Building a foam plug

I see no point putting a frame on this foam as it is very fragile and the chances to break apart from the frame are like 99%. I can't find a proper quality foam like Styrofoam locally which is more solid.
I will try to break it slowly and see how it goes.

 

I actually recommended adding a frame to the mould and bonding the foam to something substantial.I don't see any other way to apply a large force.As for Styrofoam being more solid,not very solid is my experience of it and a denser polyurethane would be a better choice as well as being resistant to the styrene in the polyester resin.Which makes me ponder if there may have been thin spots in the coating and raises the possibility that the resin has attacked the foam.

 

The white foam is EPS. It comes in different density. The denser the better detail. The denser the more expensive. We build a lot of our mold plugs with layers of 2" 4x8 sheets of xps pink insulation. It is dense and cheap. Can get at home depot. What we do is design our product as a solid model in CAD. I then slice the model into 2" thick segments. I cut each layer separately, glue together, sand, 2 layers of fiberglass cloth and epoxy. Let cure. Sand, fair, sand, fair, sand... spray a layer of Duratec or 3 layers of awlgrip 545 primer. Sand with 340, 400, 800, 1200, 2000 wet. Wax, at least 3 layers. Good to go! Can be done with 4x8 CNC router with a decent z axis travel. Can also be done with large EPS blocks. Same process.

 

You're going to need to glass the plug if you want a stable surface. Epoxy resin is foam stable, polyester is a no no. Also, you will need to make a 2 piece mold from the plug, left and right due to the shape of a kayak.

 

Here is a simple 2 part egg mold made of 2" xps foam cheap and cheerful.

 

That clearly works for you,but what a lot of work! Our OP has gone a bit quiet recently but won't be likely to call at Home Depot,unless they have expanded into Greece.
Have you ever tried polyurethane foam insulation slabs?It doesn't react with polyester resin or filler (you guys would call it Bondo but we don't have that product in Europe) and thus saves the cost of epoxy.For modest sized parts it might be less time consuming to buy slabs of tooling block such as those from Ren or Sika and save all the laminating and fairing.You can still build them up in a similar manner and with a bit of CAD manipulation they can be built up over a plywood or MDF armature to keep the volume and hence cost down.Not even that long a process with a CNC router on hand.At which point you can go straight to paint,although if you are in a hurry you can just seal the surface if the machining marks are taken out with 600 grit paper but this does mean you need to compound the fine ridges out when the mould is released.I agree that a solid CAD model is nice but if time doesn't allow the creation of a solid,a surface model is adequate and can be sliced in the same way.

Not sure how many kayaks you might have built but all of those I have seen . have been moulded in two halves with a horizontal split as this avoids the need for cosmetic work on the most visible area of the kayak and keeps the cockpit rim an even thickness when the two halves are bonded together.It would clearly be a miserable task to attempt to laminate in the ends of a 14 foot hull while operating through a hole in the middle of the boat and consequently the two halves are laminated first and then joined.Nobody enjoys the process of working in the ends,but you get adept with practice.

 

An update; my first attempt was a failure as the mold stuck to wherever I had applied a putty (not epoxy). I'm sure about that as I was taking images on every step to be able to identify the problem.
I now print and made a new item for another test and I'm currently applying wax. I used only epoxy putty/resin and I'll see how it goes when I make it and try to release it.

One more question. Due to some shapes on the stern plus the places where the fittings going is a pain to put properly the cloth. Is there a reason why NOT going to work if I make that step (applying the cloth) with vaccum?
Just to be sure that it will be perfect applied. I'm talking about vaccum only for the cloth that will go to the plug (foam) not the mold from it.

Thanks

 

I would recommend caution about applying vacuum to a foam slab.It may compress and lose the shape you created.Try a section that has no shape and observe closely what happens.If nothing goes wrong,then you can probably proceed with your plan,but if the edges distort you will have to consider another plan.It all depends on the rigidity of the foam.

 

Hi there,
I use XPS-Foam regularly to build moulds, depending on how durable I want the mould to be.
For the noses of my wingsails I milled the XPS and covered it with several layers of epoxy for stability. At last a layer of paint and then the release agent worked fine for two demouldings...
You have to be careful around the edges though, since the vacuum tends to push them round.

I am going into more detail on my insta: https://www.instagram.com/carbon_pirate/

best,

Marcus

 

That is interesting,and I thank you for confirming that high vacuum on XPS may cause distortion.It must have taken quite a few coats of epoxy to make the foam appear yellow.

 

Hi,
I think it was 3 coats epoxy.I added a before picture, that shows the difference in color.
I used a male foam plug for a hull too. That was more of an issue than the female mould. On the male plug, the vacuum distorted not only the shape of the foam core, but it also pressed the fabric a millimeter into the core. This led to wrinkles in the laminate.
More details here: Carbon Pirate on Instagram https://www.instagram.com/p/CzNzX2HtPVP/?img_index=1

best,
Marcus

 

Putties, fairing types, make a poor mold or plug surface, sticking is very common. They need to be covered by either the same resin type, a suitable primer, or another type of top coat.

 

@ondarvr you are right; the final test where I used only epoxy worked fine and I manage to release the test part.
I am using EPS200 foam, this is the only one that I can find locally and it needs a cloth to make it solid as I doubt that only with epoxy will be any solid surface to work.

 

Hi all,

I read somewhere but can't find the source again that it is possible to add the twill cloth dry on the foam, then on top of the cloth peel ply and start wetting the resin on top of the peel ply. That will leave with a smooth surface and will minimize the amount of primer that has to be added in order to cover the twill surface.
Does anyone have ever done something like that?

I'm trying to find a way to add less primer to the plug as to cover the weave of the twill it needs 5-6 coats of primer.

 

I think you have just explained to the world the negative aspect of adding glass to the top of anything that you would like to have a high quality finish.It takes a lot of work.Come to that,it always takes quite a bit of work to get a good finish.If you are able to get hold of some,I would suggest using a slab of tooling block that has been CNC machined for the detailed parts of your project.It will cost more than the same size slab of polystyrene but the time you will save will be considerable.The lower density blocks should be adequate and I wish I could recommend a variety available in Greece but unfortunately I don't know which varieties are.If you can get hold of a small slab of one of these it ought to work and all you need to do is remove the tooling marks and apply perhaps one good coat of your chosen finish.If a slightly rougher surface can be tolerated,you can just seal the surface once the machining marks are gone and then polish out any tiny ripples in the mould itself.Block Materials https://industry.sika.com/en/home/advanced-resins/model-and-mold-manufacturing/block-materials.html
Were it not for the excessive bureaucracy involved I would have recommended investigating buying a slab from PU Foam, Model Board, Tooling Board and Blocks - Easy Composites https://www.easycomposites.co.uk/model-board-tooling-board-block I would expect any of the boards-not necessarily the foams-to be suitable and they probably sell slabs which are close to the sizes you require.

The problem may come if you use a slab of tooling block next to a piece of sheathed polystyrene that compresses a small amount under vacuum.Which leads to another posssibility,that of using slabs of perhaps 25mm MDF which have been CNC machined to your shape.It is a dusty process and it will get very fuzzy after an initial coat of paint,but it will resist vacuum and isn't hugely expensive.The finished item will be quite heavy if you go this way.