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wooden hull sheathing

sailorise

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12 Nov 2005
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23
If anyone is an expert on fibreglass/epoxy resin sheathing, I would appreciate their advice. Come spring I intend sheathing a 34ft DD mahogany hulled ex lifeboat and had intended using a 600gram cloth with epoxy resin. However, I do have 40litres of 'Flaked' epoxy resin suited for blasted steel, and am tempted to believe that 'it all comes from the same pot' and use it. Alternatively, why not use polyester resin - I don't need the boat to last forever.
If anyone has enough experience with resins to help me make a decision I'd very much appreciate their email

tks
 

alb40

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28 May 2003
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Location
River Medway, Kent
My boat has been sheathed in west epoxy for about 10 years, no problems so far, but did cut out and replace a couple of areas that had come unstuck when i was last out of water. Didnt take on hardly a drop of water after relaunching after 3 months ashore. Wooden boat looks and character without the hastle of pumping when launching

Dont think polyester is suitable, as it does not bond very well to wood. Can be easily peeling off where epoxy sticks like poo to a blanket.
 

sailorise

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12 Nov 2005
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thanks alb40 That's my own acquired feeling about polyester. But - where's the proof and what about all those wooden hulls that were sheathed before epoxy became available? It may well not stick like epoxy but how long does it stick for? 10yrs 20 yrs? What I'm thinking is, will polyester do? and is epoxy 'over-engineered'?
 

Peterduck

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10 Apr 2002
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Polyester, unlike epoxy, is permeable, and so will let water through to the timber. It won't stick to wet wood, so becomes detached fairly quickly, and although I don't have definite figure on how quickly, I would expect about five years. Epoxy is not 'over-engineered' any more than steel is; it is in the application of it that the 'engineering' comes. I assume that at present, the hull is sound. If I were looking for a boat to buy, I would walk right way from one which had been sheathed, as it had obviously been done as a 'quick fix' of some fairly serious problems. Where one 'quick fix' has been used, you can be sure that others will, too. In other words, you are treating it as though you will be the last owner of the boat instead of a temporary custodian. By sheathing it, especially with polyester, you may well ensure that you are the last owner.
Peter.
 

sailorise

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12 Nov 2005
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Thankyou Peter, consider me admonished. However, in defence of sheathing, arn't you being a bit hard? I believe sheathing with epoxy has gained respectability among some very prestigous boats. But I can't help agree, if I were buying a boat that had been sheathed, I'd think twice. Maybe more. The hull is reasonably sound but I've had wooden boats all my life and have no sentimentality left for them. It's on the inside they're jolly nice.
I raised this one after a year underwater (she sat on some rocks) and the mechanical repair is not difficult but she is built of Hondurous Mahogany and my experience with that timber is that it gets brittle with age and benefits only from some reinforcement.
I shall flirt with polyester no more but stick with epoxy.

Thanks

Gordon
 

DRW

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27 Aug 2004
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Solent
It might be worth taking some good photos / video of the hull before the sheathing and then throughout the whole process.

Then when time comes to sell (or persuade some sceptical surveyor) you can show the hull condition easily.
 

Peterduck

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I'm not 'down' on sheathing per se, Gordon, as I know of a number of plywood trailer-sailers which were sheathed in Dynel and epoxy at the time of construction, and I consider this practice to be very good. Dynel is not as strong internally as fibreglass, and will not act as a separate component. Fibreglass set in polyester is a rigid component trying to adhere to a more flexible base, which is a tough call. Double diagonal construction is much more amenable to sheathing than carvel construction, though.
Peter.
 

sailorise

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12 Nov 2005
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Thanks DKW, I shall.
Yes, Peter, I suppose one might say, for DD construction, read, plywood. And as one of the prep jobs is to fill every tiny crack and seam with a mix of epoxy and filler, the base should be quite stable. Do you have any comments on the use of this 'flaked' epoxy paint used to treat steel bridges, that I already have, in lieu of the conventional epoxy. Pointless asking the manufacturers as they will just stick to the safe 'no' in fear of being wrong. I was hoping for a comment from someone who might have enough experience with epoxy to tell me what I'd like to hear. Viz, that epoxy is epoxy and the addition of flake and a colourant will have no detrimental effect on its ability to grip wood and hold on to the reinforcing membrane of weaving.
Thanks for everyones help and contribution

Gordon
 

chippie

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I have never thought of epoxy paint as being the same as the resin with a few additives.Paint seems a lot less viscous and needs a special primer to stick to wood. You may be right I dont know.

I would suggest doing some simple tests for yourself.
Make a small mix of your epoxy paint and apply it, along with some glass cloth, to a patch of timber of similar type to your boat and see how it adheres and fills the weave etc. When it has gone off see if you can tear it off the wood.

While you are at it, get another piece of wood and completely encapsulate it with your paint, let it go off and then weigh it. After noting the weight submerge it in a bucket with a brick on it to keep it there, for a month or more and then take it out, wipe dry and weigh again. Any increase in weight is water uptake.

If it passes these tests it is probably OK.

Forget about polyester.

Let us know how it pans out.

Good Luck.
 

sailorise

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12 Nov 2005
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Yes, Chippie, spot on. I was hoping my laziness would find someone else who'd done just that. But your right and I shall get on with it now. Thanks

Gordon
 

kestrel1891

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14 May 2004
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Kestrel was sheathed using Polyester in the 1960's. When I came to remove it around 35 years later the majority of it was still stuck to the Teak planking very well indeed. It was only areas that were clearly rotten, damaged or badly prepared where it had become unstuck.
 

alb40

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28 May 2003
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River Medway, Kent
Ive seen boats done in ployester before, but with mechanical fastening to make sure it didnt move. Dont know what the point was, probably a waste of time.

