Sealing Boat Tail?

[HydroJim]

I'm currently in the planning stages of all my aeromods and was thinking of the best way to seal a boat tail made out of sheet metal. To understand what I'm talking about look at the blue areas of my attached picture. I came up with the idea of using fiberglass cloth and epoxy resin when I saw some other aero mods. The only problem is, I have no idea how to do it. I looked it up on google, and I have a pretty good idea how to do it now. But, I wanna make sure my process if right so I'm asking you guys for help.

My process:
1. cut strips of fiber glass cloth
2. dip into epoxy resin
3. Lay strips onto sheet metal. Similar to paper mache.
4. Add layers until adequate. Drying time in between layers?
5. Sand down until even.
6. then everything is ready to prime and paint? or do I need bondo ontop?


I could also weld all the seams, but that seems like it would take a long time and involve a lot of grinding to get a smooth finish. What do you guys suggest?

Thanks,
Jim

PS: photo not to scale. quick sketch.

[skyking]

don't dip, paint over with a brush. The fiberglass will make a huge mess if you try to dip it.
That said, I don't know how good that will work with slick metal. Typical epoxy prep is done with rough sandpaper to give the epoxy resin some "tooth" to grab onto.
So, if you used galvanized metal now you are making potential rust areas, unless you intend to 'glass over the whole thing.

[HydroJim]

I would definitely sand the area before I applied the fiberglass. and I will be painting the whole thing so my material doesnt matter all that much.

I realized not to dip the fiberglass but to put the epoxy down. then the fiberglass. and then brush epoxy on top.

Are my steps other than that correct?

[skyking]

Jim, I tend to apply the cloth to the structure dry, and wet through it with roller and brush.
This lets you position the cloth with no trouble, without any urgency. Skip to the 1'40" mark in this video for an example:

http://www.youtube.com/watch?v=iJsHOTwQo5o

On an outside corner (convex) layup like your boat tail, I drape the cloth all the way across and let it hang past. I wet it out with a roller, brush, and use the plastic squeegee to get the bubbles out and smooth things. Don't worry about that hanging edge. You can't easily glass beyond that vertical surface. Hang the cloth just past the edge and don't worry about a little resin lost on the cardboard (you put on the floor before you started).
Continue adding cloth wherever you want, using fresh brushes and rollers with a new batch of epoxy as needed. Epoxy will become unworkable in 25~40 minutes depending on what you are working with. Old brush + new batch = bad times.
I get bags of 10 chip brushes from home depot and toss them.
For finish coats I do the same with foam brushes.
Depending on the resin system you use, come back in 4~6 hours and trim off that excess hanging cloth and resin with a knife. Much easier than sanding after it gets hard.
Once it is tack free, you can flip the part and lay up the other side. Keep adding cloth and resin for up to 24 hours. If you can't do that, after about 3 days you will have to sand before adding. That is a big pain and a step backwards.
Here is one epoxy manual with some good info:
Raka, Inc. 772-489-4070

Here is another:

System Three: Resource Library: Published Literature

Bending cloth across hard corners is tough. It does not like that and works better on radiused corners. Keep that in mind as you build your boat tail. The air prefers radiused corners as well.
Coincidence? I don't think so

[euromodder]

Why would you want to fiberglass a sheet metal surface ?
Using a silicone glue / sealant will seal the plates to the structure and reinforce it at the same time.

The joint on the car could likely do with some flexible sealant like silicone kit, as it is going to flex during driving.

[Quasimoto]

Originally Posted by HydroJim

I'm currently in the planning stages of all my aeromods and was thinking of the best way to seal a boat tail made out of sheet metal. To understand what I'm talking about look at the blue areas of my attached picture. I came up with the idea of using fiberglass cloth and epoxy resin when I saw some other aero mods. The only problem is, I have no idea how to do it. I looked it up on google, and I have a pretty good idea how to do it now. But, I wanna make sure my process if right so I'm asking you guys for help.

My process:
1. cut strips of fiber glass cloth
2. dip into epoxy resin
3. Lay strips onto sheet metal. Similar to paper mache.
4. Add layers until adequate. Drying time in between layers?
5. Sand down until even.
6. then everything is ready to prime and paint? or do I need bondo ontop?


I could also weld all the seams, but that seems like it would take a long time and involve a lot of grinding to get a smooth finish. What do you guys suggest?

Thanks,
Jim

PS: photo not to scale. quick sketch.

What type of steel are you using for the tail? If not galvanized it would be strongest to just weld it. Galvanized brings with all types of extra problems; you shouldn't weld it (toxic fumes), not much sticks to it (fiberglass, paint) without proper preparation. How are you attaching the steel to the frame? If you decide on fiberglass; you should get some fiberglass tape, which is heavier than most cloth for the corners and seams. There are many different ways of applying resin to the cloth, all which work. Lots more work than just welding and grinding.

[Sven7]

I was going to say silicone caulking like you'd use on house trim. But then it got a little confusing- like others said above, why use fiberglass over steel? Steel is heavy and if you're using glass anyway why not make the entire thing out of it?

[skyking]

I agree, I'd used foam or 1/4" plywood and glass over that. Very strong and rigid, corrosion proof.

[jimepting]

Steel is not practical for a DIY'er. It will be too heavy, and will require stong attachment points, which are probably not available.

If your design involves gores or sections of streight planes, as apparently it does, then why not just use half inch blue foam to make the gores and glue them together at the edges. You can then fiberglass the entire structure, inside and outside for a strong and light structure. You can make your attachment points from wood which you will glue into place and cover with fiberglass, making them a part of the overall structure.

See this link for a very complete development of a boat tail for a first generation Insight:

Honda Insight Tail Extension Project

[HydroJim]

Now that I see how making the boat tail out of foam works, I think that is the route I am going to go. One detail that I'm confused about is how the foam boat tail attaches to the car. It sounds like the foam is being glued to the wood frame, but that seems like a weak attachment method to me.

Anybody know how I would go about doing this?

Thanks,
Jim