Home » Public Forums » GMCnet » Fiberglass repair
| Fiberglass repair [message #117769] |
Sun, 06 March 2011 15:09  |
carnut
Messages: 11
Registered: February 2007
Location: Visalia CA
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This weekend we had a minor accident backing up in a small space. No one to blame except the old fart driving the GMC (me). The fiberglass near the RR tail light has a 3"+ diam. break/dent about 1+" deep.
Can this be repaired with the fiberglass style epoxy body putty or does it need the traditional layer after layer of glass material with epoxy resin ??
Dave Bockman
Visalia Calif
"76 Eleganza II
Under restoration
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| Re: Fiberglass repair [message #117776 is a reply to message #117769] |
Sun, 06 March 2011 16:53  |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
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The end caps are made of SMC, and I understand that the usual fiberglass cloth and resin is not correct for repairing the damage. Jim Bounds should be able to tell you the proper materials to use. I understand that this material was also used on Corvettes, so perhaps a Corvette restorer would also know what to use in repairing your taillight housing.
When I knocked off my side mirror, I found some type of two part 3M adhesive to reglue the damaged area.
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: Fiberglass repair [message #117979 is a reply to message #117769] |
Tue, 08 March 2011 09:01 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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The SMC can be repaired with Epoxy and fibreglas cloth.
do you have a pic of the damage??
I just went through this in 2007.
if it is a hole, try to patch from the rear, use paper or whatever to support the patch till it cures. It would be best to use another patch to fill the hole and shape. Bondo can be used but is touchy, it is not fond of SMC either but it does work.
sanding the patch is difficult after it has cured, fair warning.
I purchase the resin from West Marine. Might compare prices but I figure a boat supplier tohave the correct stuff. I have bought the cloth from West Marine also but I did a search and found it cheaper for more quantity.... your pic.
Repairing this is easy, but it is messy and time consuming. Thats why it is so expensive to have it done.
you can use gloves to keep the sticky off your fingers but I find the gloves get in the way. If you just use your fingers, when you are done wipe off with paper towels. You will still be sticky for about half an hour. once cured it falls / washes off your fingers....
If you have ever gotten POR15 on your fingers, you are married to it until it wears off, about 5 days.
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: Fiberglass repair [message #117980 is a reply to message #117769] |
Tue, 08 March 2011 09:14 |
gbarrow2
Messages: 765
Registered: February 2004
Location: Lake Almanor, Ca./ Red Bl...
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I have no personal experience but I have been told to use "Kittyhair" which is a pre-mixed combination of resin and chopped fiberglass strands. I don't know if the resin is epoxy or polyester. Possibly it is available either way.
I have a small crunch to repair similar to yours. I plan to use the kittyhair unless some one with experience has a good reason not to.
Gene Barrow
Lake Almanor, Ca.
1976 Palm Beach
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| Re: Fiberglass repair [message #117986 is a reply to message #117980] |
Tue, 08 March 2011 09:36 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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It is a bondo with fiberglass strings in it. It is supposed to add strength to the bondo.
I can only guess the reason they came up with it was to not use the fiberglass for repair, but the size of the repair would limit the hole size you can repair.
I found it a little different to use compared to normal bondo, the hairs tend to move around when you apply it...
If the hole is large, I don't recommend not supporting it with fiberglas behind it.
Bondo is not meant to be the sole material for a body.
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: Fiberglass repair [message #118142 is a reply to message #117769] |
Tue, 08 March 2011 22:08 |
Dr. Detroit
Messages: 158
Registered: April 2010
Location: Novi, MI.
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The repair of SMC Body panels is probably the most misunderstood process of any body repairs.
There are plenty of internet myths out there which range from release agents causing problems to vehicles from the 70's not being repairable with standard materials. The reason for the confusion is the resin in SMC has undergone changes over time and can either be a polyester or epoxy based material.
Since you never really know what chemistry was used in a particular model year, the safest bet is to use an epoxy based repair material. Also another good reason to use an epoxy based material is it's bond strength is roughly 4x that of polyester.
1973 GMC 23'
All Birch and Maple Interior Cabinetry. TZE033V100221
"The Honeycomb Hideout"
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| Re: Fiberglass repair [message #118182 is a reply to message #117769] |
Wed, 09 March 2011 09:55 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| carnut wrote on Sun, 06 March 2011 16:09 |
This weekend we had a minor accident backing up in a small space. No one to blame except the old fart driving the GMC (me). The fiberglass near the RR tail light has a 3"+ diam. break/dent about 1+" deep.
