Blistering of Finish

[Uniform Zulu]

I'm looking at purchasing an LS-3 but the owner has
noted that the Urethane finish has blistered in several
places on the tops of the wings (The glider was re-finished
in 1996). According to the owner they are very small
blisters which have left pin sized holes. I'm assuming
that this would be caused by mositure which has made
it's way below the paint? He says the trailer is dry
and has a soler vent so I would assume humidity in
the air has caused the problem? and not moisture on
the surface.

What are the implications/underlying problems of the
blistering? and could I fix this easily or am I looking
at sanding down/re-finishing the entire surface of
wings again in the near future?

Any advice would be appreciated.

[JJ Sinclair]

Moisture in the trailer has reared its ugly head once again. The
trailer doesn't have to leak in order to get it in there, it can (and
does) come from condensation. Think about what goes on in there after
you put the bird away at 5:00 PM on a humid aftrenood? Sun goes down
and the outside gets cold, but the inside is still warm and moisture
forms on the inside of the trailer. By 9:00 PM the inside air has
cooled down, but the ship is still warmer than the inside of the
trailer and moisture forms on the ship. Only way to stop this process
is to put the trailer inside a building (that's where my ship is for
the winter) or open it up and let everything air out at least once a
month. Blisters can form on Urethane in about 3 months if the above is
ignored.

What to do? Re-finish it and use Acrylic Urethane next time which
resists moisture much better, but isn't immune to the moisture bug.
The good news is the re-finish of a blistered bird wouldn't be nearly
as much as re-finishing a getcoat'd machine..................probably
about half as much. I have heard quotes as high as 25K. I have been
working with a real craftsman who is getting into the re-finish
business here in the Western US. He is quoting 15K + materials (PPG
Acrylic Urethane is up to $400/gal and it takes 3 gal to do a 15 meter
bird). Send me a note and I'll put you onto this guy. Personally, I
think anyone is nuts to get involved with the nasty business of re-
finishing sailplanes which involves 300 hours of grinding, filling,
sanding, priming, contouring, more priming, more sanding, then finally
painting the nasty stuff (if you can smell it your killing brain
cells)................and your not done yet, next comes wet sanding
with 600 and 800, then buffing.......oh, I forgot the trim and
numbers and yes, Charlie, we'll be sure and put a big black number on
the underside of the right wing, then wet-sand and buff them out for
you.
My, My, how I have carried on, Cheers,
JJ

[[email protected]]

On Dec 23, 11:21 am, JJ Sinclair > wrote:
> Moisture in the trailer has reared its ugly head once again. The
> trailer doesn't have to leak in order to get it in there, it can (and
> does) come from condensation. Think about what goes on in there after
> you put the bird away at 5:00 PM on a humid aftrenood? Sun goes down
> and the outside gets cold, but the inside is still warm and moisture
> forms on the inside of the trailer. By 9:00 PM the inside air has
> cooled down, but the ship is still warmer than the inside of the
> trailer and moisture forms on the ship. Only way to stop this process
> is to put the trailer inside a building (that's where my ship is for
> the winter) or open it up and let everything air out at least once a
> month. Blisters can form on Urethane in about 3 months if the above is
> ignored.
>
> What to do? Re-finish it and use Acrylic Urethane next time which
> resists moisture much better, but isn't immune to the moisture bug.
> The good news is the re-finish of a blistered bird wouldn't be nearly
> as much as re-finishing a getcoat'd machine..................probably
> about half as much. I have heard quotes as high as 25K. I have been
> working with a real craftsman who is getting into the re-finish
> business here in the Western US. He is quoting 15K + materials (PPG
> Acrylic Urethane is up to $400/gal and it takes 3 gal to do a 15 meter
> bird). Send me a note and I'll put you onto this guy. Personally, I
> think anyone is nuts to get involved with the nasty business of re-
> finishing sailplanes which involves 300 hours of grinding, filling,
> sanding, priming, contouring, more priming, more sanding, then finally
> painting the nasty stuff (if you can smell it your killing brain
> cells)................and your not done yet, next comes wet sanding
> with 600 and 800, then buffing.......oh, I forgot the trim and
> numbers and yes, Charlie, we'll be sure and put a big black number on
> the underside of the right wing, then wet-sand and buff them out for
> you.
> My, My, how I have carried on, Cheers,
> JJ

Note that blistering is also not uncommon with gelcoat finishes.
Same cause - voids under the finish...
Best Regards, Dave

[[email protected]]

JJ

I'd always assumed that a lot of the moisture damage occurs the other
way around. When the trailer is warming up in the morning and the
glider is cold, when moisture will condense on the cooler glider
surface. I imagine this lasts quite a while until the glider warms up.
One of the concerns I've had with solar powered fans is that they can
pump cold moist morning air into the trailer that may condense on the
glider surface, then have to pump it out later that day. My little
project to build a humidity controlled vent fan for the trailer got
sidetracked. Maybe one day I'll get back to it.


