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Author Topic: Impregnated cotton and epoxy resins ?  (Read 535 times)

dillinger 04

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Impregnated cotton and epoxy resins ?
« on: September 16, 2020, 04:44:04 AM »

Hello Everyone




I am looking for best options materials to use to skin a skeleton framed front deck, on a small model wood boat.
Has anyone here ever used impregnated cotton, and epoxy resins to be placed over a wood frame . If so can it be pulled tight like a drum with out wrinkling up. When it cures does it get as hard as fiberglass does to create a hard light strong shell that can be sanded and painted .[size=78%]  [/size]
Any help would be appreciated   



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derekwarner

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Re: Impregnated cotton and epoxy resins ?
« Reply #1 on: September 16, 2020, 08:19:24 AM »


50 years ago I helped a Mate make a few Australian surf Boards  %) we were taught that the engineering strength is that the glass fiber be it woven blanket or chopped strand mesh in monofilament......so when sanded, each solid strand of glass is encapsulated in the matrix of the epoxy resin mix and so totally impervious to water adsorption

Unsupported, glass strands or filaments have low shear and tensile strength, however the compressive strength is immense or that of the parent glass material...when the glass strands are supported in the epoxy resin is where the mechanical strength of the two are achieved

Woven cotton strands impregnated with a similar epoxy resin would when sanded back expose the raw cotton where the liquid epoxy failed to penetrate.....so the cotton would act like a straw & drink the water <:(

Cotton strands have low shear and tensile strength, but also low compressive strength


So all of this is probably the reason composite material multi million $ motor cruisers use glass fibre+ epoxy resin....over cotton + epoxy resin

Derek
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grasshopper

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Re: Impregnated cotton and epoxy resins ?
« Reply #2 on: September 16, 2020, 10:19:19 AM »

An alternative I read about in one of the old boat magazines was using a pair of nylon tights pulled taut over the hull skeleton and epoxied...

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Tug Fanatic

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Re: Impregnated cotton and epoxy resins ?
« Reply #3 on: September 16, 2020, 11:52:58 AM »

An alternative I read about in one of the old boat magazines was using a pair of nylon tights pulled taut over the hull skeleton and epoxied...
As promoted by Ron Rees. I can see the advantage of a covering that covers the whole hull with one piece of stocking but i have never been convinced of the strength nor the penetration resistance of the finished product.   

He also promotes the use of alternatives to epoxy in the laminate.
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grasshopper

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Re: Impregnated cotton and epoxy resins ?
« Reply #4 on: September 16, 2020, 01:02:30 PM »

I suppose as Dillinger only wants to do a front deck, constant immersion and outright strength may not be
major issues.
The nylon material would absorb less water than cotton and having seen how well they hold some ladies parts in place, the tensile strength may not need to come into question...😎
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dillinger 04

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Re: Impregnated cotton and epoxy resins ?
« Reply #5 on: September 16, 2020, 05:20:00 PM »

Hello everyone


Thanks for responding to my post sharing your input or involvement with working with resins and such material alike
is greatly appreciated. Sound like impregnated cotton is not the best option, nylon tights to be used as an alliterative to the cotton idea ok however I would be concerned about water intrusion, grasshopper maintained some water absorption when using such materials like nylon? This boat has a low profile design to the front a small outboard racer . When I originally started looking at this project, I wanted to do an all wood deck but this particular design to the front is warped in two directions, so sheeting it with 1 mm plywood would be quite difficult from what I gather, as bending plywood to a design like this would prove quite a change, to do due to the propriety of plywood. While exploring options for the deck RST, and Chas, machined planking the deck for construction with something like 8 mm strips of plywood. Seeing I have no pryer experiencing with planking a model deck I once again decided to explore options correct me if I am wrong but sounds like if one where to use epoxy resins no two ways about it light fiberglass over wood is the best . Planking options machined where double diagonally or single layer. any more input on this would be greatly appreciated   
 
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SailorGreg

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Re: Impregnated cotton and epoxy resins ?
« Reply #6 on: September 16, 2020, 10:43:56 PM »

I can see one issue with whatever you choose to be the fabric layer for the epoxy.  All of them are porous to a greater or lesser degree, and even if you wet out the fabric before applying, you will struggle to keep enough resin in place to do a good waterproof job, plus you may end up with lots of drips inside your hull that you can't remove.  I would consider trying planking with some thin (1/16") balsa strips to give you a lightweight base.  This will allow you to conform to both curvatures, although you will have to taper the strips slightly as you go.  You can sand the edges down to virtually nothing if you want to keep the exact same sheerline.  The joins don't have to be perfect, just use a little filler to close up any gaps.  It really is easier than many people suppose.  After planking, rub down gently to remove edges and bumps - you can afford to take away half the balsa thickness in places - then cover with glass cloth (100 gsm or lighter) and resin. 


