940 underbody rust protection advice

[Eyebrows123]

So, after 25 years and a couple of salty winters, it looks like the underside of my 940 has suffered lately. It looks like a lot of the original stone chip has started to come away and the result is there's the odd patch of surface rust on the underside. One of the rear sills has started to go, I've just cut it out and welded it up. My question really is what can I do to keep the car solid?

So far, I have wire brushed all the loose rust on the bottom back to bare metal, used bondarust zinc based primer (2 coats) followed by 2 coats of xylene based chassis black. Trouble is I'm not sure how long this will last, it doesn't seem anywhere near as tough as the factory paint. Are stones going to chip it off? Without stonechip will it last? Nervous to add stonechip as I'm thinking it could hide rust underneath it?

Basically, what is the best way to protect these cars from rust? Especially when you've had to take it back to bare metal to remove the rust, what process should i go through? Hope someone can add some advice, would be very much appreciated

[360beast]

I personally would wire brush off as much rust as possible, apply jenolite rust converter, primer, paint with a chassis paint then use some underseal on it. Then to be certain it isn't going to rust you could cover the underside in used engine oil (also helps revitalise any old waxoyl that's been used.

Don't apply waxoyl as it breaks off after a bit and traps moisture against the body.

[Kev0607]

Is "Hammerite Underbody Seal" any good? It says it has Waxoyl in it. Some say to use it, some don't.

https://www.amazon.co.uk/Hammerite-5...74368773&psc=1

[Laird Scooby]

Depends whether you want to get down and dirty doing it yourself or whether you want to pay someone and have a guarantee.

https://www.rust.co.uk/

That site does both, will either supply tools and potions for you to use or take you car, inspect, repair as necessary then treat it. They're in Spalding so a trip into the Fens for you!
Maybe!

Alternatively follow Lukes excellent advice.

[Free940]

I've had great results with POR-15 rust preventive paint, just degrease and remove all the loose rust. Apply a thin coat, and then Bob's your Uncle!

[mjk164]

Whilst you are underneath, make sure the existing drain holes are clear and I would (and I have on my own 960) drill some extra holes to ensure proper drainage. Also take the opportunity to spray the insides of all chassis parts etc. with your chosen sealant.