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Thread: Latex for laminating moulding process

  1. #1
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    Default Latex for laminating moulding process

    I donít know about you, but I really hate sanding & painting and I like to save as much weight as possible when making hulls, if I can save weight to have some movable ballast for improved weight distribution, all the better.

    I have yet to try making a female mould, doesnít make much sense for all that extra work when you laying up by hand, if I had vacuum bag I would give it a try, but the extra expense of materials for mould & vac and consumables just puts me off the idea.

    For male moulds Iíve tried it all plastic rubbish bags overlaying wetted-out cloth, stretch film wrap, heat shrink wrap and then started experimenting with latex on some moulds and have finally perfected the latex male moulding process that I would like to share. The latex is light brown in colour and semi-transparent (can see through it) and approx 0.50 mm thick and stretches about 50% of its original size, comfortably. You can find it at most baby shops, they use as for protective waterproof cover over cot mattresses etc.

    Step 1: Cut the building board so that it is 5 mm narrower than the deck line (understanding the hull is upside down on the building board) then cut same 5mm out of the frames so there is an soft slope from the sheer-line to the base of the building board.

    Step 2: Screw a 50 x 400 mm beam to the underneath of the building board so can clamp onto a mobile bench so that there is plenty of room to reach the base board, for stapling the latex along its edge.

    Step 3: Drill 5 mm holes in the base board & one frame near the bow, centre and stern of the hull, this so I can lock the mould frames to the base board using plastic tie downs to prevent any movement as I stretch the latex sheet over the mould.

    Step 4: Mask along the edge of the base board wrapping it over the frame channel to stop any epoxy dripping into the base of the frame, as I want to take the mould off the base board to use it as a hull cradle when fitting out the hull later. Apply another strip of masking tape under the sheer line along the mould so that it over-laps the tape on the base board. If you have cut a slot in the stern frame, pays to cover this as well to stop any epoxy getting in.

    Step 5: Prepare the mould with required amount of wax & just for extra security I wipe a layer of PVA release agent using a sponge to help easily de-moulding the hull later.

    Step 6: Next prepare 3 x 5mm balsa strips to staple the latex to the base board, cut it so there are two pieces for each side of the board, Iíll explain why in a little bit.

    Ready to go !

    Step 7: Cut your cloths as usual and then for this type of laminate I found epoxy with low viscosity works best: Resin @ 400 and hardener @ 200 (R&G Epoxy resin HT 2) for the hand lay-up. It wets out cloths nicely and allows air bubbles to be rolled out easily and is a super transparent (water clear) high gloss that has 45 minute pot life, hence plenty of time to work it. www.r-g.de (site is also available in English)

    I tried various other higher viscosity epoxies, but found when the latex was stretched over the edge of hull; I could not roll-out air bubbles or excess resin (under the latex) over the sheer line pressure point.

    For this lay-up I used 245 gsm twill carbon fibre as the first layer and have added dark blue U.V resistant colour paste to the epoxy which will be used with the carbon and the two outer hull 80 gsm fibre-glass layers to give the final hull colour.

    For the 245 gsm, I wetted the carbon out on an old clear plastic table cover on the bench before carry it to the mould, very simple clean way of working (thanks for that tip Jim)

    I use liberal amounts of epoxy on the all clothes as the wetted out cloths are sandwiched under the stretched latex to the mould, excess epoxy flows to the mask taped base board and you should not have any problems with pin holes in the finished hull. When youíre happy that the wet laminates air bubble free, apply another coat of epoxy on the top cloth so that it floods the top cloth, but not too much that it begins running.

    Step 7: Using latex sheet 50cm wide x 100cm (mould is 120 cm long) lay it centred over the mould so that it hangs equally done the sides of the mould. I drew a line along the centre of the latex sheet so that I could keep an eye that didnít move too far to one side or the other.

