----- Original Message ----- From: "Isaac OLEG" <oleg-i@wanadoo.fr> To: <pianotech@ptg.org> Sent: July 31, 2002 7:35 AM Subject: RE: CA gluing Grand Pin blocks....My take on it/ Richard Brekne > Hi ! > While using the thin epoxy coating holes method (and new bridge pins) > for pins that don't hold quite enough and little cracks on bridges, I > am not very sure of the holding in time of this material. > > Composite material mixing wood and epoxy will not age the same. > Epoxy used in gems (agates) to mask little defects (by inclusion under > high pressure) are first quality, and they show their presence in time > as they decompose. All epoxies--along with most other plastics--are susceptible to breakdown when exposed to ultraviolet light. They are quite stable when protected with either paints or clear finishes containing UV blockers. These UV blockers can take the form of pigments mixed into the material itself or can be included in a clear coating such as most any exterior-grade lacquer or varnish. Boats using epoxy extensively have survived quite nicely for 50+years so far and I assume--though I could be wrong--that epoxy technology has improved some during that time. > > Epoxy as the kind I use is the same as used for marine work for glass > fiber work, and don't have much strength by itself. > I believe that it will became brittle and probably dusty in awhile, > even if the sounding results are evident and the holding very good at > first. Most marine fiberglas work is done with polyesters--quite a different material from epoxy. You are correct, polyester has relatively little strength of its own. Only in matrix with the fiberglas cloth does the combination attain high strength. Many types of epoxy are used for boat building and boat repairs, but not often for fiberglas construction--it's too expensive even though its strength characteristics are vastly superior. Epoxy is quite a different material from polyester. But, as I said, it must be protected from UV light. In the case of bridge repairs, with the epoxy down in a hole somewhere, no light of any kind can get to it and it will be very stable. Even using it as a soundboard coating--as described in my current Journal articles--it will be stable as long as it is coated with an exterior-grade lacquer or varnish containing UV blockers and as long as the piano is kept indoors and generally away from direct sunlight shining on the soundboard surface. And if the piano is kept outdoors--at least where I live--I'd be more worried about how the rain than I would the sun.... > > Beside, the wood aging will probably be slower once coated, Epoxy is > certainly used in restoration of old wood for museum pieces, but then > they are suppose to stay in a stable H.R. environment (and not > submitted to vibration). Epoxies--unlike CA's--have good resistance vibration. Del
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