25 December, 2009

Coracle: A note on glues and paint

I've been researching paint and other top coats in regard to their impermeability.  The problem I find is that 2 pack epoxy  systems and even marine paints carry a hefty price tag.

The other complication is that 2 pack epoxy coatings won't flex and the craft I'm building has to flex. Since I am planning to re-coat the coracle once per year at least , my present grand plan is procedure reliant:
  • construct the papier mache hull over a plug/mould. While still on the plug, paint the 'bottom' with undercoat/sealer (which one?) and several coats of Dulux Weathershield Acrylic house paint. Let dry.
  • remove the coracle from the plug and turn it over.
  • paint the inside of the hull the same way so that there' is an inside outside layer of acrylic paint several coats thick. Then,
  • while the paint is  still wet lay down a paper layer over the hull. Let dry. Then,
  • lay down the support struts made from bamboo. Layer these with paper and cloth and coat the laid rods with Acrylic using it both as a glue and as a coating so that laid on top is paper which uses the paint as an adhesive.
  • let dry.
  • lay down several new layers of paper over the support struts and hull.Then coat these layers -- in process -- or at the end -- with Floods Penetrol to protect the paper from  water inundation.
 Rationale

Advantage: this is a cheap way to go with easy touch up and re-coating options every now and then. When acrylic dries it becomes impermeable despite the fact that it is water based.

Weathershield is used a lot by  wooden boat owners because it delivers well against the elements and costs much less than marine paint and is easy to use and apply. Since it is an exterior house paint it isn't made as marine  below-the-waterline paint -- but then I'm not going to immerse the coracle in water all the time -- only for a few hours at a stretch..

I also seek to harness the stickiness of the paint as an adhesive for paper layers on top of the paint.

Since I want to use Penetrol 
Penetrol is a versatile blend of natural oils with a penetration power 3 times more than water and a powerful bonding ability. High in solids, non-toxic when dry, colourless and with low odour it is user friendly.
I need to ensure that it isn't blended with acryclic so the separation I propose is one of drying the acrylic first before applying Penetrol.. The justification being that if the acrylic leaks I can depend on the Penetrol to slow the ingress into the paper layers.

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