Rim tire leak repair

[MBGraham]

The rims on my 98 Mercedes started to leak a few years back. I had the old tires removed. After cleaning off the rubber sealant, I found several areas where the aluminum had bubbled and corroded. The interior of these rims including the bead area were factory coated with a brown paint/coating. Perhaps an epoxy. In sanding out the corrosion and cleaning up the beads seat, much of this coating was removed.

Problem now, is what to recoat with. Getting any coating to adhere to aluminum is not easy. But because the natural aluminum oxide protective coating has been removed, I believe that a coating must be applied. Just which one and how best to apply?

 

[BrianE22]

So why don't tire repair shops turn down the bead area in a lathe? I'm guessing it would leave the bead area too thin? Machine it down and then anodize it.

 

[3DDave]

Anodization of aluminum cast alloys isn't so good; even for wrought materials it form microscopic fatigue initiation sites, which is why aircraft parts get conversion coat and then prime and paint. Machining the bead also reduces the diameter of the bead which decreases the pre-load of the tire.

 

[MBGraham]

3D-Dave - I saw that video by Kent at Mercedesource He was experimenting with Miracle paint. That paint is similar to POR15 and the paint I used called DOM16. 1-part polyurethanes. They are great for rust repairs, but need the rough tooth surface that rusted parts have. I tried to create that with 80 grit sanding. Maybe I should have painted sooner as oxide layer may have formed. There are etching primers for aluminum. I should have used one of those and perhaps a 2-part polyurethane or epoxy. These systems are used in painting aluminum boats and masts. I asked WEST Epoxy and they suggested sanding while applying one of their resins without the etching primer. Presumably sand first to create some tooth,, Apply resin soon after and sand it in. Don't give oxide a chance to form.
The shops that restore rims do a bead blast and then powder coat, I believe. This a video from one shop:

https://www.youtube.com/watch?v=guYOVPRoo_I

To get a proper job, I would probably have to go to them! I have new aftermarket rims, but they are not same quality as the originals that I would like to recoat.
Anyway, I will just "carry on" (Too cold for painting still)

 

[3DDave]

Oxide on alumininum forms almost instantly. Aluminum is highly reactive, but initially forms a tightly bound layer, unlike iron, which often forms flakes. It only gets the destructive corrosion when the local chemistry damages that oxide layer. Mechanical interlocking by "tooth" won't seal out corrosion. Conversion coating solves that.

"that video", if recent, is at least a second one. He did one in 2018 and said he would get back about how it worked but made no mention of it in the more recent video, so I'd guess it did not work the earlier time.

See

http://www.cabuk1.co.uk/FAQ 7 Oxidation of aluminium.pdf

and look for aluminum conversion coating.

 

[TugboatEng]

West System wants you to use a wire brush to scuff the surface after the epoxy coating has been applied but while it's still wet to dig the epoxy in. The wet epoxy will prevent oxygen from coming in contact.

There is a reason most aluminum boats DON'T get painted.

 

[MBGraham]

"West System wants you to use a wire brush to scuff the surface after the epoxy coating has been applied but while it's still wet to dig the epoxy in. The wet epoxy will prevent oxygen from coming in contact.
There is a reason most aluminum boats DON'T get painted.

It's true that many aluminum boats are not fully painted (we owned marine business for 27 years). But they do often have painted waterline stripes, graphics, names, aluminum drives etc. And some do get fully painted. Sailboat masts get painted - usually once anodizing has corroded ! Other products like car sheetmetal, aluminum siding, eavestroughs get painted. In other words, aluminum can and is often painted. But not so easy for DIYers!

Tugboat's reasons for West's suggestions are no doubt true. However, West did not suggest wire brushing. Probably not a good idea unless aluminum brushes are available? This is what they actually recommended:

1. We would recommend using G/Flex 655. The surface would need to be cleaned and abraded with 80 grit sandpaper within 30 minutes of epoxy application. G/Flex 655 has a consistency similar to a gel toothpaste.
2. The epoxy will cure to a hard enough surface without it (aluminum filler) so I don't think you will need it.
3. We have found that as long as you clean and abrade the surface within 30 minutes of epoxy application you get equal bonding strength to having used an etching solution. Therefore you do not have to use an etching solution or an etching primer before applying the epoxy.
4. G/Flex 655 has a consistency similar to a gel toothpaste so I don't think you'll need to thicken it any further.

The problem with this:

https://www.amazon.ca/flex-Epoxy-Sy...10e70&pd_rd_wg=jI4B3&pd_rd_i=B012RVIDW6&psc=1

Cost! There are lower cost epoxies like Gluvit (i have used that on aluminum boats to seal seams.

Anyway, I think we are done with this thread. I will just "carry on"

 

[TugboatEng]

I'm sure you observed the prevalence of pitting corrosion on painted aluminum boats vs. unpainted boats.