Epoxy and Saran wrap question
wohlsen
construction.
I have heard that common epoxies used in composite construction do not adhere to
plastic films such as Saran wrap. Is this correct? If so is it feasible to
employ it as a release agent when building a thin wall, non-structural component
such as a cowling? That is, can I wrap a male plug made of styrofoam with
Saran wrap, lay on the epoxy and glass, smooth and fill to desired finish, and
then pull out the plug and add any internal bracing necessary to maintain its
shape?
Thanks for any comments.
ransom@roboben
: Thank you to all who responded to my previous query concerning foam core
: construction.
:
: I have heard that common epoxies used in composite construction do not adhere to
: plastic films such as Saran wrap. Is this correct? If so is it feasible to
: employ it as a release agent when building a thin wall, non-structural component
relatively easy to have wrinkles and folds in the saran wrap, which then
are obviously in your end-product. Also, w/out vacuum pressure, I'm sure
that there is likely more epoxy and therefore more weight left in the result.
I've used this method making a gas tank male plug as a way to get the
fiberglass around corners held down to the foam core during cure. It looks
like it is a sticky mess, but after cure, the saran comes right off -- magic!
--
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Ben Ransom (*)
UCD Mechanical Engineering Dept. o o
bwra...@ucdavis.edu, (916)752-1834
Peter Ashwood-Smith
Most of the epoxies I'm familiar with do not stick well to Saran wraps
but that does not mean they will pull free of the Saran wrap! Whap happens
is that any little crease in the plastic will get surrounded by the epoxy
so that you will be left with little crevaces in the epoxy with bits of
folded Saran wrap stuck in them. I think you would be better to use a
proper mould release agent or wax. Actually I managed to use tin foil
with wax once when I wanted a real quick mold, it worked ok but I would
not do it for anything that requires finishing.
Peter
Stetson E
>I have heard that common epoxies used in composite construction do not
>adhere to
> plastic films such as Saran wrap. Is this correct? If so is it
feasible to
>employ it as a release agent when building a thin wall, non-structural
component
> such as a cowling? That is, can I wrap a male plug made of styrofoam
with
>Saran wrap, lay on the epoxy and glass, smooth and fill to desired
finish, and
>then pull out the plug and add any internal bracing necessary to maintain
its
>shape?
What I normally use as a release over something rough like a styrofoam is
silver duct tape. It sticks to the male plug making it easier to do the
layup over, and provides a good release. With a little cutting, it can be
worked around compound curves pretty easily. You can overlap pieces if
necessary. It'll never show on the outside of the part.
I've used saran wrap before. While it won't stick to your layup, I've
found it sometimes won't come off in one piece, leaving you to peel and
pick off the little remaining pieces.
Stet Elliott
Stet...@aol.com
Long-EZ builder
Paul Dunn
layups. We do not have this brand in Australia, but I assume it is extremely thin
polyethylene used as a food wrap.
The problems described can be avoided by using thick polyethylene sheeting which can be
bought quite cheaply in large sheets in hardware stores. Epoxy resin will not adhere to this
and it can be very easily peeled off and indeed reused many times. This thick polythene
gives a fairly smooth surface and acts as a poor-man's vacuum bag if you squeeze out
the resin a bit. It leaves a smooth surface which can be quickly sanded for bonding without
cutting into the underlying glass. It is much cheaper than peel ply and uses less resin as it
doesn't soak it up and can compress the layup slightly. Being transparent like the Saran, the
layup can be seen through the plastic and checked for air bubbles.
Paul Dunn
CSIRO Division of Manufacturing Technology
Machine Vision group
Melbourne, Australia
Seahawk/Glass Goose builder
G. A. Venkatesh
>
>The problems described can be avoided by using thick polyethylene sheeting
>which can be
>bought quite cheaply in large sheets in hardware stores. Epoxy resin will
>not adhere to this
>and it can be very easily peeled off and indeed reused many times. This thick
>polythene
>gives a fairly smooth surface and acts as a poor-man's vacuum bag if you
>squeeze out
>the resin a bit. It leaves a smooth surface which can be quickly sanded
>for bonding without
>cutting into the underlying glass.
>It is much cheaper than peel ply and uses less resin as it
>doesn't soak it up and can compress the layup slightly. Being transparent
>like the Saran, the
The role of plastic sheets is definitely underplayed in most construction
manuals and books. It is absolutely essential for working glass around
corners and bends, for keeping glass pieces from distorting while doing a
layup, for preventing dripping, to prevent bubbling in the skin while curing,
etc.
However, I would not consider it as a replacement for peel ply. If you buy
Dacron from a fabric store, peel ply is cheap. When peel ply soaks up resin,
that is resin that comes off of the structure, unlike plastic where the resin
stays on the surface. More important, with peel ply you don't have to sand
before you do another layup on it. With plastic wrap you have to.
I keep a variety of plastic sheets at hand of varying thicknesses (including
cling wrap). Some thicknesses are better suited for some jobs than others.
venky
tenh...@ix.wcc.govt.nz
>I have seen many references over the years to the use of "Saran wrap" on epoxy glass
>layups. We do not have this brand in Australia, but I assume it is extremely thin
>polyethylene used as a food wrap.
>
>The problems described can be avoided by using thick polyethylene sheeting which can be
>bought quite cheaply in large sheets in hardware stores. Epoxy resin will not adhere to this
>and it can be very easily peeled off and indeed reused many times. This thick polythene
>gives a fairly smooth surface and acts as a poor-man's vacuum bag if you squeeze out
>the resin a bit. It leaves a smooth surface which can be quickly sanded for bonding without
>cutting into the underlying glass. It is much cheaper than peel ply and uses less resin as it
>doesn't soak it up and can compress the layup slightly. Being transparent like the Saran, the
>layup can be seen through the plastic and checked for air bubbles.
Paul,
Think Glad Wrap - same stuff.
After a year or so of using both of these methods - yours and the thicker
plastic I found that Parka Nylon ( as per old ladies bowling jackets!)
purchased in fabric stores did all of the above, you didn't have to remove
it until cure and it didn't need sanding.
This fabric is thin and conforms well. If really curved surfaces are
involved, you can put several segments on. If shape is important you
can draw the shape of the laminate on the other side of the nylon
then wet out your layup on the first side. This allows you to adjust
the fibers and counter any tendancy for the layout to distort as you
stipple or squeegee. You can also cut it to shape after wetting if
you want to ( and your scissors are sharp!)
If you use white fabric you can see through it very well when it is wetted
out. The actual fabric is not that important - as long as you can
use the fact that epoxy has poor peel strength and the resin does not
impregnate the peel ply.
Cheers
John ten Have
SidLloyd
>The actual fabric is not that important - as long as you can
>use the fact that epoxy has poor peel strength and the resin does not
>impregnate the peel ply.
Word of caution: test any fabric you buy prior to doing any large
peel-ply. I bought some dacron and apparently it wasn't strong enough.
It took a couple of hours of tearing off tiny bits of dacron before it was
all off!
-------------------------------------------
Sid Lloyd
Cozy IV under construction, GlaStar in the batter's box...
email: SI...@bangate.compaq.com or SidL...@AOL.com
Don't blame Compaq for my opinions
