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Bonding seam repair

 
Old 02-25-2019, 09:59 PM
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Ksp3cialK
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Default Bonding seam repair

I know this has been asked time and time again, all the threads I find seem to be over 5 years old or are with broken picture links. Also, there seem to be many different methods of repairs.
Honestly, I'm probably just confusing myself.

3 out of my 4 fender seams have a noticeable issue. From my understanding, before I mess the car up, I need to completely grind out the old filler then bevel the edges with a soda can or something similar then glass them back using a mat? Does the old filler need to be completely gone, or is it ground down some with fiberglass put over to build it back up?

I was able to get a gallon of bondo kitty hair for $10 on clearance, will this work or should I go with some west systems stuff?

The picture attached is the worst of them all, I plan to repaint the entire car at a later point. Advice would be much appreciated for this repair.
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Old 02-26-2019, 02:55 AM
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VPA only that part number. Fresh batch if possible.

So. groove it and clean it out

Apply VPA, sand and shape

Sand and shape again or until satisfied

End results can be very rewarding
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Old 02-26-2019, 02:59 AM
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Was thinking about picking some of that up but had no idea what exactly to get. How deep should the groove be? All old filler removed so I can see the bonding strip or not that deep?
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Old 02-26-2019, 10:18 AM
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All depends, sometimes the bondo goes all the way causing a hole which can also be done with VPA depending on the size. The bonding seam will only need a 1/16 maybe 1/8 deep, just a small groove maybe 1/4 inch wide. It's just so the VPA has sort of a track to sit in. Your going to be feathering it out to a wider pattern as show in the pictures.
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Old 02-26-2019, 09:43 PM
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Keep in mind the factory never used fiberglass mat to fill the seams. The seams were the hold up in the number of Cars they could produce in a day so the fastest way was the way it was done. I remember seeing Vettes in the late 70's early 80's that had horrible seam work done especially white or silver cars. This is why GM will never build a car that needs hand bodywork in the middle of a panel ever again. Anyway the Corvette repair shops quickly figured out that hand glassing the seams was a much stronger way and didn't have to be concerned about cars coming back showing seams.
In the first picture I would assume that there is a bunch of damage that was covered up using Bondo. The Bonding strip on the backside is probably broken and or a bit of it is missing. Can You see any of the back side ? If not just grind it out and see what You have to work with. My guess is that You will be putting it back together with hand layed fiberglass but that's no big deal.
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Old 02-26-2019, 09:55 PM
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There are some really hard parts to scrape off in that back area, so I'm thinking something might have bumped it or the PO might have backed into something.
I have noticed while scraping the paint off, some areas are fairly think and easy to scrape and others are really thin and pretty hard to scrape.

The top panel does lift ever so slightly for a few inches along the seam, would matting this in be fine? Do I need to do work to the rear bonding strip?

Also, what is the best way to grind this crap out? I do not have access to air tools, I have used a Dremel and that is painfully slow, I have also used an angle grinder which is faster but I'm afraid I might slip and do a lot of damage to the car.
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Old 02-26-2019, 10:10 PM
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I have some more pictures, the first two are of the pass side ground out some.








This picture below is of the rear driver side, are the X's normal for the factory to do? The pass side was not like this.
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Old 02-26-2019, 10:52 PM
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If you just use the VPA and not do it right by glassing the seam and then using whatever "minor" imperfection repair needs to be done with the VPA it will probably crack again down the road. Ask me how I know this. I ended up doing mine twice because of that easy way out wanting to get it done. Now it won't crack again unless I get hit this time. I took a very long time to do mine the second time, three color coats and five coats of clear. The last two cats of clear were applied a week later after I left it harden up and had to completely sand the car again because I made another bad mistake and didn't check my water filter until it was too late on coat three of clear. Water and clear do't mix. Ugh! Through two more coats of clear on and color sanded it all again. Came out looking good.
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Old 02-26-2019, 11:42 PM
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I think I'll glass it in as opposed to the VPA
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Old 02-27-2019, 11:32 AM
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Originally Posted by Buccaneer View Post
If you just use the VPA and not do it right by glassing the seam and then using whatever "minor" imperfection repair needs to be done with the VPA it will probably crack again down the road. Ask me how I know this. I ended up doing mine twice because of that easy way out wanting to get it done. Now it won't crack again unless I get hit this time. I took a very long time to do mine the second time, three color coats and five coats of clear. The last two cats of clear were applied a week later after I left it harden up and had to completely sand the car again because I made another bad mistake and didn't check my water filter until it was too late on coat three of clear. Water and clear do't mix. Ugh! Through two more coats of clear on and color sanded it all again. Came out looking good.
Around how much material did you use as far as glassing in the seams? Did you use VPA for a filler or did you glass and sand low spots down? I know budget and corvettes do not go in the same sentence, but I'm a college kid on one. That being said, I do not want to buy too much and not use it again before the shelf life ends.

