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Building a wood Mast


Darrell H

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I recently aquired a 12 sailing dinghy. Needs new wood most every where. The hull is fibreglass. The Mast is wood and has delaninated and is badly warped. My question is what ratio would of resin to hardner would you use to glue-up a new mast. I'm useing VG Douglas Fir.

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Darrell,

This all depends on what brand and type of epoxy you are using. Epoxys come in lots of different mixes, I personally have seen mixes from 1:1 through to 5:1 (resin to hardener) then there are slow and quick set hardeners and thinners to make the epoxy 'bleed' into the wood.

If you could let us know what brand you are using I'm sure one of the great builders on this site will be able to fill you in on their experiences.

Hope all goes well with your project

Andrew

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To further add to Ray's excellent post- Polyester is NOT an adhesive. DO NOT try gluing a mast together with it- it will not hold up.

Use the epoxy resin/hardener ratio specified by who ever made the epoxy- as exactly as you can.

By the way- old bicycle inner tubes make great clamps for things like masts- good pressure, spreads the load evenly and won't over clamp, which is a good thing since epoxys only need to be held in close contact, NOT heavily pressurised in the clamping..

Here's a 22 foot tapered birdsmouth spar I recently built, all clamped up with inner tubes.

post-36-129497645829_thumb.jpg

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Oh - thickened definitely. The epoxy should be applied straight first, then thickened. But not with Micro balloons- that's for non structural fairing. Woodflour, Micro Fibers or colodial silica are the higher density fillers used for adhesives. I normally use wood flour with a tad of silica for filleting that is to be highly loaded. For glueing only I use either wood flour or Micro fibers. I use micro balloons for filleting in areas that are non structural and for fairing ABOVE the water line. Below the water line I use higher density stuff.

I mix to about syrup consistency. The purpose of the filler in this case is to hold some of the epoxy in the joint. Otherwsie it can soak into the surrounding wood and leave a starved joint. That's also why you should apply straight epoxy first, then come back with the thickened mix. Otherwise the wood will wick the epoxy out of the mix and again, leave a dry joint.

One thing to keep in mind with epoxy - DO NOT over clamp. If you apply too much pressure you'll squeeze the adhesive out of the joint and starve it- just close firm pressure is all that is required. One of the advantages to epoxys- they have some gap filling capacity, so the wood working doesn't have to be QUITE so precise. Not to encourage sloppy joints of course, but slight mis cuts that would be fatal with an adhesive like Resorcinal will be fine with epoxy.

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Charlie

Pardon me for asking a dumb question but you say "apply epoxy first and then thicken it with woodflour". The mast I'm glueing is a small, the rough demention is 2 pices 1x3 glued together to make a 2"x 3" x 14' mast. Are you saying apply epoxy to each side of the wood and then before joining the two pices of wood together you mix in wood flour? I've seen wood flour in the stores but I don't have a clue what it is. This is all new to me.

Thanks

Darrell

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LOL- sorry for the confusion.

What I mean is to apply unthickened epoxy, wait a bit for that to soak in, reapplying to any place that looks "dry". THEN mix up a bit more epoxy, thicken it and brush THAT on the surfaces. Then assemble and clamp.

This time of year that's not that hard to do. When working on a large layup, in Texas, in the summer time, it can get to be a real fire drill to get the epoxy spread before it starts to go off. :) But the faster you work the more time you have, since spreading it thinly slows the heat build up which slows the start of the "kick".

I've glassed hulls when the temps were over 100 degrees- talk about working FAST :lol:

And I've never been asked a "dumb" question by someone really looking to learn.

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Sanding dust from a sander works well, but it sometimes has grit from the sanding belt in it, so fillets aren't quite as smooth.. Mrthethird makes a good point about using the wood from what you are working on- the colors come closer to matching. I save small containers of various wood dusts for just that reason.

People (including me)have also been known to use common wheat flour from the grocery store. Agricultural Lime makes a smooth, high density fillet I've been told. Never tried it. I wouldn't use it for glueing though.

The wood flour you buy from the Gougeon's has a percentage of colodial silica added to smooth the blend. I usually add a bit in filletting as that seems to give you a smoother surface. Of course when you slap the glass tape onto the wet fiillet, that smooths out a lot of roughness :) I don't add it to glue joints normally.

Actually I get my wood flour from Chuck Lienweber of Duckworks. He is a pattern maker and I get the stuff in 5 gallon quantities when he comes to visit :D His sanding dust is extremely fine from the very fine grades of grit he uses to finish patterns.

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When the epoxy mixes with the wood dust, it will darken, substantially darker than the original wood. Check the color by mixing a small amount of wood dust with a drop or two of the resin (it doesn't have to be mixed with hardener for this test). Then check it against a piece of mast wood stained the color you are going to use.

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A pretty good online source of information on epoxy and it's uses comes from System 3:

http://www.systemthree.com/members/m_index.asp

If you register (free) you can download their epoxy book...about 40 or 50 pages of information. All accurate....with of course a slant towards marketing of their products. Understandable....but it is marketing. Other companies stuff works just as well.....it's just different. But the basic epoxy information is very good....and should be understood by anyone who is serious about working with the stuff.

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Darell,

Ideally you would use sanding dust from the piece of wood being used. The "wood flour" is mixed into the epoxy for the joining of the pieces. It will only be a very thin line. But, the epoxy doesn't take a stain well after it is cured. So, the answer is yes, you would want a fine line that would be close to the color that you want to end up with after staining.

Generally speaking it is better to stain the wood before applying any epoxy coating over it. This would of course apply to the surface and not a mating surface. Most epoxy lines are so fine that they are not noticable if they are closely mated and joined.

I've always had good success with oil stain finishes such as the Minwax urethanes. They are a surface stain and if applied with some attention they work out fine and can be covered with clear coats of high UV content urethane clear coats to protect them.

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except that oil based stains are NOT reccommended for use UNDER epoxy. They can interfere with the adhesion of the epoxy. The Gougeon's (and I believe MAS also) recommend either aniline dyes, which aren't particularly color fast, or water based stains. I'd bet SYS III and Raka would concur.

If the oil based stuff is COMPLETELY cured out it might work ok, but I for one don't use oil based under epoxy. I keep water based stains for that.

But then on boat work I very seldom use any stains- I much prefer the look of natural wood, with just the epoxy and varnish. But of course, THAT is my own personal quirk :)

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Thanks Charlie,

I probably should have mentioned I only apply the oil based stains over the ready to finish surfaces after all is glued up. . And not at all if they are going to be epoxy coated. I use water based stains exclusively if they are going to be coated with epoxy.

I made the mistake of trying to epoxy encapsulate after using oil stains a number of times without thinking it through. Had many issues with the epoxy and it took some time to figure out why. All of it came off and started fresh. Same with every brand of epoxy that I know of.

Back to the favorite saying of my dad. "If you have time to do it over, then why didn't you have time to do it right the first time?" :oops:

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