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Glass fibre woven cloth and epoxy resin

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Chris Walby23/10/2020 07:01:12
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1393 forum posts
348 photos

I thought I start another thread rather than hijack/off topic someone else's build log (pet hate of mine).

As I am in the process of "glassing" my Focke and searching the web for info on "how to" plus following various builds by people far more experienced than me here I keep coming around to a unanswered question.

More than one of the web experts clearly state that glassing a model should NOT be used to add STRENGTH. Improved finish, ding/knock resistance etc

The techniques I have seen scrape or mop resin off the cloth to achieve a very thin layer and thus add little weight, but fundamentally add no structural strength.

Based on the above would anyone reduce the structural components (spars, ribs, sheeting) because they were intending to glass the model?

Glass, why would you?

David Sack23/10/2020 08:37:31
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Hi Chris,

As I understand it (having read lots and made little and therefore very happy to be corrected by people more knowledgable than me) the glass fibre resin adds no strength and therefore you cannot (must not, should not, don't!!!) alter the structural components of your airframe.

The glass fibre resin build has superb ding resistance and if done properly adds little weight - see Chris McG's thread for details of glassing and 'the sauce' which improves finish with little weight gain:.

https://www.modelflying.co.uk/forums/postings.asp?th=146393&p=35

I cannot recommend this highly enough, Chris McG has written, and illustrated, an eloquent account of the glassing and finishing process.

The glass fibre polyurethane build is 'probably' as good as the resin for ding resistance, and again will not add strength, BUT because the polyurethane is water based it will soak into your balsa and add weight, and will warp structures, UNLESS the balsa is sealed - this IS from personal experience. Capitalised because I really wanted to emphasise it !

I hope that is helpful and look forward to the thoughts and accounts of more experienced builders.

Former Member23/10/2020 08:50:12

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Chris Walby23/10/2020 08:56:46
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1393 forum posts
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Thanks for the info David, I'll look in depth at Chris McG's post and yes through weighty experience I did a few trial bits and came up with my seal with sanding sealer (not water based). Credit card scraping technique, leave until just touch and skim again. Biggest current issue is making sure edges are 100% or it gives me loads of grief later to sort out.

Have I gone off topic….laugh

Neil James23/10/2020 09:09:48
64 forum posts
30 photos

I found this interesting as I haven’t done any glass covering for many years but will do so for my Phase 6 fuselage. Last time I used polyester resin (yes, it was that long ago!) but I’m keen to try a less obnoxious material so I’ve bought some deluxe materials Eze-Kote to make it a bit easier on my lungs, however water based resins seem to have received a lukewarm reception here. Are they as effective in bonding the glass cloth?

Andy Stephenson23/10/2020 10:22:43
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I would not use water based resin to attach the glass cloth to a balsa structure due to the reasons stated above, warping.

My technique is to lay the lightest weight cloth dry on to an untreated surface, pour on a small amount of laminating epoxy (SP115) and spread it out with an old credit card, this way only a very small amount of resin is needed as it squeegees out until the weave is visible all over the surface of the cloth. Meaning no glossy spots of excess resin. The following coat is when I use a water based resin as the wood is now sealed but rather than use Eze-Kote which is expensive. To fill the weave between sanding, I use Dulux Diamond Hard Glaze varnish which as near as I can tell is the same as the Deluxe materials offering, apart from the colour. This fills the weave without further mess of the epoxy.

Very much on the contrary I find this gives a great boost to the strength and rigidity of the airframe such that I CAN justify lightening the underlying structure. If you think about it a 100% glass model has no wood in it so where does the strength come from.

Richard Acland23/10/2020 10:35:37
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148 forum posts
70 photos

I tend to thin my epoxy resin with methylated spirits to give a watery consistency. this makes it much easier to brush on.

Doc Marten23/10/2020 10:48:41
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1016 forum posts
19 photos

Barrie,

Would you recommend the mini rollers instead of brushing as rollers apply the medium thinner and more evenly than a brush?

Edited By Doc Marten on 23/10/2020 10:49:14

Former Member23/10/2020 10:50:38

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Former Member23/10/2020 10:56:25

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Martin Harris23/10/2020 11:01:11
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9602 forum posts
258 photos

I'm led to believe that the "lightest cloth" is only so because the weave is more open and therefore adds useless weight as the resin fills the gaps. Be careful to choose cloth with a tight weave.

I'm afraid I too was taught the credit card method but I understand that it was demonstrated to our club by one of the foremost suppliers of scale model finishing supplies with a reputation as an expert modeller. It does not rely on scraping off large amounts of excess resin, which is applied in very small quantities and worked into the weave from the centre of panels outwards.

I would agree that glass clothing must add some strength and certainly gives more "ding" resistance but with a single layer of very light glass cloth, I'd hesitate to make structural changes based on it - even the lightest film covering adds considerable strength in tension.

Former Member23/10/2020 11:01:12

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Former Member23/10/2020 11:01:51

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Former Member23/10/2020 11:02:30

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Former Member23/10/2020 11:08:51

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Andy Stephenson23/10/2020 11:42:07
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294 forum posts
43 photos

Is the advice about structural changes because the cloth doesn't adhere to the wood well enough to add strength?

Former Member23/10/2020 11:49:18

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Andy Stephenson23/10/2020 12:00:02
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294 forum posts
43 photos

OK I see now and I would not change the internal structure of, say a wing, but I have gone down on the sheeting thickness by a small amount for two reasons, 1 because to maintain the aerofoil section due to the thickness of the cloth and 2 because this is where the strength if any is added.

Martin Harris23/10/2020 13:25:28
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I'd suggest that if you're adding any significant extra thickness, you're using the wrong cloth - or building a micro-sized model!

Former Member23/10/2020 13:37:41

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