Tech tip request: patching rust and/or paint prep: Grassroots Motorsports forum: Classic Motorsports

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April 29, 2009 4:37 p.m. Tyler H Dork

Checked out the articles and tech tips and was surprised that there isn't anything on rust repair and/or DIY paint prep.

Can anyone link me to some good online articles?

I remember a GRM issue some years back about doing your own prep for a Maaco paint job. I'll have to go pull that issue.

My new rat Miata has a 2" x 4" hole in the rocker, in front of the driver's rear wheel. Seems like a lot of Miatas are afflicted with this problem.
April 29, 2009 5:36 p.m. Toyman01 Reader

This is how I did/doing the repairs on my RX-7 (edit) except I welded everything.

http://wwwx.cs.unc.edu/~hays/crx/dx/rust_repair/

Keep in mind that rust is like rot. As you get into it you will find more rust than you planned to repair. The RX-7 started as a few bubbles in the paint and ended up with major body work. I ended up rebuilding most of the sunroof, the rain gutter around the rear hatch, and most of the top of the b pillar on the drivers side. I think i have about 500 hours in a $200.00 car. Started about 9 months ago and still don't have the thing painted. Fun project though. It was the first time I had ever done body work. It was a learning experience and practice for when I do the rust repair on my 70 Chevelle.

SOME PEOPLE ARE LIKE SLINKIES; NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
April 29, 2009 6:51 p.m. Appleseed HalfDork

If you go the weld route, the affected area is more than the hole. I'd guess you'd be looking at a 3 x 5 hole when you're done. Replacing more metal is better than a paint re-do down the road.
April 29, 2009 7:19 p.m. Toyman01 Reader

I ended up cutting out everything that was rusted and welding in new sheet. Several of the holes were fairly large.

SOME PEOPLE ARE LIKE SLINKIES; NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
April 29, 2009 9:19 p.m. Jensenman SuperDork

Per's series on the Saab had some pretty good info.

The rot you see from the outside will be just the tip of the iceberg (painfully remarked the guy who has re-rockered MGBs etc). If the side of the rocker is rotted from the inside, usually what has happened is that dirt etc has filled the rocker, this keeps the metal wet and causes rust. This unfortunately means there will be much more extensive rust present once you crack into it. BTDT.

Once all is welded back together,keep in mind that weld slag and steel particles rust FAST. That means you have to be able to thoroughly clean the INSIDE of the repaired area, remove all the slag and metal particles and then protect it somehow. Otherwise, your problem could come back! Eastwood's Heavy Duty Anti Rust preventive does a good job, there is a spraygun tool with long tubes and directional nozzles which help apply the stuff. If you can get inside the panel from the back side, they also sell some stuff called Rust Encapsulator, that's what is on the floors of the Jensen Healey. The good thing about that stuff is that it doesn't require a topcoat.
April 30, 2009 4:38 p.m. Tyler H Dork

Toyman01 wrote: This is how I did/doing the repairs on my RX-7 (edit) except I welded everything. http://wwwx.cs.unc.edu/~hays/crx/dx/rust_repair/

I already ran across your site on the interweb , in my searching. :D

Looks great, but is more work than I'm in for. This is an $850 car. If I start picking at that rocker and it is rotten, then I'm getting rid of it...or getting a parts car and taking out the sawzall. :D

I know how to cut, weld and spackle. I was curious about fiberglass mat / patches.
April 30, 2009 6:08 p.m. WLB New Reader

For a fast and cheap repair, rough up the area around the hole and apply 3M Auto Repair Tape over the hole. You can then lightly sand the tape and paint to match or. if necessary, add a layer of Bondo over the tape to match a contour and then paint.

http://www.wlbsite.com/
April 30, 2009 9:08 p.m. Toyman01 Reader

Tyler H wrote:
Toyman01 wrote: This is how I did/doing the repairs on my RX-7 (edit) except I welded everything. http://wwwx.cs.unc.edu/~hays/crx/dx/rust_repair/

I already ran across your site on the interweb , in my searching. :D

Looks great, but is more work than I'm in for. This is an $850 car. If I start picking at that rocker and it is rotten, then I'm getting rid of it...or getting a parts car and taking out the sawzall. :D

I know how to cut, weld and spackle. I was curious about fiberglass mat / patches.

That site wasn't mine, but one I found while looking into repairing the RX-7.

For a cheap easy short term fix. I found old repairs, under some of the paint bubbles on my car. They had taken a hammer and fold the edges of the rust hole in. Fill with filler sandd to shape and painted. The repairs lasted at least 3-4 years before they started to fail and look bad.

For fillers use Straight Line from POR 15. It works much better than Bondo.

http://www.porcan.com/usa/puttys.asp

SOME PEOPLE ARE LIKE SLINKIES; NOT REALLY GOOD FOR ANYTHING BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
May 1, 2009 7:04 a.m. Jensenman SuperDork

Eastwood also has a 'structural adhesive' patch setup. Never used it, no affiliation etc no warranties expressed or implied, may cause temporary blindness or extreme priapism, your mileage may vary, side effects are possible, yada yada.