Screws for aluminum siding

canman47 · Thu Sep 29, 2011 10:07 am

My latest project seems to be replacing all the screws that attach the aluminum siding on my home. The siding itself is perfect after almost 40 years, even the paint is in excellent shape but the screws have corroded to almost nothing. They used steel screws in aluminum which I understand from my research is a no-no. Something called galvanic corrosion eats up the steel screws. I have replaced some with stainless screws but now I read that stainless will eat up the aluminum. Am I correct that I should be using aluminum screws? I haven't yet found the exact style and size I want. I think I want hex head with integral washer and I should go a size bigger since many of mine are stripped out. I will also need a reasonable price since there are thousands of them. Anyone know a good source? Does it matter if it's a wood screw or sheet metal? It's going through sheet metal but into wood.

Greg · Thu Sep 29, 2011 5:28 pm

A true stainless steel screw should be fine, but finding quality stainless could be hard. Here's a tip, use a magnet if it sticks it's not stainless. Aluminum screws could be hard to work with since the are soft and could tend to twist off.

The screw type is not important, pan head, sheet metal or wood will work. You may want to jump a size to keep from stripping out.

Greg

JD · Sat Oct 01, 2011 12:00 pm

Zinc plated screws are the usual choice for aluminum siding, but they will rust over time. I have not found that they degrade the aluminum, but the rust will stain the paint. Maybe changing them out every ten years or so wold be the answer. SS screws could get a little pricey, but I wouldn't think that quality SS would damage the aluminum. Maybe I am wrong on that one. I have never used SS screws for mobile home aluminum siding.

Greg · Sat Oct 01, 2011 12:22 pm

I really can't say that I have seen an Aluminum/ferrous metal reaction in a mobile home setting, but the truck repair it is very common, just add a little road salt and the aluminum will corrode just like steel or you can have almost a welding reaction where a steel bolt goes through an aluminum frame.

Greg

JD · Sat Oct 01, 2011 2:24 pm

I totally agree. While I have seen a lot of aluminum siding corrode to dust, I have not seen it happen due to rusty zinc screws. When laying galvanized sheet goods, like cooler jacks, vents, etc. against sheet aluminum, you do need to insulate the two metals with something non-conductive, like rubber or a bunch of polyurethane sealant. Some people use roof felt. Aluminum left in contact with the ground will also rot away.

slk_ms · Mon Oct 03, 2011 11:37 am

I will be looking at this project soon as well. Two questions: should I automatically go ahead and use larger screws in case some are stripped out, and would fitting some type of felt in between keep the rust from staining the siding?

Make that three questions

What do you recommend for removing rust from the trailer siding?

1987Commodore · Mon Oct 03, 2011 3:38 pm

I would think any felt material would only trap water, and make the rust start that much sooner.
I just looked out my back window at the neighbor's place. It is an older model from back when they were only 10 ft wide, and the screw heads are rusted, but there are very few minor stains on the aluminum itself.

Greg · Mon Oct 03, 2011 5:52 pm

Since you would be buying a large quantity of screws, I think I would just go up a size and be done with it. To seal them you could just put a dab of Silicone on the hole before you put the new screw in.

Greg

JD · Mon Oct 03, 2011 7:53 pm

Where you buy screws can make a big difference in price. Most cities will have a fastener outlet of some type. Two thousand (5/16") #10 x 3/4" hex head screws can be had for $70 for zinc treated and $170 for stainless steel. The zinc screws will eventually rust. So for about a hundred bucks you can have rust free screws.

I get my fasteners locally so I don't pay for shipping, but here is an online store with pretty good prices.

http://www.boltdepot.com/Sheet_metal_sc ... -8_10.aspx

canman47 · Mon Oct 03, 2011 11:51 pm

Ok, If anyone is interested look up Galvanic Corrosion on Wikipedia and you'll find that any dissimilar metals will have an electrical difference that will cause corrosion especially in a corrosive environment like outside where water can hit it. After reading the article it seems clear to me that zinc plated steel should not be used with aluminum and neither should stainless steel. According to a chart only aluminum screws should be used in aluminum siding. I can tell you that my steel screws are to a point where many of them can be crumbled between my fingers. The siding is still perfect but with tiny rust stains. I've seen aluminum screws on a boat building web site and they say that only aluminum screws should be used on aluminum panels. I saw them sold on a web site as Mobile Home screws-if I could only remember where that site was??

Norm Frechette · Tue Oct 04, 2011 5:55 am

if you live in a saltwater environment you probably dont want to use aluminum screws. they will corrode in that environment. i worked in aerospace and all aluminum products on the satellites we were building had to be chemically conversion coated or anodized to prevent corrosion once the satellite got to cape canaveral in florida.

some stainless steels will corrode. another lesson from working in the aerospace and submarine business.

canman47 · Tue Oct 04, 2011 11:32 pm

No salt water here. I'm over 100 miles from the coast so it's pretty much hot and dry so aluminum doesn't corrode. My window and door frames are bare aluminum and they look as good as new. Also someone on this thread said that aluminum skirting in the dirt would corrode but one side of mine has been that way for 40 years and when I dug it up the metal is fine although the paint is pitted. All of this makes me still think that aluminum screws seem like the way to go.

JD · Wed Oct 05, 2011 1:17 pm

I imagine that we have already seen the last of mobile home vertical aluminum siding in new manufacture. But in all brands of older mobile homes with this siding, I have only seen zinc coated #8 and #10 hex head screws. Some screws have a better quality finish than others and seem to last much longer. But eventually, they all rust. I would certainly think that stainless steel screws would last longer than the zinc screws. I would imagine that aluminum screws are better yet, but I have never seen them used on mobile homes.

canman47 · Fri Oct 07, 2011 9:36 am

Yeah, from my research it looks like aluminum corrodes steel, but stainless corrodes aluminum. I found the aluminum screws at Mobile Home Parts Store but they are expensive and sold in small packages of 40. I need thousands! So it looks like I'm back to zinc plated steel and hoping I'm gone before they need replacing again.