Mylar Adhesive "Best Practices"

For the benefit of the group, let's hear about what works for
re-attaching mylar.

I had an older generation sailplane that when I got it had fabric tape
for sealing the ailerons and elevator, but it was due for replacement so
the upgrade was to mylar. Removed the old tape and used acetone with
lots of elbow grease and paper towels to remove the gum residue from the
tape. We used "Tessa Tape" from W&W and applied that and prior to
removing the backing pressed it down onto the gelcoat very firmly. Then
we put the mylar onto that and pressed it down firmly again. Followed
that with the safety tape and no issues for 4 years.

With that said, I later bought a factory glider and within 1.5 years a
portion of mylar was coming up on a short stretch of aileron. I removed
the mylar, cleaned with acetone, followed the same procedure as above
and that section was again coming up about 1.5 years later.

The tessa tape is very sticky stuff. I did not scuff the mylar in
either case, but in the second case, the mylar was pulling up from the
tape, not the tape pulling up from the gelcoat.

Gary Emerson wrote:
For the benefit of the group, let's hear about what works for
re-attaching mylar.

I had an older generation sailplane that when I got it had fabric tape
for sealing the ailerons and elevator, but it was due for replacement so
the upgrade was to mylar. Removed the old tape and used acetone with
lots of elbow grease and paper towels to remove the gum residue from the
tape. We used "Tessa Tape" from W&W and applied that and prior to
removing the backing pressed it down onto the gelcoat very firmly. Then
we put the mylar onto that and pressed it down firmly again. Followed
that with the safety tape and no issues for 4 years.

With that said, I later bought a factory glider and within 1.5 years a
portion of mylar was coming up on a short stretch of aileron. I removed
the mylar, cleaned with acetone, followed the same procedure as above
and that section was again coming up about 1.5 years later.

The tessa tape is very sticky stuff. I did not scuff the mylar in
either case, but in the second case, the mylar was pulling up from the
tape, not the tape pulling up from the gelcoat.

I would be very careful about using Acetone on a glider, depending on the
construction you could do damage. Reliable sources indicate that acetone can
penetrate the structure and damage the foam core in GRP/foam sandwich structures.

Not being a composites specialist I can't comment. Just try to use something a
little less aggressive - like MEK.

Any experts out there?

"Bruce Greef" wrote in message
:

snip


I would be very careful about using Acetone on a glider, depending on the
construction you could do damage. Reliable sources indicate that acetone can
penetrate the structure and damage the foam core in GRP/foam sandwich structures.

Not being a composites specialist I can't comment. Just try to use something a
little less aggressive - like MEK.

Any experts out there?





Bruce, not an expert. but I have personal first hand experience that
repair specialists use acetone routinely to clean composites when
working with gelcoat and uncoated GRP/foam. If you soaked the composite
or left it on there a long time, I could see where perhaps it could
damage something underneath, but a brief exposure for cleaning would
appear to be OK.



Larry

"01" USA

Bruce Greef wrote:

I would be very careful about using Acetone on a glider, depending on
the construction you could do damage. Reliable sources indicate that
acetone can penetrate the structure and damage the foam core in GRP/foam
sandwich structures.

I'd agree. Speaking as a model builder who molds his own composite
structures for wing D-boxes and fuselages, I'd like to make the
following points:

- the glass/carbon skin *should* be impervious to liquids but you
never know. The problem with making light, strong composites is
to get excess resin out of the layup after you've wetted out the
glass or carbon. If the wetting is thorough then blotting out as
much resin as possible and then curing under vacuum will leave
you with a compacted structure with no pinholes etc. However, if
the wetting wasn't right you will get starved looking patches that
may well be porous.

- Model dope thinner is mostly acetone. This dissolves white polystyrene
foam almost instantly. A standard way of making complex one-off glass
fuselage shells, fuel tanks etc. is to carve the shape from white
foam, cover it with glass cloth and epoxy and, when the epoxy is
cured, pour thinners onto the foam. Result: an empty shell all ready
for finishing.

- acetone wets composite surfaces really well and will wick through the
finest pores or cracks.

