The 3M 8115 discussion

[Belgian1979vette]

In another thread i posted about a problem with 3M 08115. The reason I'm posting this here is to warn about possible problems with its use, namely shrinkage and swelling.

I used the 8115 not only to glue my parts to the birdcage, but because it was advertised as usefull for bonding fiberglass and SMC, I also used it to bond a new fender to my car. Since I believed it was hard enough I filled some smaller srewholes with it and also filled the bond between the fender and hood surround with it, aka the original way the car was put together.

The pictures below show what happens when it gets heated, like when the car sits in the sun for example.

The first picture is taken before heating with an hairdryer, the second after, and the third after cooling. Notice how the seam appears when heated and disappears again after cooling....





The 8115 even starts to produce bubbles underneath the primer when it gets hot enough.

Anyway, I'm looking at substantial repairwork....when I discovered this problem I had a serious headache as a result...

Luckily I caught it before it got painted.

I dont think it will harm anything when used for bonding parts to the birdcage for example, but you sure as hell cannot use it underneath a painted surface.

Now I have to find a good way to redo everything....damn

 

[JeffP1167]

I've used stuff called vette panel adhesive think it was made by evercoat (not sure) anyways worked real good on my 82 vette.

 

[Belgian1979vette]

Well Jef, I was being told that now also,but some of these products aren't just available here over the pond. After reading a lott about this stuff, I thought it was bullet proof.

 

[MYBAD79]

I just bought some 8116 (not 8115) - it's supposed to be good for fiberglass and SMC. I am not planning on using it as filler, just as a glue..... for filler I use Evercoat SMC adhesive which I have used successfully in the past - no shrinking.

I agree, good thing you found this before painting....

 

[BBShark]

Is the area in this picture that appears raised from the surrounding surface feathered into the panel or is it more like a plug?

 

[Belgian1979vette]

More like a plug. However from what I've seen it doesn't matter if it is feathered out or not.

Talked to my painter. He has this kind of thing with repair of bumpers to, and it is gone once it has a layer of filler(bondo)over it. Don't know.

Evercoat and such is not readily available and they won't ship these with airplane...so that option is out.

 

[010752]

Most epoxy adhesives like 8115 have a certain % flex.
3m recommends epoxy primer over it and a total cure time of 7 days. Shelf life of 12 months.
You must be within those parameters, but they don't specifically recommend it as a filler too.
Your looks like an abnormal amount.

Here is a link to a recommended 3m product, if 3m is all that's available to you over there.
http://www.shop3m.com/60980030880.html?WT.mc_id=CSE-ShoppingCom

I mix my own, but you can contact a local fiberglass boat repair for their suggestions (they usually have more experience with glass than car shops) and availability of products. The higher end places will use epoxy based products.
Keep in mind, there is always shrinkage until total cure with almost all composites no matter what they claim, so following the recommendations is very important.

 

[Belgian1979vette]

What do you guys suggest ? Sanding my primer of in those areas and putting filler over it ? Grinding the 8115 out and redoing the bond lines and screw holes ...

Boy, i feel so frustraded, I (almost) hate my car right now to the point I don't want to work on her anymore.

 

[MYBAD79]

I've had a very similar issue on a urethane bumper once - different materials/filler will cause problems. If it's fiberglass/SMC use products designed fro fiberglass/SMC. If it's urethane use products that are designed for urethane....

The 8115 seems to be an adhesive and not a filler. Like many others I don't know enough about the chem composition of these products so I have to depend on what they advertise... the 8116 seems to be better for SMC.... at least that's what 3M says... I ordered a tube of this 8116 for a SMC repair, hopefully it turns out as planned.... haven't started this project yet....

I have used Bondo "kitty hair" resin with good success.... actually that's what I used on my flares and quarter panels on my '79 after I bonded the flares with Evercoat SMC adhesive.... it's been over 4 years and no shrinking, no swelling no problems.....even in the Florida sun....

 

[Belgian1979vette]

I've had a very similar issue on a urethane bumper once - different materials/filler will cause problems. If it's fiberglass/SMC use products designed fro fiberglass/SMC. If it's urethane use products that are designed for urethane....

