Anyone use automotive seam sealer instead of body filler??

[CARS]

I've been reading as much as I can the last couple weeks (still have more questions than answers). I haven't seen anyone use automotive seam sealer to seal their seams.

The idea came to me after reading the Wikibook: http://en.wikibooks.org/wiki/How_To_Bui ... op_Trailer

The author uses "bondo" (a generic term for one of the hundreds of brands of body filler) to create mouldings to hide the seams of the roof.

As a body man, body filler is the weakest thing on a body. It can crack and absorbs water. About 15 years (or so) ago, 3M came out with a roll of seam sealer that we started using instead of the caulk-type seam sealers. It looks cleaner and remains semi-flexible.

Here is a quick net search find: http://solutions.3m.com/wps/portal/3M/e ... M7FB7MWJbl

http://multimedia.3m.com/mws/mediawebse ... 008476.pdf

It would only be used on painted trailers. And I don't know if it would cure onto a latex paint. Once it is applied to automotive paint, it's impossible to remove it without scraping. I don't have any in the shop now because I do restoration work (so I have to reproduce the sloppy, brushed on sealers used till the mid 90's).

If it's never been tried before I can get a roll of it and see how it works.
Just trying to throw out another option that I haven't read about on T&TTT

Chris

[emiller]

I have used it a few times.

[atahoekid]

If it's never been tried before I can get a roll of it and see how it works.
Just trying to throw out another option that I haven't read about on T&TTT

I for one want to know how well that works. Since you have auto body experience it would be better for you to try it I think. I talked to my dad, who worked in auto body but retired about 20 years ago and he didn't know anything about the product. I used to help him during the summers of my high school years and I don't recall seeing anything like that either. I'll be following this with interest.

[CARS]

It's on the truck for Thursday's delivery.

Next question, what are the most common wood sealers used that I should try this on?

Epoxy's? Latex? ???

[cracker39]

I used Bondo epoxy auto filler on the original Squidget, and on the Squidget PT I am building now. It works great to fill and hide seams where plywood sheets join edge to edge. Before applying the plywood, I sand down half of the joining edge at 45 degrees, creating a V groove where the two pieces of plywood join. I put the Bondo in the groove, let it cure and sand smooth. It usually takes a couple of applications to get the joint so that it can't be seen when painted. The drawing below shows the technique, before and after sanding the Bondo flat. With careful sanding, the joint will be invisible when painted. I like Bondo over wood fillers for two reasons. First, I've had wood fillers cause my epoxy resin to not cure, but remain sticky over the filler. Bondo is completely compatible with epoxy resins. Second, Bondo sands very smooth. I also use it for filling countersunk screw holes and other imperfections in the plywood.

[CARS]

I understand how everyone is using it, but as a bodyman I feel that most of the builders on this forum are unaware that the product is not designed for that application.

Body filler is as generic of a term as you can get. There are hundreds of body fillers out there. Bondo is a brand name of probably the Cheapest filler known to man. It gets a well deserved bad rap in the automotive world. It is weak and absorbs water like a sponge.

In the automotive world, one would never fill a seam with body filler. It will crack and decontaminate under the stresses of driving down the road. Furthermore, it is designed to be used on bare metal that has some "tooth" (grinding marks). maybe it works it's way into the coarse end-grains of plywood and that is why it is working for you.

A fiberglass based filler would be best to use in this application. It does not absorb water. It's a little tougher to get finished off, but it is stronger than body filler.

My thought for asking this question was "what if all these builders don't know any better?". If "bondo" is working for you, great! I just want to point out that there are "more appropriate" products out there. Technology is a great thing. Bondo is the '60's answer for lead filler used in the first half of the 1900's. The automotive filler world has come light years ahead since then. Stronger, lighter, easier to work with.

I just want to try a few experiments in the shop and do some destructive testing and water tests. Who knows, maybe automotive seam sealer doesn't work with wood??? I wont know till I try!

I'll ask again. What is the most common wood sealers used by builders for me to try this on??