The moral is to test any unknown liquid of a scrap of foam (if you can
get one) before putting it on your glider unless you're certain that the
area you're working on is absolutely impervious to liquids *and* you're
sure the liquid can't run onto any part of the structure that might be
porous, cracked or has poorly adhering glue lines.

HTH


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Bruce Greef wrote:
..

I would be very careful about using Acetone on a glider, depending on the
construction you could do damage. Reliable sources indicate that acetone can
penetrate the structure and damage the foam core in GRP/foam sandwich structures.

Not being a composites specialist I can't comment. Just try to use something a
little less aggressive - like MEK.

Any experts out there?

I'm not going to call myself an expert but MEK is a much More Agressive
solvent on many substances. If I recall correctly many gelcoats are
styrene based. MEK will dissolve styrene quite readily, actually it is
was is used for model glue.

MEK also seems to disolve brain cells too, which may or may not be a
problem depending on what memories you want to keep.

Chris

FRP is not a tight surface *at all* (even if you don't see any pores).
Soaking a FRP part in acetone is certainly not a good idea.
However, wiping such a surface with acetone to remove grease or whatever
doesn't put a problem because the thin film of aceton left behind will
rapidly evaporate from the surface.
On gelcoat, however, I wouldn't use acetone, but rather ethyl alcohol.

"Martin Gregorie" wrote in message
...
Bruce Greef wrote:

I would be very careful about using Acetone on a glider, depending on the
construction you could do damage. Reliable sources indicate that acetone
can penetrate the structure and damage the foam core in GRP/foam sandwich
structures.

I'd agree. Speaking as a model builder who molds his own composite
structures for wing D-boxes and fuselages, I'd like to make the following
points:

- the glass/carbon skin *should* be impervious to liquids but you
never know. The problem with making light, strong composites is
to get excess resin out of the layup after you've wetted out the
glass or carbon. If the wetting is thorough then blotting out as
much resin as possible and then curing under vacuum will leave
you with a compacted structure with no pinholes etc. However, if
the wetting wasn't right you will get starved looking patches that
may well be porous.

- Model dope thinner is mostly acetone. This dissolves white polystyrene
foam almost instantly. A standard way of making complex one-off glass
fuselage shells, fuel tanks etc. is to carve the shape from white
foam, cover it with glass cloth and epoxy and, when the epoxy is
cured, pour thinners onto the foam. Result: an empty shell all ready
for finishing.

- acetone wets composite surfaces really well and will wick through the
finest pores or cracks.

The moral is to test any unknown liquid of a scrap of foam (if you can get
one) before putting it on your glider unless you're certain that the area
you're working on is absolutely impervious to liquids *and* you're sure
the liquid can't run onto any part of the structure that might be porous,
cracked or has poorly adhering glue lines.

HTH


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Gary Emerson wrote:
For the benefit of the group, let's hear about what works for
re-attaching mylar.

I had an older generation sailplane that when I got it had fabric tape
for sealing the ailerons and elevator, but it was due for replacement so
the upgrade was to mylar. Removed the old tape and used acetone with
lots of elbow grease and paper towels to remove the gum residue from the
tape. We used "Tessa Tape" from W&W and applied that and prior to
removing the backing pressed it down onto the gelcoat very firmly. Then
we put the mylar onto that and pressed it down firmly again. Followed
that with the safety tape and no issues for 4 years.

With that said, I later bought a factory glider and within 1.5 years a
portion of mylar was coming up on a short stretch of aileron. I removed
the mylar, cleaned with acetone, followed the same procedure as above
and that section was again coming up about 1.5 years later.

The tessa tape is very sticky stuff. I did not scuff the mylar in
either case, but in the second case, the mylar was pulling up from the
tape, not the tape pulling up from the gelcoat.

Now that we've established that the only solvent safe to use on a
composite glider is the sweat from a virgin Las Vegas showgirl,
can anyone answer Gary's question?

Thx,

Shawn

Yikes.

I once had to do extensive re-repairs to a glider whe
- a previous repairer had spliced in new wing skins
- during the repair he liberally "cleaned" with MEK
- the MEK went through the joint, and disolved the foam.
This glider flew for a while, and when it was involved in
another accident the skins all cracked in the areas
where they were no longer supported by the foam core.
All the replaced skin areas had to be re-spliced !

