AlistairM
regular
Reged: 10/06/2004
Posts: 83
Loc: Wales (Cardiff)
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The varnish on my small dinghy has flaked away leaving bare wood. Do I simply varnish straight on and sand untill a decent finish is achieved, or is something required in preparation. The boat is completly covered with a tarpaulin but "natural moisture" still penetrates.
Also can some one please settle some confusion once and for all. Can epoxy be used to fill cracks and splits in the wood, or is this a definete no no.
Thanks
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Englander
regular
Reged: 07/09/2001
Posts: 14800
Loc: Barcelona/Bollyolics
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Take all the varnish off and start again. I would use epoxy to fill the cracks, but lots wouldnt. Might need something more flexible.
But really all that varnish needs to come off, the wood has bleached also, I think it's Mahogany, so will come up a lovely reddish colour, once all the varnish is off and it's sanded. The whole boat probaly needs re-varnishing, if the varnish is all that old.
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deisel
regular
Reged: 30/01/2008
Posts: 86
Loc: rye, sussex
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You Shouldent Really Rub Bare Plywood Down They Usally Add A Diluted Coat Of Varnish First, This Stops It Splintering,
You Can Use Epoxy For Filling If You Mix In A Filler ie Silica.
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AlistairM
regular
Reged: 10/06/2004
Posts: 83
Loc: Wales (Cardiff)
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Thanks for the info, I will sand off all the varnish and reapply. This is my first "project" boat so I am looking forward to getting into it.
I am one of those rare occurances of being young(ish) and interested in wooden restoration jobs instead of out and plastic tubs.
Anyway thanks again
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Pete_Cooper
regular
Reged: 16/01/2005
Posts: 1062
Loc: West of Scotland
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I recently stripped some varnish using a hot air stripper - much easier and quicker than sanding.
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stephenh
regular
Reged: 06/01/2002
Posts: 842
Loc: London UK
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Alistair - the black marks are fungi - probably a 'blue stain-in-service' fungus . The fungus itself often blows the varnish, use oxalic acid to bleach it and sterilize the spores. And then revarnish.
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Npm
regular
Reged: 16/11/2005
Posts: 54
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Hi
It looks as though the varnish has been blown off by damp penetrating from the inside of the boat, possibly rain water gathering against the transom. I would certainly look to the inside as well, and consider the quality of your rain cover. Damp may be getting in under the drain plug fittings and rudder hanging, so make sure that the wood under them is well sealed and bed them properly in something appropriate before refitting them.
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AlistairM
regular
Reged: 10/06/2004
Posts: 83
Loc: Wales (Cardiff)
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Thanks for lots of good advice, this being my first wood project its alla bit of a learning curve.
I plan to cover the transom in Oxalic acid as indicated above then sand down and revarnish
What would be suitable for bedding the rudder pintle on??
Oh and take on board the cover issue too, I will look to enhance that also.
Thanks for the patience.
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castaway
regular
Reged: 31/12/2001
Posts: 1308
Loc: Solent
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I would use Nitromors to remove the varnish...makes it a very quick and easy job.
In case you havn't used it before, be cautious as it gets everywhere and of course use latex or similar gloves.
If its warm and the nitromors is tending to 'dry out' to quick, cover with cling film or ali foil to keep it 'working' longer.
Possibly with a dinghy sized job it might be worth applying with a mini roller.
Regds Nick
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http://uk.groups.yahoo.com/group/Halberdiers/
http://www.yotblog.com/castaway/1720/
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Woodlouse
regular
Reged: 07/01/2006
Posts: 743
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Hot air gun and a scraper to remove. Totally safe as long as you're careful not to burn the wood by staying in one spot too long. What sort of dinghy is it?
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Cuchilo
regular
Reged: 19/04/2003
Posts: 4406
Loc: London
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Quote:
a 'blue stain-in-service' fungus . The fungus itself often blows the varnish
Even if blue stain was found in hardwood ply it is a non structual defect that will not blow the varnish . Sometimes i think you guys make this stuff up for fun  
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The honest man has nothing to fear .
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stephenh
regular
Reged: 06/01/2002
Posts: 842
Loc: London UK
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Cuchillo - I’m not making it up !! “blue stain…. will not blow the varnish “ – I think it will -
Here from my BRE ‘rot’ book – there are photos similar to AlistairM’s but I’m no good at loading them:
“Blue stain in service fungus
Commonly - Aureobasidium pullulans and others
Damage characteristics -
Disfigurement of the wood and especially of clear finishes; early failure of surface coatings caused by rupture of the fruit bodies.
Discolouration caused by sap stain which has occurred in the log may still be detectable after drying and conversion of the timber…… Damage to coatings will occur through the growth of blue stain in service.
Cannot grow below 20% moisture content
Treatment - …. Dry the timber , treat with preservative containing an additive specifically active against these fungi….: apply new coating….’
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Cuchilo
regular
Reged: 19/04/2003
Posts: 4406
Loc: London
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A blue stain treatment , amazing ! What will they think of next
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The honest man has nothing to fear .
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Cuchilo
regular
Reged: 19/04/2003
Posts: 4406
Loc: London
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Sorry i wasnt very constructive there . Blue stain as i know it has no structual effect on the timber and is only found in pine . It is a fungus that attacks the sapwood and feeds on the sugars in the timber and ray cells if i remember rightly ..... It was along time ago ......Bluestain is not regarded as a defect in the timber as all it does is make the timber look blue . The staining in the Hardwood ply shown looks more to me like the start of wet rot .
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The honest man has nothing to fear .
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Igor_Korousic
new user
Reged: 23/04/2008
Posts: 5
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Don't use epoxy below waterline
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Woodlouse
regular
Reged: 07/01/2006
Posts: 743
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Care to explain why? Most production boats have a layer of epoxy below the waterline these days.
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stephenh
regular
Reged: 06/01/2002
Posts: 842
Loc: London UK
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Wet rot ? I think you are right.
On closer inspection there would seem to be more than one type of rot on the go.
The problem with blue stain is that it lies dormant as spores which then errupt as small flecks as in the photos, these break open the protective coating and let in more water and so white, brown, wet & dry rots ( take your pick !) are able to get a hold.
So the fact that it, in itself is not structurally damaging, doesn't put it on the 'harmless' list .....and it loves hardwood as well - spalted beech and ash being classic examples.
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Cuchilo
regular
Reged: 19/04/2003
Posts: 4406
Loc: London
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And there is me sat next to a sycamore spalted and blue stained side table saying it only grows in pine
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The honest man has nothing to fear .
Edited by Cuchilo (28/04/2008 09:06)
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stephenh
regular
Reged: 06/01/2002
Posts: 842
Loc: London UK
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Whoops !
We've all been there......
Nice piece of timber.....
Thats not wet rot starting on the RHS is it ?!!!! 
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LakeSailor
regular
Reged: 15/02/2005
Posts: 26244
Loc: ation : Lake District
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Strange thing to say. I gave my Heron an epoxy coating when I rebuilt her and most plywood boat builders do the same. They also use fillets of epoxy to bond the panels together.
Fyne Boats for one.
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When arguing with an idiot, make sure he's not doing the same..
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Cuchilo
regular
Reged: 19/04/2003
Posts: 4406
Loc: London
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There was a bit of everything in them . They where logs that had been felled and left to rot in my local woods . I milled them up , cut out the rot and made a table out of them . People where looking at my rather odd as i walked down the road with them
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The honest man has nothing to fear .
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