Which screw or bolt to use - aluminium to wood-clad house

pooksahib · 18 Sep 2020

Hi. When my wood-clad house was built, the builder put a block of wood behind a section of it so that a satellite dish could be put up. Said dish has rusted away so I'm starting from scratch and trying to be as corrosion-proof as possible. The bracket I want to put up is in the pic. The cladding is 2cm thick, the block of wood behind it 4.25cm.

The original bracket was fixed with M8, 50cm hex-heads. But is that the best choice? The holes in the new bracket are 10mm and the M8 head only 12/13mm. I reckon I could maybe use a bigger head and longer thread...

My thanks for any advice offered

Burnerman · 18 Sep 2020

8mm screws or bolts are perfectly adequate for this - you could use 10mm but you'd have to be spot on with your drilling.
How about stainless washers under the bolt heads?
John

pooksahib · 18 Sep 2020

Thanks John. I was thinking of plastic/nylon washers, actually. I've been told that if you put stainless and aluminium together, you'll still get corrosion where they touch. Seems odd to a layman like myself but the world is full of weirdness...

Alec_t · 18 Sep 2020

It's not that odd. Any two dissimilar metals plus moisture create an electro-chemical cell, leading to electrolytic corrosion.

Burnerman · 18 Sep 2020

You can use stainless and aluminium together with no problem.....by the time corrosion sets in as an issue we'll all be long gone.
There's a good chance the alloy bracket will be anodised, and aluminium oxide is remarkably stable anyway.
John

pooksahib · 23 Sep 2020

Hi again. I've borrowed my mate's cordless drill (I've never used one before) but he doesn't have the attachment that allows you to drill in a hexhead coach screw. Once I've drilled the pilot holes, will it be simple enough to put the coach screws in with a socket wrench? Many thanks.

Burnerman · 23 Sep 2020

Sure, a socket and ratchet bar will be just fine.
John

EddieM · 23 Sep 2020

Burnerman said:
You can use stainless and aluminium together with no problem.....by the time corrosion sets in as an issue we'll all be long gone.
There's a good chance the alloy bracket will be anodised, and aluminium oxide is remarkably stable anyway.
John

Aluminium and stainless steel together especially in coastal regions results in severe galvanic corrosion, I seriously doubt it would survive long.

https://www.wired.com/2011/06/shipbuilder-blames-navy-as-brand-new-warship-disintegrates/

Burnerman · 23 Sep 2020

Awash with salt water, I’d agree completely but in real life, I’d doubt it.
Road signs around here last quite well!
John

EddieM · 23 Sep 2020

Burnerman said:
Awash with salt water, I’d agree completely but in real life, I’d doubt it.
Road signs around here last quite well!
John

Depends where you are I guess, here on the west coast it's a no no, due to the salty conditions.

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Which screw or bolt to use - aluminium to wood-clad house

EddieM

EddieM

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