Underbody treatment

Pete

Well-Known Forum User
Times have changed and a bit Waxoyl topped off with some engine oil is no longer de rigueur.
Whats the best, layer by layer, from metal to final finish.
 

uk66fastback

Club Member
Acid etch primer on bare metal for sure. I am putting some Wurth underseal body coating on my 944 with a gun and compressor as per the factory finish and it'll be good for another 30 years. Just make sure it doesn't get chipped anywhere as when it does and the water gets in, it will then peel off. So an annual check underneath is worth it. I've thought I may get some bedliner to redo the 240 underneath.

Bilt Hamber have some good stuff as well.
 

Pete

Well-Known Forum User
Acid etch primer on bare metal for sure. I am putting some Wurth underseal body coating on my 944 with a gun and compressor as per the factory finish and it'll be good for another 30 years. Just make sure it doesn't get chipped anywhere as when it does and the water gets in, it will then peel off. So an annual check underneath is worth it. I've thought I may get some bedliner to redo the 240 underneath.

Bilt Hamber have some good stuff as well.
Yeah, this is part of my confusion, whats the acid etch primer for? Just put the Wurth on bare metal then there's got nothing for the water to get under.
 

uk66fastback

Club Member
You can put acid etch primer on but you can't leave it at that - it's just a primer. It's meant to have a topcoat of something. It's microns thick whereas the Wirth will be 1-2mm thick.
 

Pete

Well-Known Forum User
You can put acid etch primer on but you can't leave it at that - it's just a primer. It's meant to have a topcoat of something. It's microns thick whereas the Wirth will be 1-2mm thick.
Yep, what's the point of the primer, just fire on the Wurth?
 

Pete

Well-Known Forum User
To stop it rusting while I'm getting the Wurth ready! It doesn't hurt to put it on.
Maybe it does, cause if it chips the water gets underneath it and the Wurth just seals in the water. Not trying to be a smartarse here, genuinely trying to find out whats best. Recently, 3 years ago ish drove my daughters Fiat 500 off the ramps and crushed the sills broke the paint and promised I'd paint it , I didn't, it's still not rusted? Also recently removed underseal from the sills of a 70s Datsun and they were like new.
 

Turn & Burn

Club Member
The etch primer is as the name suggests to etch or key into the surface, it’s definitely not a corrosion protection. It gives subsequent layers something to bite onto. If ur going back to bare metal its essential to prime otherwise top coats can lift off.
As far as bullet proof outer coats Raptor (Load Liner) seems popular these days. I’ve used it and it looks fantastic, can also be mixed with your topcoat colour of choice.
I’ve tried brushing POR15 with mixed results, maybe I expected too much from it after having read some of the reviews, but after rotary wire brushing to as near clean metal as I could get it’s not been a total cure and it seems to chip too easily.26C6282B-F6DF-4236-89C9-50490919DE97.jpeg
 
this is what I did, I can say that over 7 years and two paint jobs its not rusted at all in my garage, which is a massive positive.

Etch
colour
gravitex in colour
colour

Then before it goes on the road, it'll get a clear wax everywhere. As mentioned, you need the stones to bounce off, something you can 'touch up' every few years.

I've smacked it with tools numerous times and its not chipped.
 

uk66fastback

Club Member
Were those sills galvanised? Anything between moisture and metal is better than nothing.

POR15 is useless on bare metal as it is for Painting Over Rust as the name suggests ...
 

Turn & Burn

Club Member
Were those sills galvanised? Anything between moisture and metal is better than nothing.

POR15 is useless on bare metal as it is for Painting Over Rust as the name suggests ...

They sills were Zintec rather that galv, zintec is more stable than galv which you really struggle to paint, the floors and rails were plain steel.
I get that POR is paint paint over rust, but if you do, and I have, it bubbles back through and looks scruffy, I’ve tried on diff casings and Land Rover axles. I think the key with POR is in using the metal prep 1st to dissolve or stabilize the rust. I just struggle with the concept of painting on rust, it’s good for a garden fence but a 1mm think metal panel I’m not so sure.
 

uk66fastback

Club Member
I agree! I've never had much (any) success with POR15. I always think it's for people who can't fix the rust! I think there are better solutions out there. I am intrigued by this tintable raptor bedliner stuff which is supposed to be as hard as nails.

So do you buy it and mix your paint with it or buy it already mixed?
 

Turn & Burn

Club Member
I agree! I've never had much (any) success with POR15. I always think it's for people who can't fix the rust! I think there are better solutions out there. I am intrigued by this tintable raptor bedliner stuff which is supposed to be as hard as nails.

So do you buy it and mix your paint with it or buy it already mixed?
I’ll have to defer to the paint shop on that one, my paint skill ends after priming! They told me that they mixed my colour into the Raptor so I’m guessing the Raptor is clear.
There’s loads of durabilty demo’s on YouTube, I watched this one..
 

moggy240

Insurance Valuations Officer
Staff member
Club Member
The Raptor is not clear but you can tint it with a coloured solvent basecoat to try and match it close to you car colour.
 

Jay.

Club Member
A combination of front main oil seal, oil pump leak, sump gasket weep keep the front rails in great condition. The gearbox generally leaking from both ends keep the middle area coated and the broken diff breather sorts out the rear.

Same approach. It's a low effort way to coat your entire underside, from engine through gearbox to the rear diff. Excellent and a 0 spanner job.
 

richiep

Club Member
For the underside of my project car I will have the following coatings present:
Novol bodywork primer
2k epoxy primer
U-Pol Raptor tinted body colour (907 dark green)
Dinitrol 9050 hi-temp clear wax in exposed but harder to reach upper areas, e.g. above fuel tank, certain nooks and crannies. Also wax on all nut and bolt heads to keep corrosion away.
Dinitrol 3125 and ML cavity wax/fluid in all enclosed structures.
General upkeep through fluid leaks as described by Johny! ;)

I would never coat a full underside with underseal again. While its fine for targeted use, I want to see what's going on underneath, not hide it under goop. It irritates me that my red Z is undersealed. That's how I got it, and I've settled for maintaining it that way with regular checks and Dinitrol top-ups, but ideally I'd like to clean it all off and start again with another approach. That's not likely to happen for some time though. Once Dixie is on the road, red Z may get some TLC and upgrades to the underside necessitating a partial strip down and then we'll see.
 

Huw

Club Member
A combination of front main oil seal, oil pump leak, sump gasket weep keep the front rails in great condition. The gearbox generally leaking from both ends keep the middle area coated and the broken diff breather sorts out the rear.

You may jest Johny but my father-in-law used to religiously coat the underside of his Humber with used engine oil every year (to add to all the other oil leaks you have already mentioned). Eighty years on and the underside is completely rust free, ok a little crusty but rust free.
 
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