The 8115 seems to be an adhesive and not a filler. Like many others I don't know enough about the chem composition of these products so I have to depend on what they advertise... the 8116 seems to be better for SMC.... at least that's what 3M says... I ordered a tube of this 8116 for a SMC repair, hopefully it turns out as planned.... haven't started this project yet....

I have used Bondo "kitty hair" resin with good success.... actually that's what I used on my flares and quarter panels on my '79 after I bonded the flares with Evercoat SMC adhesive.... it's been over 4 years and no shrinking, no swelling no problems.....even in the Florida sun....

Thanks for the info. I know evercoat formulated specifically with smc in their mind, but until now no succes in getting this product over here. They will not ship either because it is hazardous.

Anyway, I used the 8115 because it is an epoxy adhesive and they mention it to as a SMC adhesive. The shop manual for my car specifically says to use epoxy bondo which can be also used to fill the seam.

I don't think their is anything prohibiting about it's use as a seam filler. It is built up like a regular filler but has epoxy as base resin for better glueing properties...
The problem is not the filling itself, it's just that it starts to produce "ghost lines" when under influence of heat. This itself is related to the expansion rate.
After reading up on the net last night if found out that practically alle adhesives produce ghost lines, some more, some less.

Yesterday someone told me that a dryer produces to much localized heat, so I'm warming it up with IR which is known to produce someting like 80-90°C on the surface, which is the same heat as a black car in the sun (at least that is what I'm being told).

I try to localize the problems and then see later on what I need to do about it. Apparently the seam itself doesn't show as much (just a little, enough so you can see it as a darker line in the primer). The filled up holes however are more of a problem.
Since these are only the size of a screw, i think I could get away with just a tad of filler on top of them.

I will keep posting here about the progress with the IR-lamp.

 

[JeffP1167]

On my rear deck to fill the original gas cap location (1974) I bonded a smc sheet under it and fill it with bondo with cats hair. Seems to be pretty strong stuff and so far doesn't seem to have shrunk or anything and seems very strong. I also used it to fill the gap where the rear deck was cut out to install the 82 gas lid.

 

[Belgian1979vette]

This is the response I got from an 3M representative today :



"Yves,

There is no guaranteed way to repair the ghosting holes, short of putting a bonding strip behind each one and dishing each one out. Screws should never be used in an exposed cosmetic panel. The panels must be fixtured with clamps or other methods (complain to General Motors).

Regarding the other bond lines, they also exist from the factory. If you have a Corvette with no bond lines, points will be deducted in a car show by the Corvette purists.

Best regards,

Craig W. Thiel
AAD Technical Service
Building 250-01-02"

The answer is total BS. There is no way in hell a backing plate aka bonding strip has anything to do with it. The 8115 in the screw holes makes bubbles and only dimples when it shrinks back. And did you ever try to clamp a front fender in and not use screws ?? I don'th think it is even possible.

Secondly there is also swelling and shrinking in bonding seams.

Third, i'm not looking for a factory correct paintjob, but a perfect paint job.

:crylol::hissyfit:

To reply to the previous poster :

The problem seems to show only where i didn't have to fill with epoxy filler on top of it and only in those places where it is sufficiently thick enough.
I'm pretty convinced that the swelling/shrinking keeps on taking place even with what you call 'kitty hair'

 

[SMYDA]

I think a lot of the problem is coming from the "plug type" repair that you mentioned.
I don't recall if you said you used any type of backer ... Screen? etc.?
The panel needed to be feathered so there would have been
a more gradual transition from 8115 to fiberglass. Even when repairing glass
with glass, one needs to feather the panels to prevent having a line.


I have repaired many things with the 8115. The only problems I have ever
encountered was (1) zero adhesion on certain types of bumper covers ...
which isn't very common. (2) having an old batch that would no longer cure
properly..... which was even more rare. Other than this my success rate has been nearly 100%.

I have used the Evercoat Metalglaze over the top of the 8115 to finish it.


Curious ?? What kind of climate do you live in ?? Is it warm enough in general to
allow the products to cure properly so that baking them isn't a radical change from "normal" ?

 

[Belgian1979vette]

I think a lot of the problem is coming from the "plug type" repair that you mentioned.
I don't recall if you said you used any type of backer ... Screen? etc.?
The panel needed to be feathered so there would have been
a more gradual transition from 8115 to fiberglass. Even when repairing glass
with glass, one needs to feather the panels to prevent having a line.


