screws and paint problems

share hints, tips and experiences
Post Reply
User avatar
JohnK
Posts: 86
Joined: Wed Jan 05, 2005 2:23 pm
Location: Yorkshire
Contact:

screws and paint problems

Post by JohnK » Sat Apr 26, 2008 2:13 pm

I'm starting to get paint and varnish lifting off the top of many of the screws on my 1959 built Chippendale National 12, with a powdery deposit between the screw and the paint. Where they have been filled, it's lifting the filler as well. Is there a fix for this?

I'm contemplating taking it off the water this year and doing a complete strip down to bare wood, so in addition to advice, I would also be interested in a cheap plastic boat in the meantime - something like an old Lark?

Cheers,

John (N1662)

Pat
Posts: 2460
Joined: Mon Sep 27, 2004 1:42 pm
Location: West Wiltshire (Wessex)

Re: screws and paint problems

Post by Pat » Mon Apr 28, 2008 7:29 pm

Can do the cheap old Lark bit as I've a couple of Bakers going up for sale -

number 990 which has a pretty stiff hull and apart from the previous owners' interior paintwork peeling off due to pressure washing is ready to go. The plan is to thoroughly pressure wash and remove the inside paint and re-do it - NOT with household paint this time! Old but sound main and jib and a trolley. Not fitted for spinnaker. £200 o.n.o

number 551 which is also a decent little boat and the one I saved from the dinghy park auction. Needs rudder and sails though I picked up a main at Beaulieu yesterday along with a mainsheet jammer as that was stolen whilst in the dinghy park. Fitted out for spinnaker with chute - no pole. Reasonable trolley. Looking for £100 as return on investment.

Keeping the other 3 Larks!

User avatar
Ed
Site Admin
Posts: 3473
Joined: Wed Sep 01, 2004 10:11 pm
Location: Plymouth
Contact:

Re: screws and paint problems

Post by Ed » Mon Apr 28, 2008 8:35 pm

There is no fix that I am aware of for the powder on brass screw syndrome. It has a proper name that escapes me, presumably a form of oxidisation of the brass.

All you can do is chip off the knackered varnish and/or filler clean it and then dab on either some thin varnish or I often use some cyano-acrylate. This does not seem to make the screws any harder to take out. Only problem is that it sometimes seems to over-darken the faded wood around screws.....so they start out faded and end up too dark, but this is being fussy.....it works.

Then clean, sand, apply filler if needed and re-varnish.

You normally don't have to re-do the whole boat just because the varnish has lifted on the screws though.

cheers

eib
Ed Bremner
CVRDA


Jollyboat J3
Firefly F2942
IC GBR314 ex S51 - 1970 Slurp
MR 638 - Please come and take it away
Phelps Scull
Bathurst Whiff - looking for someone to love it

Michael Brigg
Posts: 1662
Joined: Fri Jul 06, 2007 7:11 pm
Location: Gosport, UK

Re: screws and paint problems

Post by Michael Brigg » Tue Apr 29, 2008 10:40 am

This is a form of "Nail Sickness." It is well described in an article here:-

http://www.classicmarine.co.uk/Articles/metals.htm

Nail sickness also describes what happens to slate and Shingle roofs when the retaining nails rust. As a generic term it describes anything (usually galvanic corrosion) that causes your screws to fail.

Brass screws suffer from Zinc loss "Dezincification" and as described here become like Crunchie bars. Work hardening makes it worse so the screw head is worse affected. The trouble is that Stainless steel replacements suffer if denied access to Oxygen so the only real answer is to Glue or periodically replace.

Green deposits are caused because any water that penetrates will cause some rot producing Acidity around the screw head, or perhaps the wood itself is Acidic. (Oak especially) This will react with the copper in the alloy. I would suggest that filling the screw hole with, and soaking the screw, in varnish before screwing it in might help to stop any contact between the wood and the metal. (This of course precludes any self tapping.) Even this seal may fracture in time however if the screw has to take any load, and also if there is any big variation in temparature causing expansion or contraction so avoid sun and frost.

The Chinese at present have such an appetite for Copper in their burgeoning industrialisation that I am told copper is currently almost as expensive as Gold! Now is the time then to get some really noble fastenings!
Last edited by Michael Brigg on Tue Apr 29, 2008 11:40 am, edited 2 times in total.
Michael Brigg

User avatar
Ed
Site Admin
Posts: 3473
Joined: Wed Sep 01, 2004 10:11 pm
Location: Plymouth
Contact:

Re: screws and paint problems

Post by Ed » Tue Apr 29, 2008 10:58 am

"Nail Sickness."

Ah, yes, I knew there was a technical name :wink:

cheers

eib
Ed Bremner
CVRDA


Jollyboat J3
Firefly F2942
IC GBR314 ex S51 - 1970 Slurp
MR 638 - Please come and take it away
Phelps Scull
Bathurst Whiff - looking for someone to love it

User avatar
JohnK
Posts: 86
Joined: Wed Jan 05, 2005 2:23 pm
Location: Yorkshire
Contact:

Re: screws and paint problems

Post by JohnK » Wed Apr 30, 2008 7:56 am

Thanks for the info (and the offer of boats). I'll try the superglue method, as I didn't fancy replacing scores of screws - especially with gold ones.
John

Pat
Posts: 2460
Joined: Mon Sep 27, 2004 1:42 pm
Location: West Wiltshire (Wessex)

Re: screws and paint problems

Post by Pat » Wed Apr 30, 2008 2:00 pm

If the screws aren't seen surely they could be replaced with stainless? Sandy did a load of these "poppers" on Half Cut and replaced screws about 3 years ago and all is still well.
Oh and what am I offerred for the old fortic water tank cluttering up my yard?

