Rust Spots on Metal Corner Bead (Interior)

[IB100]

Hi

Following a water ingress into my living room, I sanded down some damaged plaster and the metal beading before applying emulsion. Rust spots started appearing over the beading after a couple of weeks. After some internet research I re-sanded the beading and applied about 3 coats of 40% undercoat for interior and exterior metal. Spots came through again, so I applied another 3 coats but some spots are appearing again.

The metal is not flaking so I don't 'think' something like Kurust is suitable. Someone suggested pva, but I don't know if I'd be able to put an emulsion over that.

Can anyone advise me?

Many thanks

 

[vibrobullit407]

I assume you touched up with water based undercoat. Try just touching up with an oil based undercoat.

Do not use PVA it is not designed for this!

 

[dcdec]

Neither is OBU in this situation. Think about it, if that u/c makes contact with bare plaster/water ingress your gonna end up with bigger problems than the original fault, its called saponification, it is of course unlikely but poor advice none the less and showing ignorance of surface and coating.
I don't know why everyone suggests OBU for these problems when there are proprietory 'designed for' primers available. U/C is not designed to go straight over bare metal either.
Zinsser bin would be my choice but i'd have a quick look at the zinsser range to see if there's anything more specific, 123 can go over galvanised but not sure about bare/ferrous metal

Plaster beading should be galvanised and doesn't normally cause problems, my guess is by sanding it down you removed it down to 'bare' metal.

 

[vibrobullit407]

I bow to your superior knowledge here dcdec. Just giving advice due to what has worked for me in the past. Never had any problems with doing it this way!

 

[joe-90]

Saponification is to do with making soap.

Beading rusts when the wall is damp. A shellac based product is poor in damp conditions.

Oil paint works - whether you like it or not.

 

[IB100]

Thanks for all your responses, I used an oil based undercoat, thinned with white spirit. So I guess I'll investigate the Zinsser range, but avoid shellac?

 

[joe-90]

It's not worth buying a load of expensive primer that's not needed.

Aluminium primer is good if you really want to go that route. What you really want to know is why it is rusting in the first instance. It has to be a damp issue.

 

[TheDec]

Thinning here is the important factor, if as you have said you have done this then you are fine to apply your finish coats.

Sorry, firstly you wil need to establish the cause of the ingress of moisture and cure it prior to application, and make sure that all affected areas have dried out.

Dec

 

[dcdec]

So saponification isn't a paint defect then?

When you googled it probably didn't explain that when alkali salts drawn out with the damp meet the oil resin it causes ____________________

Answers on a postcode and get a free entry into a draw to win your very own copy of if you can **** you can paint

 

[vibrobullit407]

So saponification isn't a paint defect then?

When you googled it probably didn't explain that when alkali salts drawn out with the damp meet the oil resin it causes ____________________

Answers on a postcode and get a free entry into a draw to win your very own copy of if you can p**s you can paint

Send me a copy so that I can read it in the bath cleansing my self with this by product!

Google is a wonderful thing!

 

[joe-90]

So saponification isn't a paint defect then?

When you googled it probably didn't explain that when alkali salts drawn out with the damp meet the oil resin it causes ____________________

Answers on a postcode and get a free entry into a draw to win your very own copy of if you can p**s you can paint

Didn't need to Google it - it is schoolboy knowledge.

 

[vibrobullit407]

Didn't need to Google it - it is schoolboy knowledge.

I'll admit I didn't know what it was but had heard the use of the word before! Can't say that I've encountered it either.

Have you encountered it before dcdec? And if so how often?

 

[TheDec]

Iv'e come across this problem a number of times, on saying that and perhaps more often come across surfactant bleed.

Dec

 

[Starspark1]

Dont disagree with joe-90 guys he seems to know everything!! Until of course you prove he doesnt as in this case and //www.diynot.com/forums/decorating/ceiling-preparation.326025/ then he resorts to name calling.