Rusting windows screws (stainless steel?)

[The Lame Goat]

I bought my boat on a good survey a few weeks ago. One of the main things the surveyor pointed out was that the stainless steel screws securing the windows were rusting and should be replaced before they become too corroded to unscrew. Some are clean and shiny, some very rusted, one head has come off.

 

He recommended replacing them all with aluminium pop rivets as these last well and are easy to drill out.

 

Can stainless steel screws rust in this situation, and if so what advice do you have for remedies here? The windows all seem fine so I don't want to remove them all prematurely if I can avoid it.

 

For the moment I've just sprayed them with WD40 and taken one out to look at. It is 1 1/4" self tapping and I'm skeptical that it is stainless - maybe galvanised? I know nothing about boats or screw materials so any comments welcome, particularly...

 

Would simply replacing these screws would be adequate? If so, what with?

 

Thanks

[Jerra]

Hi welcome to the forum.

 

I know nothing at all about what would be best for your windows but I seriously doubt a stainless steel screw would/could rust. Be eaten away by the reaction between different metals but not rust as in iron oxide.

 

No doubt somebody will be along soon to say I have got it all wrong.

[Rebotco]

If it is rust, and the screws are stainless and the windows are aluminium, it can only be from the steel cabin sides. If so, maybe one of the proprietry rust converter fluids could dissolve the rust from the surface of the screws.

But its more likely some previous owner has replaced some screws in the past, using ordinary plated screws instead of stainless.

False economy?

[Timleech]

Almost certainly plated screws. I used to be dubious about pop rivets for this sort of thing, but I've been converted, reckon they are as good as anything. Make sure you use aluminium rivets, and put the tip into clear silicone sealant before fitting.

 

Tim

[fudd]

Stainless screws should be driven in using a stainless bit. Otherwise any residue from the ferrous pozi bit will rust.

[Grace and Favour]

AFAIK, stainless steel screws will not rust - it's worrying if a surveyor thinks they have

[fudd]

Also, stainless is quite brittle. Maybe a shock or heat could help release them.

[Rebotco]

Even aluminium pop rivets are not necessarily rustproof.

The shank that breaks off inside the aluminium cylinder is usually steel, leaving a steel "plug" which can and does rust.

(unless technology has changed in the last 15 yrs!)

[n.b.Goldie]

Not all stainless steels are equal. Some will rust. Marine grade stainless screws are available on ebay for not a lot.

 

Regards

Ditchdabbler

[Ex- Member]

There are different grade S/S screws, however even the lower 304 grade stainless would usually take donkeys years to rust. You can check gen S/S with a magnet as S/S in not magnetic.

 

I would use brass screws, don't like rivets.

[nb Innisfree]

There are different grade S/S screws, however even the lower 304 grade stainless would usually take donkeys years to rust. You can check gen S/S with a magnet as S/S in not magnetic.

 

I would use brass screws, don't like rivets.

 

A magnet will stick to some SS kitchen sinks.

[Tonka]

Do the screws screw into the metal cabin or the wood that is the otherside of the metal. I ask as I had a M Heywood boat that did it this way which meant that the holes in the metal were big and when I chaged the screws I had to get size 12 diameter but short.

[Phil Ambrose]

A magnet will stick to some SS kitchen sinks.

It is not possible to make a sink out of true stainless steel because the sinks are made in what is known as a deep draw press tool and if you tried to use true stainless in the press tool all that would happen is that a hole would be punched through the sheet used to form the sink, I know because I was a toolmaker and made many press tools. So sinks are in fact stain resistant.

 

Phil

[Rebotco]

Stainless steel is not a single material.

It is a whole family of differing materials. Each with its own set of properties.

They vary considerably in terms of corrosion and chemical resistance, magnetic properties, stain resistance, hardness and so on.

Various additives in the manufacturing process produce specific properties to suit different applications.

So you have to choose the correct version to match a particular purpose.

[XAlan W]

Even aluminium pop rivets are not necessarily rustproof.

The shank that breaks off inside the aluminium cylinder is usually steel, leaving a steel "plug" which can and does rust.

(unless technology has changed in the last 15 yrs!)

You can buy pop rivets with a sealed up/ blind inboard end so that the steel shank that breaks off is not exposed in any way on the inside & the outside can be sealed

[smileypete]

A good way to put stainless self tappers in is to first tap a thread with an identical steel self tapper, the steel ones should be 'case hardened' and so much stronger.

 

Then load the hole up with decent goo like Marineflex or Sikaflex, so the stainless self tapper will be well bedded in, the hole in the steelwork is potential starting point for rust if water gets in.

 

If the screws are breaking and there's rust in the holes, it sounds a 'quick job' where neither was done...

 

cheers, Pete.

~smpt~

Edited May 19, 2013 by smileypete

[adrianh]

Check that any rust treating product is safe to use on aluminium - they are generally not as they are a form of acid.

You can buy all stainless steel pop rivets, also, as previously stated use the closed type to prevent liquid passing down the shank and into the boat.

Much better to invest in a set of thread taps (probaly M4 thread) and use A4 grade stainless steel machine screws with the correct head form (panhead or countersunk - pozi drive or hexagon socket)

[alan_fincher]

There are different grade S/S screws, however even the lower 304 grade stainless would usually take donkeys years to rust. You can check gen S/S with a magnet as S/S in not magnetic.

 

I would use brass screws, don't like rivets.

Bad advice I'm afraid.

 

If the window frames are aluminium alloy, and you use brass screws, the galvanic action between the two will eat away the window frame at the holes around the screw heads.

 

I know this because I bought a boat where brass screws had been used to secure aluminium framed windows.

 

This is a definite "don't do"!

[The Pipe]

Bad advice I'm afraid.

 

If the window frames are aluminium alloy, and you use brass screws, the galvanic action between the two will eat away the window frame at the holes around the screw heads.

 

I know this because I bought a boat where brass screws had been used to secure aluminium framed windows.

 

This is a definite "don't do"!

I thought it was dam good advice all he needed to add was a couple of wires some orange juice and he could get rid of the battery bank.

[The Lame Goat]

Wow, what a fantastic load of helpful responses!

 

I think the screws may be plated so I'm going to assume that and try replacing them with some new screws as I think that will be easier than pop rivets, but we'll see after I've done a trial!

 

Thank you very much!

[Ex- Member]

Bad advice I'm afraid.

 

If the window frames are aluminium alloy, and you use brass screws, the galvanic action between the two will eat away the window frame at the holes around the screw heads.

 

I know this because I bought a boat where brass screws had been used to secure aluminium framed windows.

 

This is a definite "don't do"!

 

 

Fair enough alan, I didn't know that, fortunately I'm no fan of aluminium fittings so nothing alloy on the boat screwed in with brass screws. I'll remember that though.

[Phil Ambrose]

You have to remember that Brass loses it's zinc content by electrolysis, this can often be seen when removing Brass screws from timber that has been wet, the screws have a distinct coppery colour.

 

Phil