Fiberglass seperation

Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small
strips (1/4" or so) seem to want to seperate. Is this common or did I
mix the epoxy wrong? The big parts are staying together, the fiberglass
itself is staying to gether but the small parts are seperating from the
foam.

Lou

Could be a number of things. The smaller the part, the less bonding
area there is to hold everything together and the easier it might be
for separation to occur. If the small parts and large parts are bonded
the same, the strength shouldn't change. Looks like the mechanical
application AFTER the bonding has occurred is causing the separtation,
not the bonding technique specifically. Using a wrong bandsaw blade
could also aggravate the problem, and using this technique might not be
the best route anyway. For flight structures, I always used a dremel
with a cutoff disc or saw blade to make the final cuts needed. Makes a
much cleaner cut than a bandsaw blade and no separation between the
foam and fiberglass. Hope this helps

Neal

Lou wrote:
Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small
strips (1/4" or so) seem to want to seperate. Is this common or did I
mix the epoxy wrong? The big parts are staying together, the fiberglass
itself is staying to gether but the small parts are seperating from the
foam.

Lou

It sounds like you didn't prime the foam with resin before aplying the
fabric
in the layup process. A common failure in Boats when corners are cut on the
layup
process.

Lou wrote:
Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small
strips (1/4" or so) seem to want to seperate. Is this common or did I
mix the epoxy wrong? The big parts are staying together, the fiberglass
itself is staying to gether but the small parts are seperating from the
foam.

Lou

Actually I did prime the foam first.
Lou

On 24 Sep 2006 02:28:05 -0700, "Lou" wrote:

Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small
strips (1/4" or so) seem to want to seperate. Is this common or did I
mix the epoxy wrong? The big parts are staying together, the fiberglass
itself is staying to gether but the small parts are seperating from the
foam.

Lou
I'm going to need to make some assumptions, so I'll start by assuming
that you are using epoxy such as the West System and that the foam is
the blue building material trade named Styrofoam. I'd suggest staying
away from the white foam or bead board which isn't nearly as strong.

Another assumption is substituting the word seal for prime. Typically
the foam is "sealed' with either a layer of epoxy, resin, or
microsphere or Q-cell mix (microspheres are mixed with the epoxy or
resin to reduce the weight, fill voids, and still give a good bond.)

Usually the microsphere mix works better than straight epoxy for
sealing the foam, but follow the directions for what ever you are
working on.

So... based on the above... I'll start out by saying I believe what
you are seeing is normal. I'll also note that small sandwiches of
fiberglass and foam are no where near as strong as pieces with larger
areas. I rarely see a sandwich made smaller than one inch and then
there are flanges of 3/4" to nearly 3" depending on the use.
The only pieces I've seen that didn't have a flange when they were
created were control surface ribs and bulkheads.

As far as cutting sandwiches, I cut oversize and sand to shape. As
Neal said, using the Dremel cut off rather than a band saw is a good
idea as are patience and a good dust mask. (not one of the little
fiber ones either)

NOTE the pages pointed to by the links below are relatively large with
lots of relatively small photos. A few of the photos in the
builder's diary link to larger versions. I'm using Vinyl Ester Resin,
but other than viscosity and cure time epoxy is going to work much the
same.

Control surface rib construction shown a bit over half way down on the
following page
http://www.rogerhalstead.com/G3_file.../glasair12.htm

Bulk head construction is shown about half way down the following page
with the bonding in place a bit farther down.
http://www.rogerhalstead.com/G3_file.../glasair10.htm

I'm guessing this problem is pretty much a function of size.
Small sandwiches with open edges are not strong until they have been
bonded into place. Both the ribs and bulkheads shown above are very
fragile until bonded into place and this foam is much stronger than
the blue Styrofoam (TM) Follow the instructions on what ever you are
building and good luck.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Lou wrote:
Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small
strips (1/4" or so) seem to want to seperate. Is this common or did I
mix the epoxy wrong? The big parts are staying together, the fiberglass
itself is staying to gether but the small parts are seperating from the
foam.

Lou

I have made a substantial number of parts using 1/4 inch foam as the
core material and have never experienced any problems with peeling. I
have cut the parts with a band saw as well as the dremel and never had
any problems with separation.

I believe the key issue is use of the right foam core material and
preparation. The foam must contain openings for the microepoxy to
penetrate. I spread on the microepoxy mix and pressed it into the foam
followed by the wet glass. That was covered by pealply and where
possible a layer of plastic and weight. So far, I have never had any
problems with this method.

Is it separating on both sides or just the bottom? If just the bottom
Maybe you just need a smaller insert in your table or a sacraficial
backer board and maybe a fine toothed blade

Roger (K8RI) wrote:
Both the ribs and bulkheads shown above are very
fragile until bonded into place and this foam is much stronger than
the blue Styrofoam (TM) Follow the instructions on what ever you are
building and good luck.


If you're using the blue stryrofoam, rough it up good with sandpaper
before priming it. It comes with a very smooth finish from the factory,
and there's nothing for the epoxy to grab hold of. It holds much better
if you sand off all the shiny until the surface has the texture of good
suede leather.

If you're building a smaller part that needs just a little more
stiffness, try getting a bundle of the fan folded 1/4" foam. It will
split down the middle and has a paper like film between the front and
back halves. Get it to splitting in the corner and you can slide your
hand through it in karate chop fashion to split them apart. Hold one
half up to the light, and you'll notice hundreds of pinholes. Keep the
expoxy/micro mix thin, and it will run through the holes. When you do
your layup, the two sides will be locked together with hundreds of epoxy
pins going through the foam.

I did some tests of a sample of this vs straight layups of various
thickness and compositions. Overall, the 1/8" foam sample came out at
only 60% of the weight and 50% stiffer. Trying to tear it apart around
a headlight portal, where I needed to remove the foam layer, had me
convinced that this was solid stuff (I also got to create a few new
words...but children might be reading). You won't be able to do it with
out a pair of pliers.