[cracker39]

Body filler is as generic of a term as you can get. There are hundreds of body fillers out there. Bondo is a brand name of probably the Cheapest filler known to man. It gets a well deserved bad rap in the automotive world. It is weak and absorbs water like a sponge.

So far, there are no problems with the Bondo Lightweight Body filler that I used in the seams and screw holes on the 5 year old Squidget After the filler and skin was sanded smooth, I coated the entire skin surface with epoxy fiberglass resin that was lightly sanded to smooth and scuff it before finishing with a Zinser primer and Glidden latex porch and deck enamel. With all of that on top of it, the Bondo filler can't possibly get wet and absorb water.

That's my story and I'm sticking to it. And, sticking to using the Bondo on my PT.

[john]

Cracker,

I like Bondo over wood fillers for two reasons. First, I've had wood fillers cause my epoxy resin to not cure, but remain sticky over the filler. Bondo is completely compatible with epoxy resins. Second, Bondo sands very smooth. I also use it for filling countersunk screw holes and other imperfections in the plywood.

I'd like to add that during my rushed standy build that it also cures very quickly. All filling than sanding, filling then sanding and perhaps one last filling and sanding can be done in a single day.

I am curious, though, about that stuff in the tube. I believe that when I have seen it used it shows as a bead usually in hidden areas; under a trunk lid in the corners on the body of the car for instance. Can the stuff be sanded smooth like fillers?

[cracker39]

I'd like to add that during my rushed standy build that it also cures very quickly. All filling than sanding, filling then sanding and perhaps one last filling and sanding can be done in a single day.

I agree...add one more reason why I like using Bondo body filler on my plywood skins.

[48Rob]

After the filler and skin was sanded smooth, I coated the entire skin surface with epoxy fiberglass resin that was lightly sanded to smooth and scuff it before finishing with a Zinser primer and Glidden latex porch and deck enamel. With all of that on top of it, the Bondo filler can't possibly get wet and absorb water.

Hi Dale,

I'm not disputing your success, sounds like it is working well for you.

In general, unless you also completely seal the edges and back of the panels, moisture can still migrate through the wood and make contact with the filler/coatings "from behind".

Probably won't be an issue if everything inside is kept dry.
A leak somewhere down the road that would allow moisture to get inside the wood...or a window left open and rain/snow inside all winter are the kinds of high humidity needed for moisture to cause failure.

Rob

[cracker39]

In general, unless you also completely seal the edges and back of the panels, moisture can still migrate through the wood and make contact with the filler/coatings "from behind".

Rob

On the Squidget, I bought 1" x 1" aluminum angle that I cut and screwed to all of the joints where the wall joined end and roof panels. For the joints running side to side, across the cabin, I had strips of 2" wide aluminum bent to fit the angles and screwed to those joints. I put poly caulk beneath the aluminum. It also gives it an "industrial" look. I"ll do the same for the sides of the PT, but will probably put glass cloth and resin on the joints running side to side.

You can see the aluminum trim in these two end shots of my Squidget.





I also plan on putting 3" wide molding on the chassis and lower 1" of the walls to protect those lower edges. One of my customers built his Squidget with the lower molding as seen in the photo at the URL below.

http://www.thesquidget.com/squidgetbuild.html

[eamarquardt]

I used Bondo epoxy auto filler on the original Squidget, ........and on the Squidget PT I am building now. It works great to fill and hide seams where plywood sheets join edge to edge........... I like Bondo over wood fillers ............ Bondo is completely compatible with epoxy resins. Second, Bondo sands very smooth. I also use it for filling countersunk screw holes and other imperfections in the plywood.

Lottsa truth there, however, Bondo apparently makes two types of fillers. Polyester based and Epoxy based.

You can put epoxy stuff over polyester but using polyester over epoxy can be iffy as the styrene may disolve the epoxy.

I like "microballoons" and epoxy for a filler.

Here is an interesting thread:

http://www.boatdesign.net/forums/fiberg ... 19179.html

It gets a bit testy though, ha!

Here is another with some more thoughts:

http://www.boatdesign.net/forums/materi ... 16587.html

Cheers,

Gus