Degraded brass screws

[brian_n]

Hi All
Badly corroded brass screws in a light plywood deck, too fragile to remove, too damaged to retain. I hate the idea of fibreglass but a thin strip over the deck/hull join, leaving the screws in place ?
Brian_n

[rasorinc]

What will hold the deck on when the screws fully corrode and the deck becomes loose. Fiberglass tape won't do the job.

[brian_n]

Good question any ideas ?
Brian

[hoytedow]

I would install some sister screws in bronze.

Drill them out and replace with bronce or monel. Do´nt apply glass on outworn wood.

Regards
Richard

[Landlubber]

...do not waste time anywhere on a boat with brass screws, even in lockers they eventually simple fall apart.

Brian, you can make a hollow drill by using a tube ( or buy a plug cutter of the right size). What you do is find the length of the screw (trial and error) then drill around the screw shaft with the hollow drill to the required depth. Then they are easily removed (as per the wooden plug) with a small twist of a screwdriver to pop them off. Insert new wooden plugs with epoxy into the drilled out holes, trim off with the chisel, then start over again with new fasteners if you still feel they are required, or allow the wooden plugs and epoxy to do the job. This is how we fix nice teal panels such as deck coamings or cabin sides when finished bright. The screws if used are plugged then trimmed, or the dowels if used are trimmed and left flush. Other than one size up, there is no visible display of anything being done.

[hoytedow]

You could even use trunnels if you go the plug route.

[hoytedow]

See here.: http://en.wikipedia.org/wiki/Treenail

[Landlubber]

.... "the dowels if used are trimmed and left flush"....they would be trunnels if shaped as dowels instead of plugs. The wood grain in a dowel is with the length of the dowel, in plugs it is across the length of the plug.

[hoytedow]

Thanks. I didn't think about grain direction, assuming grain was longitudinal.

[brian_n]

Thanks gents for your interest and suggestions. The main problem is the very small size of the components. The deck is 3/16 ply and the member it is screwed into [the outer gunwhale] is a parallelogram 14x17mm. The screws are far to corroded to remove and the chances of drilling them out without the drill wandering off into the surrounding timber not good due to the small size of the screws. Landlubber I like your idea best but have some reservations due to the thin deck. Is there enough wood there for the epoxy to grab. Also the heads of the undamaged screws are about 7mm diameter. How much more will the tube drill extend this. Say another 3mm ?. The top of the member is only 14 and that dimension decreases as the gunwhale follows the slope of the topside.

[Landlubber]

......OK, then sister them between screws that are there.

the boat was probably made using resorcinol glue then, so it will still be OK hopefully.

[brian_n]

OK a plan is emerging. The screws are only 2" apart but that is enough for sistering. I will investigate the possibility of obtaining tube drills in 1mm increments. In addition I realise that the tube drill solution does not need to have the hole extend to the bottom of the screw. I just needs to be deep enough to give good adhesion to the epoxy. The rest of the screw can just stay there. Considering this and the gap filling ability of epoxy there may be no need for plugs, just a good stiff epoxy fill. Plugs in 1mm increments may be a bit hard to come by also. Considering the damaged condition of the edge of the deck it seems unlickly that varnish is an option so a nice paint job would cover all sins. The alternative is removal and replacement of the deck and outer gunwhale, very nice to be able to inspect the inside of the hull but. Decisions decisions !!.
Regards Brian

[troy2000]

Interesting discussion. Keep us up-to-date on the project.