Hi everyone,

You will find the shrinkage in all epoxies. I have worked for years on gliders and you will see the sam thing there through a gelcoat. The epoxy will shrink and the gelcoat will shrink. The only way around it is to fly a nearly infinished glider for one year and do the final finishing after that. The shrinkage after one year is usually minute.

There is a high risk associated with post cure. The epoxy softens!! when you heat to approximately 50 - 65 deg C. Typically the postcure is done in proper molds and significant care is taken that the molds can deal with this temperature without distortion. If your wooden boat has significant internal stresses, you will find that a postcure will deform the boat. The degree of deformation is dependent on the internal stresses. Furthermore the air in the wood will expand and you may see local lifting of the fiberglass as the epoxy softens under heat.

I would certainly not recommend a postcure at high temperatures of a wooden boat. The best option to minimize the effect of the fiber glass texture showing through is to use two 3oz layer with a tight weave instead of one 6 oz layer. This is at least my plan although it increases the cost.

Andreas

: Hi gang - My post of September 4 regarding the changes in epoxy/varnish
: finishes on my boats only brought one response. I emailed MAS Epoxies with
: the same question. Here is their verbatim reply: In a message dated
: 9/11/2000 2:13:49 PM Eastern Daylight Time, MASEPOXIES writes: > J: Yes
: pro builders have the same problem. What you are experiencing is a very
: well known phenomina of immaging or printrhrough. This means two thing,
: one you sevel of finsih and gloss are excelent, and two your boats are
: aging in a normal fashion and experiencing a slight degree of additional
: curing. With this slight additional cure comes a minute amount of shrink
: and thus immaging of the glass especially noticable on a dark very glossy
: finish. To reduce the immaging the boat needs to be thermally aged prior
: to final sanding and finish. How to do this is the tough part. Some folks
: heat (120-130) then cool the part a few times (thermal cycling) just like
: in real life. In simple terms the next time you sand and refinish the
: problem will likely dessapear for ever unless the boat is taken to a yet
: warmer environment (southern floridda and stored in a black bag). The pros
: tell the owners that their is always going to be some immaging and when
: they repaint the boat the problem will releave itself. Sorry I can't be of
: greater help.

: Thanks for your question Tony

: In spite of the typos, I thought the response was very informative. None of
: the books I've read on strip building mentions the effect, although it is
: apparently common. Is this effect only with MAS, or does West , System 3,
: Raka, etc. have the same problem? I wonder how I could "thermally
: age" the epoxy without exposing it to sunlight with no UV protection.

: I will still build! - John