Can this be repaired with the fiberglass style epoxy body putty or does it need the traditional layer after layer of glass material with epoxy resin ??
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Dave,
Before you do anything else, get the Gougeon Bros. (West System - no connection to West Marine) books on how to do this stuff. They do not (didn't used to) address repairs to SMC (what GMCs are made of) because they do boat stuff. If you dig around on the West System you can probably down load and read the books right now. I keep a set in my coach office library.
My advice comes in three parts, Get and read the books, buy good materials (West is a known product, but there are others) and tools, learn about dealing with SMC - this part follows closely.
About dealing with SMC: Sheet Mold Compound is delivered as a floppy matrix of resin, glass fiber and release agent. It is tossed into the hot tooling and pressed into the final shape. In the process, the resin reacts with the heat and cures real fast. The glass fiber is trapped it place, and the mold release agent is freed so some of it can move to the hot surfaces and keep the new piece from becoming a permanent part of the tooling. There in is the rub.... After you sand, grind or cut the SMC, the release agent is exposed to bleed out into what you want to be a bonded joint. Remedy: Just - like Immediately before you coat that surface with epoxy, clean it well with too much acetone.
About the materials: Buy epoxy that has mixing pumps available and BUY THE PUMPS. If you buy and use the pumps to measure the resin, you will never have a mix failure. West also has some little repair sets, but they are too small for very much of anything serious. There may be glass mat offered, but it has a binder that is supposed to dissolve in a polyester or vinylester resin, but will not in epoxy and so will never actually saturate and bond. DO NOT buy polyester or vinylester resin as neither is a good adhesive and both are very mix critical. (If you miss, it may either never cure or set up before you finish stirring.)
The cost of the materials and tools may look expensive, but if you take it too a shop, that may change. The other thing to remember is the the remaining tools and materials will only be wasted if you never - ever have to patch the glasswork again.
I don't know about the others, but the shelf life of the West products is about forever, just store it carefully.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Fiberglass repair [message #118186 is a reply to message #118182] |
Wed, 09 March 2011 10:23 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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Matt
West marine carries the West system epoxy. Partly because I was too lazy to find it else where, I bought mine from West Marine. I did by the glass cloth there the first time but I found by searching the web I got a lot more for much less dollars.
I did not have a problem with the release agent and the epoxy, my work was done in 2007. I had a small issue with the bondo. I used some bondo in two places, the gen set door and a body panel.
The genset door did not have any problem accepting the bondo. I had broken the corner off the door when a cattle trough jumped in front of me when I was backing up. nice ragged edge. I was able to saturate the edges with epoxy and clamp together overnight. The next day it was cured and solid. I did reinforce from behind with epoxy and glass cloth. the bondo was applied to the front and sanded down. no problem.
The body panel, in only one spot makes me think there was a cleaning issue before paint. This spot was done toward the end of the project and I was wanting to get done as the cold weather was coming. the paint flaked off after about a year, only where the repair was made. sanding cleaning and painting seems to have fixed these issues. I will point out that this repair was directly behind the rear wheels and it gets a lot of splash and rock attacks going down the road.
What is a problem and I don't have the definitive answer for repair, is where there is stress on the SMC panel, such as on the front where there are hinges or where the panel attach with fasteners. The stress creates hairline cracks. there was no way to get the epoxy in the cracks so I reinforced with epoxy and glass cloth on the rear behind the crack.
All in all, the repair was rather simple though time consuming. Take your time and think out what you are going to do and you should be ok.
I would not be afraid to go after a repair on SMC as long as you are using the Epoxy resin and fiberglas cloth. sand down to the SMC, all paint has to come off, clean and do the repair.
if the damage is very large you may need to make a mock up of the shape, try to do this behind the panel. I think Emery had a thought on this at one time and talked about it.
Using plastic on the surface gives a fairly easy to remove mold surface. One gentleman used to make his own door covers and would make the mold of foam and such and would cover that with clear shipping tape. After waxing the tape he could then apply the fiberglass to the shape of the mold.
Note: the Grill IS NOT SMC, and this method will not work on it.
food for thought...............
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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| Re: Fiberglass repair [message #118357 is a reply to message #118186] |
Thu, 10 March 2011 17:44 |
Dr. Detroit
Messages: 158
Registered: April 2010
Location: Novi, MI.