I have repaired many things with the 8115. The only problems I have ever
encountered was (1) zero adhesion on certain types of bumper covers ...
which isn't very common. (2) having an old batch that would no longer cure
properly..... which was even more rare. Other than this my success rate has been nearly 100%.

I have used the Evercoat Metalglaze over the top of the 8115 to finish it.


Curious ?? What kind of climate do you live in ?? Is it warm enough in general to
allow the products to cure properly so that baking them isn't a radical change from "normal" ?

Well the climate is pretty moist, winters around 0°C and summers of around 25-30°C. The repairs were all done in summertime.

Don't know about the "slug problem". With the kind of swelling I'm seeing, i dare to say that it wouldn't matter much if the repair was feathered in or not. It would bulp out anyway and show. You can feel the edge pretty good.

I have two other guys among who Big G and dub saying that the 8115 doesn't react to well to solvents in paint and such. Don't know maybe that's the culprit.

Yesterday a boroughed a IR lamp and went around the car in periods of 10 minutes putting heat to every and intire part of the car. I was being told that IR heats the surface to a temperature which is comparable to a black car in sunheat (80-90°C). The seams at least were not showing. The screw holes first became a very tiny bubble and then collapsed to a dimple in the paint. When heating it becomes a bubble again and so on and so forth

 

[Ozzy]

I think a lot of the problem is coming from the "plug type" repair that you mentioned.
I don't recall if you said you used any type of backer ... Screen? etc.?
The panel needed to be feathered so there would have been
a more gradual transition from 8115 to fiberglass. Even when repairing glass
with glass, one needs to feather the panels to prevent having a line.


I have repaired many things with the 8115. The only problems I have ever
encountered was (1) zero adhesion on certain types of bumper covers ...
which isn't very common. (2) having an old batch that would no longer cure
properly..... which was even more rare. Other than this my success rate has been nearly 100%.

I have used the Evercoat Metalglaze over the top of the 8115 to finish it.


Curious ?? What kind of climate do you live in ?? Is it warm enough in general to
allow the products to cure properly so that baking them isn't a radical change from "normal" ?

Well the climate is pretty moist, winters around 0°C and summers of around 25-30°C. The repairs were all done in summertime.

Don't know about the "slug problem". With the kind of swelling I'm seeing, i dare to say that it wouldn't matter much if the repair was feathered in or not. It would bulp out anyway and show. You can feel the edge pretty good.

I have two other guys among who Big G and dub saying that the 8115 doesn't react to well to solvents in paint and such. Don't know maybe that's the culprit.

Yesterday a boroughed a IR lamp and went around the car in periods of 10 minutes putting heat to every and intire part of the car. I was being told that IR heats the surface to a temperature which is comparable to a black car in sunheat (80-90°C). The seams at least were not showing. The screw holes first became a very tiny bubble and then collapsed to a dimple in the paint. When heating it becomes a bubble again and so on and so forth

I would grind the problem areas out and fill with an epoxy such as West Systems with micro-spheres added to the consistency of tooth paste.

Feather the areas out to 5 times the thickness of the panel material.The center of the feathered area will end up as a hole the size of the original hole.
For backing just use a piece of metal tape.

Once the area is built back up to flush with the surrounding area, I would then prime with SPI epoxy and continue to sand and blend the repair with SPI epoxy until the surface is ready for top coat paint.

Not all epoxies are a viable option to build with, SPI works great, but I asume there are others that will work ok also.

I would NOT use any type of polyester filler, ie.bondo,, kitty hair,rage, etc. They will all shrink back at a different rate than the fiberglass.

Don't hate the car, hate the bad advice you followed to start with.
Now get out there and fix it :thumbs:

 

[010752]

I think a lot of the problem is coming from the "plug type" repair that you mentioned.
I don't recall if you said you used any type of backer ... Screen? etc.?
The panel needed to be feathered so there would have been
a more gradual transition from 8115 to fiberglass. Even when repairing glass
with glass, one needs to feather the panels to prevent having a line.


