body filler

[Jay H]

Hey folks, got a question here that I am hoping someone might have some experience with. Can you put Bondo brand autobody filler on a fiberglass egg without it separating or eventually delaminating?
I have been repairing some damage to the fiberglass body and very slowly building up the layers and it really labour intensive. I have tried a variety of glassing methods, chopped fibers, straight resin, even resin thinned with Acetone. I used the acetone mix to fill pinholes. I have had good success but honestly the bondo body filler achieves the same appearance much faster and with way less sanding. According to 3M, Bondo Body filler is usable on fiberglass,
So, yes I am looking for the easy way out!

[Rick Mooyman]

I used Evercoat Kitty Hair for my fiberglass repairs and seems to be holding up well.

[FRED SMAILES]

I put a bunch cheap body filler on mine over 10 years ago, still there no problem.
First 2 are from 03 last one '14
fred

[FRED SMAILES]

Better pic?

[captsteve2002]

Bondo will soak up water and fail in time. There are a number of very good fillers on the market. For small pin holes I like to use Marine Tex- that can be bought at Ace Hardware Stores. It is an epoxy base, harder to sand, but doesn't allow water to soak in, and fail. I also use a product called Red Hand, Manufactured by International Paints. Smallest container i have seen is 1 qt. part A and 1 qt. part B. Might be a bit much having 1/2 gal. of filler. This I have seen at West Marine. Good luck with your project

[D White]

Originally Posted by captsteve2002

Bondo will soak up water and fail in time. There are a number of very good fillers on the market. For small pin holes I like to use Marine Tex- that can be bought at Ace Hardware Stores. It is an epoxy base, harder to sand, but doesn't allow water to soak in, and fail. I also use a product called Red Hand, Manufactured by International Paints. Smallest container i have seen is 1 qt. part A and 1 qt. part B. Might be a bit much having 1/2 gal. of filler. This I have seen at West Marine. Good luck with your project

This is absolutely untrue from an obvious boat guy...Bondo WILL NOT FAIL EVER ON YOUR TRAILER...IT IS WHAT IT WAS ORIGINALLY DESIGNED FOR. THE ABOVE POST IS NOT CORRECT...PERIOD... Fiberglass Dave

[Andrew Gibbens]

The important thing when adding body filler to cured fiberglass is to thoroughly sand all the area the filler has to stick to. This doesn't mean waving some abrasive near it but actually going over every square inch of the area. This is required whether the filler is being added to the 'back' (fiberglass) or 'front' (gel coat) sides.

My former boatbuilder boss was adamant that this should be done with not-too-coarse abrasive - 40 grit looks like it is aggressive but it has only half as many 'points per inch' as 80 grit, so 80 is a better choice.

[padlin00]

Used it on Corvettes, non came back due to bondo failure.

[Thinh]

...Talking ab body fillers of all types ( fiberglass/steel sheet-metal or aluminum), they are OK in term of body works, smooth outcomes for pin-holes...IMO, it is good but not for strength. So, when working with fiberglass, I used BOTH, FG resin for strength and body fillers for final. Before applying base coat and clear coat or...one-shot-for-all, making sure apply primer. That is my own application...With big jobs of F.G, also using super-glues, metal brackets and rivets first of all...

[Jay H]

Thanks for the excellent advice everyone. I have fiberglassed and worked the surface right up to the final layer but I have been struggling with getting the finish that I wanted before I start painting. I was sure that Bondo style filler would work but the internet is rife with contradictory info, so I figured I would call on the experience of this group, thanks. (and Dave White - thanks for responding, I was really hoping you would!)
Fred thanks for the pics and the testimonial, your body work looks great.
I am excited to get back to finish the job.
Jay

[padlin00]

Have always used glazing putty for a great finish. After sanding final body filler coat put on a coat of primer, sand lightly with fine paper. Any imperfections will show up and can be filled with a thin coat of glazing putty, red provides the longest working time, very slow drying, dries very hard, make sure it's a thin coat, wet sand with 400, prime again. Bondo makes a glaze/spot putty that's supposed to be easier to work with.