Karma: 0
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Matt,
Class A body panels do not have a release agent in the matrix. This is an internet rumor that keeps on growing and needs to die.
If they did have release mixed in the matrix, painting the panels would be a nightmare. Paint would not stick anywhere or would fisheye like crazy without special preparation and adhesion promoters.
The parts release from the Class A side of the tool and rides back with the core because there is draft and the surface is polished to promote release of the part. The part is then lifted from the "core" side of the tool either by hand or a built in ejector system.
Ken
1973 GMC 23'
All Birch and Maple Interior Cabinetry. TZE033V100221
"The Honeycomb Hideout"
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| Re: Fiberglass repair [message #118367 is a reply to message #118357] |
Thu, 10 March 2011 19:57 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| Dr. Detroit wrote on Thu, 10 March 2011 15:44 |
Class A body panels do not have a release agent in the matrix. This is an internet rumor that keeps on growing and needs to die.
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Still -- Bottom line: Regardless of if, where and how about release agent, from the experience of people who have repaired GMC's, use quality EPOXY if you want a quality job.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: Fiberglass repair [message #118368 is a reply to message #117769] |
Thu, 10 March 2011 20:10 |
Dr. Detroit
Messages: 158
Registered: April 2010
Location: Novi, MI.
Karma: 0
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Yes. As I mentioned in post #8 of this thread, epoxy materials are the safest bet.
Here's a link to the General Motors SMC Repair Procedure. It's for the Lumina Vans but the techniques can be applied to our motorhomes. It will help any novice understand better because it has lots of pictures of the repair process.
http://www.tech-cor.net/AutoResBulletin/1990-1/1990-1.htm
Ken
1973 GMC 23'
All Birch and Maple Interior Cabinetry. TZE033V100221
"The Honeycomb Hideout"
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| Re: Fiberglass repair [message #118402 is a reply to message #118357] |
Fri, 11 March 2011 08:03 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Dr. Detroit wrote on Thu, 10 March 2011 18:44 |
Matt,
Class A body panels do not have a release agent in the matrix. This is an internet rumor that keeps on growing and needs to die.
If they did have release mixed in the matrix, painting the panels would be a nightmare. Paint would not stick anywhere or would fisheye like crazy without special preparation and adhesion promoters.
The parts release from the Class A side of the tool and rides back with the core because there is draft and the surface is polished to promote release of the part. The part is then lifted from the "core" side of the tool either by hand or a built in ejector system.
Ken
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For non-automotive readers: Class A parts are those finished for appearance.
Ken,
What you are saying is completely true with current technology SMC panels, but the coaches were not assembled with those processes.
There are lots of rumors that need to die. Here we have a problem in that it once was true in some cases.
Story Time:
In the late 60's I was a tech in an R&D lab at Allied Chemical. (Yes, I had a shoreside for a few months.) We were simultaneously working on process improvements for SMC fender liners (for Ford Bonco IIRC) and create a Class A paintable process as well. We were not the only program in Allied an we heard that Monsanto was also on the same track.
The fenderliners did indeed have a release agent in the matrix and without serious additional processes (that included chanting, arm waving and magic feathers) it was completely paint proof. (Stories available in exchange for beer.) We tried to several ways eliminate the release agent with the only result being useless parts and some very expensive tool cleaning.
About the time we closed out, we were successfully running with a temperature sensitive micro-encapsulated release system that could be successfully final processed running at rate. When I left, it was not clear if the first process would be a special primer or a cleaning operation. The process was expensive and there was a lot of worry about marketability to automotive. We were making nice looking parts, but repair of damaged areas did require high solvent cleaning to achieve an effective bond. As a tech, if it was stinky, sticky and nasty, it was my job. None of the materials we used could be used in production today because of the high VOC.
One of the snowmobile companies was actually waiting for us to give them the final word on process definition so they could start production. Strangely, they would not accept the process until we had clarified the repair requirements.
If I have to patch the SMC of the coach again, I am going to do a solvent wash prior to the first epoxy application. It's cheap enough that the risk of a bond failure is not something I want to accommodate.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Fiberglass repair [message #118496 is a reply to message #118402] |
Sat, 12 March 2011 00:01 |
Dr. Detroit
Messages: 158
Registered: April 2010
Location: Novi, MI.
Karma: 0
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Matt,
With all due respect, one part from the early days does not condemn a process to be soaked in mold release forever.
