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      A Few Simple Rules   05/22/2017

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Phillip

Sealing wood prior to fibreglass

23 posts in this topic

I am building an International One Metre R/C Proto (mydesign) to be fiberglass over a balsa core, with the intent that it be brightfinished.

 

In the interest of weight management, I want to limit theamount of epoxy soaked up by balsa.

 

My thinking is that I could use a "wash" coat of de-waxedshellac (thinned with alcohol) on wood, followed by the epoxy and glass.

 

Advantage: (1) addsome colour to the pale balsa, and (2) limit the absorption of the heavierepoxy.

 

Concern: That I seriouslydetract from the adhesion of the epoxy/glass to the wood.

 

Any thoughts on this process will be greatly appreciated…

 

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you could try screeding the balsa with epoxy thickened with fumed silica/cabosil/aerosil (all similar products). Use a flexible plastic applicator made from a plastic ice cream container or yoghurt container.

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We made 100 One Meter One Design bopats in `1994 and 1995. The laminate was one layer of 3/4 ox mat and one layer of 6 ox coth with just a tad extra mat around the base of the keel and rudder. Our hulls weighed just under a pound. They were so strong the boats could t bone at full speed with no damage.

 

I did build one prototype with a core and about the only difference we could feel was in our wallets for all the extra work and material.

 

 

 

Is your minimum weight for the hull under a pound or are you just wasting effort??

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Thankyou for the kind response. The weightcalculation for hull is approximately 0.8 pound/ using a layup of 1x2 ozfollowed with 1 maybe 2x3/4 oz.

 

Once Ipull the hull off the hardback I’ll have a better feel…

 

What’syour read on pre-sealing the balsa to stop weight buildup from the epoxy?

 

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Design displacement is at 4.009 kg. (4 kg being the min.)

 

My goal is to use to corrector weights to optimize sailing trim.

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MT's suggestion is better than shellac or spackle, in my experience. If you want yellow add pigment(s).

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Bruno, thatwould be my preferred solution. But,nothing is easy to find here in China. It’s now costing me a fortune to buildthis boat because nothing is available in less than industrial quantities(anyway I can’t find ‘em). I have toimport everything (for which the ChiComs tax me heavily – doubles the price).

 

Case inpoint, I wanted to buy WEST Epoxy here, only to be offered 5 gal. drums fromsuppliers.

 

I guessmy real question is: What strengthproperties do I give up when I pre-seal wood?

 

I’ve triedto research engineering sites with no definitive answers…

 

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Do you have any boatbuilders in your vacinity, if you do you might get all the help and advice you need from someone who speaks English and is happy to share their knowledge.

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MT,nothing here (I'm lucky to look at water). I considered a trip to McOnaghy or J-Boats, but knowing the ChiCom BS,understood that I probably couldn't get beyond the gate.

 

Perhaps this is my call for help..

 

(why doesn't punctuation transfer from "Word" doc?)

 

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epoxy and csm?

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Sorry, sir. "CSM"; what is CSM?

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csm = chopped strand mat

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I am building an International One Metre R/C Proto (mydesign) to be fiberglass over a balsa core, with the intent that it be brightfinished.

 

In the interest of weight management, I want to limit theamount of epoxy soaked up by balsa.

 

My thinking is that I could use a "wash" coat of de-waxedshellac (thinned with alcohol) on wood, followed by the epoxy and glass.

 

Advantage: (1) addsome colour to the pale balsa, and (2) limit the absorption of the heavierepoxy.

 

Concern: That I seriouslydetract from the adhesion of the epoxy/glass to the wood.

 

Any thoughts on this process will be greatly appreciated…

 

 

 

We made 100 One Meter One Design bopats in `1994 and 1995. The laminate was one layer of 3/4 ox mat and one layer of 6 ox coth with just a tad extra mat around the base of the keel and rudder. Our hulls weighed just under a pound. They were so strong the boats could t bone at full speed with no damage.

 

I did build one prototype with a core and about the only difference we could feel was in our wallets for all the extra work and material.

 

 

Is your minimum weight for the hull under a pound or are you just wasting effort??

 

Good lord you guys build heavy.