Darryl


On Dec 23, 8:21 am, JJ Sinclair > wrote:
> Moisture in the trailer has reared its ugly head once again. The
> trailer doesn't have to leak in order to get it in there, it can (and
> does) come from condensation. Think about what goes on in there after
> you put the bird away at 5:00 PM on a humid aftrenood? Sun goes down
> and the outside gets cold, but the inside is still warm and moisture
> forms on the inside of the trailer. By 9:00 PM the inside air has
> cooled down, but the ship is still warmer than the inside of the
> trailer and moisture forms on the ship. Only way to stop this process
> is to put the trailer inside a building (that's where my ship is for
> the winter) or open it up and let everything air out at least once a
> month. Blisters can form on Urethane in about 3 months if the above is
> ignored.
>
> What to do? Re-finish it and use Acrylic Urethane next time which
> resists moisture much better, but isn't immune to the moisture bug.
> The good news is the re-finish of a blistered bird wouldn't be nearly
> as much as re-finishing a getcoat'd machine..................probably
> about half as much. I have heard quotes as high as 25K. I have been
> working with a real craftsman who is getting into the re-finish
> business here in the Western US. He is quoting 15K + materials (PPG
> Acrylic Urethane is up to $400/gal and it takes 3 gal to do a 15 meter
> bird). Send me a note and I'll put you onto this guy. Personally, I
> think anyone is nuts to get involved with the nasty business of re-
> finishing sailplanes which involves 300 hours of grinding, filling,
> sanding, priming, contouring, more priming, more sanding, then finally
> painting the nasty stuff (if you can smell it your killing brain
> cells)................and your not done yet, next comes wet sanding
> with 600 and 800, then buffing.......oh, I forgot the trim and
> numbers and yes, Charlie, we'll be sure and put a big black number on
> the underside of the right wing, then wet-sand and buff them out for
> you.
> My, My, how I have carried on, Cheers,
> JJ

[jerome]

JJ Sinclair a écrit:
> Moisture in the trailer has reared its ugly head once again. The
> trailer doesn't have to leak in order to get it in there, it can (and
> does) come from condensation. Think about what goes on in there after
> you put the bird away at 5:00 PM on a humid aftrenood? Sun goes down
> and the outside gets cold, but the inside is still warm and moisture
> forms on the inside of the trailer. By 9:00 PM the inside air has
> cooled down, but the ship is still warmer than the inside of the
> trailer and moisture forms on the ship. Only way to stop this process
> is to put the trailer inside a building (that's where my ship is for
> the winter) or open it up and let everything air out at least once a
> month. Blisters can form on Urethane in about 3 months if the above is
> ignored.
>

> JJ
>

Your comment shows a complete misunderstanding of the physics of water
vapor. For condensation to occur, a surface must be colder than the
saturation temperature of the surrounding air; not hotter.

[JJ Sinclair]

You could be right, Darryl. The point is moisture does get inside an
otherwise tight trailer and it then becomes trapped in there. I have
opened a lot of trailers over the years and found droplets hanging
from the inside of the trailer and inside the cockpit (that's why the
metal parts in the cockpit get a coat of rust over the winter). On one
trailer that hadn't been opened in 5 years, I found moisture inside
the instruments and the fungus on the fuselage saddle had grown right
into the gelcoat, we had to beat it off! Our little glass birds don't
like moisture, I tell owners to pull it out, put it together, take a
tow and let everything dry out, every mounth (if your bird is sitting
at the gliderport all winter long)...................also keeps you
proficient.
JJ


