wooden hull sheathing

Peterduck

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I've never heard of acetone being able to absorb water, but methylated spirit certainly does. However, I think that the need is to have the moisture level of the full thickness of the timber down to the required low level, not just the outer millimetre or so. This will require the patient drying by warmth and dry conditions.
Peter.
 

sailorise

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Thanks Michael I found the sites interesting and very informative, albeit they told me things I didn't want to hear!

Peter, as no glue or paint penetrates timber more than a mm anyway, then it sounds like Methylated spirits will work well. I'll experiment.
 

Boatmik

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[ QUOTE ]
I've never heard of acetone being able to absorb water, but methylated spirit certainly does. However, I think that the need is to have the moisture level of the full thickness of the timber down to the required low level, not just the outer millimetre or so. This will require the patient drying by warmth and dry conditions.
Peter.

[/ QUOTE ]

I agree completely Peter on the acetone. It sounds like witchcraft!

"draws it out". Maybe some use an oatmeal poultice! :)

Acetone and water don't mix. So it won't have any effect in drying the water from inside the timber.

The acetone wil evaporate from the epoxy matrix leaving microscopic tunnels that water molecules (being smaller) will find it easy to travel down.

See my previous post in this thread about the water absorbtion of thinned epoxies.

The hull needs to dry naturally. By the time it is fully stripped, sanded etc it will probably be getting close.

I suspect the wood does not need to be "dry right through" though - for a traditionally built boat it would take months. But the timber that the epoxy contacts need to be dry.

Give the WEST system people a ring and ask them what their guidelines are.

They have a little monograph with a great deal of useful information - very cheap too - "Wooden Boat Restoration and Repair. An excellent resource.

Best Regards
Michael Storer
 

Blueboatman

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OK I've read all the above....
Not mentioned:
You can key the wood by rough grinding sanding 80grit or less when prepping the surface.
The voids will pretty much fill themselves as you squeegee the cloth on,the thing is-is the viscosity of your wonder epoxy fluid enough to impregnate the cloth? Do a test laminate as suggested above.

Now how much glass cloth you going to use? 600g?
Use will depend on the rigidity-or otherwise-of the d/diag hull.
When laying teak decks over epoxy for example the decking is kept thin,6mm, so as to not have sufficient strength to sheer the epoxy glue joint when it expands or contracts.
D/Diag is not quite like stable plywood...just make sure the hull is not flopping around all over the place in its existing state,otherwise you are going to have to a) grind out those seams and epoxy glue them all first abd b)think about putting on a lot more than 600g cloth to create effectively an outer hull structure rigid enough to support the loose hull within...With a stable d/diag hull the cloth is merely the waterproof membrane with as a bonus some added degree of stiffening thrown in..

Not wishing to worry or complicate things but imho worth thinking about before getting started,good luck,do it right and you are giving the boat a new lease of life.
 

sailorise

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Thanks Boatman, I've sandblasted the hull and buzzed it over with the heaviest grit paper I could find. The hull is reasonable sound but seams have opened as it dries out. I shall fill the seams with 'Epoxy Lightweight Filler'. The cloth is Fothergills Engineered weave of 720grams, Surplus Navy.(Which is a bit heavy but it's cheap @ £1/M) Yes, I shall do a test first and tks again for encouragement.
 

Boatmik

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What Grit Sandpaper When Preparing for Epoxying

HI All,

Blueboatman's post is excellent advice.

One departure though - and it probably is not all that critical - my feeling is that epoxy is so effective that it can bond many different surfaces with different textures etc better than other glues. And from what Blueboatman posted it is clear that the method that he uses for surface preparation has reliable results. I have also heard of others using it also with reliable results, but there may be a better, more scientifically based solution.

Part of any bonding to timber requires that the glue goes up the into the ends of exposed wood cells - they are like tubes. If too coarse paper or a blunt blade is used the ends of the cells get crushed rather than being clean cut so the resin can't get in so easily with the result that the bond is weaker.

Weaker is a relative term - it may still be strong enough.

However the best bonding surface is freshly planed timber. But no-one is likely to plane the surface of a finished boat as the final surface - don't want flat bits everywhere and it is an awful amount of labout. But it does indicate that planing tools should be kept sharp - whether a thicknesser or a handplane when preparing stock.

The best sanded surface uses finer grades of paper. The source I have extracted the information from is (the link should be clickable - about 500kb PDF file)
Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

This article is well worth reading through, but indicates finer grades than 100grit and does mention 320 being used in some of their tests and demonstrations.

It is also important that the sandpaper be sharp.

There is a neat little test that can be used to check whether the surface is OK for bonding by placing a water droplet on the surface and see if it "beads up" or spreads out on the surface.

An good adhesive needs three properties
1/ it has to wet the surface
2/ it has to harden
3/ it has to be able to transmit loads from one side of the join to the other.

The water droplet test takes care of the wettability of the surface. I have only heard of the test before but haven't tried it - however I imagine that oily timbers like Teak or Australian White beech will always repel the moisture.

At the same time there is a strong track record of these oily timbers being glued to decks in a reliable way even without fastenings - so the test is an indicator only. (as teak repels water I would not suggest using glued teak structures for any critical part of the boat without applying the appropriate fastening schedule)

Best Regards
Michael Storer
 

huldah

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Reference using meths to remove water.
Though meths absorbs water, I don't think will work if used to remove moisture from timber. Most of the meths will be absorbed into the timber and then evaporate. During evaporation the temperature will drop and condencation will form from the air.


Philip
 

ccscott49

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Cascover was neither epoxy or polyester resin, it was/is cascamite glued, nylon scrim. Epoxy sheathing from new is a very good idea as was cascover from new. Putting it on later has problems, but I know of two other lifeboats that have been sheathed in cloth and epoxy, a very good method, but they were done in controlled conditions after every scrap of paint was removed, the rot cut out and repaired and then dried. After all of this the sheathing was applied. It works, but has to be done correctly. Not just a bodge job to hold a load of crap together.
 
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