Could a plywood coated with epoxy canoe be used as a mold?

[yoram]

and we call the shiny coat formika but i don't know the English term.

[pistnbroke]

If you just cover the outside with polyester and mat thats a male mould and you will have a lot of sanding to do .....if you make a special canoe with external frame and shiney inside thats a female mould and you put the poly and mat inside and you dont have any finishing to do ( if you use gel coat)

[yoram]

ahhhhhhhhhhhhhhhhh ok. i understand now. thanks.

what is the difference between mat and cloth?

[pistnbroke]

yes formica ..but thats not cheap you can get coated plywood......for the female mould I used stips of mat 300 mm wide and layed one across the width ..wet it in ..then overlap the next 200mm ..wet it in ...and the third overlap 200 mm on the one before and keep going ...I therefore got 3 layer thickness with interlapped mat and its easy to handle ...you must do the job in one go wet on wet ....allow 5 hrs !!!!

[pistnbroke]

matt is chopped strand matt ..the cheap random fibreglass strands ..cloth is woven like material and more expensive ..I use 500g mat its faster than 250g ( 500g mat takes 500g resin per sp metre to wet it out ....)

[yoram]

ok thanks. is it possible to coat the whole female mold with one sheet of cloth (300 gr) and then wet it with epoxy? is it practical? would it keep the shape of the mold or it will be a problem? is it enough from strength point of view or you need more layers?

[pistnbroke]

yes possible when you have had some practice ..but you would need to coat it and then pollish it for the female... strength stiffness not a problem if you have external frame !!!!!.remember epoxy goes off in 24 hrs polyester in 15 min

[yoram]

so let me try to describe the process so it is totally clear for me; there is a female mold, i put the cloth inside and cover well the whole inner side of the mold with the cloth. then add the epoxy or polyester, wait for it to dry and then take the hardened cloth out? the outer side of what came out is smooth and needs very little sanding and the inner side needs more sanding? is it enough with one layer of 300 gr/sq meter cloth and about 300 gr epoxy or polyester? no need for second layer? and when you say "strength stiffness not a problem if you have external frame !!!!!" do you mean strength of the mold or of the the actual boat/canoe?

[pistnbroke]

sorry you can use a layer of cloth for the outer layer ...on top of the gel coat but you need ast least three layers to build it up to the thickness you want say 4 mm .....you would not use epoxy for the actual boat if you use epoxy for the mould ....polyester will not stick to the epoxy so if you use epoxy for the actual boat you may not get it out and its very expensive....I think a trip to the library for a good book is what you need ....

I cannot teach you what to do ..you need a small projet to try out your ideas and get some practical experience ...

epoxy sticks to wood very well ....polyester does not ....

[yoram]

ok, pistnbroke. thank you very much for your time and patience.

[rwatson]

Yoram, the amount of fibreglass cloth and chooped strand matt you will need for any small boat will exceed 300 gram.

You will need possibly many layers, usually alternating woven cloth and chopped strand matt.

Do build a test panel an notice how flexible it is - unless it is moulded with curves, it will be very floppy.

I recomend you build quite a few test panels to get a 'feel' for both the method and the resulting strength. If you lay them out on formica, you will be able to peel them from the flat surface and have a very smooth finish to one side. Coat the formica with some sort of wax, or buy some special mould release from you fibreglass store.

Its a lot of fun.

[yoram]

thanks a lot, rwatson.
basically i am looking for all kind of different ways and methods to build a simple canoe as a hobby class in the school i am working in. i want to try first to do it my self and then it will be easier to do it together with the students. i do not present myself as a boat builder, it is just a class where we build together a canoe. the mold system is interesting and i would like to try it, like you said, first on a very small scale just to get the feel of it. i am trying to get the simplest, easiest, cost effective and enjoyable way to build a canoe.