using a canoe for a male mold

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#1

I am so glad I found this forum. Hope you guys can help me.

I have two canoes. :smiley: One homebuilt woodstrip (epoxy/F/G with 6 coats of UV varnish) and an ABS royalex. They are both my “Babies” and I’d hate to ruin either one. I’m thinking of using one as a male mold to lay up another hull. No vacumn bagging, just fabric, epoxy and sqeegees.

Am I way off base here? :shock:

Will the epoxy cause any damage to either the royalex or woodstrip?
What about the heat from curing?
What sort of release wax/agent should I use? And how should I apply it?
Will I be able to get the new hull off without ruining my existing canoes?
How do I get the release agent and wax off the canoes when I’m done?

The technique I have in mind calls for leaving the bow and stern open until removal so the sides can be flexed, then closing them up seperately.

I have tried posting this question on canoe and kayak builders forums without much success. Most said “DON"T DO IT”. But then they never had done it.

One fellow did say he used heat shrink window plastic to cover his woodstrip canoe and laid up a new kevlar hull over that. When it was cured it supposedly popped right off and the plastic left a reasonably smooth inside finish.

As far as the fabric I haven’t made my mind up as yet. Carbon fiber or one of the new carbon/kevlar hybrids would be nice. I am thinking one layer of CF and then one layer of 4-6oz S glass on the exterior, with some kevlar in the ends and bilge for reinforcement, then a few transverse ribs to firm up the bottom and prevent oilcanning.

Thanks for your ideas!

#2

You’ll want to use polyester gel coat as a surface coat, followed by polyester resin and chopped strand mat. You can use epoxy, but you’ll have to mix graphite and silica to thicken the epoxy to create a pseudo gel coat layer. This is really messy and exposes you to two carcinogens (graphite powder and silica). You also don’t want to use chopped strand mat with epoxy, so you’d have to use glass cloth and then reinforce it with a thicker material like coremat. In comparison, polyester is much easier to work with.

Will the epoxy cause any damage to either the royalex or woodstrip?
What about the heat from curing?

Polyester and epoxy resin cure via checmical reactions that produce heat. Heat is the most likely cause of damage to your parts. As long as you build your mold slowly, you should be fine. Most people stick to less than 3 layers during a 24 hour period to keep the heat down. Better slow and safe than fast and sorry here.

What sort of release wax/agent should I use? And how should I apply it?

I’m fond of Part All release wax and PVA. Apply part all like you would car wax, but allow the coats to cure for 5-30 minutes before buffing. You should also use a lot of coats if you want to insure that you don’t ruin your plugs. 10 coats would be ideal. Then you can spray on a fine layer of PVA.

Will I be able to get the new hull off without ruining my existing canoes?

You mean the hull mold? Just use plastic wedges and you should be fine.

How do I get the release agent and wax off the canoes when I’m done?

PVA comes off with water. The wax should come off with a rub down of denatured alcohol.

The technique I have in mind calls for leaving the bow and stern open until removal so the sides can be flexed, then closing them up seperately.

I have tried posting this question on canoe and kayak builders forums without much success. Most said “DON"T DO IT”. But then they never had done it.

Well, there’s definite risk involved. You should be prepared that the worst case scenario is that you ruin your existing canoes. But as they say, nothing ventured, nothing gained. Being experienced greatly minimizes your risks, as does taking the appropriate precautions and thoroughly planning your project before you start.

One fellow did say he used heat shrink window plastic to cover his woodstrip canoe and laid up a new kevlar hull over that. When it was cured it supposedly popped right off and the plastic left a reasonably smooth inside finish.

You could try using stretchable bagging material for vacuum bagging as well.

#3

I did this. I took a canoe that I owned that had a very smooth gelcoat surface and polished it to remove some scratches and then I applied Mothers pure carnuba wax. I applied at least 6 coats and buffed each out. Then, I sprayed the canoe (plug) with polyvinyl alcohol. I then sprayed the plug with orange tooling gelcoat to about 30 mils. Then I layered it with 8 layers of fiberglass mat using molding polyester resin. The original plug (CANOE) has an elliptical shape with a greater than 180 degree arc. This required that I create a parting line. So, I did the plug in two parts. Use aluminum 90 deg angle aluminum.
I did a longitudinal line. This has beed a severe headache. I recommend that a transverse parting line be used if possible.
I reinforced the mold with ply wood ribs.
The mold came off the original canoe without sticking. In fact, It came off too easily. The critical aspect is the wax and PVA. WAX,WAX,WAXPVA,PVA

Now, you have a female mold.

A few pieces of advice:
start applying the fiberglass mat as soon as the orange tooling gel coat has gelled. Do not wait till tomorrow. Apply at least 3-4 layers then let this gel and cure for at least one day. Then apply 3-5 more. The more the better in order to have a very stiff female mold. The mold is very big and cumbersome. It must be as stiff as possible in order to avoid distortion under its own weight.
Use metal angle aluminum at the parting lines. It you use fabric and resin, It will chip and crack. I made this mistake.
You will need to build flanges, use 3/8 inch plywood.

Now, I have a question for you:
Do you have a fabric layup scheme? I need one. I can’t find any on the internet or in any books. I have a tentative plan. What dou think of this?

layers of fabric:
OUTSIDE TO INSIDE

  1. 4oz plain weave S-glass (Abrasion resistance)
  2. 5.7oz 2X2 Twill carbon (Stiffness and beauty)
  3. 5.7oz kevlar (strength and weight)
  4. 4inch wide ribs (stiffness)
  5. 5 oz polyester/fiberglass blend (because it is cheap i.e. $5.00/yd) (
    covers the bottom and ribs only)
  6. 1 extra layer of #5 in the midships and 2 extra layers in the bow and
    stern (BIAS cut)
    7 2 narrow strips (4-5 inch wide) of carbon in the bow and stern.
    All of the layers will be vacuum bagged.
    The resin is System 2000 (Fiberglast) epoxy
  7. I will probably use composite gunwales. i.e. graphite braided tubes
    with Backer Rod foam core and a wooden seat with wooded hangers.

Is this a good plan?
Do I have too many layers of fabric on the sides of the canoe?
Any additional Advice?

#4

I guess it depends on the type of canoe you want. Looks like you are building a heavy, expedition canoe that will be tough enough for extreme use CIII-IV whitewater. . I would guess the weight of this boat would be over 60 lbs and maybe even approaching 70.

If you want a lightweight tripping canoe (less than 50 lbs) I would forego #'s 3 and 5.