Good luck and have fun!

Greg

dillinger 04

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Re: Impregnated cotton and epoxy resins ?
« Reply #7 on: September 17, 2020, 05:03:55 AM »

Hi Greg


Thanks for the information you posted greatly appreciated, my guess a CALPER would be a useful tool to determine the width of each plank needed to be cut measuring the distance between each stringer layout and measure the next down the line? Would you start with one side working upwards along the deck or would you start from the top working downwards or does it make any difference where you start when you start to plank a deck. What fillers would you recommend
When I was looking at supplies 1/16 balsa wood I came across bamboo strips light and strong do not know would you need special resins to adhere to bamboo after all bamboo is grass not wood? but they do use it in the construction of surfboard anyway just a though.  anymore info would be greatly appreciated.
the length of the boat is 500 mm / beam 232


   

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RST

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Re: Impregnated cotton and epoxy resins ?
« Reply #8 on: September 17, 2020, 09:06:37 AM »

I tend to steer towards obeche rather than balsa these days.  Plus I can get it from the local Hobbycraft.  Takes allot less to get a good finish.  Bit stronger so can use slightly thinner sheets if you need to bend it.
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tonyH

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Re: Impregnated cotton and epoxy resins ?
« Reply #9 on: September 17, 2020, 09:31:07 AM »

One simple alternative that's worked for me for lifeboat covers etc.
1. Cut piece of fabric to shape but a bit oversize. I used a piece from old work trousers.
2. Cover workpiece with 1 or 2 layers of clingfilm. You can always sellotape cardboard strips under to soften shape.
3. Wet fabric with resin.4. Place on desired area and smooth out.
5. Leave to dry.6. Remove, trim to size, stick in place with Araldite (Other adhesives are available) and fill and fettle as required.

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SailorGreg

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Re: Impregnated cotton and epoxy resins ?
« Reply #10 on: September 17, 2020, 09:54:54 AM »

Hi Greg


Thanks for the information you posted greatly appreciated, my guess a CALPER would be a useful tool to determine the width of each plank needed to be cut measuring the distance between each stringer layout and measure the next down the line? Would you start with one side working upwards along the deck or would you start from the top working downwards or does it make any difference where you start when you start to plank a deck. What fillers would you recommend
When I was looking at supplies 1/16 balsa wood I came across bamboo strips light and strong do not know would you need special resins to adhere to bamboo after all bamboo is grass not wood? but they do use it in the construction of surfboard anyway just a though.  anymore info would be greatly appreciated.
the length of the boat is 500 mm / beam 232


 

I would start with a central fore and aft plank then work outwards each side.  I wouldn't worry about calipers, just do it by eye, shaving a bit off to let each piece lie well against its neighbour.  Obviously the narrower each plank is the better the match to the gentle curve, but I would guess 8-10 mm wide strips will give you a good result.  Ordinary wood filler from the hardware shop is fine, or even polyfilla or similar.  Just rub it all down when filled and it's ready for coating.  RST suggests obeche instead of balsa, that would be fine, it all depends what you can lay your hands on.  I would steer clear of bamboo.  It is very light and strong but very hard, so rubbing down would be a complete pain.  What you are after is an easy, lightweight base for the resin/cloth, it doesn't have to be particularly strong in itself.
Have fun
Greg

Colin Bishop

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Re: Impregnated cotton and epoxy resins ?
« Reply #11 on: September 17, 2020, 10:37:05 AM »

When using a filler don't choose anything harder than the wood itself otherwise you are likely to get hard ridges and soft hollows on the hull as the wood and filler rub down at different rates. Balsa can be very soft so you would need a very soft filler.

You can buy the specialist model making stuff from De Luxe materials

https://www.modelshopleeds.co.uk/catalog/product_info.php?products_id=5822

but Wilko do something cheaper and proably quite good enough

https://www.offerscheck.co.uk/wilko-decorator-interior-filler-lightweight-ready-mixed-600m/wilko/628419

Another good option is Red Devil lighweight filler which is readily available.

A second advantage of this type of filler is that it is also useful for filling grain or the mesh in GRP cloth before final painting.

Colin
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Tug Fanatic

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Re: Impregnated cotton and epoxy resins ?
« Reply #12 on: September 17, 2020, 12:48:52 PM »

When using a filler don't choose anything harder than the wood itself otherwise you are likely to get hard ridges and soft hollows on the hull as the wood and filler rub down at different rates. Balsa can be very soft so you would need a very soft filler.

...........................You can buy the specialist model making stuff from De Luxe materials

https://www.modelshopleeds.co.uk/catalog/product_info.php?products_id=5822

but Wilko do something cheaper and proably quite good enough

https://www.offerscheck.co.uk/wilko-decorator-interior-filler-lightweight-ready-mixed-600m/wilko/628419

Another good option is Red Devil lighweight filler which is readily available.