    This is where you will need another set of hands, preferably two if available. Firstly using staple (6mm) the latex to the base board across the stern, then stretch the latex along the length of the hull until it covers the bow, pulling the latex toward the floor, equally on both sides. (donít worry about the centre part of the mould yet)

    Step 8: Now at the bow only, staple each side of the latex to the base board with staples approx 2-3 cm apart at the bow end for first 10 cm. So we now have the bow & stern stapled to the base board.

    Step 9: This next step is important DO-NOT staple the centre part of the mould, you now need to smooth out the latex over the mould with your hand and then using hard sponge or rubber roller, ROLL OUT the AIR between the latex and the wet cloth. Start from the centre line running roller down the sides until youíre happy that you have all the big air pockets rolled out. You will see smaller pin head air pockets under the latex, donít worry about them yet, weíll take them out later.

    Step 10: Now with one person each side of the mould, have them equally start pulling the centre section latex toward the floor, as you staple the balsa strip (over the latex) to the base until both sides are completely stapled to the board.
    Most important, DO-NOT release TENSION of the latex until both sides are stapled down, otherwise, as the latex un-stretches, it will gather the wet cloth up the hull under the latex and you will have a hell of a time trying to rescue it (depending on number of wet layers you have)...believe me, I aborted one hull when tension was slowly released and it had moved wet cloths too far before I realised what had happened ...then it was too late.

    Finally after stapling has been completed you can finally roll out those small pin head air bubbles until you canít see them anymore and youíre done.

    One beautifully finished glossy hull, NO fairing, sanding, primer and more sanding and painting which gives significant weight saving estimated around 80-100 gsm. Whole exercise takes me about 20 mins.

    With a normal hand lay-up, when the fibre had gotten hard enough I would trim of overhang, with latex, it is hard to see when the cloth is ready (canít touch the cloth) once I peeled the latex off too early and the cloth moved as it was still too tacky, so now I just leave it until it fully cured then, Dremel off the overhang excess cloth.

    Iíve found you can use each side of the latex once with epoxy, tried washing it warm soapy water but could not get all of the epoxy off completely, if anyone has any helpful tips I would appreciate it.

    It is an easy and clean lay-up, hope my learningís are helpful to anyone else wanting to try this method; I for one will only use this method from now on.

    Cheers Alan
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    You can only create, what you can imagine

  2. #2
    Join Date
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    Default Re: Latex for laminating moulding process

    Hi Alan -

    thanks for the explanation and details. Very informative - and caused me to consider an alternative - but not sure it would work. I will try to explain, and you can consider and "poke holes" into the thought.

    Being a bit experienced in screen printing, we make up a wooden frame and pre-stretch the screen fabric and staple to the screen. This form is then filled with paint/ink, and a rubber squeegee is drawn over the inside of the screen frame pushing the ink/paint through the unfilled pores of the fabric and transferring the design to the shirt, glass, plastic, etc. Screen is lifted , printed item removed and process repeated.

    Here is my thought......
    1. Build a wooden frame with a center opening that will easily fit over the boat. Perhaps bigger than needed.
    2. Cut latex to be slightly oversize of the hull mold and staple to the wood frame.
    3. Apply your glass fabric/epoxy/etc. to the hull mold
    4. Hold wood frame with latex above the hull and lower the frame. Because the latex is still smaller than the hull, eventually as you lower the frame, the latex starts to stretch over the hull.
    5. You can use quick clamps to hold the frame down sightly, and maybe eliminate the need for a second person.
    6. The frame is held down and latex stretched to cause resin to be expelled around perimeter of deck (hull is upside down) much the same as your method.
    7. When cured you can remove the clamps and lift frame (and latex) up and off.

    Picture the process like a big vacuum forming plate, only the latex replaces the styrene and no heat is needed.

    As I say - I haven't tried, but am wondering what issues you see that might prevent this. One might be able to hinge the frame at stern or bow, then lower and hold with a clamp at the opposite end. once in place, use clamps around the remaining sides to stretch latex further.

    Just a thought as I read your explanation.

