bonding plywwod to steel

[capt'n ron]

how well will good plywood bonded with epoxy to clean sandblasted (surface has good tooth) steel. after bonding and shaping ply it will be sheathed with 6 oz., faired and painted. will it stay on for a few years of dry sailing?.

[Bergalia]

From past experience (Araldite) bonds well between steel and timber - if steel has good, clean, grease-free surface and is well scoured for keying. If possible (assuming steel is not an exterior plate) drill small holes (1/4 inch dia by 1/4 inch deep) at intervals along steel to allow 'nipples' of epoxy to gain extra 'bite'.

[capt'n ron]

bergalia, define "exterior". this question is directed towards a center board that i plan to build some foil onto by applying plywood and shaping a profile. as mentioned, then sheath it with 6 oz. cloth and epoxy. i could also drill/tap and screw the ply onto the steel for assurance. i have never heard of "araldite", what is it?

[Bergalia]

Ah, Capt'n ron... a slight misunderstanding. I thought you might be refering to interior fittings - panels, facing bulkheads etc. The exterior steel sheets I referred to was the hull itself (too deep a hole would precipitate leaks).
But even on a centreboard (though never having built one) I would suggest shallow drilling will add to the ply 'grip'.
Araldite (a UK make of two part epoxy glue...) I believe it was the world's first epoxy invented, by a Dr De Bruno at Duxford in Cambridge).Though I may be wrong.
I remember as a teenager visiting the tiny factory there just before the coronation of of Elizabeth. (The English call her Elizabeth 2, but of course we Scots - although now domiciled in Australia - call her Elizabeth 1 - as we've never had a previous incumbent of that name.) Anyway - I digress. Araldite was developed to re-tyre the Coronation Coach. It was a spin-off from Aerolite the two part epoxy devoloped by De Bruno for 'glueing' aircraft skins.
But as to building a centreboard - I'll leave that to wiser heads than mine - and there are many in this forum
:cool:

[PAR]

One of the great things fiberglass can be used for is centerboards and rudders. I wouldn't bond plywood to the centerboard plate when you could have an all 'glass or foam and 'glass layup instead. It's a lot easier to shape foam then ply.

You'll want more then a 6 ounce layer of cloth on this board, regardless of the core material you use. It will get beat up and the heavier layup will help protect the plate from moisture, not to mention a wood core which will swell under the laminate if used and breached (which will eventually happen)

[D'ARTOIS]

ARALDITE is made by CIBA GEIGY and one of the, or the oldest epoxy's on the market.
I used it already in 1966 to glue magnesium to magnesium, than "baking" it. It still holds after 41 years. It is also used in the aircraft industry to glue alu to alu
or alu to other metals.

It is an INDUSTRIAL epoxy, available in diferent formulae's.

For only bonding wood to metal, Aerodux 500 can be used too. In that case the glue joint should be as thin as possible.

[Bergalia]

Sure is great stuff, friend D'Artois. Sorry to cap your story - but I've still got a Japanese jade vase which had a large chunk broken away at the rim and it was repaired by building up Araldite and then being carved back into the correct shape of the missing section...And this was done by De Bruno at the small factory in Duxford - in 1950. The repair is almost 'impossible' to spot - unless you know were to look. :cool: