The Naiad Voyages

Mark Austen

2018.04.05 - So Then, What Next?

The next stage of the hull work is the waiting game, waiting for the supplies to arrive. Strictly speaking I have enough to get started and the rest should arrive in time but I'm not willing to bank on that.

One of the problems that epoxy has is what is know as amine blush. It is a waxy residue that forms on the surface of the epoxy during the curing stage especially if the temperature is cold or the air has a high humidity. The problem is with the word 'waxy' and you have to remove the amine blush if you want anything to stick to the epoxy such as paint or antifouling or even more epoxy.

If you are going to overcoat the epoxy with another layer of epoxy, then you can apply this before the first coat has cured and before the amine blush has started to form, pretty much as soon as the epoxy stops being tacky. The test is to press your finger lightly onto the epoxy surface and if it is not sticky but you leave the impression of your fingerprint in the epoxy, then it is ready for the next coat. This is good as the second layer of epoxy forms what is known as a primary bond to the first. That is, the two layers are bonded together chemically at the molecular level. If you leave the epoxy to properly cure, then remove the amine blush, you will have to lightly sand the surface and remove the shine so that the next layer has something to grip onto. This is known as a secondary bond and it is purely mechanical, the second layer of epoxy is being held in place by the scratches in the surface of the first also known as the key.

Obviously, the primary bond is the best as strongest and therefore most desirable.

Now it may be that the copper epoxy can be applied after the tack stage but as it is a different epoxy chemically this may not be either possible or desirable, in the which case, the problem will be the amine blush.

The cheap and easy solution is hot soapy water as the blush is water soluble but you must rinse away all traces of the soap and make sure that the epoxy is thoroughly dried. Then you sand and overcoat.

The not so cheap and harder solution is peel ply. This is a fine nylon mesh that has been coated with a release agent so that the epoxy cannot stick to it. You lay the peel ply on the wet epoxy so that the peel ply becomes imbedded in the surface of the epoxy, making sure that there are no air bubbles preventing the peel ply from touching the epoxy. Then, when the epoxy is completely cured, you pull the peel ply off. It takes the top layer of epoxy with it, including the amine blush, and leaves behind an epoxy surface that is covered with imprint of the mesh, lots and lots of fine channels all over the epoxy. Think of that, removing the amine blush and keying the epoxy surface in one go.

Guess which of the two choices I'll be using!

I really did not want to wash the hull with hot soapy water and then rinsing it off with a garden hose whilst in the workshop!

Ideally, the copper epoxy may be applied before the full cure. I have asked the inventor of the system for his advice and I'm waiting to hear back from him before being able to decided what happens next.

As I said at the beginning, the waiting game...