I'll have to try the plastic overlay approach sometime... it sounds
interesting.

Brian


"derbyrm" wrote in message
m...
I screwed up on my first boat with the wide over narrow, wet on wet. Now I
use the plastic overlay and avoid almost all the effort you describe while
still getting a high glass/epoxy ratio for taped joins. It doesn't really
matter which goes on first anymore.

Roger

http://home.insightbb.com/~derbyrm

"Brian D" wrote in message
. ..
Makes sense, but note that the gap can also be filled with thickened
epoxy mixes. If you are being religious about it, you'd use glass
microfibers plus silica (to make the mix nonsagging.) If you are going
with the wet-on-wet approach, then the outer layers of glass tend to
press down those selvage edges and what's not entirely pressed down will
typically fill with epoxy anyway ...and you can spot and fill bubbles
(syringe) after curing as well. But if allowing each layer of tape to
cure prior to applying the next, then the thing to do is to use a carbide
scraper (plus light sanding) to taper the selvage edge nicely AND fill
the remaining 'gap' (as you call it) with thickened epoxy. Most people
will just use phenolic microballoon or glass microsphere mixes for this,
but like I said, if you were entirely anal about it, you'd use glass
minifibers and silica to fill the gap with something that has a bit more
tensile strength. But IMHO, using glass minifibers and silica would be
ENTIRELY unnecessary. If the structure is weak enough to gain from such
techniques, then you've already blown it and should re-think your
engineering anyway.

Brian D


"derbyrm" wrote in message
m...
For strength, there needs to be a high ratio of glass to epoxy, thus one
squeegies (sp?) out as much resin as possible. If the selved edge of
the narrow piece creates a step that wasn't sanded down, the wider layer
of glass will bridge the step and the space under the bridge will be
filled with air. That's why the plastic sheet overlay is so effective.

Roger

http://home.insightbb.com/~derbyrm

wrote in message
ups.com...
cavelamb wrote:
(corrected to bottom posting to preserve teh thread)

If you go from the smallest piece first you have a chance of
trapping
concentric rings or squares of bubbles in the laminate. Sam


wrote:

Can you explain a bit more on your observation of this problem? I
don't quite follow you.

Thanks.

Jay Chan


You need to try it to see for yourself.

Bubbles are bad.

The are air spaces inside the laminate.

Not good for dimensional stability - or strength

But why putting the smallest piece first will increase the chance of
having air bubbles inside the laminate?

Jay Chan