Are black goo and MOTs compatible?

[swee'pea99]

The reason I ask being, my sister's car failed its MOT and she needed a new one straightaway. Longish story short, she now has a Honda Jazz with a brand new MOT but with an advisory on corrosion on the underside. I'm more than half-minded to get under the beast, clean it off with a wire brush, and spray it liberally with this...

Horrible - it coats everything with thick, sticky black stuff that 'protects surfaces from corrosion'. Having used it, I can believe it.

I suppose the first question is, would I be totally wasting my time? Ie, it wouldn't work anyway, bound to get washed off, whatever. The second being, my nightmare scenario is my sister taking it to the MOT station next year and them taking one look at this filthy black goo and concluding well we can't really see how bad the corrosion is, err on the side of safety: failure. Is that possible/likely? Or do MOT stations have objective ways of assessing things like corrosion, whether or not black goo is involved?

Or if anyone else has found a good way to stop underbody corrosion in its tracks that doesn't involve filthy black goo?

Any thoughts and advice - thanks in advance.

 

[Gunk]

The reason I ask being, my sister's car failed its MOT and she needed a new one straightaway. Longish story short, she now has a Honda Jazz with a brand new MOT but with an advisory on corrosion on the underside. I'm more than half-minded to get under the beast, clean it off with a wire brush, and spray it liberally with this...

View attachment 825524

Horrible - it coats everything with thick, sticky black stuff that 'protects surfaces from corrosion'. Having used it, I can believe it.

I suppose the first question is, would I be totally wasting my time? Ie, it wouldn't work anyway, bound to get washed off, whatever. The second being, my nightmare scenario is my sister taking it to the MOT station next year and them taking one look at this filthy black goo and concluding well we can't really see how bad the corrosion is, err on the side of safety: failure. Is that possible/likely? Or do MOT stations have objective ways of assessing things like corrosion, whether or not black goo is involved?

Or if anyone else has found a good way to stop underbody corrosion in its tracks that doesn't involve filthy black goo?

Any thoughts and advice - thanks in advance.

Managed to get a Mini through the MOT by wire brushing the subframes, removing all the flaky rust and then painting with smooth Hammerite

 

[tyred]

When I got it about 4 years ago, the original coating was starting to flake off my Yaris and a lot of surface rust was developing. I wire brushed underneath and gave it a couple of coats or red oxide primer.

I then painted over that with thick black underseal, which fell off after one winter, leaving the red oxide!

The red oxide painted surfaces remain rust free. I always have a poke around when I change the oil or am under the car for any other reason.

 

[wafter]

Wire brush and black waxoyl would be my choice; preferably done in the summer when it's bone dry to ensure there's no moisture trapped within although of course that gives it time to degrade further over the winter..

 

[Fastpedaller]

Galvanising paint has worked well for me - this stuff is great, but it takes about 10 minutes to get it stirred to a uniform consistency because the zinc is so heavy and settles to the bottom

 

[biggs682]

If you have the cash get the underside ice blasted and re treated with modern protection

 

[fossyant]

Don't you'll just hide the issue. Clean it off, then treat it with a rust inhibitor, then spray over with something like Buzz weld chassis protector - it goes on clear so you aren't hiding anything, but it stops rust. Don't spray with any black messy stuff as the car will carry on rusting behind it.

 

[fossyant]

Start with this stuff - the rust will turn a black colour

https://www.amazon.co.uk/Aquasteel-Rust-Converter-Primer-Litre/dp/B003QZ3GNE

 

[fossyant]

then use this

https://www.buzzweld.co.uk/chassis-...2-qoJDSpT5VjTF4VLICMuLITzXNf9haxoCXuQQAvD_BwE

or this

https://www.buzzweld.co.uk/ace-25l-...DqVTcN_pMhXFtEIb5NGGoCWN-L8QpOoBoCvFEQAvD_BwE

Difference is the cheaper one is more natural, but takes a bit longer to dry.

I use the smaller/more expensive aerosol version as I'm only 'topping' up on my vehicles.

 

[swee'pea99]

Thanks all, that's really helpful. That Buzzweld stuff in particular looks the business! All I need now is a few days of dry. Might be waiting awhile...

 

[fossyant]

Drago and I use the buzz weld. Does work very well. I use aquasteel on any rust and have used on older cars with good results.

 

[Jameshow]

I think I should do my mini as it's a known problem!

 

[Profpointy]

Managed to get a Mini through the MOT by wire brushing the subframes, removing all the flaky rust and then painting with smooth Hammerite

Pah amateur stuff! I wire brushed leaving huge holes in the sills which I "repaired" by thickly painting with Hammerite and the surface tension of the sticky paint was sufficient to fill the gaps. It passed more
than one MOT sunsequently