epoxy & meths plus nail/screw sickness

[Richard_Blake]

Can I really use meths to thin ordinary epoxy to impregnate wood? Does it work with all or most makes of epoxy? Can I glue on top of it? Any experiences, good or disastrous, gratefully recieved and read (promise I won't laugh - I've had my share of disasters). My favourite local epoxy manufacturer (Polyservice in Amsterdam) makes a special impregnating (or injecting) epoxy. Could I thin that even further with meths, or is it a totally different animal? Do I add the meths after the usual one-minute-minimum mixing, and how much do I put in?

Other epoxy query - the nitty griity: how well does it insulate fastenings against electrolysis? We've inherited an amazing mix of metals in Edith, and I'm thinking along the lines of "impregnate to insulate" - but only locally around fastenings. Larch planking basically OK, but poor quality galvanized screws (probably electroplate) among some bronze and good quality gal. have made black and crumbly spots. (We're talking above the waterline - below was effectively taken care of some years ago.) All the old screws above waterline - replanking job 1970s - were plugged over with polyester - yes, it has absorbed moisture and even if the plug looks good, when you remove it there's damp underneath and the screws revealed are horrible. We're planning on removing those that will, and insulating those that won't - then refasten as necessary with sil. bronze - also squirting epoxy into the holes first. Then we plug properly with wood, epoxied in with Polyservice's excellent flexible epoxy paste which we know well. Comments, again, gratefully recieved. What our instincts say, although it's not perhaps an accepted mix, is after the refastening to give the planks the raw linseed oil/cuprinol mix they're crying out for, before recaulking traditionally. By the way - for the really nasty bits: has anyone some experience of the "Re-planking with a router" method described in CB nr. 65, Nov. '93"? Rout out half the depth, and laminate in a new half-plank on top?
All the best to all.



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[Freebee]

ive no idea about meths but you can thin it with acetone.

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[chippie]

I have used meths to thin epoxy with great success. I add it to the mixed epoxy at a ratio of one to one which gives a nice runny mix. With this mix I have pre treated plywood by rolling it on until it absorbs no more. I have also used it on solid timber stringers before fitting.
I have done a fair bit of research on this around the net and also asked questions of a relative who works in the lab of a composite supplier. His reccomendation was that it would be ok as long as one waited until it had set before glassing over to avoid evaporative bubbles forming underneath the glass. I have found that working on plywood that has been warmed by the sun helps absorption quite a bit as the meths evaporates off quite quickly.
This method is for penetration and it is wise to give a final coat of undiluted epoxy on the finished item. Wooden boat magazine has a forum with quite a lot of discussion on this subject. a google search should find it for you.
With regard to the insulation of different metals I would think that undiluted epoxy would do a better job, It depends to some extent on the type of construction your boat is, as epoxy systems work on keeping eveything as dry as possible as opposed to a traditional build which depends on the wood being wet to swell up and close up the hull. If the fittings are to be in dry timber -no problem. Locally around fittings in wet timber -not so good in my opinion.With what you propose , the hard thing would be getting everything dry enough.
I have done the half-plank type repair successfully on a dinghy but it was of glued construction and wasnt dependent on fittings to hold it together.
Send me a private message if I can be of any further help.

Good luck.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by chippie on 07/07/2003 01:45 (server time).</FONT></P>

 

[Gordonmc]

As others have said, meths can be used to thin epoxy to aid penetration. Our American cousins have a commercially available equivalent, CPES which stands for Clear Penetrating Epoxy (something). I have never seen it for sale on this side of the pond.
Some warnings, though. The wood being treated must be dry or the epoxy will trap moisture creating more problems for the future. It will also stop the wood from taking up. The epoxy will prove useless if only one side of the wood is treated.
Can't help with the second question. The only similar use of a router I have come across was to open out a seam with a V shaped arbour to take a spline.
Good luck with the project.

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[BrendanS]

There is a commercial equivalent available in this country, in most DIY stores like B&Q and Homebase. Just called wood hardener, made by the likes of Cuprinol, and also own brands.

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[richardandtracy]

Wood Hardeners

Most one part DIY wood hardeners from B&Q etc are polystyrene dissolved in [originally] acetone or an EC approved alternative. This is not necessarily a good way to go. It certainly is nowhere near as good as thinned epoxy for keeping moisture out. Also, on a cost per litre basis, it makes epoxy look cheap.

Regards

Richard.


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[Richard_Blake]

Many thanks folks, for good new information and confirmation of some of our ideas. The boat is now in the shed and we're up to our ears with cleanoff and bilge-drying in order to get working effectively. Topsides now stripped of paint - and indeed, even when the old polyester stopping over the crews looks perfect, with no blackening of the wood, the screws underneath..........
Thanks, Chippie, for the offer of advice - I'll take you up on it when we get our heads a little more together. Edith is very traditional larch (1.25") on oak (sawn, double, min 3.5 inches square) and is originally a 1911 Aldous smack, 35 foot. Converted to yacht in the 70s, we think, when frames and planking were replaced except bottom three, the hull was raised a strake and a mahogany cabin added. This, we found when we bought her unfinished and acquired sails, made her a touch tender, so half the lead ballast is still inside, and half is in great scarfed cast blocks under the keel, with a massive new keelson on pillars and a lot of keelbolts holding it all together. This was a controversial job, and a difficult decision, but the keelson was necessary anyway, and the results in sailing were great. Better balance and stiffness. Possibly a touch more rolling under motor alone, but we're actually still under-ballasted, so more in, spread about more, and we'll see.....

So, people, I'm sure I'll come back to the original subjects and others soon with more cries for help, but think I'll do it by starting a thread on Classic Boat section, where one stays on the same page a little longer!
Thanks again
Richard



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