On Dec 23, 1:09*pm, " >
wrote:
> JJ
>
> I'd always assumed that a lot of the moisture damage occurs the other
> way around. When the trailer is warming up in the morning and the
> glider is cold, when moisture will condense on the cooler glider
> surface. I imagine this lasts quite a while until the glider warms up.
> One of the concerns I've had with solar powered fans is that they can
> pump cold moist morning air into the trailer that may condense on the
> glider surface, then have to pump it out later that day. My little
> project to build a humidity controlled vent fan for the trailer got
> sidetracked. Maybe one day I'll get back to it.
>
> Darryl
>
> On Dec 23, 8:21 am, JJ Sinclair > wrote:
>
>
>
> > Moisture in the trailer has reared its ugly head once again. The
> > trailer doesn't have to leak in order to get it in there, it can (and
> > does) come from condensation. Think about what goes on in there after
> > you put the bird away at 5:00 PM on a humid aftrenood? Sun goes down
> > and the outside gets cold, but the inside is still *warm and moisture
> > forms on the inside of the trailer. By 9:00 PM the inside air has
> > cooled down, but the ship is still warmer than the inside of the
> > trailer and moisture forms on the ship. Only way to stop this process
> > is to put the trailer inside a building (that's where my ship is for
> > the winter) or open it up and let everything air out at least once a
> > month. Blisters can form on Urethane in about 3 months if the above is
> > ignored.
>
> > What to do? Re-finish it and use Acrylic Urethane next time which
> > resists moisture much better, but isn't immune to the moisture bug.
> > The good news is the *re-finish of a blistered bird wouldn't be nearly
> > as much as re-finishing a getcoat'd machine..................probably
> > about half as much. I have heard quotes as high as 25K. I have been
> > working with a real craftsman who is getting into the re-finish
> > business here in the Western US. He is quoting 15K + materials (PPG
> > Acrylic Urethane is up to $400/gal and it takes 3 gal to do a 15 meter
> > bird). Send me a note and I'll put you onto this guy. Personally, I
> > think anyone is nuts to get involved with the nasty business of re-
> > finishing sailplanes which involves 300 hours of grinding, filling,
> > sanding, priming, contouring, more priming, more sanding, then finally
> > painting the nasty stuff (if you can smell it your killing brain
> > cells)................and your not done yet, next comes wet sanding
> > with 600 and 800, then buffing.......oh, I *forgot the trim and
> > numbers and yes, Charlie, we'll be sure and put a big black number on
> > the underside of the right wing, then wet-sand and buff them out for
> > you.
> > My, My, how I have carried on, Cheers,
> > JJ- Hide quoted text -
>
> - Show quoted text -

[Peter Thomas]

Having observer the shrinkage in a 5 year old ASW 27
and 28, bear in mind there are no perfect 30 year old
gliders. put the wings in a plastic tent for 2 weeks
with a dehumidifier and the blisters will probably
disappear.

although i prefer gelcoat for repairability, in strong
uv conditions automative paints last longer, it is
quite possible that nothing much will happen to the
LS3 for 10 to 15 years

I have 1 glider which lives in cool and damp conditions,
the fuz was sprayed with paint 20 years ago after a
major repair , mostly over gel, no primer, still there
with a few blisters. Another, part but not all of the
gel was removed fom the tops of the wings and a thin
coat of new gel applied, 10+years ago. the old stuff
shows at the edges, but most is shiny and white (I
have regelled lots of other bits of the glider, some
bits have small blisters after a year, possibly because
the gel is to thin).

sounds like you have an honest seller, you have to
be realistic. gusssing the price range you will spend
a lifetime looking for the perfect glider

Pete

At 06:48 23 December 2007, Uniform Zulu wrote:
>I'm looking at purchasing an LS-3 but the owner has
>noted that the Urethane finish has blistered in several
>places on the tops of the wings (The glider was re-finished
>in 1996). According to the owner they are very small
>blisters which have left pin sized holes. I'm assuming
>that this would be caused by mositure which has made
>it's way below the paint? He says the trailer is dry
>and has a soler vent so I would assume humidity in
>the air has caused the problem? and not moisture on
>the surface.
>
>What are the implications/underlying problems of the
>blistering? and could I fix this easily or am I looking
>at sanding down/re-finishing the entire surface of
>wings again in the near future?
>
>Any advice would be appreciated.
>
>
>
>

[Peter Thomas]

Having observer the shrinkage in a 5 year old ASW 27
and 28, bear in mind there are no perfect 30 year old
gliders. put the wings in a plastic tent for 2 weeks
with a dehumidifier and the blisters will probably
disappear.

although i prefer gelcoat for repairability, in strong
uv conditions automative paints last longer, it is
quite possible that nothing much will happen to the
LS3 for 10 to 15 years

I have 1 glider which lives in cool and damp conditions,
the fuz was sprayed with paint 20 years ago after a
major repair , mostly over gel, no primer, still there
with a few blisters. Another, part but not all of the
gel was removed fom the tops of the wings and a thin
coat of new gel applied, 10+years ago. the old stuff
shows at the edges, but most is shiny and white (I
have regelled lots of other bits of the glider, some
bits have small blisters after a year, possibly because
the gel is to thin).

sounds like you have an honest seller, you have to
be realistic. gusssing the price range you will spend
a lifetime looking for the perfect glider

Pete

At 06:48 23 December 2007, Uniform Zulu wrote:
>I'm looking at purchasing an LS-3 but the owner has
>noted that the Urethane finish has blistered in several
>places on the tops of the wings (The glider was re-finished
>in 1996). According to the owner they are very small
>blisters which have left pin sized holes. I'm assuming
>that this would be caused by mositure which has made
>it's way below the paint? He says the trailer is dry
>and has a soler vent so I would assume humidity in
>the air has caused the problem? and not moisture on
>the surface.
>
>What are the implications/underlying problems of the
>blistering? and could I fix this easily or am I looking
>at sanding down/re-finishing the entire surface of
>wings again in the near future?
>
>Any advice would be appreciated.
>
>
>
>

[Uniform Zulu]

I would agree with you Darryl; I looked at a glider
early in the morning once on a clear, cold day (perfect
conditions for dew and condensation). The exterior
of the trailer was covered in dew and the inside was
not much different. Not obvious at first but as soon
as we opened the trailer and ran your finger down the
wing it was wet with condensation.

