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Author Topic: Using glass cloth over balsa plank on frame hull  (Read 3556 times)

Builder1

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Using glass cloth over balsa plank on frame hull
« on: August 11, 2011, 03:52:04 PM »

I am using glass cloth painted over with 'dope' to cover a balsa plank on frame hull. I have sanded the hull and filled the larger gaps with a model filler. Other than applying multiple layers of cloth any ideas on how to obtain a smooth hull finish prior to painting???
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pugwash

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Re: Using glass cloth over balsa plank on frame hull
« Reply #1 on: August 11, 2011, 04:46:11 PM »

Perhaps I am wrong but whenever I use glass cloth (of the very very fine variety) I bond it on to the hull with resin not dope
then when it is cured it is easy to rub down to a fine finish - not sure dope will allow you to sand down like that, plus with resin
you are adding a hard skin to the balsa which will help to protect it from knocks

Geoff
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Paxton

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Re: Using glass cloth over balsa plank on frame hull
« Reply #2 on: August 12, 2011, 05:51:03 AM »

I agree with Pugwash.  After planking I coat the hull with thinned epoxy resin, fill with auto spot putty/filler and then use fine glass cloth and epoxy resin again.  It can be dry and wet sanded to a fine finish.  Epoxy doesn't smell as bad as glasfibre resin, but you still need to use it outside or in a well ventilated area.  I use acetone as a thinner for the epoxy and have had very good results.
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Colin Bishop

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Re: Using glass cloth over balsa plank on frame hull
« Reply #3 on: August 12, 2011, 08:05:32 AM »

Or you can try the new polyurethane resins which are water based one part with no mixing needed and with damp cloth clean up such as Eze Cote by Deluxe Materials. Less messy.

Colin
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Builder1

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Re: Using glass cloth over balsa plank on frame hull
« Reply #4 on: August 12, 2011, 08:48:33 AM »

Thanks for all the suggestions. Very Helpful. As I have already put one layer of cloth on using 'dope' can I now add another layer using the resiin or will this create problems??

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Colin Bishop

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Re: Using glass cloth over balsa plank on frame hull
« Reply #5 on: August 12, 2011, 09:09:56 AM »

Quote
As I have already put one layer of cloth on using 'dope' can I now add another layer using the resin or will this create problems??

Difficult to say really. Dope is normally used to cover balsa with modelling tissue. It soaks into both and fuses them together to give a tough skin over the wood which can be lightly rubbed down for a good finish. More tissue and dope can be added where necessary and it will blend in.

The question is to what extent the dope on your hull has actually bonded the glass cloth to it and I think you need to test that. If the bond is poor as, I suspect it might be, then you will have problems as the underlying dope will have soaked into the hull and made a hard surface which it might be difficult for resin to get a good grip on.

Can you post a picture of what it looks like at the moment?

Colin
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nick_75au

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Re: Using glass cloth over balsa plank on frame hull
« Reply #6 on: August 12, 2011, 09:34:40 AM »

Unless you have strength issues or areas where the glass has been sanded through don't add any more glass.
You need to make a fairing putty, now I haven't done this with dope but I reckon you could make a thick paste of dope and micro balloons, this is standard procedure with epoxy. The consistency has to be like peanut butter, use a credit card or bog applicator to smooth the concoction onto the hull and fill the weave, sand and paint.

I have used cloth and single pack polyurethane over a hull with reasonable results.

Nick
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tonyH

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Re: Using glass cloth over balsa plank on frame hull
« Reply #7 on: August 12, 2011, 09:48:55 AM »

One material I have tried on a couple of occasions is the fine white 'scrim' used by SWMBO in the garden. It seems to stick well with either sanding sealer or resin and is fine enough to give a decent finish. It may not be quite as strong as glass mesh but it's works for me. It's also rather cheap!

Tony
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bobk

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Re: Using glass cloth over balsa plank on frame hull
« Reply #8 on: August 12, 2011, 10:24:47 AM »

Has anyone else used Gyproc coving adhesive for modelling?  Back in the early Seventies I had a commission from the MOD contractor firm I worked for to produce a part sectioned half submarine hull of about 3 ft.  Sectioned areas were the control room and weapons control compartment.

I used ply bulkheads on a hardwood wall mounting board, with a balsa-planked skin to get the shape.  The nice thing with Gyproc adhesive is it is in powder form, mixed with water to the consistency needed, and it applies easier than plaster, smoothing with a damp cloth.  Within about quarter of an hour it is as solid as concrete but still easy to sand to a smooth finish.

OK, this was a static model and the material was probably too heavy to shape a working model in this form, but I have since used Gyproc sparingly as a finishing filler on a steam driven HMS Cressy I built a couple of years later.
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Circlip

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Re: Using glass cloth over balsa plank on frame hull
« Reply #9 on: August 12, 2011, 11:24:26 AM »

You could rescue by "Flood Painting" the hull with straight cellulose thinners, peeling the glass off, letting the hull dry, sand and then re-cover using tissue. Look for FLJ's piece on tissue and dope covering.

   Regards  Ian.
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