MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Effective Body Underside Priming

I would really appreciate help from those of you who have experience in effective underside paint preparation. I've been searching the internet and this MG forum for rust prevention painting methods. I don't have spraying equipment in my garage so hope to use single pack treatments.

What are your opinions or experiences of zinc phosphate brush applied primer paint?

Can this be effectively applied over factory black undercoat on new body panels or on well cleaned undercoat of existing panels? Or, should all such undercoating be first removed before applying the new zinc phosphate coat?

If clean metal surface is needed, do I need to use an etch primer or to sand the metal surfaces before applying zinc phosphate primer?

I'm considering applying MIPA stone chip underseal, over which I plan to apply the top paint coat.

Many thanks,
Brian
MGB GT, January 1967

Brian McIlvenna

Brian

I have used Bondaprimer on my floors. Some people claim that it has lasted 20+ years, although it has probably been reformulated since then.

It has all original metal. Some if it had rust, which I treated with Trustan rust converter, the rest was original factory primer beneath the underseal.

I applied the primer by brush, although I will probably spray it when it comes to doing under the front wing area.

Dave O'Neill 2

Dave,

I'll look up your suggestions, thanks. I am fitting new floor pans as well as middle and outer sill sections for both sides. I have been in negotiations about having the underside of the car vapour blasted to remove underseal, dirt and grease. From previous work done, I expect very little evidence of rust.

I would like to be able to brush on my suggested zinc phosphate primer over original panel base coat or factory black undercoat of new panels, then apply the underbody schutz, and finish the underside and inner wing areas with the finish colour.

Brian
Brian McIlvenna

Have recently used RustBuster's two pack chassis paint on various items, front cross member being one. Brushes OK with a little thinners, seems very tough! No long term experience though.
Allan Reeling

Brian,
I have used both Galvafroid and Zinga extensively over many years. It needs to go on bare metal to be effective - the Companies offer precise instruction - I put ships' bottom paint (not anti-foulling) and the usual black sludge ontop. Occasionally one has to cut into a bit that has been prepared earlier and it is always gratifying to find that the metal is still rustfree. Both products are expensive so, if you can't afford to put two coats everywhere - at least cover the welds.
Of the two - I prefer Zinga

R
Roger W

Roger,

I have investigated the Zinga treatment; it is very interesting. I've spoken to a Zinga representative on the phone and he underlined the need for a particular roughness profile needed to give the treatment purchase.

What metal preparation did you use for the Zinga treatment? I've looked into a bristle blaster, which retails for £330 on ebay for an air driven type. This is a lot of expense I feel and would take a very long time to cover the whole car underside, inner wings and wing undersides.

Thanks,
Brian
Brian McIlvenna

Brian,
Sorry it has taken a long time to come back. The offical answer seems rather off-putting. I use a rough emery cloth followed by a thorough clean using either the Zinga thinners or carbon tetrachloride. On large areas I use Zinga spray but a brush on the smaller fiddly bits. Always use a brush on welds but spray over if they are adjacent to the large areas.
The interesting question is always about what if anything comes next. I have left Zinga uncovered for protracted periods and been suitably impressed how it resists oxidisation. I believe one should use yellow chromate as the next coat but I haven't seen it for years. Instead, I use a mysterious blue liquid which was marketed to cover galvanised garage doors. Because it's as viscous as water, the jar has lasted forever - anyway then use normal primer/undercoat and chassis paint with sound-deadening sludge ontop.
You will only do this once !
R
Roger W

Roger,

Thanks for the reply. Did you find that the rough emery cloth provided a good key for the Zinga treatment? What grade did you use? The company representative did state that anything other than a particular ISO roughness grade would result in the coating peeling or falling off.

Cost of Zinga is high but if it does succeed in providing an effective sacrificial anode to ward off rust, I feel it is worth it. The surface preparation is just the major hurdle.

Thanks,
Brian
Brian McIlvenna

Brian,
Your observations about the value of Zinga echo my own.
On the big spaces, I start with a rough and finish with a medium and then clean thoroughly. I mix the Zinga also very thoroughly. The brushed first coat can look rather thin but the second coat sticks evenly. Sprayed Zinga looks even from the start but I still do a second and third.
As you say - preparation is so important but so is the next layer -

Good luck but don't forget the inside of box sections - My present favourite wax once again ( after a gap of many years) is Dinitrol -
R
Roger W

Roger,

Thanks again. I'm investigating using vapour blasting by a local company; they won't tell me the blast medium but state that glass bead is not used as it imbeds in the metal surface roughness troughs, which later detach and leads to rejection of protective coatings.

I want to use Zinga within the sill section too as they are being replaced. The factory black primer on the new panels will need to come off and weld-through primer used on panel edges that will be welded.

Do you know what readily available product will remove the panel factory black?

Are you confident that emery cloth preparation provides sufficient key for the zinc treatment? Do you know anyone else that has used Zinga treatment on classic restoration projects?

Thanks again for your input.

Brian
Brian McIlvenna

Brian,
Last question first; I first used "Galvafroid" maybe twenty years ago on the advice of a marine coating expert - and found it very effective although, looking back, it was not as easy to apply as Zinga. Both keep the area covered totally rustree for many years.

I have not been in a position (not needed) to apply the Zinc coat to the hidden sections of say the sills - I have always relied on cavity wax - initially Dinitrol, then Waxoyl, then Supertrol and now Dinitrol again - each topped up at two year intervals - the brand changes for a variety of reasons - and worth a separate discussion.

It follows that I have not needed to remove the factory coating. Your local bodyshop will advise. My own view is that one should always use a zinc coating on any welding which otherwise is likely to be the first area to rust.

As an unrelated point, the formerly very rusty footwell of our 1800 was coated many years back - and gets wet from time to time but remains rustfree.

All our cars are used the year round - the B is very manageable on slippery surfaces - they are treated like any modern car - live outside much of the time/ get wet and dirty / salty / cleaned by hand very occasionally - have bits repainted from time to time - all three are very presentable (and reliable).

Good luck with yours
R
Roger W

This thread was discussed between 13/11/2014 and 29/11/2014

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now