Sealing edges of wheel well - PeachParts Mercedes-Benz Forum

Graham · #1 06-03-2014, 09:55 PM

I don't know how many times I have sanded the edges of my wheel well sheet metal, painted with POR15 and then overcoated with matching body paint on outside edge.

But each year, the rust comes back. It seems that the edge of the metal doesn't get properly coated even although I have slathered on the POR. No problem on the inside, probably because it is easier to build up some POR thickness.

Anyone Have any better ideas?

jmk · #2 06-19-2014, 04:48 PM

Are you getting enough topcoat on to protect the POR? It won't handle UV, and with the extra stress of being by a wheel well.

Also, if you used a cheaper paint, they may have skimped on the UV absorbers, allowing enough UV through to kill the POR.

Graham · #3 08-08-2014, 11:40 AM

Quote:

Originally Posted by jmk

Are you getting enough topcoat on to protect the POR? It won't handle UV, and with the extra stress of being by a wheel well.

Also, if you used a cheaper paint, they may have skimped on the UV absorbers, allowing enough UV through to kill the POR.

It is hard to get the topcoat on in any thickness. Problem is mainly on the sharp exposed edge.

I was looking at a new Mitsubishi Outlander the other day. On the rear wheel wells, they appeared to have a heavy bead on the edges of the wheel well. Next time I have to do this, I think I might first paint with DOM16 (similar to POR, but UV resistant) and then apply a bead of seam sealer along the edges. Then spray with acrylic (I am using colour matched spray can made up at NAPA Canada.)

jmk · #4 08-11-2014, 07:07 PM

that may actually be a material called "chip guard" in the industry. It is an extra thick coating designed to resist chipping and breakthrough. There must be a refinish version of it. That would solve your problem.

jmk · #5 08-11-2014, 07:16 PM

Here you go:

http://secure.hmswarehouse.com/TECH/DELTRON/DX54.pdf

That is the refinish version of chip guard.

Hope this helps.

Graham · #6 08-11-2014, 08:30 PM

jmk,
Thanks for the idea. I actually already have a chip guard product that I bought for this purpose. But I have not used it.

Rust on my wheel wells starts on the very thin edge of the metal. Even with the metal on each side protected with POR or similar, rust starts along that edge which is too thin to get much of any kind of coating on.

That is why I am thinking about something thicker. POR has a putty in a tube (POR+filler probably). It might stay in place. But seam sealer is really cheap and seems to work elsewhere in exposed location, so also thinking of using that.

Problem with stone guard, could be getting it off if and when rust reappears and repainting is needed

Had thought about the stoneguard tapes, but shape of wheel well edge is quite complex and I could not see how to apply it.

I am sure I am not alone in this. Maybe I have repaired those edges just one to many times

jmk · #7 08-18-2014, 07:33 PM

It is possible that the metal is too thin. Also, POR can't tolerate UV (aromatic isocyanate), so your topcoat can hide to visible light, but it is UV transparent.

How I handled those edges, esp. when the metal has gotten too thin, is to use two component fiberglass built up with multiple layers of fiberglass cloth. It makes a very strong repair that is impervious to rust.

For purists, it tends to be a bit sacrilegious, but it works very well for cars you use and aren't taking to shows.

You have to use the 2k fiberglass, and stay away from Bondo. It is very water soluble. The moisture then weeps into the metal, rusts, and the repair falls out.

The strength comes from using the fiberglass cloth. Using multiple layers makes the repair much stronger.

Duner · #8 12-17-2014, 09:56 PM

Take this FWIW but I have had same trouble as you on my winter non MB car.
Properly repair and paint not only what you can see but also the other side of the lip or pinch weld and lip. Mask off the outer edge. Here is the fun part. Purchase a tube of 3M8609 windshield install urethane and carefully smear a coat on the repaired area up and around to the topside which is perfectly clean and Zero rust.
If htere is a pinch weld I go in from the top side and even tho it more than likely is sealed from the factory I give the inner fender wheel well a coat of either 3M Rust Fiter I (I for interior) or Fluid Film , both come in rattle cans. Be sure to cover the metal edge where your rust has been starting. I have never painted the urethane but you probably could.
The secret is proper preparation for the urethane. Have fun and good luck!

oldsinner111 · #9 12-19-2014, 10:03 AM

I use to have a late 60s fiat,in the driver handbook,it mentioned taking car to a place they have to immeress under carriage in used
oil.Then clean good in the spring.

Duner · #10 12-19-2014, 07:31 PM

The oil bath treatment actually works quite well. I am quite sure my magiacl mystical superior motor car would have a fit if I subjected it to such treatment.

Graham · #11 12-23-2014, 09:49 AM

In Canada and perhaps in USA, there is a product called DOM-16 which very much like POR-15. But it is UV resistant. However only place we can find it here is at NAPA and they only sell black. My 300D is white

I do use it on other parts of car - it s 1/2 the price of POR15.

Most of the problems start on the sharp inner edge of the fender lip which is hard to get protected. These are newer replacement fender so no problem with metal thickness.

Paint used is a proper automotive paint made to match colour at NAPA paint dept. They all seem to be water based these days

Smearing the urethane over the edge is the sort of thing I have been thinking about. Perhaps using POR-putty in tube might be able to build up a bead on the sharp edge. Also have thought of spraying with stone guard or even using the tape (but shape is complex).

Anyway ongoing problem especially with our winters & salt.

Duner · #12 12-25-2014, 06:22 PM

I have used 2 part Dura glass green body putty. Great stuff.
Fibreglass cloth applied with polyster resin.
Fibreglass cloth appied wtih epoxy resin.
Fibreglass cloth applied with POR 15 black paint to stop rust. Don't laugh it really works.
Multiple coats of POR 15 paint.
The urethane fix was the fastest easied and long lasting on perfect substrate.
Expirement on something before commiting to fender repair. Seal unused portion in tube and save in freezer. It will keep for a long time. Urethane cures faster the hotter out side temps are.
Have fun.

jmk · #13 01-05-2015, 04:20 PM

I definitely would not laugh at the fiberglass POR mixture. It would probably work quite well. I used to do the same thing except I used roofing tar. POR would probably work better.

Yes, you need to cote around the edge. Since it is a replacement fender, the problem may be the electrocoat (or lack thereof). Sharp edges in high exposure areas are tough to coat, and e-coat is designed to wrap around and protect edges.

Encasing the edge with 2k/polyurethane/fiberglass cloth or POR-15/fiberglass cloth would probably be your best bet. You want to create a hermetic seal so water cannot get in. Make sure the surface is clean before you reapply (no rust, but it doesn't have to be down to bare metal. actually bare metal is not preferable.)

Make sure the fiberglass is 2k, not 1k. You need all the performance you can get along that edge. I know a lot of these things claim penetration through rust, though the inherent instability of iron oxide (it expands to 10x the volume of steel) in a harsh environment always makes me question coating through rust.

Alastair · #14 12-11-2015, 03:14 PM

Clean to bare bright shiny metal, coat with two coats of Etch Primer, lightly rub down then a couple of coats of top-coat.

Job done.

Ive found that rust repair success depends on how well the metal is cleaned of rust traces Before any paints are applied...

Over the years, Ive tried all sorts of so called Rust Cures, claiming neutralization, rust-penetration etc etc--Nothing actually does what it claims, Only a back to shiny-steel and etch-prime plus top-coat does the job with reasonable success.

POR-15 is just mediocre--Defo NOT worth the price!

Hammerite--Might as well NOT Paint it at all--Utter rubbish!

Rust NEVER Sleeps.....