 | Home > Technical > Galvanised chassis paint question. |
 
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| I Like Old Skool Member Since: 23 Feb 2015 Location: Manchester Posts: 767   
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I'm about to paint a new galvanised chassis before fitting it.
After looking around I kind of settled on this satin black chassis paint from here https://www.paints4trade.com/chassis-paint...0597-p.asp Plan is to treat the galv with mordant solution then use the paint which claims to be suitable for direct application to metals without primer or undercoat. The mordant treatment should prepare the galv surface for perfect adhesion of the paint according to their own description? Trouble is, I contacted the paint company just to double check my plan and they have told me to use a primer after the mordant wash and before applying the chassis paint. Cost of the primer is £50 so this bumps up the order value quite a bit on top of the mordant solution and chassis paint. https://www.paints4trade.com/rapidguard--u...1094-p.asp The primer description mentions various surfaces it can be applied to but not specifically galv surfaces. On the face of it, the advice to use this primer almost seems to contradict the product instructions. I'm not looking for ultimate corrosion resistance as it's already galvanised. I just want the chassis black and to stay black for a couple of decades without chipping easily or flaking off due to poor adhesion. Does anyone have any experience of these products or know if the combination is the way to go? My cynical side is telling me I'm just being upsold a product I don't need and my big worry is that it may actually perform worse than the chassis paint applied directly to the treated metal surface? |
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18th Apr 2024 10:16pm |
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| NickMc Member Since: 01 Oct 2014 Location: Norn Iron Posts: 1571  
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I use Galvacoat from my local galvanisers
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18th Apr 2024 10:29pm |
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| paul 123 Member Since: 10 Jul 2022 Location: norwich Posts: 76 
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when i did mine i used twash etch primer primer then 2 coats of black chassis paint.
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19th Apr 2024 6:28am |
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| douglasgdmw Member Since: 07 Oct 2014 Location: Kilmarnock Posts: 27 
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I had a new galvanised chassis for my Series 2a and the people doing the restoration used the Raptor product (smooth coat) so maybe worth contacting Raptor to see whether there is a product that meets your needs there - looking at the website (not the best tbh https://raptorcoatings.com/en/ ) they have something equivalent?
No actual experience but if you are going to all the bother of fitting a galv chassis and painting it, I would want it looking as good as possible for as long as possible - Land Rover S2a - Defender 90 SW |
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19th Apr 2024 7:59am |
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| MarkBrown Member Since: 03 Oct 2022 Location: Mid Wales Posts: 326 
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I can help with this. I used the same method as you have suggested, galvanised chassis, mordant solution, then chassis black. The process was to paint the chassis with mordant, also called t-wash, this will blacken the galvanised surface ( this does seem to only work on new galvanised surfaces ) then wash it off. I chose a combination of spraying and brushing and applied three coats. I used the same company and have found the paint to adhere well, apart from on new, unprimed steel, which appears to need a primer. It’s also a really good paint for wooden boxes used in the back. I hope this helps.
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19th Apr 2024 8:51am |
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| Linds Hanson Member Since: 16 Jan 2021 Location: Cornwall Posts: 443
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Just use Buzzweld T wash and Galv in one
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19th Apr 2024 9:37am |
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| I Like Old Skool Member Since: 23 Feb 2015 Location: Manchester Posts: 767
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I have used T-wash before on my previous chassis swap. I only painted the rear crossmember that time but this time want to do the whole chassis as it is more visible on the early series vehicles. I'm familiar with the t-wash process and the amazing blackening effect which gives a clear indication of treated or untreated areas and shows any patches that need more attention. Just read a bit about etch primer and t-wash, seems like the active ingredient in both is usually phosphoric acid which reacts with the surface to ensure a good bonding surface. My non scientific mind makes me think the t-wash system is a better way as the unreacted acids are washed away after treatment, unlike the paint which will hold it in place to continue attacking the chassis long after application? I think maybe the paint people misunderstood my query and thought I wanted maximum corrosion resistance when I actually asked how to make sure the paint sticks. They have suggested a corrosion inhibiting primer(Zinc rich?) which IMO is unnecessary on a zinc coated chassis? Getting even more technical, my understanding is that the galv layer on a chassis works by being sacrificial and will corrode/oxidise preferentially to the steel which inevitably will form by-products that cause the paint to bubble and separate, so maybe whatever paint I use, it will unavoidably start to fail after a period of time? I just don't know? If only there was some technical boffin, independent from the paint suppliers that could tell me 'THIS' is what you need to do..... |
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19th Apr 2024 10:26am |
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| MarkBrown Member Since: 03 Oct 2022 Location: Mid Wales Posts: 326
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A newly galvanised chassis is a thing of beauty, one that’s been subjected to a year or so of use isn’t. At least if the black paint comes off it’s easy to touch up. Mines been painted since 2019, seems resistant to the jack and as it’s been back on the road two years is now covered in mud - I’m not that into washing cars, we live down a muddy track so it’s largely pointless, they get done every 6 months, then not much underneath. From what I can see it still looks good, as it should really. I’ve so far decided against underseal.
Last edited by MarkBrown on 19th Apr 2024 4:41pm. Edited 1 time in total |
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19th Apr 2024 1:51pm |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3213  
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That is not correct. The reaction between the acids in the etch primer will stop once equilibrium is reached.
This is also incorrect. The protection of the cathode (the steel) by the anode (the zinc) is also a factor of the surface area ratios. Since basically there is 0 surface area of the steel, as it is covered by the zinc, the depletion of the zinc is really really slow. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing 2012 90 CSW, 2.2TDCI, Santorini Black |
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19th Apr 2024 1:59pm |
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