Advice - Rust on new metal roofing sheets

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Hello,

I fitted some metal sheets to a garage roof in August 2023 (5 months ago).
Sheets are Tileform sheets from cladco. It says they are made from galvanised Swedish Steel with a hard-wearing Prelaq Mica coating.
roof sheet is - 41/1000 Tile Form 0.6 Thick Mica Coated Roof Sheet.

on a later inspection I noticed rust on most of the metal sheets. Pictures of the worst areas.

Has anyone else had early signs of rust on newly installed metal sheets?
If so what do you think caused it?
My biggest question, what can I do about it?
 

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You could ask the suppliers to inspect it but I suspect they will say that it is swarf from the holes drilled to fit the sheets that have not been removed. That's what it looks like from the pics to me.
 
You could ask the suppliers to inspect it but I suspect they will say that it is swarf from the holes drilled to fit the sheets that have not been removed. That's what it looks like from the pics to me.
I have reported it to them. They initially said its because they were stored outside. However they were stored outside for less than a week at the tail of summer.

Thats possible! Thank you i never thought of that.
Do you wipe/blow the roof after drilling the bolts?
Bolts were self drilling ones recommended by cladco.
 
I agree it's from the self drilling Teks swarf , same thing would have happened if a drill had been used.Ive seen similar when sheets have been cut with disc cutter.
Its the raw edges of the swarf that rusts which then stains the sheet
 
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Thank you.
Is it possible to remove and how would you recommend removing it?

I tried wiping with a wet cloth, it reduced it but did not remove it completely.
 
Thank you.
Is it possible to remove and how would you recommend removing it?

I tried wiping with a wet cloth, it reduced it but did not remove it completely.
Perhaps a light abrasive polish like Brasso might remove it.
 
Though the electroplating or hotdip applied coating of zinc which makes steel "galvanised" does galvanically protect the steel even where the plating is removed, those places will still corrode.
As the protection happens, the zinc itself is slowly removed, so it doesn't last forever anyway.
If you rip the metal apart with screws, nails, or cutting it, at the micro scale you leave a highly reactive surface ready to go.

Best I know of is one of the "Rust-Remedy" / Kurust /Naval Jelly solutions which will react with the unprotected steel and leave a phosphate, or similar, coating on it. I believe it's basically phosphoric acid, but there's probably more to it.
Nitromors do one : https://www.halfords.com/motoring/p...or-500ml-767598.html?stockInventory=undefined

Research it a bit, there may be notes about galvanised steel.
If you have "white rust" whichis the zinc corroding, you can remove it with weak acid such as vinagar.
You want NO oil/ grease, so a detergent may be appropriate to clean it. There's a pre-cleaner which I think is called CLR which is designed to remove calcium salts and whatnot. If you paint slightly corroded galv , the paint is likely to flake off. There are special paints for galv.
There are sprays designed for local application to "repair" galv but I don't know about them.

Ultimately, it'll last longer if it's painted, though that's something you don't want, I daresay.

If you live near sea air or other pollution sources, the zinc won't last long anyway.

A mistake many make with Kurust etc is to dip a brush into it, then onto the surface to be treated. That carries iron particles back into the Kurust, so you gradually stop the stuff working as it has already reacted before you apply it. IE tip some which you'll use all of, into a small dish, etc.
 
In theory it should only stain them if they are quality sheets .
Ive set many thousands of teks in agricultural buildings over many decades and not seen a sheet rust through despite not removing swarf but they have either been well galvanized and or plastic coated.
 
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