[D White]

Originally Posted by padlin00

Have always used glazing putty for a great finish. After sanding final body filler coat put on a coat of primer, sand lightly with fine paper. Any imperfections will show up and can be filled with a thin coat of glazing putty, red provides the longest working time, very slow drying, dries very hard, make sure it's a thin coat, wet sand with 400, prime again. Bondo makes a glaze/spot putty that's supposed to be easier to work with.

Red putty is not catalized and will shrink...also it is made to go under primer, not really over....the accepted method is body filler, CATALIZED glaze if needed, primer, sealer, paint...Fiberglass Dave

[padlin00]

Originally Posted by D White

Red putty is not catalized and will shrink...also it is made to go under primer, not really over....the accepted method is body filler, CATALIZED glaze if needed, primer, sealer, paint...Fiberglass Dave

Guess I've been doing it wrong all these years. I don't feel bad though, 3M has it wrong too.

Directions for Use
1. Do not apply when ambient temperatures are below 55ºF or above 110ºF. Use in
a well ventilated area away from sparks or open flame.
2. For best results Apply only over clean sanded primed surfaces. (Use
compressed air to remove any dust contamination).
3. Apply using a plastic or metal spreader pressing the putty firmly into the
imperfections; keep the application thickness to 1/16" or less. Apply in thin coats
instead of one thick application.
4. Allow to dry for 20 minutes at 72°F prior to sanding. Sand (wet or dry) using
3M™ abrasives in the following sequence P180, P220, P320. Note: As with any
putty, longer drying times will occur with high humidity, thick applications and
low temperatures.
5. Re-clean surface prior to priming or top coating. (Follow paint manufacturer’s
recommendation for priming and top coating).

[D White]

Originally Posted by padlin00

Guess I've been doing it wrong all these years. I don't feel bad though, 3M has it wrong too.

Directions for Use
1. Do not apply when ambient temperatures are below 55ºF or above 110ºF. Use in
a well ventilated area away from sparks or open flame.
2. For best results Apply only over clean sanded primed surfaces. (Use
compressed air to remove any dust contamination).
3. Apply using a plastic or metal spreader pressing the putty firmly into the
imperfections; keep the application thickness to 1/16" or less. Apply in thin coats
instead of one thick application.
4. Allow to dry for 20 minutes at 72°F prior to sanding. Sand (wet or dry) using
3M™ abrasives in the following sequence P180, P220, P320. Note: As with any
putty, longer drying times will occur with high humidity, thick applications and
low temperatures.
5. Re-clean surface prior to priming or top coating. (Follow paint manufacturer’s
recommendation for priming and top coating).

I stand corrected...no one I know in the business has used red glazing for the last 30 years...so if you want to use it, follow the above directions or the directions on the tube...Fiberglass Dave

[Jay H]

I will look into glazing putty next time I am in CTC or Autopro. Honestly though I usually just skim coat a really thin layer of bondo over my sanded bondo repair. With a thin coat and lots of pressure using either a narrow plastic or steel spreader I have always gotten what I thought were good results.
By the way, I put body filler on the repairs today and sanded the area. I am very pleased. my goal was to even out to the level of the gel coat and since I was working on the top back corners it was important to maintain the profile.

[D White]

Originally Posted by Jay H

I will look into glazing putty next time I am in CTC or Autopro. Honestly though I usually just skim coat a really thin layer of bondo over my sanded bondo repair. With a thin coat and lots of pressure using either a narrow plastic or steel spreader I have always gotten what I thought were good results.
By the way, I put body filler on the repairs today and sanded the area. I am very pleased. my goal was to even out to the level of the gel coat and since I was working on the top back corners it was important to maintain the profile.

Red putty is lacquer based and not really compatible with anything but lacquer products although some people still use it with everything, so they still make it. Your way is better and will give you less problems.