Adhesive: Fiberglass to Metal

[DeanM2]

My Winnebago Class A has several places where the factory used adhesive to bond fiberglass pieces (such as the front and rear hoods) to metal frames/structures. A few of these bonds have failed. The adhesive never pulls away from the fiberglass, the joint always fails at the bond to the metal as I believe the factory paint on the metal parts is coming off of the metal. Previously, I have repaired some of these by applying fiberglass resin/cloth from the fiberglass, around the metal. But now I have some problems where I can't phsically get fiberglass around the metal. I need to squeeze in a bunch of goop, slop it around the metal, and hope it holds.

What is a recommended adhesive for bonding fiberglass to metal parts in an RV? Hopefully having the following properties:

• Black in color
• Rated for outdoor use and temperature extremes.
• A bit flexible after cure so it doesn't fail due to vibration.
• Fairly thick so it doesn't run before it cures.
• Can be used with a thick bond-line; up to a 1/4".

Thank you for any help.

[Jim_HiTek]

Many of us have shrugged our shoulders and avoided using the same method of attachment that's well known to fail after a few years. So we just drill from behind the bracket through to the front, and then either install stainless bolts, or screws.

In my case, I've been using SS 6-32 flathead screws countersunk on the surface with plastic insert locknuts and SS flatwashers. In the 7 years since I've done that to the rear and front of the RV, not a single failure, no rust, no cracks in the fiberglass, and they are so small, they're barely noticeable so I haven't even dabbed them with paint. Only prep work was to hold the brackets in place so I could use the drill and drill through the holes in the brackets. Just 2 per bracket btw. I need a RT angle drill for some of them, but so far those particular brackets are still holding and haven't needed to use one yet.

Here's my ad free blog articles about the job: Bodywork - Rear

Another ad free article: Bodywork - Front

Have fun with it and if you choose to re-epoxy the brackets, note that from what I've read by others you'll have hours of fun with the prep work. Using screws means a few minutes of work, total.

[rk911]

What about JB Weld?

[bigb56]

Originally Posted by DeanM2

My Winnebago Class A has several places where the factory used adhesive to bond fiberglass pieces (such as the front and rear hoods) to metal frames/structures. A few of these bonds have failed. The adhesive never pulls away from the fiberglass, the joint always fails at the bond to the metal as I believe the factory paint on the metal parts is coming off of the metal. Previously, I have repaired some of these by applying fiberglass resin/cloth from the fiberglass, around the metal. But now I have some problems where I can't phsically get fiberglass around the metal. I need to squeeze in a bunch of goop, slop it around the metal, and hope it holds.

What is a recommended adhesive for bonding fiberglass to metal parts in an RV? Hopefully having the following properties:

• Black in color
• Rated for outdoor use and temperature extremes.
• A bit flexible after cure so it doesn't fail due to vibration.
• Fairly thick so it doesn't run before it cures.
• Can be used with a thick bond-line; up to a 1/4".

Thank you for any help.

I fixed mine with 3M 5200, it fits everything on your list except it is white. It also requires humidity to fully cure and can take several days to a week to fully cure, but I can guarantee you it won't ever come off.

[Rob_M]

Yes 3M 5200 would probably work well. Get the surfaces super clean first of course. The trick will be holding the parts tight together while the 5200 cures.

It’s used all the time in marine applications to bond components to boat hulls. They say if you ever want to remove the part don’t use it. Use 4200.

[Hikerdogs]

SEM makes another product called 39537 Adessive sealant. It's a 2 part acrylic used to bond fiberglass and plastic parts to metal substrates. It's typically used by body shops to bond door and body panels to the framework.

We used it on our 2001 Adventurer headlight bucket when it detached at about 20,000 miles. The repair was still intact when we traded the unit off 12 years and 100,000 miles later.

This stuff does the job, but it's expensive. It sells for between $50.00 and $75.00 depending on where you buy it. We bought ours at a local body shop supply house.

[Terraboat]

3M 5200 is available in black:https://www.3m.com/3M/en_LB/p/d/v000085090/

In the boating world, we call it 52,000! It's nearly impossible to break the bond (don't ask me how I know).

[Rob_M]

Just found out they make a fast cure 5200 also.

[bigb56]

Originally Posted by Terraboat

3M 5200 is available in black:https://www.3m.com/3M/en_LB/p/d/v000085090/

In the boating world, we call it 52,000! It's nearly impossible to break the bond (don't ask me how I know).

Good to know, maybe I should have used that on my Winnebago roof edge seal instead of clear Proflex.

[DeanM2]

Originally Posted by Jim_HiTek

Many of us have shrugged our shoulders and avoided using the same method of attachment that's well known to fail after a few years. So we just drill from behind the bracket through to the front, and then either install stainless bolts, or screws.

Thank you for your response.

O.K. I know that a mechanical bond is better than an adhesive bond for this type of situation but I just couldn't stand the thought of drilling through my fiberglass and having a bolt. But after your response, I took a good look at the situation and it would be impossible to properly clean the surfaces involved. So, I went out and looked at the back of motorhome (diesel pusher) and found that the rear cover already has some factory stainless bolts being used on the rear cover. So... I drilled some additional holes through the fiberglass and underlying metal frame, and filled them with stainless Button Head bolts. Problem solved in about 15 minutes. They actually look pretty darn good.

[Jim_HiTek]

Yeah, many have used SS button head bolts and from the pictures and real life examples I've seen of that, they do look good. If the heads aren't too big. In my case, I have a many drawer cabinet I carry from my engineering days that's filled with hardware. And rather then let all the hardware I've accumulated over the decades go to waste, I initially thought that my flathead SS screws would work best on the sides of the rear grill as shown in this picture. So nothing would poke out and get caught when that grill was opened and closed. They worked so well, and just two of them, that when the bottom rear 'bumper' loosened up because of failed epoxy, that I stuck with them. Then later, the front grill also loosened up and so I just carried on with the 6-32 hardware. Still working well after all these years.





Just a suggestion that you tighten the nuts so they are just 'snug'. That way there's some give and slop so driving or frame twisting up and down curbs won't promote fiberglass cracking. Though I'm not sure that would happen anyway, but it doesn't hurt to try to prevent it. I've been on some pretty rough roads over the last 7 years, and so far no cracking around the drilled holes.

[Olive]

Over 10 years ago I had a similar problem. Winnebago techs said to use a construction adhesive which I did. I bought it at HD or Lowes. Now many years and almost 100k miles later it is still holding strong

[Rob_M]

Originally Posted by Olive

Over 10 years ago I had a similar problem. Winnebago techs said to use a construction adhesive which I did. I bought it at HD or Lowes. Now many years and almost 100k miles later it is still holding strong

Like Liquid Nails brand?

[Olive]

I don't remember the brand name I used. It was the heaviest duty the store had.

I cleaned the areas and sanded a bit before using the adhesive. Later I was at Winnebago Customer Service and was going to have them repair it with what they used but they left it alone because they couldn't get it apart. As I said earlier that was at least 10 years ago, probably more.