Built a dozen US One Meters over the years. Balsa strip with one layer of Very Thin (1/20th oz?) glass over. Often used a woman's stocking rather than glass, it's just thick enough to hold the resin. If you use poly resin, it won't soak in much at all. Bare hull finished with a coat of paint and no interior structure weighs around 4 oz, I'm under a pound after installing structure and electronics! Finished with my 4 lb keel I end up right around 5 lbs. (US OM don't have min weights, I like em light.)

 

As for pre-treating the balsa and getting a nice look for bright finish - simple wood stain like you buy in any hardware store works great. I have used water based an oil based, neither had any adhesion problems (although I preferred the water base for ease of use and to be sure no oils are preventing epoxy adhesion.)

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Presently doing refinishing work on oiled teak adjacent the companionway. (Looked nice for a long time, but beginning to show water damage).

 

Found the teak is apparently coated with shellac under the oil(?). Surface is soluble in denatured alcohol and behaves like shellac. Call to West Systems led to suggestion to try removing shellac with alcohol, as epoxy wouldn't bond well over shellac.

 

Been scrubbing with denatured alcohol, then sanding to 220 grit, then epoxy (105/207). Anywhere the shellac isn't completely removed, the epoxy does not wet out, leaving small spots, streaks, etc. of blotchiness. Have had to sand out to bare wood and start over. Part of the problem is that the shellac isn't visible on the surface after scrubbing and sanding. Until the epoxy is applied, the surface looks and feels quite uniform.

 

I wouldn't like to see you put shellac on your surfaces and then try to epoxy over it. I don't think you'll get a good bond at all.

 

I can't think of any clear coat finishes that won't penetrate balsa. I think the best you're likely to do was suggested above: thicken the epoxy with fumed silica to limit penetration. (Of course the silica is heavy, so it might be worse than the epoxy mix alone. Try a test piece and see.)

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OM, not sure how you got the weight that low. 3mm balsa for hull (total area 3211cm2) alone weighs in at 4.2 oz, and that's without glue. My hat's off to ya.

 

Regardless, I'm still trying to figure out if I'm safe sealing wood with shellac then using epoxy.

 

Alternative building methods are not on the table. As I noted earlier, getting supplies here is like finding hen's teeth (e.g. "Home Depot" - yes, there is one - only sells spackle in 25 kg sacks). Balsa was only available in blocks x 1 m and priced per pallet...

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Thanks for the info Jax. This shellac is de-waxed (I mix it myself). Epoxy should arrive from Australia, next week. I'll try a test strip then.

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epoxy and csm?

No, it wil be woven glass. CSM is too heavy.

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epoxy and csm?

No, it wil be woven glass. CSM is too heavy.

ok, thanks for clearing that up. most times when some one talks about 1oz, it is csm (and csm in not compatible with epoxy).

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epoxy and csm?

No, it wil be woven glass. CSM is too heavy.

ok, thanks for clearing that up. most times when some one talks about 1oz, it is csm (and csm in not compatible with epoxy).

 

As far as I recall most csm is now compatible with both poly and epoxy these days. This definitely was a problem in the past with the binder used in csm. Perhaps one of the experts can chime in on this though.

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epoxy and csm?

No, it wil be woven glass. CSM is too heavy.

ok, thanks for clearing that up. most times when some one talks about 1oz, it is csm (and csm in not compatible with epoxy).

 

As far as I recall most csm is now compatible with both poly and epoxy these days. This definitely was a problem in the past with the binder used in csm. Perhaps one of the experts can chime in on this though.

 

Most CSM is held together with a binder that breaks down when it comes into contact with styrene which is the solvent in polyester and vinylester resins. As epoxy is solvent free the binder will not break down so the csm will not be drapable, so it could work on a flat surface, but quite why anyone would want to use epoxy with csm is beyond me.

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thicken the epoxy with fumed silica to limit penetration. (Of course the silica is heavy, so it might be worse than the epoxy mix alone. Try a test piece and see.)

 

Nope, for 2 reasons.

1. He said he wanted a bright finish. He will get whitish streaks and a generally dull appearance.

2. The epoxy will still soak in, just as much as if it wasn't thickened.

 

It's good that the resin soaks in. It fortifies the wood and makes it incredibly strong yet very light. You won't be adding but an ounce or so of weight, it's not like it will make it a brick.

And again, don't glass it like it was a full size boat, it does not need to be demolishion derby proof.

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