Masking Tape Damage to Nitrocellulose Lacquer...............
Guitarmakermark
Unmasked a nitro-finished guitar on which I did some repairs, found to
my dismay that the guitar's back has distinct lines and mottling in
the nitro where the tape had resided.
I'm presuming some chemical compound (a plasticiser?) in the tape's
adhesive has migrated into the nitro lacquer, swelling the finish
under the tape.....the tape was on the guitar for several days.
I am hoping the lacquer will offgas the offending compound over the
next several days, and that I won't need to sand the swelled area flat
and buff out.
Indeed, it seems to me that it would be counter-productive to level-
sand so early in this process, since the lacquer might settle back
down to "normal" on its own, and to sand it out at this point would
result in a negative image of the same damage later on, due to finish
shrinkage after sanding, as a result of the off-gassing.
Has anyone here had this problem?
Any thoughts, please?
Thanks!
Mark
David Hajicek
before. But as you say, give it a day or two to outgas and maybe it will
correct itself.
Is it just swelling or is it also cloudy?
Dave Hajicek
"Guitarmakermark" <Guitarm...@Yahoo.com> wrote in message
news:9f1697b7-6b46-4e89...@k13g2000prh.googlegroups.com...
Guitarmakermark
Nice to see you again!
I forgot to mention, this was indeed the blue "long mask" tape from
3M.......I just left the tape on the guitar too long.
To answer your question, I don't see any cloudiness in the affected
area of finish, just seems like swelling only.
Let me know what you think, David, and thanks again for answering up.
Mark
David Hajicek
Here's one more thought.
Maybe the tape transferred solvent from the nitro you sprayed through the
tape to the finish? If that is the case, the swelling should go down by
itself.
If the finish isn't cloudy, that's good news. I would put some low heat
(lamp, sun) on the affected area and try to cook off the solvent or
whatever. After a day or two, I would sand it flush and polish it out.
Let me / us know how it goes. And good luck.
Dave
"Guitarmakermark" <Guitarm...@Yahoo.com> wrote in message
news:29f85af0-37cc-4004...@l5g2000pra.googlegroups.com...
Guitarmakermark
I had not sprayed any finish on this guitar. The tape on the guitar's
back was the tail end of having masked off the top for fretboard
reshaping and re-fretting.
I would be nervous about applying heat to this swelled area of finish;
I think I would rather wait several days to let it offgas naturally,
then re-level and polish.
Thanks again!
Mark
Benoit Meulle-Stef
Dear Mark:
What guitar is it?
Benoit
Guitarmakermark
It's a Martin D-28, Circa 1994.
Mark
David Hajicek
"Guitarmakermark" <Guitarm...@Yahoo.com> wrote in message
Benoit,
Mark
> Dear Mark:
> What guitar is it?
Mark:
I have seen what you describe from laying a finished guitar on a vinyl mesh
pad. I got a little bump every place it touched. I think I sanded it back
and added another coat of finish. And that worked fine.
As you say, wait a few more days until it shrinks back as much as it can.
By then it won't shrink any more for an awful long time, if any.
The bumps could be very small as the shinyness of the finish amplifies the
appearance.
Good luck.
Dave
Dave
Guitarmakermark
Yep......we all know about that nasty vinyl allowing its plasticizer
compounds to leach into lacquer. It just never occurred to me the
same type of problem would occur with 3m blue tape! My fault, though,
for leaving the tape on the instrument for so long.(several days.)
The re-fret turned out really well, though, and I made and installed a
bone nut and saddle. The guitar now speaks with a much greater
authority than before, finish goof-up notwithstanding.
This Martin had taken a fairly significant set (up-bow) in its rather
rubbery neck, so it was time to plane the fretboard in addtion to re-
fretting with Martin's oversize fretwire. The fretboard had .036 of
relief, without strings. Has correct and controllable relief now,
since the re-fret.
Now I just need to set the finish straight, before surrendering the
instrument to its rightful owner!
Take care, and thanks again!
Mark
Benoit Meulle-Stef
Benoit
Alan D.
the Blue long mask is NOT to be useed for lacquer. 3-M says that the ONLY tape
for lacquer is the Green.
That being said, the green tape is now labeled as "Painter's Tape" or similar
and there is _no_ mentiong of lacquer on the inside printing. The green tape
_use to be_ labeled specifically for lacquer, same tape number. But when they
went to calling it painters tape it too started makeing this wrinkly track line
stuff on lacquer. What a disaster, had to completely sand back level and
re-spray a dread because of that.