    Dick

  3. #3
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    Default Re: Latex for laminating moulding process

    Hi Dick, sounds reasonable enough, need to make up a frame and base to clamp it too once you've lowered it over the mould (stretch the latex) when I've got some time I'll think about giving a go, thanks.

    Cheers Alan
    You can only create, what you can imagine

  4. #4
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    Default Re: Latex for laminating moulding process

    Hi Alan & Dick
    very interesting explanations.

    I will probably transfer the ideas into a drawing for both suggested methods .

    The rectangular frame, I assume, is lowered onto the mould and the latex probably will not exerce a sufficient pressure all around the deck line since is needed some tollerance to pass, unless I do not understood well ! sorry.

    Questions :
    1 - Is the use of stamples will damage the latex for further moldings ?
    2 - How much it cost ?

    Cheers
    ClaudioD

  5. #5
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    Default Re: Latex for laminating moulding process

    Claudio -
    You are correct in your observations..... in Alan's process, the latex actually wraps under the hull so it is very tight to the gunwales. In my idea, it is tight but not as much as Alan's - so I don't know if it would leave air bubbles along the shear line of the glass hull.

    This summer, when warm weather returns (???) I may try this using an RG65 for test hull.

    Chaars, Dick

  6. #6
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    Default Re: Latex for laminating moulding process

    This is my understanding about the question above, please correct me if wrong !!
    It may be possible to substitute the sliding method by adding some soft compound inside the frame edge or foam as such to ensure a compression action all along during lowering manouvre !
    cheers
    ClaudioD
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    Last edited by claudio; 03-28-2011 at 12:15 PM.

  7. #7
    pisek Guest

    Default Re: Latex for laminating moulding process

    Hi all.

    Any idea where to buy this latex in sheet? I could only fined a liquid one here in Slovenia.

    Thanks

    Damjan

  8. #8
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    Default Re: Latex for laminating moulding process

    Hi Guys,

    Claudio your drawing on the left (above) is what I did, only difference was I did not have high enough frames, so I cut the mounting board to be narrower than the the mould & stapled the latex on to the edge of the base board using 3 mm thick basla strips.

    Staples do not damage the latex providing you pull them out straight, if you pull them side-ways the staple could tear the latex.

    I paid 4 Euro for metre sqaure sheet which I cut in half and could use for four hulls, that works at 1 Euro per hull, far easier to but more than try & clean the latex after use. I found I could use each side of 1 latex sheet only once as the residue left after de-moulding is hard to remove, tried washing it in warm soapy water but did not help very much.

    Here's one supplier, caution if you under 16 years old ask your dad (not mum) before going there, there are some things your parents may not want you to see http://www.preisroboter.de/ergebnis1355500-0-0.html and they don't work on boats anyway

    As I said earlier, you should be able to find latex sheet in most baby shops, depending where you live.

    Cheers Alan
    You can only create, what you can imagine

  9. #9
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    Default Re: Latex for laminating moulding process

    Looking at Claudio's frame plan, I consider it is a little too complicated, I like to make it as simple as possible.

    Lay the latex over the mould and then stretch it along the length of the hull so you can staple down the bow and the stern only (at sides only) this leaves the centre part of the mould free & you can then easily roll out air bubbles from the centre to the rails, before finally stretching and stapling the latex down around mid ship area.

    With the frame you would possibly trap the air once frame is down and then have to work the air bubbles out, then it will be more difficult to get air out from underneath the latex and there is also the possiblity surplus epoxy may not work its self out, once the latex is tight against the edge of the mould.

    Cheers Alan
    Last edited by K1W120; 03-28-2011 at 01:36 PM.
    You can only create, what you can imagine

  10. #10
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    Default Re: Latex for laminating moulding process

    Alan
    the frame solution was suggested by Dick and myself I tried to figure out how can be made.

    One supplier I found is :

    http://www.supatex.com/index.php?opt...id=3&Itemid=75


    I do not recall the thickness you used, but I believe that 0.45mm should be OK ?

    Cheers
    ClaudioD
    Last edited by claudio; 03-28-2011 at 01:53 PM.

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