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Any tips on glassing a model?


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For several years I've been glassing some of my models, rather than using iron-on film, using 25g cloth with West Systems epoxy resin.  On the whole I've been quite satisfied with the results, but one thing still bugs me:  Most of the on-line tutorials I see mention using a credit card to spread the resin around and squeegee it into the cloth, and to scrape off any surplus so as to leave a smooth surface.  I stipple the resin onto the cloth will a small stiff brush to ensure good adhesion to the wood, but there's no surplus to scrape off and, when the job has cured, it looks like a textured fabric finish.  To get a smooth finish I then have to use filler primer and plenty of sanding.

 

So I'm curious, do you seal the wood (usually balsa) in any way before applying cloth and resin, so that less resin soaks in and more is left filling the weave?  If so, with what -- a 'priming' coat of resin, or something like sanding sealer?  Or do you just apply a second coat of resin after the cloth/resin has cured?

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I found foam rollers work best for applying the first coat of resin, rather than credit cards, supplemented with foam wedges for jabbing resin into corners etc. It is not necessary to seal the wood first, but it should be sanded really smooth and imperfections filled with filler before applying the glass. The first coat of resin, rolled through the glass, should be just enough to stick the fibreglass down to the wood. Most people apply a second or "flow" coat of resin (rather than a filler) and this should just fill the weave, but no more. I found a one-inch brush most satisfactory for this second coat of epoxy resin. (I suspect that quite a lot of the variations in technique are a matter of personal taste.) The really heavy lifting is in the sanding after each coat has dried. Then the primer for the paint is applied - best to use a compatible epoxy primer rather than a car primer; then more sanding; then the paint coat(s).

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Start with a  good fine sanded finishing with 360 wet and dry used dry, all ready in a nice warm room at around 20/25°c is best, this makes sure that the resin

polymerises properly and hardens quickly so that it doesn't soak into the wood too much, a good quality roller, I apply a nice even coat to the wood to avoid dry patches then carefully apply the glass and a quick roll from the centre to the outsides to the ends will avoid wrinkles and at the same time begin to wet out the cloth,then sparingly apply what resin is needed to wet it out, no more no less, keep it closed up in the room and don't keep opening the door, the draughts will stop the resin from polymerising,,, then a proper car 2 pack polyurethane filler paint and get your sanding blocks and wet and dry out,,,

aile resiner-2048.jpg

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I’m with John on this one, a small foam roller is by far the easiest way.  The roller doesn’t snag the same way as a credit card.  If you look up Bucks Composites, they have a ‘how to’ article which explains it.  ( I’m nothing to do with them by the way) 

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Thanks guys.  I tried a foam roller once, but found my brush easier mainly, I think, because of the hassle of having to transfer the resin from the mixing beaker into a tray for the roller, and then clean the tray and roller afterwards (I dispose of the mixing beakers and brushes).  I also fill and sand down the model as has been described.

 

So in a nutshell, it seems all I'm doing wrong is simply not applying enough resin.  This is partly because I know it creates runs, like paint, if there's too much on.  So for my next job I'll wait until the weather's warmer (I work in my garage), coat the model with resin first before applying the cloth and more resin, and then use toilet paper to take up any excess.

 

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It’s a more complex process, but if you want minimum weight and a really good finish you need to be looking at vacuum bagging. It initially seems intimidating but I have a simple setup using a fish tank pump that I’ve used a few times with success - the only difficult bit is getting the Mylars in the right place. It’s scary when you unpack your first part, but the finish is far far better than you can achieve without the bag, with the added bonus you don’t need to use those nasty two pack paints.

 

Pics from my Limit EX build of many years ago…

 

https://www.rcgroups.com/forums/showpost.php?p=20873214&postcount=232

 

https://www.rcgroups.com/forums/showpost.php?p=21050310&postcount=252

 

Of course you are welcome to borrow my setup if you’d like to Allan.

 

 

Edited by MattyB
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Quite simply, there is no right or wrong way to apply glass but just the method that works for the individual, or a combination of various techniques. I suggest making up a series of test pieces to experiment with - mix and match until you find a system that works for you.

For what it's worth, I find that  applying the cloth to the workpiece and then spreading out the resin (slightly thinned with meths) using a credit card works for me. Tricky corner areas on fuselages might need a touch of stippling with a small brush. Avoid applying too much resin no matter how it's done, because the cloth tends to float up rather than stay flat to the workpiece.

A useful tutorial here https://www.youtube.com/watch?v=gDNZ-j8r1Tc that details the technique and that I pretty much follow it to the letter. Using a single edge razor blade to remove any excess sounds unlikely but does work very well indeed.

Good luck - very rewarding when you get it right.

Edited by Cuban8
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I recently heard of a technique where a silicone rubber sheet is laid over the first coat of wet resin and weighted down around the edges. The effect of this is to pull the cloth tight to the surface of the wood to leave a shiny glass like finish without having to go through all the trouble of applying a second coat and all that wet sanding. I guess this similar to vacuum bagging with mylar but without the vacuum.

I've tried this with limited success because it leaves voids where air is trapped but the silicone sheet I used was hastily made by casting some old rather viscous moulding compound I had left over from a job some years ago. My thinking is that if the silicone sheet is thin enough the air trapped air could be visible through the sheet and rolled out with a wallpaper roller.

Has anyone else had experience of this technique. A while ago there was a trader at a flying show who was promoting this method alongside his glassing products but I can't remember the name.

If it could perfected this would render the surface ready for painting (in one resin coat) all but for a light keying with some fine sandpaper.

