# Forum Home Renovation Roofing  Help! The gal/zincalume is eating my roof.

## GOM

In March this year I had the rusty old Klip-lok roof replaced with new Zincalume Klip-lok. As part of the job I asked for metal gutter-guard to be installed over the 42m length of gutter. The roofer installed sheets of Locker Group perforated metal 300mm wide. This is secured along one edge by the clips that hold the front edge of the Klip-lok, passes over the Zincalume box gutter, then is riveted down to the Colorbond flashing on top of the fascia. This arrangement does a good job of shedding leaves, as they blow straight across the gutter-guard and over the edge of the fascia board. 
  However, despite my requesting Zincalume gutter-guard, I believe the roofer has given me galvanised gutter-guard. The roofer claims that his invoice says it is Zincalume but Locker Group does not make perforated metal in this hole pattern (R03230) with Zincalume, only with galvanised (or stainless or aluminium, but its certainly not these). If you zoom into the photo you may see the spangly looking galvanised finish.    
  The problem is that I have just noticed that there appears to be corrosion and/or efflorescence building up where the gal gutter-guard rests on the Colorbond flashing.   
As the roofer explained at some stage you can run gal onto Zincalume/Colorbond but not Zincalume/Colorbond onto gal. The way I understand it from searching this forum, water from the Zincalume Klip-lok would be reacting with the gal gutter-guard, causing it to corrode prematurely. This water (some of which travels over the top of the gutter-guard) is then depositing zinc salts on top of the Colorbond flashing on the fascia.   It would also be doing the same thing inside the Colorbond box gutter, and depositing zinc in my rainwater tank (our only supply of drinking water).  
  The other possibility is that the white patches are the start of major corrosion where the gutter-guard and the Colorbond fascia meet (as water tends to pool there after rain). Either way, I will be left with stains of zinc and rusted iron running down the fascia boards, and possibly with the flashing, gutter and gutter-guard being eaten away. 
  I can see three ways out of this:    I      could demand that the roofer replace the gutter-guard with Zincalume. This      would require lifting the Klip-lok sheets and some of the flashing to      remove the clips. I am not keen to do this, as it basically involves      replacing the roof which might bankrupt the roofer (if I could persuade      him to come back). Now that winter has hit, the job would be tricky.    I      could drill out the rivets along the top of the fascia, lift the front      edge of the gutter-guard by a centimetre, and put a non-metal barrier      between the gutter-guard and the Colorbond flashing (rubber or silicone).      That way the gal gutter-guard would continue to corrode faster than it      should, but I would avoid any reaction between the gal and the Colorbond      flashing.    I      could lift the gutter-guard and smear silicone over the whole area where      the gutter-guard overlaps the flashing, then push it down again. If I      smear silicone over the top as well, this might encase the gutter-guard      and stop any reaction continuing.  
  Any thoughts on whether I have the onset of serious corrosion, and what to do about it?  
  Cheers, GOM

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## barney118

It looks like gal to me, I think you will struggle to fix just replace  
Sent from my iPhone using Tapatalk

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## cyclic

Water running off zincalume/colourbond will rust galvanised metal which is why galvanised gutters and rain water tanks didn't last long when theywere fed from a zincalume/colourbond roof, and neither will your galvanised leaf guard. 
In one of the pics I am sure I can see rust. 
The roofers job is to know this and use the correct materials accordingly. 
Aluminium is compatable with zincalume.

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## phild01

Useful reading here http://steel.com.au/~/media/Files/Bu...5june2008.ashx

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## GOM

Thanks for the replies. Thanks also to phild01 for the link - very interesting reading. 
I'm still not sure though whether the white material on the Colorbond flashing is just a deposit of zinc salts corroded out of the gal gutterguard and just being deposited on top of the Colorbond flashing, or whether it's a sign of serious corrosion setting up in the Colorbond. If it's the former, I might be able to fix that by just separating the two, but if it's the latter, the gutterguard just has to go. 
Thanks, GOM

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## METRIX



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## GOM

Thanks Metrix, 
That table doesn't tell me what corrosive action I might get between the galvanised gutterguard and the Colorbond flashing that it's sitting on. 
Cheers, GOM

