My 79 zx has a small rust buble, about 1 1/2 inches square, over/under the top windshield trim.  The windshied is cracked and scheduled to be replaced.  I want to repair the rust buble while the glass is out.  I suppose Bondo could do the job but is there a better product that would be as easy and better to use? 

Edited September 12, 20231 yr by mayolives

I don't know what your body work experience is but that 1.5" rust spot will probably be 3-4 x as big once the glass is out and you start digging, if you find perforations in the metal you are going to want to cut that metal out and weld in new metal.  If it is just surface rust make sure you get all of it down to bare clean metal.  If you can, epoxy prime the area before you start using the filler, bondo, Evercoat,UPOL they are all good products.

If you must use “bondo” on bare steel (don’t! Prime it first, epoxy primer is good), use the short strand fiberglass filler rather than regular light weight filler. It soaks up WAY less moisture from the air than standard bondo. Standard bondo on bare steel is the fastest way to get that steel rusty and have that bondo go byebye.

Bondo ( plastic body filler) is really not a suitable material for dealing with rust holes. It is not water proof so moisture can travel through it and continue the rusting process. Grannyknot is correct that the hole is probably larger than you suspect once you get back to sound metal. I also agree with the sentiment that you need to get the metal clean. I would also add a step of treating the rust with a phosphating chemical. This chemically converts what minor rust is left. If I was going to try to fill a hole after this and didn't have access to a welder then I would use short hair fiberglass resin. Fiberglass resin is totally water proof after it's cured. But bare in mind that fiberglass resin gets much harder than filler! It's harder to shape and finish well. Once the hole is sort of filled and sealed up you can use filler over the primed resin to make it smooth.

I highly recommend you visit the POR 15 website to educate yourself on products for your repairs. As @Patcon recommended, once you remove all of the affected metal you need to neutralize any remaining surface rust. The POR product "Metal Prep" is one of those products and it leaves a protective barrier coating that is ready for your primer or other product.

Here is your starting point: https://por15.com/

This forum, https://www.autobody101.com/forums/index.php?sid=f044bf1f351a02abe241234902095df9

is a great place to learn.

On 9/13/2023 at 2:37 AM, grannyknot said:

This forum, https://www.autobody101.com/forums/index.php?sid=f044bf1f351a02abe241234902095df9

is a great place to learn.

I get a FORBIDDEN Error 403 when i try to access this resource..  is it because i'm in europe? strange..

Maybe,  the link worked for me

I'm getting the same error.

Probably the EU authorities "protecting" us from learning too much.....

 

Worked for me, first brexit benefit I've found!

Worked for me, first brexit benefit I've found!

Yeah, I hear that loudly! On that note some US based muscle car fora I used to read became inaccessible post GDPR but work again! :D

The ONLY benefit!

The last thing i want to do is humiliate people but.. yes, the first thing i said to myself was.. they are going to regret that!  All that paperwork alone (something i REALLY HATE!!)  Comes back..  tonnes of work, for what?

It was just a big mistake.. get back in there! TODAY!!  🙂 

Back on topic, guys, thanks for testing that site! Thanks, Chas!