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1 hour ago, Cuban8 said:

 . . . For what it's worth, I find that  applying the cloth to the workpiece and then spreading out the resin (slightly thinned with meths) using a credit card works for me. Tricky corner areas on fuselages might need a touch of stippling with a small brush. Avoid applying too much resin no matter how it's done, because the cloth tends to float up rather than stay flat to the workpiece. . . . 

 

Yes, the floating up thing is noticeable in some localised spots, resulting in small 'blisters'.  I hope to meet MattyB this afternoon, so will discuss vaccuum bagging with him.  Overall it seems like I'm doing most things right, but just need more care over quantity and application of the resin.

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This method appears on a USA web site and has been used by one of our club members for strengthening his foam models. He was kind enough to pass the method to me and it maybe useful to others.

1st coat impregnates wood and sticks fibre glass cloth to it.

2nd coat fills weave on f/glass cloth.

3rd coat gives a smooth finish ready for priming.

1.       Cut cloth 1 inch overhang on the object

2.       Wet and dry the object 220 grit remove dust

3.       Mix two parts resin 50 – 50. That is 200g resin 200g hardener and 200g meths,a 1 to 1 ratio mix until liquid is not cloudy.

4.       Apply resin mix on pre positioned cloth, put blob in the middle and work out from this, ensure to go round the edges and check for bubbles etc

5.       Leave to dry (overnight)

6.       Remove overhang with sharp knife then wet and dry, remove dust.

7.       Repeat stages 1 – 6 on opposite side of object. (wing, fuselage etc)

8.       Mix resin (epoxy) but use only 50% meths i.e. 100g this time. Coat both sides leave to dry then sand dry (220 grit)

9.       Repeat above leave to dry then 400 grit for finishing and priming/polishing.

A fourth coat can be applied is desired

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I have to admit that I haven't tried using anything other than the credit card method and I'm not claiming it's a better method than others but it works for me - and uses an incredibly small amount of resin.  I have to wonder whether vacuum bagging may encourage over generous application with the excess being drawn into the wood?  Cloth floating on resin makes it sound as though there's an awful lot of it about with some techniques!

 

One thing which may make a difference - and I don't recall it being mentioned - is using 3M Spray Mount or similar to hold the cloth in position.  I was shown to give the airframe the merest waft of it and the cloth then stays exactly where you lay it but can be removed and repositioned if a mistake is made.  I don't find any tendency for the cloth to drag, despite using quite reasonable pressure while squeegeeing the resin from a small pool.

 

Mixing 600g of resin/thinner at a time?  That seems like whole 8 oz pots being mixed at a time if my estimate of density isn't wildly wrong...I'd be feeling wasteful if I mixed up a 20th of that amount at a time and I wouldn't expect to use a full pair of pots to cover a decent sized model - or do you expect to do the whole job in one go?

 

 

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I have been glassing models for many years now and have tried a number of techniques, some fine and others not so.

Initially I brushed it on then sanded down until blue in the face, good finish but far too much work.

I have tried using peel ply a few times but it tends to remove too much resin and have now settled with brushing on resin in strips then going over with a foam or fluffy mini roller. This applies a minimal amount because I am always striving for the lightest possible result; another coat would just add weight.

I then sand lightly with 120-180 grit and apply a coat of Halfords grey primer mixed with a little sanding sealer and lots of baby powder. This sands down very easily and fills the weave. A light sanding with finer paper is followed by a brushed coat of dope thinned 80% which seals the dusty surface and prevents the base coat of colour from pulling away with masking tape.

Even in a warm room it is essential to leave the resin for at least 48hrs before sanding otherwise the paper will clog.

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With glassing there are several ways that work.

But not everybody finds they get on with somebody else technique.

I had a modeller ask me for help because he couldnt get his cloth to lay flat. I explained that he should try a different brand of cloth. I told him what I use, but he was adament he knew better. Anyway he couldnt get a good result and bad mouthed using glass from then on.

This video shows how your cloth should behave, if it doesnt then change materials.

Cheers

Danny

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I think that all of these replies prove that what's been said about finding a method that suits and works for the individual is the way to go. With the exception of one or two very basic no-nos like using way too much resin or working in cold conditions, there really isn't a wrong or right way, providing the end result is satisfactory.

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  • 1 month later...

I've just about finished a wing, using sanding sealer before glassing.  Compared with my previous models, which I glassed without using sanding sealer, the first noticeable difference is there was much more epoxy lying on the surface of the glass, so I can see where the idea of using a credit card to scrape it off might be useful.  But sanding down the surplus was relatively easy, so I think I'd rather do that than risk having the weave show through, as it might if all surplus is scraped off when wet.

 

Then after one coat of high-build primer sanded back, it looked good enough to me so I applied a light coat of regular primer from a rattle can and am now in the process of air-brushing the colour coats of water-based acrylic.  The whole lot will be sealed with Humbrol clear satin enamel after insignia etc.  Previously I'd used several iterations of high-build primer and sanding to get rid of the visible weave, but this time no sign of any weave anywhere.

 

That seems to be what works for me, so thank you for the suggestions.

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I recently used Peel-Ply for the first time. It's very effective at reducing the amount of epoxy remaining on the surface at it soaks up all the excess. It does leave a weave pattern on the epoxy when peeled off but it's easy to sand off. To fill the remaining weave a coat of domestic white emulsion paint let to dry and sanded right down till the only remaining paint is just visible in the weave. I find this much cheaper than using spray filler primer for the first coat.

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