Glen-L.com

Just a quick question about zinc plated screws;

If you were to use zinc plated screws, totally encapsulated in epoxy, what might be the result?

I'm thinking that if everything is encapsulated in west system no moisture can enter and any old fastener would work. Could it be?

Thanks

When you drive the screw with a screwdriver, you will possibly damage the zinc coating. In the short term, it would probably not rust too much, but over a period of years, I'd think that it would rust because the epoxy is not 100% waterproof and there is a certain amount of moisture in the wood anyway.
I wouldn't chance it!

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David McAdam
Squirt Gallery - Its BACK!!
http://one.xthost.info/boatbuilder/boat/
BOAT IS NOW SOLD

I agree with David, the zinc coating on plated screws is very thin and will almost certainly be scratched by the screwdriver, then there is enough moisture in the timber to rust the screw.

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Graham in Shepperton, England

Good, Quick, Cheap, pick any two.

you will do the best with silicon bronze, last forever.

even stainless screws don't last, and in some cases, the lack of all moisture is a screws undoing. Stainless needs oxygen to prevent it from rusting and in a totally encapsulted environment they will rot away.

sailor

In order for the fastener to oxidize, it requires oxygen doesn't it?

Kirk

I had a bonfire a few weeks ago with an old sailboat as the fuel. The boat had been built using plain screws (not plated with anything), zinc plated screws and bronze screws. This was above and below the waterline. Apparently whatever was handy was used. There wasn't much left of any plain screws that moisture had gotten near as could be expected (boat was around 30 years old). Zinc plated fared better but not great. As has been mentioned, the zinc appeared to have been scraped off in some spots and corrosion started. The bronze screws looked as good as new.
The screws were bad enough but the plywood was rotten in quite a few spots and on further digging, I found rot in frames and finally in the keel. I believe the rot occured due to the boat not being finished properly.
Doug

I can report a similar experience. I'm currently restoring a 1950s Thames Runabout, marine ply on oak frames, which was built using one of the old style waterproof adhesives and mostly brass screws.
The brass has survived like new (this boat has lived in fresh water all it's life, the brass may have fared worse in salt water), but the few zinc plated steel screws that I found were all very badly corroded. The plated screws were used for later repairs and alterations, they weren't part of the original construction so are considerably younger than the rest of the boat.
As for rotten wood, the ends of some of the oak deck beams had rotted, a new deck had been fitted at some point so I assume rain water had got in around the edges of the deck and done the damage.
The water had also penetrated the top edge of the side planking in some places, and the wood was crumbling when I removed the mahogany rub rails which were keeping it together.
The glue is mostly holding well, but those old adhesives are inflexible, and in places the planking had cracked away from the frames. The breaks are all clean, it's the glue that's given rather than the wood.

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Graham in Shepperton, England

Good, Quick, Cheap, pick any two.

Here's an over simplification to the issues of bedding stainless screws. The initial layer of oxidation is actually what makes stainles steel stainless and prevents further deteriorization. Stainless should not be bedded or encapsulated. They're great fasteners for above deck. However, I'd use Silicon Bronze for fastening in the construction phases. In the big picture it's a very small price to pay for a large investment.

What I get out of the story is, it doesn't matter what kind of screws you use, the boat will last, it's just the screws that go bad.

and what about "inox marin" screws?

Theo,

J'imagine que tu veux dire 'vis inoxydables' ?? Le lien ci-dessous explique bien le sujet :

Using stainless steel in a boat Webletter 32

Paul Kane Chelsea, PQ

Building the Glen-L Hot Rod

Think about it, those silicon brass scews that last so long are weak as heck. One good hard twist and they break. So if the epoxy or glue breaks down they aren't going to hold.

On the other hand, even if you completely ecapsulate a zinc screw in epoxy it is going to get oxidized because water passes threw epoxy and paint and the water will carry the oxygen. Water just passes through epoxy slower than polyester resin and through paint slower than epoxy. Also, water escapes back out slower than it gets in with polyester resin. That's why you paint epoxy to make the water travel through it slower.

As for screws, do what Graham always tells folks, glue, screw, dry and take the screws out and fill the hole. You can use any kind of screw you want if you do this. In fact, it may be a better way to go, because you won't have a screw attracting water to a concentrated spot in the wood.

"Zinc plated" is not a specific term. There are two types of coatings commonly used on screws: electroplate and hot-dipped galvanized.
Electroplate is pretty and very smooth. This finish will not hold up whether scratched or not.
Hot-dipped galvanized is a very hard coating. It is possible to expose steel if the heads are stripped out and then they are vulnerable at that point. But otherwise, I have stories of people replacing the planking on '50s era boats and using the same hot-dipped galvanized screws to re-apply the new planking. I would add that the screws we used to get in the 50s through 70s were much better than those currently available, both in the quality of the steel and galvanizing. The problem is that it is hard for domestic manufacturers to be competitive. Most steel screws are imported on the basis of lowest price; quality seems to be only a marginal factor.
One other point: brass and bronze are not the same animals. We would never use brass for structural applications.

Barry--so your saying it's ok to use bronze screws for putting on planking, but not Brass.....I was going to use stainless on my 1948 23' Express, but not now. Not after reading up on it in the news letter. Darn..I thought I had at least one area I didn't have to worry about.

Bronze would be the best. Brass is soft and breaks more easily.
Although some builders of trailerable boats are using stainless, it is not considered good practice because of potential creavice corrosion.