The Coolbox Project

18th August 2012 - The Coolbox Project

So with the space now set up for the cool box, I quickly got the space insulated.  I used 3 thicknesses of 25mm foil faced isocyanurate foam, typically found in lofts etc and readily available at hardware and building stores.  This gives me 75mm of insulation, which is a bit of a compromise.  100mm would be preferable, but I had to rationalise the space to allow up to 9 typical 2 litre bottles.

Cool box space ready Insulation fitted Insulation fitted - inside box

With final dimensions of the insulation, I started developing a mould for the cool box liner.  Many projects I have researched for cool boxes online typically just lay up glass directly onto the insulation.  I wanted to do something more finished.  I think though, I was a little ambitious for my first attempt.  I proposed a glear epoxy gelcoat with alufibre laid up behind, with further laminations of glass with white pigmented epoxy.  Here is the process I took to get the first prototype out...


Step 1... Build a mould

So I started y developing a mould with Conti board.  Cheap and perfect for the purpose, the surface releases well with minimum waxing.  It produces a slightly matt surface, with the minimum of polishing required usually.  I took the inside dimensions of the fitted insulation and made allowances for some air space between the final mould, and an allowance for the laminate thickness.  The mould was developed with hot melt glue, parcel tape and placticine as follows:

Contiboard in stock Planning underway Sides developed

I routed the edges and lightly sanded them to ensure perfection, then any gaps I applied some plasticine with a plastic blade.  Then once the top went on, I used parcel tape to cover the exposed wood chip and ensure release.  With the top on, and some further filling with plasticine and I covered the edges with tape again.

Looking down into the mould Top on and ready to route Top on and routed

With the tape in place round the edges, I applied a plasticine fillet round the base using my new fillet tool.  This produced an excellent result around the base of the mould tool.  I was impressed with the results of this technique.

Mould making tools Filling with plasticine Tape applied to edges

So with the edges taped and the plasticine fillet applied, I proceeded to wax the mould.  This took 3 waxings, which took place over a couple of hours to allow the wax to dry and be buffed, then re applied.  Preparing moulds is a time consuming, meticulous task.  Like many things, time and detail invested in this stage produces the goods later.

Plasticine fillet applied Mould waxed and ready to start laminating The wax


Stage 2 - Laminating... or where I screwed up!

So I started by applying epoxy gelcoat.  My reasoning for using clear epoxy gelcoat was hardness.  Epoxy gelcoat is much tougher than polyester gelcoat, but its really brittle and expensive.  In hindsight, I now know that a laminate for epoxy gelcoat should be thick to minimise flexing, or the gel will crack a lot, like mine did!  Also, clear gelcoat will show every mistake and is next to impossible to fix if it goes wrong.  That was my second mistake.  A white polyester gelcoat would be flexible enough and not show the mistakes below it, and any minor imperfections would be easy to fix.  I was trying to run before I could walk!

Once the gelcoat was on I let it tack up, then laid on the alufibre.  This was another mistake.  I laid it on dry, and it bonded in places with the gelcoat.  This "fixed" the weave in places, so it would not lay down and conform to the gelcoat.  The right thing to do was to prime the surface with epoxy, then lay the fibre to allow it to be massaged into place, then consolidated.  the result of my mistake was to introduce irrecoverable voids between the alufibre and gelcoat.

Critique on the mould tool:  This was an overall success.  It released well enough, and I only need to refine this a little.  I don't need as much hot melt glue next time so the interior piece de constructs easily.  The contiboard, the packing tape and the plasticine all worked well together to build a useable tool.

Conclusions: Next time, do it in white polyester gelcoat and a thick polyester lay up.  Prime the gelcoat with resin before laying up.  Thicker build up of laminate is required to ensure minimal cracking of gelcoat upon release.  Mould was good though, and released fine.  I might wax a bit more for the second attempt.  Adjust mould tool slightly for easier release.

Gelled, laminated and clingfilmed

So here are a few pictures of the results.  Although it produced a perfectly functional moulding, and in places it looks pretty darn good, the overall effect is patchy and messy.  I will improve for the next time around.  Just wish I hadn't drained out so much epoxy on this.  I suppose it has been a useful learning experience, and I know what is possible for next time.

The result Not many voids Every flaw in the laminate visible...
Cracking of the very brittle gelcoat Bunching of the laminate causing voids Line of laminate edge difficult to hide

Last Updated (Saturday, 18 August 2012 23:43)