I am hoping to do some long overdue underside/chassis maintenance this year (not welding, just preventive painting)
I am a complete novice, so am going to need tips on peoples past experience
at the moment its all just looking a bit brown/rusty at the moment .
wouldnt mind waxing the chassis rails as well.
Do you think we could have this as a "sticky" I saw the 'waxing' sticky in the useful tips but it was to with car cleaning
Plenty of options and prep is still the key to a good result.
1: Remove all old underseal/paint/rust. You can start by having the underneath steam cleaned, or just tackle it all with a paint scraper/wire brushes/white spirit or heat.
2: Treat surface rust with something like Loctite 7503 (Tannic Acid) or Phosphoric Acid, or one of the Bilt Hamber products.
3: Prime with a zinc rich brushable primer, I have found #1 Rust Beater Primer by Hammerite to be very effective.
4: Paint with a good chassis paint. Rustoleoum/Por15 or again Bilt Hamber stuff
5: Coat high impact areas with Dinitrol/Waxoyl Underseal
Avoid Smoothrite as it goes brittle PDQ flakes and falls off, same goes for Hammerite top coats.
So it's basicaly, Clean, Treat Rust, Primer Protection, Seal finish with chassis paint, + extra protection for high impact areas like sills and wheel arches.
May as well check for any serious rust before you start - whack with small hammer/poke with screwdriver will soon find it. Easier to fix before it all gets coated with flammable paint/waxoyl.
I was looking at the POR15 range, but wherever I look its out of stock!
Recently practical classics done a test on these paints, somthing came out better than POR can anyone remember which it was. ( think I have thrown away the mag )
Hi Zippy, I agree with much of what Moggytech says, except on rust converters. i've never come across one that works. Try one then scratch it and you'll see some rust underneath waiting to munch away at your car again. They are basically rubbish, they work for a while by covering the rust having converted only the top layer.
I would :-
1. Remove all underseal (hot air gun/ scraper/ solvent)
2. Remove ALL rust- use coarse wire brush on grinder, followed by fine wire brush (on drill or grinder). This is messy- use protective equipment- eye protection, dust mask, ear plugs, decent work gloves, etc.
3. Apply rust REMOVER- usually phosphoric acid based, wipe off excess, let dry , then.
4. Go over with wire brush on drill. repeat 3 and 4 till the car is all clean steel. (protective equipment again!, these acids are toxic/ hazardous)
4 1/2. at this point some of the underside may need welding, unless you are lucky.
5. Sand to give a key, then degrease (panel wipe)
6. Brush on zinc primer- available from paint factors- you want the heavy cans that are 90% zinc. 2 coats let dry.
7. chassis black, 2 coats. I got a 5L can from Partco/Unipartl
8. when dry, waxoyl or Thick dinitrol on the underside, Dinitrol 3125 in the box sections.
Yes - you must remove all the rust and then use the phosphoric acid treatment. If the rust is coming through from the other side of the panel (or chassis member) then it is absolutely a waste of time to try to treat it - it must be cut out and new metal installed if it's to last any time at all.
BMC is right. I dont try and treat rust anymore on my projects. I get rid of it alltogether!
The ultimate if you can afford time/money has to have the car media blasted, then chemically dipped (and e-coated/ etch primed), other than that lots of hard work with wire brushes on power tools.
I think a distinction has to be made regarding minimal surface rust and fairly deep structural rust that has weakened the metal. For deep rust panel replacement is the only option for a lasting repair.
However for minimal surface rust, sanding back to good metal seldom gets all of the rust out. This is where Tannic acid does work. It converts the remaining rust molecules into a stable compound, and further slows the development of future rust.
It's not unusual to find a bit of flaking chassis paint/underseal on a small area of a large panel, and I have no reservations about doing chemical remedies for such minor rust issues.
zippy500 wrote:
Recently practical classics done a test on these paints, somthing came out better than POR can anyone remember which it was. ( think I have thrown away the mag )
The Product you are thinking or is by Bilt Hamber the cavity wax is Dynax S50 and the rust converter is Hydrate 80.
They have a full range of all the above-mentioned produces and it is all top quality gear I can recommend this from my Experience of use. I too saw the test and results in PC a couple of year ago and I would never use any other now.
I tried the Bilt Hamber "converter" and was again very dissapointed. It does turn the top layer of rust black (this is where all the loose surface stuff has been removed with wire brushes/ abrasives)
but if you scratch the black layer there is, again, sadly rust underneath, and worse than that, any cleaned bare steel on the piece now has a layer of rust on it. The Hydrate 80, being supposedly "best on market" was the last straw for me and rust converters. You need to remove ALL the rust not try to convert it.
I've tried all the "converters" on the market I could find and they are all rubbish. All contained phosphoric acid and (i think) a polymer base so paint will stick to it. All are a tempory fix only.
Phosphoric acid, BTW, in rust REMOVERS such as Jenolite liquid, are fine to use. (although toxic/corrosive so be careful!) Better still if you can get phosphoric acid in the cheaper form of "milkstone remover". Its exactly the same- just phosphoric acid in water, but cheaper. Sadly I dont live in a dairy area so none near me.
I used the hydrate 80 on some very rusty wheel after sanding them first. Then painted over it and the rust has not shown its face again yet. That was a couple of years ago now.