If I do purchase this LS-3 it will be living in climate
controlled comfort for the winter. Even if I have to
take it out of the box and put it in my heated garage.
Winter is probably the worst offender with constant
temp. and moisture swings for months with the trailer
being closed (for those of us in colder climates that
can't pull the glider out in 3 feet of snow!).


At 21:12 23 December 2007, wrote:
>JJ
>
>I'd always assumed that a lot of the moisture damage
>occurs the other
>way around. When the trailer is warming up in the morning
>and the
>glider is cold, when moisture will condense on the
>cooler glider
>surface. I imagine this lasts quite a while until the
>glider warms up.
>One of the concerns I've had with solar powered fans
>is that they can
>pump cold moist morning air into the trailer that may
>condense on the
>glider surface, then have to pump it out later that
>day. My little
>project to build a humidity controlled vent fan for
>the trailer got
>sidetracked. Maybe one day I'll get back to it.
>
>
>Darryl

[Ian[_2_]]

On Sun, 23 Dec 2007 22:58:15 +0000, Peter Thomas wrote:

> although i prefer gelcoat for repairability, in strong uv conditions
> automative paints last longer, it is quite possible that nothing much
> will happen to the LS3 for 10 to 15 years

I owned a glider for over 10 years which the previous owner had sprayed
polyurathane over the gelcoat. Repairs of small scratches and dings are
not a problem.

- Firstly clean off all the wax with acetone.

- Then sand out the damaged area.

- Brush with polyurathane primer (this is a thick coat which builds up
like gelcoat). You may need a number of coats. If you use quick drying
"hardener" in the polyurathane, the paint on the wing drys faster than
the paint in the cup gets hard. If you put the wing in the sun you can
paint a number of coats with it, waiting for each coat to set before
applying the next, before the mix goes off in the cup. You need to build
up enough material to facilitate the re-finish.

- Wait for the paint to harden fully. (8 to 24 hours).

- Sand (wet) to restore the profile. You should end up with a perfectly
finished job, except the repair will be yellow and the wing is white.

- Now spray the yellow with a coat or two of aerosol "appliance white"
spray paint. That goes on very thin and drys very quickly.

- Then can carefully wet sand the aerosol with 2000 grit (just a few
strokes or you will go right through the very thin layer), buff and
polish and the repair becomes invisible. (If the job is not 100% you may
get a brown "water mark" around the sprayed area - normally due to wax on
the wing, but even this is very easy to ignore and virtually
unnoticeable).

Currently I have a share in an LS3a that has gell coat which requires a
re-finish. I would never consider re-finishing a glider with gell coat
instead of PU, and I would not buy a new one without PU. If the factory
price for PU was not reasonable I would get it sprayed after market,
before the gell coat starts cracking up and needs heavy sanding.

If the refinish job on the original poster's LS3a was done properly, I
would gladly swap his blistering PU for our cracking gell coat. (But not
the rest of the glider, we have a totally sorted out instrument panel,
new chute, decent Komet trailer and lots of little things that make it a
very nice glider....).

Ian

[Brad[_2_]]

I painted my Apis 13 kit with Prestec. I think this is referred to as
a "gel-coat" but is really just a thickened polyester high gloss top
coat. The stuff sprays easily and wet sands easily too, and it is not
that expensive.

But..............it seems really prone to the blistering that everyone
is talking about. These are not particularly large, somtimes they
appear as a sheen if you look at the wings at the right angle, in
other places they are maybe a mm in dia and .003 tall, true bumps. The
first time I noticed them was after the first winter it was painted;
we pulled the sailplane out of the trailer, and the L.E. of the wings
were covered with them, luckily the smaller version of the bumps. I
unfortunately have no place other than the trailer and the outside
ramp to store the glider, and there is no electrical source for a
small heater or de-huminidifier in the winter.

The "good" news is these bumps mostly dissapear by mid-spring. Luckily
only a small portion of the airframe has them, and they seem to be
random as to where they show up. Guess at some point I'll have to
bring everything home and spend a winter sanding and re-painting.

Happy Holidays everyone.

Brad
199AK