For heavens sake, if you aren't expert, don't go
messing about with solvents you heard recommended
on RAS. Someone could get hurt, maybe you.

Be safe out there !
Best Regards, Dave

Bruce Greef wrote:
Not being a composites specialist I can't comment. Just try to use something a
little less aggressive - like MEK.

Any experts out there?

"Shawn" wrote in message
. ..
Gary Emerson wrote:
For the benefit of the group, let's hear about what works for
re-attaching mylar.
Now that we've established that the only solvent safe to use on a
composite glider is the sweat from a virgin Las Vegas showgirl,
can anyone answer Gary's question?

Thx,

Shawn



Hmmm, let me get the mental image here . . . Nah, ain't gonna find one of
those I bet!

I sort of thought we had answered Gary's question, but will add:

If the double sided tape has come loose in just one spot, simply pushing it
back down will not work or work for long. You might get away with raising
the Mylar seal and quickly wiping the detached surfaces with a Q-tip dipped
in Acetone. Then warm the surface and use pressure to re-bond the tape. This
will work for a while . . . but is not a long term fix.

If the debonded area is at the end of the tape, then remove the top seal
tape and peel back the Mylar until you get past the debonded area (the Mylar
doesn't come off easily). Tape the Mylar out of the way. Remove the old
double sided tape in the affected area. If there's adhesive residue to deal
with, before trying solvents, try using some packing tape or cloth tape like
a "tack strip" - - apply tape to old residue, push down and then pull
straight up. In many cases, sometimes after several applications of the tack
strip, the old adhesive residue will be cleanly removed. Sand, clean,
replace double sided tape as previously noted and as you would if replacing
Mylars.

all the best,

bumper

bumper wrote:
"Shawn" wrote in message
. ..
Gary Emerson wrote:
For the benefit of the group, let's hear about what works for
re-attaching mylar.
Now that we've established that the only solvent safe to use on a
composite glider is the sweat from a virgin Las Vegas showgirl,
can anyone answer Gary's question?

Thx,

Shawn



Hmmm, let me get the mental image here . . . Nah, ain't gonna find one of
those I bet!

I sort of thought we had answered Gary's question, but will add:

If the double sided tape has come loose in just one spot, simply pushing it
back down will not work or work for long. You might get away with raising
the Mylar seal and quickly wiping the detached surfaces with a Q-tip dipped
in Acetone. Then warm the surface and use pressure to re-bond the tape. This
will work for a while . . . but is not a long term fix.

If the debonded area is at the end of the tape, then remove the top seal
tape and peel back the Mylar until you get past the debonded area (the Mylar
doesn't come off easily). Tape the Mylar out of the way. Remove the old
double sided tape in the affected area. If there's adhesive residue to deal
with, before trying solvents, try using some packing tape or cloth tape like
a "tack strip" - - apply tape to old residue, push down and then pull
straight up. In many cases, sometimes after several applications of the tack
strip, the old adhesive residue will be cleanly removed. Sand, clean,
replace double sided tape as previously noted and as you would if replacing
Mylars.

all the best,

bumper


I have had experience removing tape adhesive using adhesive remover
made by PPG and 3M. I don't have the part number in hand for these,
but you can get information on the web. The adhesive remover does not
contain acetone or MEK and is not nearly as volitile, however it is
flammable. It states that it does not leave a residue. It must have
time to evaporate thoroughly, before any new tape should be applied.
Another possible adhesive remover is a citrus based "goof-off" or
another citrus cleaner. Gel coat is micro porous, but the volitile
fluids like acetone if used very sparingly on a clean rag should not
cause issues with the sub structure. I agree to use caution if you are
not sure, don't use it.

When placing the new tape be sure the surface has no wax or any other
residue. My tapes have held on fine for several years. I used the
TESA tape from W& W's and new mylar with the seal tape over as
described at length above. I used a plastic squeegee to smooth the
pressure on the tape and had no voids in the adhesion. The whole
assembly was then rubbed down and allowed to sit a couple of days
before flying. This allowed the tape to achieve maximum adhesion
charachteristics.

I think the operative condition is clean and dry before applying new
tape and seals.