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## METRIX

Correct, but the below is an extract from Bluescope Technical Bulletin which may help 
In corrosive environments, where low coating mass galvanized steel purlins (≤200g/m2 zinc coating) are used to support ZINCALUME steel or COLORBOND steel roof sheeting, 
the purlins may be subject to accelerated corrosion. Such that the zinc coating is completely consumed.  
In such cases, the roof sheeting is then left in direct contact with the base steel of the purlins allowing sacrificial corrosion of the ZINCALUME steel coating to occur. 
To avoid this situation, BlueScope Steel recommend that heavy coating mass and/or post painted purlins be used, In severe environments, where COLORBOND Stainless steel is specified for roof sheeting, 
BlueScope Steel recommend that galvanized purlins be insulated from the roof sheeting, to avoid dissimilar metal corrosion (stainless steel/zinc corrosion couple)  
This can be achieved by means of an inert polymer separation tape, adhered to the top surface of the purlin.  Corrosion technical bulletins

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## GOM

METRIX, that's very helpful. 
That says that the coating on the gutterguard is busily sacrificing itself. Once it has achieved that task, the Colourbond will then start sacrificing until there's no coating left and my flashing will be destroyed. Unless I can get the "polymer separation tape" between the gutterguard and the flashing, the flashing's had it. 
It might have been possible to apply such a tape before the roof was laid, but I don't think it's possible now. (The gutterguard is 1mm thick and quite stiff, so it will be hard to lift it up. Also, it's fitted under the flashing at the end of each gutter run, so I'd have to lift both the end flashing and the Klip-lok sheets to be able to raise the gutterguard enough to be able to lay any tape the whole length of the fascia). 
I think I need to remove the gutterguard. To do this without lifting the roof, maybe I could cut it along the edge of the Klip-lok, leaving the part that is covered by the Kipl-lok (since it is pinned down by the lok-clips that hold down the roof). Then to replace it I might be able to slide some Zincalume gutterguard under the edge of the Klip-lok and rivet it down to the flashing over on the other side of the gutter. 
Does that sound feasible? GOM

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## METRIX

If your concerned about it coroding, I would persue the people that did the roof and gutter guard for you, you should not be fixing up something if it was done incorrectly.
I would be seeking something in writing from them, ensuring that the products they have used are compatible.

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## GOM

METRIX, you're right. I am pursuing this with the roofer. What I was looking for is an idea of what the possible solutions might be and how likely they are to work. You and the other posters have been a great help in clearing things up in my mind. 
Thanks.

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## GOM

There have been some new developments with my gutter guard. I have had a close look at it and discovered some faint markings which indicate that it really is Zincalume, not galvanised. I've added the red letters in this photo to help in reading it:   
Also, in some of the worst areas where the white patches have appeared you can now see rust developing:   
Then, when you look close up, you can see that the rust appears to be starting on the walls of the holes punched in the Zincalume:   
So, I think I now understand why the corrosion is happening. The holes have been punched out of Zincalume sheets, so that there is no protective coating in the holes. The exposed holes are starting to rust, but the first part of that process is that the Zincalume sacrifices its zinc/aluminium coating first, leading to the build-up of the white salts on the gutter guard. That process can only go so far before the steel in the holes starts to rust. Eventually (according to the Technical Bulletins that METRIX put me onto) the gutter guard will lose all its coating, the coating on the Colorbond flashing will start sacrificing itself, and then the gutter guard and the Colorbond will rust away. 
My current remedy is to try spray painting the gutter guard to provide some protection to the bare metal in the holes. That may only serve to block the holes. If it works though, I (and the roofer) may cut the gutter guard about 1cm out from the edge of the Klip-lok, take it away for painting, then put it back on using hinges so that it can be lifted up to allow for cleaning out the gutter. 
Any thoughts on that proposal would be appreciated.

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## phild01

You'll have one heck of a job trying to get full coverage inside the holes by spray painting.

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## GOM

phild01, you're probably right. It should probably be replaced with aluminium gutter guard. The portion under the edge of the Klip-lok will have to stay, because it's pinned down by the Klip-lok and the lok-clips. I'll probably stick with the idea of hinging the gutter guard. 
Thanks for the reply.

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