I really like the West Systems stuff because I have had great luck with them, just do not want to spend the money on a gallon of epoxy when a quart will do, same with the VPA, do not want to spend $150 on a gallon when I can use one or two quarts and still save $50.
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Old 02-27-2019, 02:09 PM
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Originally Posted by Ksp3cialK View Post
Around how much material did you use as far as glassing in the seams? Did you use VPA for a filler or did you glass and sand low spots down? I know budget and corvettes do not go in the same sentence, but I'm a college kid on one. That being said, I do not want to buy too much and not use it again before the shelf life ends.

I really like the West Systems stuff because I have had great luck with them, just do not want to spend the money on a gallon of epoxy when a quart will do, same with the VPA, do not want to spend $150 on a gallon when I can use one or two quarts and still save $50.
I honestly do not remember exactly how much I bought, since I already had some on hand and used only what was needed and only had to do both front fenders. I wish I could help you on that one. West should be OK also. However, as far as filler goes, I only used what was minimally needed to finish the job and I do mean minimally. If you are going to do all the seams, I guess it could take a gallon...maybe, but maybe a half gallon would be enough. What really costs out the (blank) is the paint materials. I painted the entire car and used the Sikkens system for the seal/primer, (sealer is a must if you do not know the car owners and has been repainted before) but not the paint and clear which you really should stick with one paint system to ensure you don't have compatibility issues. I word of caution here...TheSikkens system IS very expensive, but it is also a VERY good high end product. I went with PPG high end system. If you are on a budget, Skikkens is NOT the system for you. As an example, a gallon of PPG base coat metallic (Dark Claret) was $520 a gallon and a gallon of PPG clear was $325 and was a few years back, so I'm sure it's more now. That does not include reducer, hardener, sandpaper etc, etc... You can easily spend over $1K on supplies. Just remember, if you buy cheap paint products, you will regret it later if you keep the car. It's a "you get what you pay for" kind of thing. A nice high end gun is also key as long as you know how to use it properly. I have seven guns including an IWATA air brush and used my IWATA LPH400 to paint the base and clear coats using an orange 1.4 nozzle for base and silver nozzle for clear. I love my IWATA guns, they always do a great job. Other's will work as well and are personal preference items, just don't use a Harbor Freight gun special to paint it. Hope this helps a little.

Here is a pic of a fender that was done about six years ago, they both look the same, no orange peel and still looks great.

Last edited by Buccaneer; 02-27-2019 at 02:21 PM.
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Old 02-27-2019, 06:01 PM
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The kitty hair you bought for $10...I would not use. Use it on something else...but not on your Corvette.

I can say this....Your seam repairs need to be bonded back on using some of the current 2 part adhesives in a cartridge. Such as SEM 39747.
Then the excess needs to be ground back and fill over it with VPA...

Laminating fiberglass over it will not do jack squat. in those photos you posted. the photo in POST #1 and the photo in POST #7. IF you feel that laminating over these areas and HOPING that it is solid....I will wait to see what happens IF you do this.

As for applying fiberglass and resin in your seam is up to you if and when you decide to get the panels bonded back toe the bonding strip. I can say I have NEVER filled in a seam with fiberglass and resin in order to correct the factory problems at the seams. .In the 30+ years of doing this stuff.... I have NEVER had any issues with the seam having ANY problems.....mainly because I use the Vette Panel Adhesive ( VPA).

The 'funny' thing is that if people stop and think about it. The bonding seam bonded onto the back of the two panels.....regardless of what panels you are wanting to use as an example.. It is reinforcing the area.....SO the gap...or visible seam...is what it is. AND the reason the seams show up in the factory cars is due to the VOLUME of cars being made every day....and the jigs they used to get it to what they felt is good enough for the standards they had at that time....and TIME

NOW.,..flash forward to today....and people want to make these visible seams not show up and conjure many different ways of doing it. Some 'feel' that laminating it makes it stronger. But funny how GM way of doing it did not cause the panels to fall apart DUE TO it has a bonding strip under these panels.

And for what it is worth...if the car gets hit...the body is going to bust....no way around it.

Like I mentioned...I have countless Corvettes that have the VPA in the tapered out seams and I can tell you that they DO NOT FAIL.

SO...do as you like. I am not trying to tell you what to do. Only how I know what works. I am very very good at laminating and not getting air bubbles into my laminations and NOT having my fiberglass mat swimming in a pool of resin.....so IF you feel that you can do it correctly...then have at it.....Because improper laminating is not good and all of your thoughts of what you think is doing good...is not. Ask me how I know this due to what I have repaired over the years when people 'attempt' to laminate and do a poor job and then wonder why it failed. BUT I can say that IF you think you are going to jamb fiberglass and resin in your separated panels where they became un-bonded from the bonding strip...I would SERIOUSLY think again on that....because THAT WILL have a very high percentage of being able to FAIL.


So...the chose is yours....both ways showing excellent results...but one is much more involved....so it is up to you.

