Underbody/chassis protection

[charlysays]

I was a fan of epoxy mastics but tbh I'm reverting back to high zinc 1k primer, then seam sealer, then some chassis paint/ gravitex as appropriate then clear anti corrosion wax like dynax UC. Keep it clean and top up the dynax every year or so. As for prep, needle gun and a degreaser is an acceptable minimum with some scuffing added for good measure.
The issue I've had with epoxies is that even with what seems like a thick coat I've had the odd rust spot show up through it. Also where it gets damaged (e.g by a rock bending a panel) the rust gets under the edge of it much like it would with powder coating which is not encouraging considering how laborious it is to prep for it.
This was with meticulously prepped steel too, very well degreased and keyed up.
As such my go to primer for underbody (and even top sides) is bilt hamber Electrox. It's self etching, has a ridiculous zinc content which results in an electrically conductive film and it dries hard and grips well. It's what you want as a first layer as it'll protect the steel much like galvanising.

 

[rcx132]

I have thick dinitrol in a semi open cavity and it's lasted 8 years and is still working.

 

[julianf]

My feeling is that anything hard has to go on a nice surface.

Otherwise you are coating a friable surface with a hard layer, and the water will get in and get trapped, and it will be worse than if nothing was there.

Sure, stripping back to metal and painting is best. But, if that's not going to happen, then I don't believe the "toughness" of the coating is of any advantage at all. And, indeed, is a disadvantage.

Something creeping and penetrating will never be described at "tough" and, of course, anything that creeps and penetrates will get abraded / washed away by road grime also - but maybe only in the places where the road grime dries rapidly anyway? Ie the places where grime just sits and rusts out stuff (the less exposed places) stay coated a little longer?


I don't think any of it is great (apart from a full prep and paint) so it's working out the least bad option. I reckon my feelings are on semi regular application of somthing that is, very intentionally, not "tough"

 

[Gareth J]

Depends how long you want to keep it for, how much you are willing to put to it now and how much ongoing maintenance you find acceptable during that time.

Vehicle maintenance is only really managed decline (palliative care?) so, if you can get the expected lifespan of the whole machine in perspective and the amount of work you want to do during that expected lifespan, it'll guide the decision.

The hard part is sticking to the plan!

 

[bricol]

20 yrs of experience of coatings under my Lancia, which used to be used every day, in all weathers, especially winter (Caterham 7 not ideal in bad weather), did 100,000 miles in the first 8 yrs, lived outside for most of it, showed me

Epoxy on blasted steel was excellent. Needed blasting again to get it off.
Epoxy on wire wheeled, flap wheeled/disc-ed, scraped steel was pretty crap - pretty easily removed in large, flat, lumps. Water had got under it in places.
"Conventional" paint layers on wire wheeled, flap wheeled/disc-ed steel was much better than epoxy on the same surface.

I over painted the epoxy with machine enamel of a contrasting colour (simply because I had it) and then applied Waxoyl underbody shultz (as it was what I had) to provide a more resiliant, flexible layer to help "bounce" crap away. Seems to have worked.

Cavity waxes etc need reapplying/topping up every few years - they are not fit and forget.

However, if the original coating was intact, I tried to leave it alone - I figured if it was still stuck, it would remain stuck and the original galvanising/anti-corrosion coatings would remain undamaged under it - I'm not a fan of deliberately bare-metalling everything - whatever the coating I would apply, it wasn't going to be as good as the original, undamaged stuff.

 

[RonMig]

If there's much bare rusty metal after removing loose flaky paint & rust (like on my 23yr old Disco 2) I'd go with ACF50.
I wait for the warm weather then jet-wash the chassis, & when it's dry a few days later takes about 30 mins to fine-mist-spray it with a £25 Fast Mover HVLP mini spraygun at very low pressure which I keep just for this. A small compressor can easily keep up.
I think I used about 300ml last time.
1litre is ACF50 is around £38. (was £26 when I bought my 2nd bottle 2yrs ago)
Also comes in a spraycan version, not tried that but think it's roughly the same deal without needing a compressor etc.
Just have to reapply every 12 to 18 months or so.
Info on here -
https://learchem.com/products/acf-50.html

 

[steveo3002]

^ how long have you been using the acf50?

 

[arther dailey]

old style dirty sump oil with parafin to help creep still works

 

[fizzy]

Jotun 90AL is better over rusty steel than shiny steel. Rough surfaces are better. Sand blasting is best but so messy and very hard work. Needs a big compressor as well.

 

[vw1]

I had one of the small hand held gun type blasters on my 270ltr compressor for very small areas under the car it was fine but I understand not everyone has this setup.

Areas I could get to by hand I used old hand chisel to remove the black stuff . I then cleaned with brake clean in spray bottle. 80grit by hand two weeks of it on and off very hard work on your back and had no nails left lol.