There are many liveboards around me that bodge up their boats with polyester. Its supprising how easy you can peel it off in big sheets, even when laminated to new wood. I think most people see fiberglass as fiberglass, and buy polyester just because its cheap. Ill have the last laugh when mine outlasts theirs tho!! ha ha!!!

my boat was sheathed at the same time as some new wood and a spot of refastening. Its really on there as an alternative to caulking the sod, as opposed to being structural. Its actually a damn sight cheaper than buying the goo and taking the time to caulk. Plus i can leave it without the pumps on, and no water will appear (apart from that bl##dy pain of a teak deck, which incidently, is also getting covered with epoxy when the weather warms. Started it last year. Costs less to sheath than that sikaflex stuff, plus i think it will look nicer than a shabby deck once painted with non skid)

As for your epoxy paint, id leave alone and stick to conventional epoxy resin like west. better safe than sorry.
 

Peterduck

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I haven't come across, or even heard of, 'flaked' epoxy paint before. Do you have any idea what the flakes are, and/or what they're there in the paint for? It sounds a bit like the flashy 'sparkle' paint used on plastic ski-boats to attract the boating community's jackdaws.
Peter.
 

ashanta

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With exception of those that are designed to be covered when being built such as Wharram?
 

sailorise

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12 Nov 2005
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Flaked Epoxy is, I think, the inclusion of glass flake to produce a 'toughened' finish. Used on bridges and other steel structures. Very very very resistant to impact, scuffing,UV, total emmersion in salt water and attack by jackdaws. Was expensive and came in very impressive drums. Supplied by Leighs Paints Transguard TG123 Epigrip M922 to the Highways agency as item No 123.RT98-7.2.3. Their leaflet mentions it only for blasted steel. But we are often - if not always - the victimn of commerce, I wondered if this wouldn't 'do'. So I shall test it and let you know the result (as well as Leigh Paints)
 

Grajan

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24 Jun 2004
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Location
N. Ayrshire
Cascover sheathing was just that! a cloth impregnated with an epoxy paint
Traditional decks were sometimes T&G timber with an application of "smudge" (a mixture of putty & paint) applied then a preshaped piece of canvas laid on top and the "smudge" squeezed up through the canvas allowed to dry then painted.
 

oldharry

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30 May 2001
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North from the Nab about 10 miles
Polyester resin does not adhere well to wood, and as has already been pointed out do not move with the wood, so breaks free very easily, and quickly. The real danger is then that water gets into the gap - and gives ideal conditions for rot ot develop.

Basically if polyester has been used it will accelerate the faults it is trying to hide.

Epoxy sheathing in whatever form is a totally different matter: epoxy sticks very well to wood, and the bond should be stronger than the timber itself. I have a 25 year old cascovered from new plywood boat - and the hull remains as good as new!

However, a word of warning for really succesful sheathing the timber must be as dry as you can get it! 15% moisture content is often quoted as the upper limit - which is about the average content of plywood coming from the store. Also, any previous paint coatings must be competely removed - old paint forms a very effective barrier, stopping the epoxy adhering to the wood.
 

Boatmik

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2 Feb 2006
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There are two main types of epoxy available.

1/ HIgh solids - no thinners added
2/ Others with thinners added

If the epoxy you have on hand is not high solids it is better not to use it.

If it is high solids it may be OK but you really should speak to the manufacturer.

The High Solids ones are suitable for the protection of wood as they will prevent moisture entering and so will keep moisture content down to where rot is very unlikely to occur.

Preventing the absorbtion of water also prevents the timber from expanding or contracting much at all. The result is that the surface won't move so it wont stress up the sheathing particularly across joins - so it becomes unlikely that the sheathing will be split by swelling forces.

The way to identify whether the epoxy is "high Solids" is to ask the supplier or read the can.

For a quick test you can smell the stuff. Both resin and hardener should not have a solvent smell. It is common for there to be an ammonia type smell particularly after taking the lid off, but no solvent smell at all.

Generally the prices of epoxy break into two groups. A more expensive group of resins that are high solids and thus very suitable for boatbuilding or durable architecture projects and then a range of much cheaper epoxies that have kept the costs down by adding thinners.

There are some exceptions to each group but the general rule is "you get what you pay for"

There is further information here Epoxy vs thinned epoxy
and here

Epoxy vs Polyester (as it was mentioned in one of the posts above)

Best Regards
Michael
 

sailorise

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12 Nov 2005
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23
Thankyou so much for your advice and information everyone.
Meanwhile I have been to see a 70ft ex mgb sheathed with exactly the same products I'd proposed. And it was an outstanding success.
Regarding the importance of dried wood, I wondered if the 'moisture-curing-alluminium-rich "Aluthane"' might be the answer to boats dried outside. The american manufacturers assured me that it was a good base for Epoxy.
Elsewhere I was advised that a soaking with Acetone just prior to using Epoxy would 'draw the moisture out'. But I don't know enough about chemistry to understand why that would be so. Could it combine with water molecules to create a lower evaporation temp? Could it russle any damp into globules to be 'washed away'? I don;t know. He didn't know. Who does? In any event it must be worth trying as I agree; dry wood is the most important pre-requisite of a successful bond.
If anyone is contemplating the same project, get in touch and I shall pass on everything I've learned to date. To their economic advantage.
 
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