Long Term Corrosion Study

[tom h]

Even though my 87GN is a low mile, garaged, So Calif car, I've been a little concerned of the light surface rust that has formed in inaccesible places.

Examples: section of firewall that didn't get fully spray painted from above or below; insides of lateral, body stiffening channels; body sheet metal in the narrow space between the outside of frame rails and the inboard of body, etc.

Ordinary spray Paint, or even POR15, is not the solution for these confined spaces: it won't flow & cover uniformly, and it won't bond because the surface is inacessible and cannot be prepped.

So I've started to do a practical, long term corrosion study. It's not completey scientific or exhaustive, but I think it will give me a solution that will work , at least in milder climates.

The test sample is lengths of unplated steel. All I could easily locate is hot rolled, with mill scale, so I grinded off the mill scale to present a bare steel surface.

I sprayed sections of the bare steel with several types of coatings (more later), and the coated & bare steel sample are left exposed in my back yard.

I will also "scratch" the coatings to simulate nicks and dings from tools or gravel, and observe how well the coatings recover or heal.

Coatings considered but NOT used in the test:
-- waxy black coating sprayed on frame at factory. Cannot locate any source for it!
-- 3M rubberized undercoating #08883. I've read it's not intended to be 100% moisture proof, plus doesn't really flow to cover all surfaces. Plus, I've seen cars that have rusted through those rubbery coatings.

Aerosol Coatings I did use in the test:

1) 3M Rust Fighter-I , # 08892. Leaves a slightly sticky, light beige (almost transparent) coating. Flows and is said to "self heal" when scratched.

2) CRC SP-400, #03282. Seems similar to 3M, but leaves a noticeably yellow color film.

3) LPS-3, #00316. Billed as a "Heavy-Duty corrosion Inhibitor", but seems and feels like a heavy grease.


Test has only been going 1 week, so no conclusive "best coating" yet. The bare steel has developed big blotches of surface rust, and all 3 coatings have stopped rust after 1 week. Weather has been cool with a couple days drizzle and rain

Will update this post periodically on the coatings' performance.

If anyone has suggestions on how to make the test more meaningful or useful, let me know!

 

[tom h]

Update of steel bar test sample after about 2 weeks.

LPS-3 :
Very light surface rust starting to appear in places.
No rust in scratch mark, the LPS3 "flowed" and re-covered the scratch.

CRC SP400 :
No surface rust.
Beginning of rust in scratch mark (no "healing" or flow of the film).

3M Rustfighter :
No surface rust.
No rust in scratch mark, the coating flowed and re-covered the scratch.

Slight edge to the 3M Rustfighter, at this point.

 

[timmyp]

This is interesting. As a body tech and old car lover i am faced with this dayly.

Couple of things I though of is, 3m weld through primer, heated and not( have heard adhesion is poor until heated ((around a weld area)). An epoxy primer(DP50) over an acid etch or a metal treatment, will the scratch heal or spread under coatings?

Keep up the posting
Thanks

 

[tom h]

well, I've never personally used the PPG DP50 or other epoxy primers, but I would think all conventional paints (including POR15, that I do use) are NOT going to have any "healing" properties after they've dried. But these paints are so tough & dureable once they've cured, normal chipping is not likely to occur.

I've played around with the 3M weld-through coating, it seems to make pretty good corrosion resitant coating, in general, but like any paint, needs full access to the panels being painted.

My main purpose in this study was, What to do with the inaccessible and generally not visible, recesses and nooks and crannies on a vehicle?

Here's my Dec 13 update, it's now been 4 weeks of outdoor exposure:

Continuation of trends from Dec 2.

LPS-3 :
Noticeable surface rust has spread on steel bar.

CRC SP400 :
No surface rust.
Noticeable rust in scratch mark.

3M Rustfighter :
No surface rust, at all.
No rust in scratch mark.


Clearly, 3M is the best performing coating. It's about 3-4 times more expensive than the other products ($12-15 per aerosol can), but worth it IMO.

I'm going to continue the test, to see how long the 3M holds up. 3M only intends Rustfighter for non-exposed panels, but it's doing very well exposed directly to the elements.

Of course, none of these coatings are appropriate if appearance matters: Rustfighter is a non-hardening, waxy, slightly sticky coating. But it can be sprayed into semi-inaccessible locations , and will drip and cover metal that doesn't get directly sprayed.

More expensive than an aerosol can (part # 08892), but 3M also makes:
#08891 quart cans (about $16-20),
#08997 spray applicator gun ($60-70),
#08898 flexible 36 inch wand ($13-15) with tip adjustable from 180º to 360º spray pattern.

For the vast majority of us who cannot do a "body off" detailing, the Rustfighter could be very helpful for warding off rust in:
-- concealed portions of frame rails,
-- body stiffening channels on underbody,
-- insides of door panels,
-- insides of rocker cover sheet metal, under door sill,
-- certain portions of the trunk,
-- unprotected seams between panels,
-- inside of body cavity where the air vent on door jamb leads to (you might not like what you see in there!).

Rustfighter is reversible, ie, it can be washed off with strong solvents (lacquer thinner, carb cleaner, etc).

 

[zam70]

Good info - THANKS for your efforts.

 

[TurboBob]

what about application to already (slightly) rusty metal?

For instance, inaccesible places like the bottom door seam. Mine is showing signs of slight rust. I wanted to plug the drains and pour in something that will flow into the seam and stay there. The 3M sounds promising.

Bob

 

[tom h]

Originally posted by TurboBob
what about application to already (slightly) rusty metal? Bob

Bob, the 3M seems to stick tenaciously to everything including slight rust. The 3M seals and cuts off moisture and oxygen from getting to the metal.

The 3M should halt any further rusting, although it won't "convert" existing rust like POR is supposed to do.

Using 3M to seal inaccesible seams is an ideal use for it.

BUT plugging the drains at the bottom of a door is NOT a good idea!! Any moisture that does get in, needs a way out, so it doesn't turn into a fish tank. This is true on any part of the body ... make sure any "weep" holes stay clear and open.

 

[TurboBob]

I agree on the drains, the idea was to block them temporarily so the 3M compound could 'fill' the door slightly and put some 'pressure' on the seam so it would weep in further......

I would unblock the drains after a period of soak time.

Thanks!!!

Bob

 

[Kenny E]

test

Has anyone used the Corroless rust incapsulating and inhibitor primer that Eastwood sells. I did as Bob suggested to my Red car for the same reasons. I scraped all the seam sealer I could get at off the bottom's of the doors, blocked the drain holes and poured in the corroless primer it worked its way around most of the openings drained the excess,resealed and painted that was five years ago and it still looks the same.

 

[tom h]

Dec 19 update -- 5 weeks of outdoor exposure.

Continuation of same trends.

3M Rustfighter coated surfaces are still completely rust-free !

 

[RegalX2]

Tom,
You might want to look at Daubertchemical.com,I have used a 2 step process using their products, doing factory recalls for corrosion protection of subframes. The first step is a penetrant that really seems to penetrate surface rust. Then a second parrifin based coating was used.
Jim