Cracks are bad news, right?

I suspect any reputation regarding Grob gelcoat might have to do with the fact that so many of them are tied out all year long in harsh climates. Interestingly, there was a HUGE difference in the amount of gelcoat damage on my recent Grob refinish project between the SW side (sunny side) and NE side (shady side) of the fuselage. The glider is tied outside with the left side subject to sun pretty much all day, while the right side is not. Sunny side gelcoat was crazed in all directions, while shady side crazing was limited to fine lines in the direction of the finish sanding.

P3

On Monday, July 2, 2012 10:41:14 AM UTC-4, Grider Pirate wrote:
On Jul 2, 5:55*am, Terry Walsh wrote:
"Probably the worst culprit is the
Grob 102/3

Despite all their other reported issues Grob is famous for having one of
the more durable Gel coats Don.

Terry Walsh

At 12:26 02 July 2012, Don Johnstone wrote:





- Show quoted text -

Yup. Grob gelcoat seems to be about the best I've seen. I'm partner
in a Janus C that had gelcoat literally blowing off of the top of the
wing. The bond had failed so completely that I didn't sand the
remaining gelcoat off, I SCRAPED/CHIPPED it off using a pnuematic
scraper (see the terrifying video on YouTube "Removing Failed Gelcoat")
(sorry, I can't provide a link right now). 5 gallons of PCL
PolyPrimer, lots of sanding, and gallons of PPG concept, followed by
more sanding and buffing. If it still looks good in 5 years, I'll
declare victory.

On Monday, July 2, 2012 8:58:18 PM UTC-4, Papa3 wrote:
I suspect any reputation regarding Grob gelcoat might have to do with the fact that so many of them are tied out all year long in harsh climates. Interestingly, there was a HUGE difference in the amount of gelcoat damage on my recent Grob refinish project between the SW side (sunny side) and NE side (shady side) of the fuselage. The glider is tied outside with the left side subject to sun pretty much all day, while the right side is not. Sunny side gelcoat was crazed in all directions, while shady side crazing was limited to fine lines in the direction of the finish sanding.

P3

BUT- If it had not originally been done in Scwhabelack it would be much worse.
Grobs surive abuse much better than most other types.
UH

On Sunday, July 1, 2012 7:23:38 AM UTC-7, JJ Sinclair wrote:
Remember the crack in the engine mount that failed and brought down the airliner? How about the B-52 that taxied onto the runway, applied full power and the left wing fell off! This all started as a crack near the spar after an air-refuling mishap. Would you fly a wood sailplane with cracks in th skin? No way, don't walk, run away from that puppy! Would you fly an aluminum ship with cracks in the skin? That old girls been rode hard and put away wet, right? Fear of cracks is in our DNA. Remember; Step on a crack and break your mothers back?

So now you find a crack in the skin of your fiberglass sailplane. Bad news, right? Actually no. Fiberglass sailplanes are covered with a thin layer of rock-hard gelcoat that was placed over a flexible structure. I remember the DG-400 at Minden, that had been flown extensively in wave conditions. It was literally covered with cracks. The wings had cord-wise cracks every half inch on both sides of both wings. This ship was flying regularly and was considered airworthy.

Yeah, but I got a crack coming from the corner of my spoiler box, is my wing going to fall off? Nope, when your wing skin was laid up in its mold, the fiberglass cloth wouldn't fit tightly into the corners and around the edges of your spoiler box, so filler and extra gelcoat was applied all around the spoiler box to allow the cloth to smoothly overlap the box. The corners of the box are stress concentration points and cracks will quite likely appear there. How deep do these cracks go? All the way through the gelcoat and filler, but they stop when they reach the fiberglass cloth because they are gelcoat cracks migrating IN from the rock-hard coating, NOT cracks in the fiberglass migrating OUT!

Once again, this is just my humble opinion, but it was formed after 40 years of grinding out your cracks and finding no structural issues.
:) JJ

JJ is the expert here ! And this advice is solid in
99% of cases, But....

Many years ago I started rebuilding a wreck which had
a few cracks that looked not dissimilar to the photos
that started this discussion. Unfortunately, they were
caused by a structural problem under the gelcoat - an
improper repair done years earlier (and not in the logs).
It was a LOT of work to rip out all the improper repair
mess and correct it. More work in fact than repairing
the prangage that had totaled the ship prior I bought
it from the insurance company.

Bottom line: Get somebody REALLY EXPERIENCED to look at
anything you're considering purchasing ! It could save
you a lot of money, or even more...

Hope that helps,
Best Regards, Dave

On 7/1/2012 7:04 PM, hretting wrote:
WOW...looks like Bob is still working on that novel. Bob??? are you in prison? I'm thinking 'pet mouse'.
LOL dude, you sho no a lot of wods.
R


Chortle! Twitter cut me off.
BW

On Jul 2, 7:58*pm, Papa3 wrote:
I suspect any reputation regarding Grob gelcoat might have to do with the fact that so many of them are tied out all year long in harsh climates. *Interestingly, there was a HUGE difference in the amount of gelcoat damage on my recent Grob refinish project between the SW side (sunny side) and NE side (shady side) of the fuselage. * *The glider is tied outside with the left side subject to sun pretty much all day, while the right side is not. * Sunny side gelcoat was crazed in all directions, while shady side crazing was limited to fine lines in the direction of the finish sanding.

P3







On Monday, July 2, 2012 10:41:14 AM UTC-4, Grider Pirate wrote:
On Jul 2, 5:55*am, Terry Walsh wrote:
"Probably the worst culprit is the
Grob 102/3

Despite all their other reported issues Grob is famous for having one of
the more durable Gel coats Don.

Terry Walsh

At 12:26 02 July 2012, Don Johnstone wrote:

- Show quoted text -

Yup. *Grob gelcoat seems to be about the best I've seen. *I'm partner
in a Janus C that had gelcoat literally blowing off of the top of the
wing. *The bond had failed so completely that I didn't sand the
remaining gelcoat off, I SCRAPED/CHIPPED it off using a pnuematic
scraper (see the terrifying video on YouTube "Removing Failed Gelcoat")
(sorry, I can't provide a link right now). *5 gallons of PCL
PolyPrimer, lots of sanding, and gallons of PPG concept, followed by
more sanding and buffing. *If it still looks good in 5 years, I'll
declare victory.

Has anyone looked into using the vehicle wraps (3M) instead of paint?
They seem to last OK on cars, trailers and boats. Would that be a
cheaper alternative?