pressboard ( Masonite or more modern equivalent. ) It ( while dry ) it going to be stronger and more stable, and possibly available in a thickness between 1/8" and 1/4". Worth considering. The whole idea of layering more than one sheet ( actually, cold molding/laminating )in place, without clamps seems like a great deal of work and offers much room for error. I'd try to do it with a one sheet thickness of <something>.

 

[Leviathan1]

The stuff from Lowe's is most likely Luan Plywood. Luan is a mahogany, but the method of construction is different from marine plywoods. Luan is typically used as an underlayment for vinyl floors because of the long straight grains. If you check, the number of plies in the luan usually is only 3 -5 plies. Check on marine plywood and you will find the number of plies to be greater. The number of plies in the sheet is what gives plywood it's strength. Luan plywood is usually bonded with a waterproof glue but I am not sure it would be as water resistant as the marine environment would require.