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the rocker

Lightweight finishing for foam veneer wings?

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the rocker

What are peoples ideas on a lightweight finish for foam veneer wings? This is for a 2.5m electric soarer, I did try Eze dope a number of years ago with tissue but it didn't seem to work too well. Maybe it was me? In more recent times G4 pond sealer instead of epoxy with glass cloth, this is on larger scale models though. I'm open to ideas, would a thinned varnish work? Does J Perkins sanding sealer attack foam?

TIA, Matt

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satinet

How good is the veeneer? If it's one of those blejzyk jobs you can use a water based stain. 

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mikef

I would expect a cellulose based sanding sealer to attack polystyrene (white) foam.   I have only ever had one foam/veneer wing, a  Chris Foss Centiphase,   I used light glass cloth and epoxy on it and I think it's still fine after about 35 years. 

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isoaritfirst

2.5mtr electric soarer - probably not that worried about a few grams of weight.

Unless you are looking to compete in thermal comps and need to hang for 10 minutes, a little bit of weight is very rarely an issue - more likely its an advantage.

Why not film them. some films are significantly lighter than others, and wrapping increases the strength by a fair amount.

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pete beadle

Hi Matt

I would advise using 25 gsm cloth using epoxy skinning resin applied with a "cube" of foam.........brush the veneer clean of any dust, lay a piece of glasscloth larger than the panel you are covering by about 2" all round, mix the skinning resin, pour out small "puddles" of the resin onto the cloth, press the cube of foam down in the centre of each puddle working outwards , keep widening the circle of resin, working the cube outwards until all the resin in the puddle is applied, repeat until all the wing is covered then repeat for the top and bottom of each of the wing panels

When you finish you should have a matt resin covering using the smallest possible amount of resin you'll need - works for me

The finish will be waterproof and, if you want to cover the whole wing with clear varnish you'll get the lovely view of the veneer that people compliment you on!:)

Regards

Pete

BARCS1702

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oipigface

There’s a firm called FighterAces in Co Durham which used to have an excellent website including very detailed instructions about the process Mr Beadle has outlined. The website seems to be a bit of a disaster area now, and I have been unable to find the link. I’ve probably still got a downloaded pdf. Let me know if you are interested and I will search for it.

FighterAces will also happily sell you materials including L285 laminating epoxy, which I have found to be excellent for this kind of job. I used to use West System, but no more. Don’t try ordering online. Phone them up instead!

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the rocker

Thanks for the replies, I have used laminating epoxy from Easy composites in the past with 25gsm cloth on scale power models and gliders. There seems to be an 18gsm cloth on the market which I have purchased a square metre to give a go. I think using a light cloth and peel ply will do the job of keeping the weight gain minimal, then to finish off a coat of acrylic lacquer? 

A lesson learned was keeping the sanding sealer away from the foam cores, now I don't bother.  Just lay the cloth on and then roller out from the centre. Seems to work fine, doe's the sponge technique work similar?

Going off on a tangent has anyone tried the Z-Poxy finishing resin?

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pete beadle
20 minutes ago, the rocker said:

A lesson learned was keeping the sanding sealer away from the foam cores, now I don't bother.  Just lay the cloth on and then roller out from the centre. Seems to work fine, doe's the sponge technique work similar?

Going off on a tangent has anyone tried the Z-Poxy finishing resin?

Hi Matt

1) IMHO using a sponge allows you to get better coverage using less resin, plus it makes the mopping-up of excess resin with kitchen roll unnecessary

2) I've used Z-Poxy finishing resin for many years now, as long as you remember the 50/50 mix you should have no problems.......oh, and BTW you can get it cheaper than Amazon sells it for:yes:

Regards

Pete

BARCS 1702

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satinet

Zpoxy isn't bad.  It's not at the level of something like west systems or similar.

But zpoxy is a good option if you don't intend to use a lot of glue and buy a small batch.

Otherwise it works out cheaper to buy say 1kg of resin with a hardner. I've been using west systems 205. I've had it a few years. Still going ok. 

Better resin wets out easier etc. But zpoxy finishing is certainly upt o the job described.

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the rocker

After a couple of years my resin is now brown, the composites company say that the resin is thixotropic and the brown colour is moisture and to throw it away. To prove a point a small amount was mixed, it never cured properly!

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pete beadle

Hi Matt

If you don't use your skinning resin for years it isn't a problem UNTIL YOU OPEN IT

Once you open the two containers the contents WILL age ......that is why you should only buy the amount you need for the job you need to do

Regular users of large amounts of two-part resin are usually careful to replace all lids, keep the remainder(s) in a cool, dry place and DON'T leave the stuff unused for years expecting it NOT to age

IMHO price is not the really important thing, how the resin performs in use is far more important:thumbsup:

Regards

Pete

BARCS 1702

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satinet
9 hours ago, the rocker said:

After a couple of years my resin is now brown, the composites company say that the resin is thixotropic and the brown colour is moisture and to throw it away. To prove a point a small amount was mixed, it never cured properly!

Hydroscopic? 

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oipigface
48 minutes ago, satinet said:

Hydroscopic?

Hygroscopic?

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satinet

That's it. The fumeister told me to be careful with epoxy a few years ago. Definitely keep it sealed. My west systems is still working ok. Laid up some carbon last night. Rubs down fine. 

I find the 30 minute pacer stuff goes off quickly. Not had much luck with it in recent years.  Mind you i do tend to lose the plastic caps. 

Thixotropic agent is the stuff you use to thicken the epoxy. As it goes I've got a tub on my bench. Not to be confused with micro ballons which are a filler.

20191123_090921~2.jpg

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oipigface

Try L285. Better than either West or Z-poxy.

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the rocker
8 hours ago, satinet said:

Hydroscopic? 

Quite right, I have baby brain.

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isoaritfirst

Well I never knew that.
and I say hydroscopic regularly  at work  

Hygroscopic Versus Hydroscopic

You might encounter the word "hydroscopic" used in place of "hygroscopic". Although hydro- is a prefix meaning water, the word "hydroscopic" is a misspelling and is incorrect. A hydroscope is an instrument used to take deep sea measurements.

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satinet

It's Greek i guess. 

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