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Old 02-27-2019, 06:49 PM
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I have also used the two part 3M product that is awesome and put that on other parts of the fiberglass and was great. Sandable as well and extremely hard when dry. You use it for boding door skins on.
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Old 02-27-2019, 06:55 PM
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Originally Posted by Buccaneer View Post
I have also used the two part 3M product that is awesome and put that on other parts of the fiberglass and was great. Sandable as well and extremely hard when dry. You use it for boding door skins on.
Some of the 3M stuff is good to use...all depends on what it is you are doing....but I just use the SEM 39747 seeing how the SEM products are epoxy based...as long as the bare steel is covered with it...the metal cannot rust. I have no clue about the 3M stuff.....and sometimes I use the LORD FUSOR adhesives...because some of them can be applied on a specifically primed surface.

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Old 02-27-2019, 11:01 PM
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^^^THIS^^^
A friend of mine swears by SEM two part with a gun and I know its good stuff as well and did borrow it once. It was impressive stuff. It's more what you are comfortable with I guess.
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Old 02-28-2019, 05:22 PM
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^^^^
YEP....Some swear by using 'this or that'. Sometimes it really does not matter...but sometimes it does. And what can often times be the deciding factor is when a person uses 'something' .... they can see how well it works 5, 10 or 20 years later.

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Old 03-01-2019, 09:12 PM
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So if I'm understanding this correctly, grinding out the seam and filling it in with VPA will be fine? Matting in fiberglass will potentially cause more problems down the road? The 2 part stuff is the best but expensive for only a few ounces

I do have some g flex left from West systems that is a 2 part, I used this stuff to glue the header bar back on and it's holding solid after a year. Any reason this would be a bad idea?

I'm thinking about going with only the VPA now. Sorry about all the questions, I'm just try to learn from others experience so I don't make mistakes others have. I greatly appreciate the help so far!
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Old 03-02-2019, 10:50 AM
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Use the SEM 39747 bonding adhesive. As Dub said it's epoxy based but its also has a little flex to it so you don't have to worry about the panel cracking above or below the repaired area.
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Old 03-02-2019, 01:22 PM
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Panel adhesive is meant to glue two flat surfaces tight against each other, not butted edge to edge. The VPA filler is for non-structural repairs, says so right on the can.

The panel adhesive would work to glue the bonding strip back onto the 2 panels. To do that, you'd need to open the seam of the bonding strip and properly glue it back on with the panel adhesive. Otherwise, glass over the seam which basically removes it. I wouldn't use panel adhesive as a seam filler from the front on those panels where the bonding strip is broken between them. You're saying the 2 sides of that bad seam can move independent of each other, so you know the bonding strip is broken off in that area.

Watch some youtube videos on boat repair. This one is a pretty good intro. Take a look at the size of the bow of the boat behind him in certain views.


Last edited by lionelhutz; 03-02-2019 at 01:34 PM.
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Old 03-02-2019, 06:40 PM
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Originally Posted by Ksp3cialK View Post
So if I'm understanding this correctly, grinding out the seam and filling it in with VPA will be fine? Matting in fiberglass will potentially cause more problems down the road? The 2 part stuff is the best but expensive for only a few ounces
OK...IF you are JUST re-working the seams and filling them in. Using VPA is going to do just fine and NO NEED to laminate it. Not like I have been doing this for decades and ONLY trying to tell you what I know that works. But go ahead and laminate if if you want to. No need to do it the way I do it.

Laminating in fiberglass mat and resin CAN cause for problems IF the person does not do it correctly. NOT an opinion...but a fact. Why do I write this...because I have to fix those type of repairs that were done rather poorly.

YES...only needing few ounces of the 2 part adhesive is...just what it is...and sometimes. there is no way around it.....unless.....you are the type of person who wants to find a 'cheaper way' . heck...a person doing by themselves is already saving so much money due to not having to pay someone....but still they freak out on having to spend money on something that they only need a little bit of. And then.....they find some cheaper alternative...and use it...only to find that POSSIBLY in the future that repair will come back and THEN they wish they had spent the money when they had the chance. SO...when and if a person chooses to use a product that they ahve not confirmed will do the job...they are just asking for trouble....if...the reason is cost.

Originally Posted by Ksp3cialK View Post
I do have some g flex left from West systems that is a 2 part, I used this stuff to glue the header bar back on and it's holding solid after a year. Any reason this would be a bad idea?
I would contact West Systems and tell them what you are planning and see if that product....as long as it is still good....would work. I do not use it so I cannot say with 100% certainty that it would work. I am sure that this product will work due to West Systems products are really well known for their effectiveness.

Originally Posted by Ksp3cialK View Post
I'm thinking about going with only the VPA now. Sorry about all the questions, I'm just try to learn from others experience so I don't make mistakes others have. I greatly appreciate the help so far!
I MUCH RATHER you ask questions than not ask any questions. So....seriously...if you have any questions...ask away.

All I know is that from the photos of your car....if it were in my shop. I would prep and clean out the separated panels seam areas...inject in the SEM 39747 (because I keep it on hand). Any of the oozing SEM product that comes out on the outer area gets ground back to where I can only see the thin seam of it. ThenI would apply the VPA.

NOW.....due to ONLY seeing what you have allowed us to see in your photos. I have run across some scenarios where I have needed to laminate in some West Systems epoxy resin and then finish out the area.....but those areas are usually on the flanges of the panels where the bumper makes contact.

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