Veneered foam vs traditional built up construction

[Alan Gorham_]

I have built one set of wings where I used a sheet type of double sided tape called Gudy 870 to stick the veneer to the core. It was fiddly to lay out and trim the sheet of Gudy and I find the Copydex method suits me better.

[Matt Carlton]

I used to use Copydex but it really does stink. Plus it never really goes off but stays rubbery. I think that there are much better alternatives available. There are foam safe spray adhesives and I even think Aliphatic resin is a better bet than Copydex, but of course YMMV.

In terms of veneer, nylon fabric and pu varnish might be an alternative? I've also considered using Mylar sheeting. An experiment I thought of was to cover a wing with a printed paper (wrapping paper?) and bonding a thin Mylar sheet over the top to give a glossy, smooth surface. Whether it would work is up for debate. If anyone has an old wing core and shucks, it might be worth a try?

[kc]

Copydex is good but it goes off if you store it for a few months. I have lost count of the number of bottles thrown out as hard & useless. Only buy what you can use quickly.

Thixofix would surely melt white foam wouldn't it? It is ( was ) based on a solvent something like petrol I think. Fine on ply doublers but not foam.

Veneer sheets need to be a bit oversize to allow trimming back to the foam and placing it exactly is quite difficult. It is important that the LE & TE are firmly glued ( epoxy) to the veneer not just the foam. So a 19 inch wide sheet ( if you can really buy it that wide - most is narrower ) would only cover about 9 inches span twice ( upper and lower sheets ) when allowing for trimming after glueing..

I will start a separate thread about card construction.

[Alan Gorham_]

Of course you can use thin G10 GRP sheet stuck to the foam core with foaming PU Gorilla Glue. Mick Reeves sells this as "Proskin". Whether this is cost effective I don't know, but one supposed benefit is that being a composite surface it does not need sealing prior to paint.

I'll say again that the advantage (to me) of using a latex type glue such as Copydex is that you apply it to the foam core and the wood skin and then let it dry. You can then roll the core onto the wood and the dry glue will grip on contact. I much prefer this method than applying a "wet" glue as I would expect the veneer to skid around on the core. Not very helpful, especially when veneering a curved turtle deck.

I've never thought latex glues had a strong smell.

[Alan Gorham_]

Posted by kc on 13/10/2020 16:31:00:

Copydex is good but it goes off if you store it for a few months. I have lost count of the number of bottles thrown out as hard & useless. Only buy what you can use quickly.

Thixofix would surely melt white foam wouldn't it? It is ( was ) based on a solvent something like petrol I think. Fine on ply doublers but not foam.

Veneer sheets need to be a bit oversize to allow trimming back to the foam and placing it exactly is quite difficult. It is important that the LE & TE are firmly glued ( epoxy) to the veneer not just the foam. So a 19 inch wide sheet ( if you can really buy it that wide - most is narrower ) would only cover about 9 inches span twice ( upper and lower sheets ) when allowing for trimming after glueing..

I will start a separate thread about card construction.

Interestingly, I have a part used 5L bottle of Styccobond (the carpetfitters version of Copydex) that I bought in 2014. Just opened it and used it for the first time in over a year last week. Absolutely fine.

[Nigel R]

Posted by kc on 13/10/2020 16:31:00:

Thixofix would surely melt white foam wouldn't it? It is ( was ) based on a solvent something like petrol I think. Fine on ply doublers but not foam.

I thought Thixofix was a latex/water base? However, I've never used it.

I do use Evostik - which is definitely solvent based and melts foam - for ply doublers and sheeting built up wings. I find it great for those applications, although you obviously need to be extremely careful about aligning things before allowing the glue to grab.

Matt, Alan, Ron - thanks. Good point about cutting two blanks at once.

[kc]

Styccobond has various numbers . F1 seems to be like Copydex according to the info, but is only available in 5 litres at about 37 pounds.

Thixofix seems to contain Toluene, acetone etc according to the data sheet so I reckon that would destroy white foam. Plenty of info about the hazards too. I would only use it outdoors. Looks & spreads like Peanut Butter. It's main advantage is the surfaces are re-positional for a short time if you don't get the alignment right first time.

[Alan Gorham_]

Yes I used the F1 variant of Styccobond. Just lloked at my invoice when I last bought some 6 years ago and it was £22. How much is a small tub of Copydex that you say goes bad quickly?

[Nigel R]

Posted by kc on 13/10/2020 17:19:33:

Thixofix seems to contain Toluene, acetone etc according to the data sheet so I reckon that would destroy white foam. Plenty of info about the hazards too. I would only use it outdoors. Looks & spreads like Peanut Butter. It's main advantage is the surfaces are re-positional for a short time if you don't get the alignment right first time.

Yes, best forgotten in context of foam then; seems quite similar to evostik but less 'grab' ?

[kc]

Copydex costs from 3 to 6 pounds for 125ml depending on where it's bought. 125ml might just be enough for a wing when diluted.

It's possible my Copydex went off when the cap was not airtight, but it happened so often that the cap ( with a brush ) seemed tight to me on several occasions yet dried out.

Thixofix spreads very easily and does not go 'stringy' like Evostik Impact ( or whatever it's called now ) so is quite superior.   However if one is glueing ply doublers to fuselage then there seems to be no need to use a contact adhesive as PVA works well just takes a day to dry.   Boddo's instructions on my first model mislead me for 2 decades!   PVA works OK and no smell. 

Edited By kc on 13/10/2020 17:46:20

Edited By kc on 13/10/2020 17:52:08

[Nigel R]

Evostik is best spread quickly. Old credit card squeegee for doublers. You can spread a very thin layer if you move fast. Bit off topic for veneered foam.

I have read about using thinned resin for attaching the veneer too. Spread very thin then weighted down whilst it dries. I seem to recall there is a trick to stop the resin soaking too far into the wood but cannot remember it.

[Nigel R]

Alan, when you use copydex / styccobond, do you get the veneer in place then put the wing back into the offcuts? Or does it grab immediately?

Edited By Nigel R on 14/10/2020 09:07:12

[Alan Gorham_]

No, you use the Copydex as a contact adhesive. Apply it to both the veneer and the foam. Let it dry and then place the veneer glue side up in the offcut. You then use the edges of the offcut to align the edges of the wing panel (say both trailing edge corners and bring the panel down very slowly and carefully so that the entire trailing edge of the panel grabs the veneer. Once that is successfully attached you "roll" the wing panel down onto the veneer.

[Gordon Price 1]

So Balsa cabin do not stock Obechi veneer anymore.

Does anyone have a suppler that still has stock?

It seems like there is no demand so it is no longer imported to the UK.

Gordon

[kc]

Welcome to the forum Gordon.

In the days when foam wings were popular other veneers were used for kit wings such as mahogany. Obeche might be lighter but in that thickness it's not significant. Obeche was cheaper and was easily available. So check around for Veneer Suppliers / Marquetry Suppliers in your area and see what is available in the size you need. For traditional reasons I suppose there are many veneer suppliers in the River Lea/ East London/ Essex/ Hertfordshire area.

[Gordon Price 1]

Hello. I am in Glasgow. I have now found and ordered Koto veneer in 0.6mm thickness. Its heavier than obechi but is in stock and fairly cheap. I will report further on that. Still have one option on an Obechi equivalent that I am chasing.

More to follow.

Gordon