Michael Brigg
Posts: 1662
Joined: Fri Jul 06, 2007 7:11 pm
Location: Gosport, UK

Re: screws and paint problems

Post by Michael Brigg » Wed Apr 30, 2008 7:16 pm

The problem with stainless steel is that it it is at the end of the day only stain-less. The reason that it does not rust quite like mild steel is that it can form a stoichiometric oxide layer on its surface of Chrome oxide, known as a ceramic surface, which is also transparent hence the permanent shiny appearance.(Actually the shiny surface of metals is a function of "free" electrons (which defines a metal's chemistry and are also the reason why metals can conduct electricity as these "free" electrons are also free to move within the crystal structure of the metal.)

Electrical conduction is then the achilles heel of these stainless metals since it allows corrosive cells to set up if there is any contamination of the screw hole with a less noble metal (Zinc for example from the old corroded brass.) this in turn may lead to pitting of the stainless metal which will then rust like any other iron.

The more aggressive corrosion of stainless steel is generally described where there is a high exposure to chloride gas (such as in the roof of a swimming pool, or these days worse still, Ozone) or high temparature such as a heat exchanger or exhaust system. Mechanical failure in such circumstances is potentially disastrous.

In the context of boating, the loads are rather less extreme but in an anaerobic situation (such as damp wood) acids can form with resulting production of Chloride from the salt in seawater and some oxidation may then occur. It is quite a bit slower than would be the case with mild steel so although not perhaps a threat to structural integrity, unsightly rust stains are likely to develop.

This is the reason I believe that in bigger boats mild steel is used in favour of stainless for fastenings below the waterline where there is likely to be no Oxygen exposure. (And for that matter for Keel bolts.)
Michael Brigg

User avatar
Ed
Site Admin
Posts: 3473
Joined: Wed Sep 01, 2004 10:11 pm
Location: Plymouth
Contact:

Re: screws and paint problems

Post by Ed » Thu May 01, 2008 9:31 am

I am surprised that mild steel screws are used with any regularity in boats.

Having tried to remove them from hog of MR 999 a Chippendale MkIX, I would of said they pretty much weld themselves into place and are quite impossible to remove. On the other hand they did not appear to have rusted to the point of danger of failure.

What about Bronze or Silicon-Bronze? I always understood these were the preference for under-water fixing? I have only very rarely used them and only then, because I do to due to unavailability of correct size in Brass.

eib
Ed Bremner
CVRDA


Jollyboat J3
Firefly F2942
IC GBR314 ex S51 - 1970 Slurp
MR 638 - Please come and take it away
Phelps Scull
Bathurst Whiff - looking for someone to love it

Garry R

Re: screws and paint problems

Post by Garry R » Thu May 01, 2008 9:36 am

I use

http://www.screwsline.co.uk/brass_wood_screws_csk.php

to buy brass and stainless screws- they are relatively cheap I think although there has been a large price increase on these due to world price hikes on metals. However their service is very efficient - phone up and speak to the very pleasant lady!!

User avatar
Ed
Site Admin
Posts: 3473
Joined: Wed Sep 01, 2004 10:11 pm
Location: Plymouth
Contact:

Re: screws and paint problems

Post by Ed » Thu May 01, 2008 9:41 am

Nice to see they do chromed brass screws, so favoured by Fairey marine.

Mind you.....it isn't often that someone comes up and comments on the fact that I have replaced by chrome screws with stainless ones!

cheers

eib
Ed Bremner
CVRDA


Jollyboat J3
Firefly F2942
IC GBR314 ex S51 - 1970 Slurp
MR 638 - Please come and take it away
Phelps Scull
Bathurst Whiff - looking for someone to love it

Rich
Posts: 88
Joined: Mon May 15, 2006 10:02 pm
Location: United Kingdom

Re: screws and paint problems

Post by Rich » Thu May 01, 2008 1:11 pm

It is highly possible that the Chrome finish may be an imitation chrome (usualy a tin\cobalt mix) which may not be an exact color match if matching with exisiting chrome plated screws or fittings.

Screws are normaly plated using a barrell process and the last barrel chrome line in the UK closed some years ago. They can still be chrome plated by a dipping process but this involves wiring each individual screw onto copper wire before plating, very labour intensive and not cost effective. Like most things the majority of screws sold now come from the far east but unfortunately non of the Chinese non ferrous screw manufacturers I have visited thru my job have been able to offer barrell chrome plating unlike nickel plating which is readily available. Even in China environmental legislation is slowly taking hold and genuine chrome plating uses some very nasty chemicals.
Rich

User avatar
Ed
Site Admin
Posts: 3473
Joined: Wed Sep 01, 2004 10:11 pm
Location: Plymouth
Contact:

Re: screws and paint problems

Post by Ed » Thu May 01, 2008 1:20 pm

Well, how about that.....amazing what you learn on the CVRDA Forum!

As I said....I think it reality, I will stick with just using stainless - no one seems to complain much :wink:

cheers

eib
Ed Bremner
CVRDA


Jollyboat J3
Firefly F2942
IC GBR314 ex S51 - 1970 Slurp
MR 638 - Please come and take it away
Phelps Scull
Bathurst Whiff - looking for someone to love it

Post Reply