Epoxy's and ferro-cement

Epoxy's and ferro-cement

I have always believed that the expansion rate of ferro-cement and epoxy are roughly the same, and have used epoxy extensively on my boat to attach various wooden fittings to the hull. Recently however I used it to attach a circular wooden base to the deck to house a solar vent, and the fitting has pulled away on one side. The timber used was fairly hard (might be oak), and there seems to be ferro still stuck to the epoxy. There are under-deck fittings stopping me from putting screws in from underneath. What's the best course of action.

Dave Carroll....davecarroll@postbox.co.nz

Hi Dave, interesting problem and not unusual. As is common there is a difference in the practical applications of a definition from the pure theoretical one. Yes the two do have different expansion rates, but there are many practical uses where adverse effects are minimal. From experiments done back in the 60's, it seems that conclusions were drawn that as a mix the two could not be combined for hull construction for any lasting positive use. Over the years I have experimented more and more as well as studying the results of epoxy use on ferroboats. Although I have not used it in a mix during construction.....I have used it to make a mortar mix for larger repairs....in small quantities as a filler....as a protective skim and surfacer....as an adhesive direct to both hulls and decks for fitting out. In all instances considerable care and preparation is needed as there are many pitfalls leading to failure. In your case it's hard to define the problem accurateley without seeing first-hand. I would hazard a guess that the plaster deck in the area where it has lifted, was faulty with either voids, sandwich effect, or a surface crust formed from too much/or metal floating by the plasterer. Regards

Colin Brookes....colb@xtra.co.nz

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