Which screws for aluminium cladding?

[The Agrarian]

I'm reusing some 2nd hand poultry cladding, and have been warned not to use steel nails or screws, as they will react with the sheet and rot a hole around nail.

Finding the right type of screw or nail at builders merchants hasn't proved be simple. None are very sure of the right answer. Can anyone who knows this subject here keep me right? Thanks

 

[Exfarmer]

There must be a rubber washer . Tech screws are the norm, specify ones with a washer, there may be a trade term for these

 

[Beowulf]

Aluminium screws or nails are the only way of avoiding the galvanic corrosion entirely. You can get away with galvanised steel at a push though, as the zinc will usually provide enough of a barrier to prevent the reaction between the dissimilar metals.

 

[Exfarmer]

Do not of course screw to steel

 

[2wheels]

as ex farmer says, worked for us 30 yrs ago and the roof is still good.

 

[The Agrarian]

This is screwed to wood.

I was wondering if zinc would be unreactive enough to do the job. Hard to know how much of a coat is on screws, and whether contact with the sheet over the years at the hole edge would rub enough zinc off to bare the steel.

 

[Beowulf]

This is screwed to wood.

I was wondering if zinc would be unreactive enough to do the job. Hard to know how much of a coat is on screws, and whether contact with the sheet over the years at the hole edge would rub enough zinc off to bare the steel.

You would have the same problem using the rubber/plastic washer, as only the rear face of the screw head will be isolated from the aluminium sheet. The threads are still more than likely going to be touching the aluminium sheet.

I would theorise that the by using galvanised screws you may benefit from the zinc acting as a sort of sacrificial anode, much like it would on a ship's hull.
My chemistry knowledge isn't strong enough to be sure either way though, and I wonder whether zinc may not have enough driving voltage to work properly in a non saline environment where the electrolysis levels will be relatively low. Though of course that same low electrolysis will be of benefit by impeding the very galvanic corrosion you are trying to prevent!

Who knows, but personally I would just use aluminium screws and then I wouldn't have to think about chemistry on a Tuesday evening!

 

[br jones]

Stainless steel screws from screwfix

 

[2wheels]

if it it tanalised wood you will need a barrier between the wood and the alu sheeting. strips of dampcourse will do the job.

 

[The Agrarian]

Which brings me to another question.

On two of the bays where i need it to be non-drip, I was intending to use the foil backed roll out material. Anyone know off the top of your heads if this is aluminium foil?

 

[Dave.p]

We used galv drive screws with dowty washers, still good after 40 yrs

 

[ronnyray]

Use stainless steel screws. Any other form of steel screw will corrode the aluminium.

 

[The Agrarian]

Funny I've just read on a UK website that stainless screws are more reactive with aluminium than zinc coated steel.

 

[Robert K]

If you need an tek screws I have some left over from a shed

 

[H200GT]

I have an old aluminium box profile sheet roof. Just lately been having the odd small leak, and i have found small holes like wood worm on some sheets. Sealed them up with pu adhesive.

I guess they are coming to the end of their useful life, about 36 years old from data i can gather on when building was built. Not too shabby really.

They have steel tecks, but the sheets seem fine around the screws, the holes have appeared in the open sheet areas

 

[Pond digger]

We have a shed with corrugated, aluminium roof sheets. It’s fixed with galvanised roofing nails, and I haven’t noticed any corrosion. It’s probably 50yrs old.