I have found that if you use it on older lacquer it is not so much of a
problem. On newer lacquer, such as finish that has cured out a month and had
been buffed, then you can get away with masking for short (less than a day)
time periods. But don't leave it on overnight. This makes for a PITA if you are
doing things like a sunburst to the top and want to mask off the rest. You
shoot part of the burst and then have to pull all the masking. Then replace it
all the next day for the next pass of the burst, etc. Similar for repairs and
such.
3-M swears that it is the same formulation, but my experience says it is not.
The old green tape could be left on new lacquer for a week w/o problems. As I
mentioned earlier... Arrrrrggggghhhh! I haven't found any other brands of tape
to be safe on lacquer, new or old.
Alan D.
Guitarmakermark
I guess I'm glad to find out I'm not the only one to encounter this
hidden trap!
I read in Stew-Mac's Guitar Repair Guide about a self-adhesive paper,
called Sign-Painter's tape, which supposedly is useful for masking
guitars.
Me wonders if the adhesive on that material will present the same
problem.........hmmmm.........there's a sign painter right around the
corner from where I work....think I'll go ask him about that stuff.
Thanks for posting, Alan.
Mark
Cyberserf
> Arrrrrggggghhhh! I have been around and around with 3-M on this. They say that
> the Blue long mask is NOT to be useed for lacquer. 3-M says that the ONLY tape
> for lacquer is the Green.
>
> That being said, the green tape is now labeled as "Painter's Tape" or similar
> and there is _no_ mentiong of lacquer on the inside printing. The green tape
> _use to be_ labeled specifically for lacquer, same tape number. But when they
> went to calling it painters tape it too started makeing this wrinkly track line
> stuff on lacquer. What a disaster, had to completely sand back level and
> re-spray a dread because of that.
>
> I have found that if you use it on older lacquer it is not so much of a
> problem. On newer lacquer, such as finish that has cured out a month and had
> been buffed, then you can get away with masking for short (less than a day)
> time periods. But don't leave it on overnight. This makes for a PITA if you are
> doing things like a sunburst to the top and want to mask off the rest. You
> shoot part of the burst and then have to pull all the masking. Then replace it
> all the next day for the next pass of the burst, etc. Similar for repairs and
> such.
>
> 3-M swears that it is the same formulation, but my experience says it is not.
> The old green tape could be left on new lacquer for a week w/o problems. As I
> mentioned earlier... Arrrrrggggghhhh! I haven't found any other brands of tape
> to be safe on lacquer, new or old.
>
> Alan D.
>
> >Hello All,
>
> >Unmasked a nitro-finished guitar on which I did some repairs, found to
> >my dismay that the guitar's back has distinct lines and mottling in
> >the nitro where the tape had resided.
>
> >I'm presuming some chemical compound (a plasticiser?) in the tape's
> >adhesive has migrated into the nitro lacquer, swelling the finish
> >under the tape.....the tape was on the guitar for several days.
>
> >I am hoping the lacquer will offgas the offending compound over the
> >next several days, and that I won't need to sand the swelled area flat
> >and buff out.
>
> >Indeed, it seems to me that it would be counter-productive to level-
> >sand so early in this process, since the lacquer might settle back
> >down to "normal" on its own, and to sand it out at this point would
> >result in a negative image of the same damage later on, due to finish
> >shrinkage after sanding, as a result of the off-gassing.
>
> >Has anyone here had this problem?
>
> >Any thoughts, please?
>
> >Thanks!
>
> >Mark
Yup...green is clean.
-CS
David Hajicek
Any thoughts on the light blue plastic artist striping tape?
It sounds like one shouldn't leave any tape on lacquer for very long.
Dave Hajicek
Guitarmakermark
Fortunately, the guitar I was working on sanded out and buffed out
just fine.
Many thanks to all who posted!
Mark
Alan D.
I haven't had much trouble with the light blue striping tape, but in general
one doesn't leave it on very long. I mostly use it for masking bindings and I
pull it while the finish is still curing out. That being said, I don't use it
any more, I use the grey/brown looking plastic stuff from the automotive paint
store. They come in various thicknesses and are pretty solvent resistant. I
like to use them for masking the binding on mandolins when shooting colors. It
is just a bit stretchy so you can wrap it around moderate corners and it lays
down rather nice. If you leave it on too long though the adhesive gets a bit
gummy but you can clean it with naphtha. The only caution with this is that is
plastic, so you need to be careful not to shoot too much over the tape in one
pass or it might develop runs, the stains and finish don't really stick to it.
Alan D.