A second advantage of this type of filler is that it is also useful for filling grain or the mesh in GRP cloth before final painting.

Colin

I am not sure if you are referring to the Red Devil or the Wilco product but please confirm that you use an interior filler to fill the mesh in GRP on a boat hull? Even with paint that sounds doubtful.

 If it isn't it sounds much easier than either the car body filler or the multiple layers of resin (+rubbing down) that I have used.
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Colin Bishop

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Re: Impregnated cotton and epoxy resins ?
« Reply #13 on: September 17, 2020, 01:04:11 PM »

It was suggested by Dave Milbourn to fill in the grain in Lite Ply before covering with glass cloth but I also found it handy for remedying any mesh showing through afterwards and also irregularities. I should have mentioned that I did seal over it with more resin (Eze Kote' in my case) beore painting. In that case it was something of a leveller to avoid the multiple resin coats you mention but I did not use it over large areas.

A decent paint finish should be sufficiently waterproof but you are right that the filler is best kept under the final resin coat wherever possible. It certainly works well on the bare wood.

Colin
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dillinger 04

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Re: Impregnated cotton and epoxy resins ?
« Reply #14 on: September 17, 2020, 05:05:05 PM »

Hi guys


Thank you so much for the advice and information wow ask the experienced model builders in wood and glass and get the answers that is great! appreciated . Question when planking for best results would it be best to start from the back transom forward instead of using the mahogany side sheeting provided in the kit? for the back end shown in the picture I provided? Or would in be ok to transfer the curve to the planks and cut to match the mahogany side sheeting profile, where the material plastic foil would normally meet the mahogany, but instead in this case it would be wood planks, then butt the planks close to the mahogany fill any gaps between the sheeting and planks or would this present a problem? Obviously there would be a difference in thickness in wood or could you just sand down to the thickness of the mahogany side sheeting which I think is 1 mm to avoid a lip forming where the mahogany meets the plank strips on the side of the deck . Thanks
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RST

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Re: Impregnated cotton and epoxy resins ?
« Reply #15 on: September 18, 2020, 12:32:36 AM »

Quote
Unsupported, glass strands or filaments have low shear and tensile strength, however the compressive strength is immense or that of the parent glass material...when the glass strands are supported in the epoxy resin is where the mechanical strength of the two are achieved

...Hmm, In my memory, glass fibres are made from solid "glass" which is not good in tension but better in compression and no bending.  When it's turned into a fibre, it's far, far better in bending and very high tensile strength (but no compressive strength at all).  The binding "polymer" (whatever it is) is usually rubbish in tension but good in compression.  It's when the two are combined in a matrix of fibres oriented in your chosen direction (or all in the case of CSM) that the synergy is made.   Nobody would mould a big hull from cotton sheet because it's not the right base-material and doesn't suit application.

...Lets not get mixed up with details on here anyway.

Dillinger have you tried anything yet?  Your ultimate intentions are still a bit unknown.  I would have had no problem using some cloth and diluted epoxy to do what you originally asked -as far as I know it's been done in aircraft for donkeys and model aircraft last long enough also. To be honest I'll reckon allot of us on here (myself included) have stretched material and painted with dope, thinned epoxy or just paint before.  Not meaning to be aggressive but what is the actual goal of doing this because there's always lots of options and on forums usually everyone wants to do things their own way.  If you have some ideas now the forum is full of previous builds and how to's etc.  But you can still be here in spring if you need a complete how to a-la Airfix kit.  I'm not having a go, but sometimes I think I'm not the only person just wanting to say -have a go and try yourself becuse you might get on well with something from the start, and none of us have this part in our hands so how can anyone come up with a single fix that individually suits you?

Sorry -not meaning to come across bad -but time to go try something I think!  The sooner you try you can see where it might / might not work, and lastly, there is the old paper and card method -by that I mean try with paper or card strips first before you commit!
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dillinger 04

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Re: Impregnated cotton and epoxy resins ?
« Reply #16 on: September 18, 2020, 03:35:04 AM »

Hi RST


Sorry as I tend to get carried away to much asking questions. My goal is to make the front deck on the model look more uniform like if you were to skin it with plywood so as to not see the peaks, and valleys, so to speak of the skeleton frame stringers and ribs.
The kit just provides some plastic film Oratex that you just iron on to the front and your done. I hate the idea of looking at the frame work like you would on a wood model airplane skin. I decided to explore different options, seeing the deck is warped in two directions and plywood is difficult to bend like that. That is when you guys suggested the planking method of build construction on a contoured design deck like this . I know I have not gotten started yet but by just posting on here and asking questions I am learning a lot and I do appreciate all the help input advice best way to go about this that is great!  Thanks
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