I have repaired many things with the 8115. The only problems I have ever
encountered was (1) zero adhesion on certain types of bumper covers ...
which isn't very common. (2) having an old batch that would no longer cure
properly..... which was even more rare. Other than this my success rate has been nearly 100%.

I have used the Evercoat Metalglaze over the top of the 8115 to finish it.


Curious ?? What kind of climate do you live in ?? Is it warm enough in general to
allow the products to cure properly so that baking them isn't a radical change from "normal" ?

Well the climate is pretty moist, winters around 0°C and summers of around 25-30°C. The repairs were all done in summertime.

Don't know about the "slug problem". With the kind of swelling I'm seeing, i dare to say that it wouldn't matter much if the repair was feathered in or not. It would bulp out anyway and show. You can feel the edge pretty good.

I have two other guys among who Big G and dub saying that the 8115 doesn't react to well to solvents in paint and such. Don't know maybe that's the culprit.

Yesterday a boroughed a IR lamp and went around the car in periods of 10 minutes putting heat to every and intire part of the car. I was being told that IR heats the surface to a temperature which is comparable to a black car in sunheat (80-90°C). The seams at least were not showing. The screw holes first became a very tiny bubble and then collapsed to a dimple in the paint. When heating it becomes a bubble again and so on and so forth

I would grind the problem areas out and fill with an epoxy such as West Systems with micro-spheres added to the consistency of tooth paste.

Feather the areas out to 5 times the thickness of the panel material.The center of the feathered area will end up as a hole the size of the original hole.
For backing just use a piece of metal tape.

Once the area is built back up to flush with the surrounding area, I would then prime with SPI epoxy and continue to sand and blend the repair with SPI epoxy until the surface is ready for top coat paint.

Not all epoxies are a viable option to build with, SPI works great, but I asume there are others that will work ok also.

I would NOT use any type of polyester filler, ie.bondo,, kitty hair,rage, etc. They will all shrink back at a different rate than the fiberglass.

Don't hate the car, hate the bad advice you followed to start with.
Now get out there and fix it :thumbs:

I agree other than the microsheres, you can buy ground glass fibers, same place as the spheres. BTW, the glass spheres are in a lot of the panel adhesives to prevent resin squeesout.
West System is good, similar to the stuff I use, less the 1% shrinkage to cure. And use a rough grit when grinding.

You didn't answer if you had used epoxy primer before???

 

[Belgian1979vette]

Yes, I used an epoxy based coat as the first two layers on top of the smc.

What you discribe looks a lot like the epoxy bondo/filler I have here to do some repairs on top of my smc.
I never noticed it to shrink in a way that a repair would be visible.

I do have the microfibers to mix into epoxy resin. I used it once, but it stayed rather fluid and would be difficult to smear into the seam if you ask me. For the rest i have little experience with that.

You know, i need to get myself as far as to start grinding into the primer again. Damn, the thing was completly finished for painting and it could have been great.

Thanks

 

[GTR1999]

Interesting, I was planning on using the 8115 to bond the headlight support under the nose.

This is not my area of expertise that's for sure. What I did the last time I worked on the '69 (5 years ago!) was to use the 8115 to bond the support to a NOS bonding strip like the factory used. Originally it was riveted together.

Ok so when ever I get back to this( months,years??) do I go back and use the 8115 or use bonding adhesive?

 

[010752]

8115 is a bonding adhesive. But they have many more including structural adhesives too.
Here is some info
Doesn't mention it as a "filler".

Notice the mention of "ghost lines", but also a pretty good guarantee if really valid.

http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSu7zK1fslxtU4Y_vP8mvev7qe17zHvTSevTSeSSSSSS--


Notice their stats say prepped with 50 grit.

http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSu7zK1fslxtUN8txm8_Bev7qe17zHvTSevTSeSSSSSS--

3m has hundreds of adhesives, maybe best to call the local rep for the best product.



Here is a new backer stip I made out of 1/16" stainless to replace the rusted stripped out one for the compartment hinges.

Ground with 30 grit

Homemade epoxy brew

Supported till cure

Should last a while as long as I don't strip the holes.

 

[Belgian1979vette]

Well as far as their explanation on only bonding goes : i bonded the round thingies that go under the hood to keep the insulation in place on my L88 hood and gues what, they are showing ghost lines too.

An informed man ...