Richard,
You have unwittingly got a major problem to deal with.
The problem stems from the fact that epoxy exotherm and cure is reduced by
both film thickness and additives, in your case the expancell which further
reduces resin density and increases the surface area open to moisture
retardation.
The conclusion I came to long ago when met with the first example of a
builder's dilemma similar to yours is to use the Ampreg fast hardener which,
for this purpose is really a must. I have finished 8 Europas by the way
aswell as several sailplanes and I am trained in re-enforced plastics and
you can safely assume I know a bit about this.
There appears to be a common conception that the finish is not structural
and therefore requires less attention to cure temperature and humidity. This
is absolutely not the case and in fact if anything the expencell/resin mix
must be treated to extra care for the reasons mentioned above.
If any non cured or partially cured resin remains before applying further
finish coats, even if it is sandable, which yours clearly is not, then the
whole thing will require refinishing within a year of looking complete. This
will be due to the hydroscopic nature of the hardener continuing to absorb
moisture through the finishing layers LONG after it initially reacted more
readily with moisture than resin and retarded its own cure. Both persistent
osmosis and film adhesion problems are the end game if not properly treated
first.
I sympathise but you must remove the finish cancer that you have
accidentally seeded. There is not nearly enough attention to this in the
manual in my opinion.
Let this post be another warning to others, you can contact me off line for
more detail on what must be done to remedy this.
Regards
Gary McKirdy
garymckirdy@gloverb.freeserve.co.uk
---- Original Message -----
From: "Richard" <riddon@btinternet.com>
Subject: sticky poxy
> I am filling & sanding my flying surfaces at present. Most of the major
> filling & sanding is done but I mixed a batch of filler about a week ago
> which is still sticky. I used factory supplied ampreg and expancell. I was
> filling in some small dents and 'craters' so I smoothed a very thin layer
> over the whole surface and finished it off by running a warm spatula over.
> It hasn't gone off properly. It feels slightly tacky to the touch and my
> sandpaper clogs up very quickly with sticky blobs when I try to rub it
back.
>
> I wondered if it might be Amine Blush so have tried scrubbing the surfaces
> both with a vinegar solution and with a detergent solution but to no
avail.
>
> Has anyone else experienced a similar problem. If so, what have I done
wrong
> and how do I avoid a repetition. Also any suggestions how I might remove
> this sticky mess so that I can start again.
>
> Richard Iddon G-RIXS (was filling & sanding, now twiddling my thumbs!)
>
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