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Rust proofing rear subframe

5K views 18 replies 9 participants last post by  Nyxeris 
#1 ·
The subframes on both my 1ers are starting to look a little corroded on the lower more exposed edges, I guess where they are more susceptible to stone chips, salt and spray.

I have bought a second hand subframe off eBay that compared to most 1ers I've seen has very little rust. I plan on sanding, painting and poly bushing before fitting to the car. My question is from others experiences what are the best DIY paints to inhibit corrosion on steel? I was planning on using a wire brush and file on any visible rust to take back to bare metal and then treat with something like Hammerite primer/rust convertor. Any of the subframe with good OEM paint I will just key and paint over.

Are the chassis specific Epoxy paints better than something simple like Hammerite primer and top coat with Waxoyl sprayed into all the members? I don't want to spend hundreds but want a finish that is going to last. The OEM finish on the subframes is pretty terrible in my opinion. Strangely the M3 subframes seem to suffer less than the non M 1 and 3 series.
 
#3 ·
jonwilli said:
Are the chassis specific Epoxy paints better than something simple like Hammerite primer and top coat with Waxoyl sprayed into all the members?
MP's advice is the best, but if you want the DIY approach the epoxy paints are the best approach IMO.

I had a kit car years ago at I used for track days. With some work I had to do on it I painted the frame with some 2 pack epoxy paint. You can thin it down to use in a spray gun, but as it was in an area that wouldn't be seen I used it thick and simply painted on with a nice thick layer.

It hardens same as an epoxy resin as you'd expact and not the thin coat of paint you'd get off hammerite etc. I'd say it ends up being the closest you can get to powder coating as it's a nice thick solid coating. It resists chips etc really well and I'd always use again for that sort of thing.

Also spraying Waxoyl (or modern equivalent) inside is always a good idea anyway.
 
#4 ·
marco_polo said:
Shot blast to bare metal, then hot dip galvanised?? You could park it in the sea then. :)
I would have thought the heat would cause it to distort?

Sandblasting and either powder coat or painting with etch primer then 2k paint top coat would be a better bet IMO.

The subframe on my 2011 car is looking a bit scabby and will need attention during the warmer months.
 
#6 ·
I wouldn't bother with waxoyl, it's been obsolete for years. If you want something oil based Dinitrol is a better option but I'd rather use a rust-inhibiting cavity wax like Bilt Hamber's Dynax, it dries semi-hard and actually prevents rust whereas waxoyl etc. just stops water reaching the metal (or traps it underneath) and stays greasy for all eternity. I use their BH's Dynax UB on bolt heads etc. when I'm changing stuff under the car and it works like magic.

Redish Motorsport use the POR15 prep/paint 'system' on their E46 underside restorations, that's what I'd use if I had the subframe off the car. The results they get are epic.
 
#8 ·
Nyxeris said:
Redish Motorsport use the POR15 prep/paint 'system' on their E46 underside restorations, that's what I'd use if I had the subframe off the car. The results they get are epic.
A quick Google and that POR15 paint sounds like good stuff and relatively easy to work with. Will have to look at some more reviews this evening. Like this though, maybe top of the list for now. :thumbs:
 
#11 ·
Just don't get the POR-15 paint on your skin. There is nothing that will clean it off and you will have to wait for your skin to naturally shed to get rid of it. Brilliant stuff and very good for sealing metal. RUST SEAL is also an alternative to POR and can be a bit cheaper.
 
#14 ·
Im not a big fan of POR15 personally as it can flake/peel if not applied perfectly, i restored the underneath of my old Evo2 using POR15 and relevant prep fluids etc, for first year it looked amazing under there even MOT man was asking what i had used, however another year down the line and some areas where starting to peel back and rust showing through, i think the problem is getting the surface perfect which working underneath a car on axle stands its hard to do and i should of had it on a spit and bare metal'ed the whole thing but took long enough as it was just cleaning it all back, it protected well enough but not the miracle many people will tell you, i guess doing a subframe off the car after blasting it wouldnt be so bad but keep it out of sunlight after painting as UV breaks it down if i remember right.

There are better products out there like Expoy mastic etc but all depends how much time and effort you want to put in.
 
#15 ·
THETYRANT said:
Im not a big fan of POR15 personally as it can flake/peel if not applied perfectly, i restored the underneath of my old Evo2 using POR15 and relevant prep fluids etc, for first year it looked amazing under there even MOT man was asking what i had used, however another year down the line and some areas where starting to peel back and rust showing through, i think the problem is getting the surface perfect which working underneath a car on axle stands its hard to do and i should of had it on a spit and bare metal'ed the whole thing but took long enough as it was just cleaning it all back, it protected well enough but not the miracle many people will tell you, i guess doing a subframe off the car after blasting it wouldnt be so bad but keep it out of sunlight after painting as UV breaks it down if i remember right.

There are better products out there like Expoy mastic etc but all depends how much time and effort you want to put in.
Nightmare. I feel your pain there.

I did a similar thing on an E36 and used epoxy mastic in the end but I never felt like it was as hard as the por15.

Having said that I don't know how you'd remove the por15 if you needed to.
 
#16 ·
I've used POR15 on the chassis of my TVR Chimaera and I rate it highly, very good paint. As with any coating preparation is everything and you need the full kit to do it properly, including the de-greasing agent and the Prep&Ready (Which I think is phosphoric acid based which kills any rust and etches the steel, without this it won't last long. Try and remove all paint for the same reason. Shot blasting would be good, but if not, buy a 'twisted rope' wire brush for your angle grinder, they are excellent at removing paint and rust (wear eye protection!!). I wouldn't use powder coat as this suffers from capillary corrosion underneath the coating when it chips (and it chips easily). Hot zinc would be great but I doubt anyone would do it as there are a number of sealed hollow sections and you must have open sections for hot zinc to allow for expansion and draining of the zinc fluid - Sealed sections can cause serious issues and the plater's won't touch it. Go with POR15, and good luck!!
 
#17 ·
JLCJ66 said:
I've used POR15 on the chassis of my TVR Chimaera and I rate it highly, very good paint. As with any coating preparation is everything and you need the full kit to do it properly, including the de-greasing agent and the Prep&Ready (Which I think is phosphoric acid based which kills any rust and etches the steel, without this it won't last long. Try and remove all paint for the same reason. Shot blasting would be good, but if not, buy a 'twisted rope' wire brush for your angle grinder, they are excellent at removing paint and rust (wear eye protection!!). I wouldn't use powder coat as this suffers from capillary corrosion underneath the coating when it chips (and it chips easily). Hot zinc would be great but I doubt anyone would do it as there are a number of sealed hollow sections and you must have open sections for hot zinc to allow for expansion and draining of the zinc fluid - Sealed sections can cause serious issues and the plater's won't touch it. Go with POR15, and good luck!!
:thumbs:

Something like this?
 
#18 ·
I used to use Hammerite smooth on stuff like this, but it is not as good as it used to be. Possibly down to a more environmentally friendly formula?

What is the best way of treating the internal surfaces? If water/salt gets in it will rust from the inside out eventually.
 
#19 ·
symonh2000 said:
What is the best way of treating the internal surfaces? If water/salt gets in it will rust from the inside out eventually.
I vote for Bilt Hamber Dynax, used it on the Defender to good results. As I said above it's wax-based and contains rust converters/inhibitors so injecting it actually helps stop any rust you can't see rather than just keeping water/salt away from the metal like waxoyl or anything bitumen based does. It dries semi-hard too. Big fan of that as going under the car when there was waxoyl on usually cost me the clothes I was wearing!
 
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