Once happy panel wipe then jouton 80 winter grade as it was December time in warmish home garage with 1.8 / 2mm gun.

Some with have other methods but this was mine. Restoration still in very slow progress vw 1970 beetle.

 

[rcx132]

If there's much bare rusty metal after removing loose flaky paint & rust (like on my 23yr old Disco 2) I'd go with ACF50.
I wait for the warm weather then jet-wash the chassis, & when it's dry a few days later takes about 30 mins to fine-mist-spray it with a £25 Fast Mover HVLP mini spraygun at very low pressure which I keep just for this. A small compressor can easily keep up.
I think I used about 300ml last time.
1litre is ACF50 is around £38. (was £26 when I bought my 2nd bottle 2yrs ago)
Also comes in a spraycan version, not tried that but think it's roughly the same deal without needing a compressor etc.
Just have to reapply every 12 to 18 months or so.
Info on here -
https://learchem.com/products/acf-50.html

I'm not convinced by ACF50. Its too thin for use on exposed undercarriage. And it's not manufacturer recommended for cavities, though I can see it working in cavities. I have the stuff but use it on unexposed surfaces only.

 

[RonMig]

^ how long have you been using the acf50?

Done 3 applications on the truck so far, now on year 4 so will apply again this summer; also used it on a motorbike and 2 other smaller cars, plus on some cast iron stuff in the garden, & none of the treated bare metal parts show any sign of new rust...

So I'm happier using this than waxoyl or underseals, as they just seem to hide the problem areas and in previous years I've seen these fail with creeping rust / flaking, whereas the ACF50 treated parts still have the protection film in all the nooks and crannies.

 

[steveo3002]

Done 3 applications on the truck so far, now on year 4 so will apply again this summer; also used it on a motorbike and 2 other smaller cars, plus on some cast iron stuff in the garden, & none of the treated bare metal parts show any sign of new rust...

So I'm happier using this than waxoyl or underseals, as they just seem to hide the problem areas and in previous years I've seen these fail with creeping rust / flaking, whereas the ACF50 treated parts still have the protection film in all the nooks and crannies.

ive started using it on sheltered bits

 

[arther dailey]

bought some acf 50 for mitsi chassis last year , stuck it safe now can t find it , due to tidy up, typical

 

[rcx132]

bought some acf 50 for mitsi chassis last year , stuck it safe now can t find it , due to tidy up, typical

Haha that happens to me. I do a big tidy up to find whatever I've lost.

 

[bigegg]

Opinions on international paints "Interseal 670hs" 2-pack epoxy "maintenance paint" as a chassis paint?

My plan is to 36grit sand everything I can get to, then lather with phosphoric acid and overcoat with the 670hs.

 

[Dcal]

Opinions on international paints "Interseal 670hs" 2-pack epoxy "maintenance paint" as a chassis paint?

My plan is to 36grit sand everything I can get to, then lather with phosphoric acid and overcoat with the 670hs.

I've not used 670 but it's a surface tolerant epoxy mastic primer so it will be fine and similar to the other epoxy mastics recommended on here.
I have used Interzone 954 and like it but I don't know if it's better or worse than Jotun 90. (I doubt there is much in it)

I wouldn't bother with the phosphoric acid stage, because International won't have tested their paint systems with it.
I'd just stick with what they say on the TDS, but it's your car so you can do as you please.

 

[Erie Fred]

One word....."Plastics".....
The sheets I fastened up underneath with tye wraps have been doing great at
stopping the spray of sand, salt and other junk.

Why not bolt them on ?
In case I slide into a ditch, they would rip off and ruin stuff, with tye wraps, they come off easier, for less damage.
Never had one come off in regular driving, and haven't had to test the "ditching" part yet.

 

[arther dailey]

bought some acf 50 for mitsi chassis last year , stuck it safe now can t find it , due to tidy up, typical

finally ,as ever , moving something else and found the new un opened rust proofer ,result

 

[Morrisman]

Acid is a strange thing, if you submerge metal in it will remove the rust. But if you have an acidic atmosphere due to unwashed acid it will ACCELERATE rusting at an alarming speed! Unless you're able to remove a part, and submerge it in neutraliser and wash, I wouldn't use acid.

I did my trooper using a needle gun and MBX tool to remove loose rust, and then thick Dinitrol. It's lasted a few years already.

Jotun or paint is only useful if you can get back to clean metal. It won't grip otherwise and the rust will spread under the paint.

I remember using a bucktfull of muriatic acid (concrete cleaner) to de rust steel pipe. I made the mistake of leaving the bucket in the workshop, uncovered, when I went away to work for five weeks. When I got back every piece of raw metal in the workshop had grown a layer of rust…..