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MG Midget and Sprite Technical - Flash Rust

Getting really frustrated with flash rust appearing overnight on new panels that have been prepared for welding and part welded in.

As I am very new at welding it takes me a few sessions to complete all the welds on some of the larger panels and that leaves sections of bare metal exposed.

After completing some of the welds in the evening, I come in the next day only to find a perfectly thin layer of rust on any bare metal on the panel that was welded the night before.

It must be some sort of reaction to cause it to rust so quickly as other bare pieces of metal in the workshop have not rusted at all for months!!

Does anyone know how to remove this rust with a spray solution that will allow me to put in a clean weld?

Thanks

James
James Paul

James, If you are just trying to clean it up to do more welding, I would think a wire brush on an angle grinder or drill motor would do it just fine. If you are talking about painting, then you need to get into chemical fixes.

Charley
C R Huff

Hi James
You can get weld thru primer from your local motor / paint factor or even Halfords.
Alan
Alan Anstead

James,

This is what I've used for weldthru'

http://www.bilthamber.com/paints-and-coatings/etchweld

I find all their products very good - no connection !

Think I may still have a spray can if you want to try it.

R.
richard boobier

A couple easy options

When done for the night, just wipe a thin coat of motor oil over the top and wash off before next use with some acetone, or break cleaner in a spray can

When done for the night, get a cheap spray can of spray primer $1 cans...and just coat then use acetone to remove it before welding the next time


Ither option should work okay

Post some photos of your work, we want to see

Prop
Prop and the Blackhole Midget

Use Kephos (AKA Henkel Paint Grip 253). It's a weld-through solvent-based phosphating solution that protects bare steel from flash rust. Simply wipe it on with a rag and let it dry (takes about 5 minutes).

Kephos can be painted over, so no risk of contaminating your steel.

Edit: weird. Kephos doesn't seem to exist in the UK.
Growler

Aha! http://stowlin.com/products/henkel-products/henkel-bonderite-o-pc-253/
Growler

The usual motor factors will sell 5l cans of "metal prep" or similarly named generic products very cheaply. It's basically a degreaser and weak phosphoric acid solution that you dip, brush, spray or just wipe over the metal. It eats out any surface flash rust pretty well instantly and protects the steel surface from re-rusting for several weeks. Probably the same stuff that Growler has linked to.
Guy Weller

Weld through primers and similar products are apparently excellent though I've never used them. I have a soft circular wire brush in an electric drill and I find that gets rid of 90% of the problem in a few seconds. When the welding and grinding is finished, I go over the area with the wire brush and then treat the seams with Kurust or similar and then thin primer that will get into all the nooks and crannies. If the work is on the outside of the car the job is finished in the usual way. But if the work is hidden underneath I'll usually give it a good spraying of WD40 after the top-coat of paint has been applied.

Nick Nakorn

Brake cleaner and welding do not go together for health reasons. Read the warnings before suing it as under certain circumstances it can give off deadly gases.
Alan
Alan Anstead

Hi and thank you for your words of wisdom!

I did have a can of weld-through primer, but I was convinced that the welds were not as clean as on stripped steel.

But from what you guys are saying that it should be fine and produce strong welds.

I will look at getting some more primer, may be another brand will be better??

As always you can follow my journey on my blog:

http://1965mgmidgetrestoration.blogspot.co.uk/

Richard I will be working tonight from about 8:30, pop down to the sawmills if you're about!

I'll update you all.

Kind regards

James
James Paul

To follow up on alans comment about brake cleaner and welding

Alan is absolutly correct, very dangerous, I did mention using brake cleaner to remove wiped on oil as it breaks down oils quickly and flashes off clean, I should have added to make sure the surface to be welded was clean of the brake cleaner

Prop
Prop and the Blackhole Midget

This thread was discussed between 15/08/2014 and 20/08/2014

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