The part you described suffered from a few ills if it would not eject from the tool without slathering it with release. I suspect that it was a deep part with minimal draft that was not designed from the start as an SMC part. As a result your group ran into the problems they did. However many of those learning experiences were captured and condensed into a publication available from the SMC Automotive Alliance called the SMC Design Manual, Exterior Body Panels of which a physical copy is in my reference library. It's just one of the many physical manuals I've picked up over the last 26 years of working with SMC and just about every other form of composites out there every day of every week.
Regarding the differences in material from back then to now, actually the chemistry has been pretty consistent from the first SMC panels until the EPA started to clamp down on styrene emissions recently. Obviously there are different recipes but in the 70's it was either a polyester, vinylester, or epoxy resin. Polyester was most common followed by vinylester then epoxy.
To add further details I have copied and pasted an offline discussion I had with another member at his suggestion. Here's my response to his questions:
The problem with internet searches is that the sites that come to the top are the ones that are viewed most often not the most accurate. Unlike books and manuals internet sites are not subject to peer review and fact checking. As a result much of the information out there on the world wide web that is found as the result of an internet search may not tell the whole story. At my workplace when someone brings me a source from google or any other internet search, I ask them to find the information from an accurate source. While the info on the web may be valid (capable of being justified) it is not always accurate (free from failure, error or defect).
To be clear, I do not dispute that some SMC materials are formulated with high quantities of Release as part of the matrix to facilitate ejection from the tooling. However from my experience those parts are typically a complex surface structural part that is part of the underbody or chassis and do not receive paint or e-coat treatment for appearance purposes. Further, a higher quantity release is typically a bandaid solution for poor part design or a poor tooling condition and is never part of the up front planning of any well executed plastics project. The big reason release it is not specified up front is because it adds cost. Albeit a small percentage of the cost of a part is the release component, it is still a cost driver and as such it is typically used in higher quantities only when needed. The releases commonly used in plastics are fatty acids, wax acids, polyol esters and stearic acid. Some are more compatible with paint finishes than others but all must be used only in light duty applications if the part is to be decorated with paint with good results.
That said, unless we are working with an underbody or other structual part there will not be enough relase agent in the part to thwart bonding of adhesives, repair materials or paint. If significant amounts of mold release exist then you could expect to see bond failures and "fisheyes" everywhere in the paint. Since all of the parts on the GMC are big rounded shapes with plenty of draft the likelyhood of the panels having enough release to cause such problems is minimal at best. Also considering that the panels have remained bonded to the frame and the paint on the coaches from the factory was relatively smooth I would expect that release agents in the material were minimal at best.
Having been part of the launch teams on vehicles which used SMC panels such as the 2000 Mercedes CL, 2001 Ford Explorer Sport Trac, 2001 Ford F150 Super Crew, 2000 F150 Harley Edition and the ill fated 2003 Lincoln Blackwood I can say from firsthand experience that painting SMC is a nightmare to start with. The primary problem is the outgassing and bubbles that wreak havok on the paint finish, and then there are the deformation issues that adhesives bring to the table. Adding significant amounts of release to the matrix would further complicate the issues and as a result it is not done on class A panels. As a matter of fact many of the Part Detail Drawings have very specific notes forbiding mold release.
With regard to repair materials, although the primary ingredient in our SMC body panels was most likely polyester, the use of polyester resin for structural repairs is generally discouraged. This has everything to do with the fact that polyester is not very effective as an adhesive and not that it is incompatible with our SMC panels. So the question is what should be used for repairs on well cured SMC? The simple easy answer is Epoxy. It's a much better adhesive and has 2-3 times the tensile elongation of polyester. That alone is why epoxy is recommended. It has nothing to do with the release as the internet would lead one to believe.
Now does this mean that if one chooses to use polyester as a repair material that failures are eminent? No. As a matter of fact there have been numerous successful repairs done on SMC panels using polyester resin and fiberglass. However their success is based on the fact that the panel is likely in a low stress area and that the adhesion limits of the polyesters properties have not been exceeded. Would I recommend that polyester is used? Probably not.
In closing it's worth noting that if our panels were loaded with enough release to readily fail polyester bonds it will also certainly fail most other bonds including common urethanes and epoxies. Since this is not the case, as I stated the internet rumor of SMC bond failures being caused by the release needs to die.
1973 GMC 23'
All Birch and Maple Interior Cabinetry. TZE033V100221
"The Honeycomb Hideout"
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