Cratch board maintenance

[Rob L]

I am stripping down my cratch board and plank to bare wood to give them an overhaul. - I did not like the look of the coloured varnish used by the previous owner/manufacturer.

I am no woodworking expert, and I am a newbie narrowboater, so please bare with me.

 

The bare wood looks like it might be Sapele. It has a slight reddish tint to it that I quite like. The general condition seems ok, but there are a couple of areas that have blackened slightly, presumably where moisture has penetrated. But these are small and the wood seems sound.

 

I would like some general advice on how to stain and/or varnish the wood to give it a nice appearance and good weatherproofing quality. Can anyone suggest a good stain or varnish to use for the job, and should I treat the small blackened areas first?

 

Also, it currently has perspex sheet in the triangular 'windows'. This has discoloured and scratched. Should I replace with new perspex, or would safety glass be a better option?

[Mike Jordan]

Hi Rob

 

If the discoloured areas of the timber are sound to the touch, it should be possible to bleach away the black using a solution of oxalic acid crystals, these are available from your local chemists. Caution! oxalic acid is toxic and needs handing with care.

I suggest you google oxalic acid and look at one of the sites explaining the methods of safe use and concentration required.

On the rare occasions I stain timber I favour the use of spirit based stains which don't raise the grain of the timber like the water based ones. I think Its better to use a weak solution of stain on the grounds that you can go darker if needed but overdoing the colour may mean more sanding to get rid of it.

My own preference is for natural wood without stain, thinning the first coat of exterior varnish (or yacht varnish) 50% with white spirit to allow it to soak into the timber, following up with two full strength coats of gloss varnish.

The believe best type of glazing is 6.4mm thick laminated glass, this is safe, tough, and stays in place even if you are unfortunate enough to break it. Toughened glass is also safe but can't be cut to size while you wait and shatters into tiny bits if broken.

Plastics materials are both easy to scratch and tend to yellow in time.

Best of luck with the project.

Mike Jordan

[Rob L]

Thanks Mike,

 

I will look into the Oxalic acid crystals. I haven't finished all the sanding yet, so will get everything stripped first, and asses the damage.

 

Thanks for the tip regarding stain and varnish. I agree about the stain; little at first, if any at all. I would like to keep the wood reasonably light and just bring out the natural colour and grain.

 

My original perspex is indeed dull, scratched and slightly yellowed. I am definitely leaning towards replacing it with safety glass.

 

Thanks again for the advice.

 

Rob

[nebulae]

Agree ,use Oxyalic Acid to bleach out stains. Always got it from local chemist,but have struggled recently. Available on line no problem. If you use a stain,I suggest you test on scrap wood first.,as manufacturers idea of finished colour does not always turn out accurate.Use best quality marine varnish.but you will need to maintain it regularly to keep the look. Tung oil is an alternative to varnish and will last better,but does not give a deep gloss finish.

[Rob L]

I will definitely try the oxalic acid. I have seen an impressive demo of it at work here:

http://www.constructionchemicals.co.uk/Oxalic-Acid.html?gclid=CODx5LfiwMMCFSfLtAodmiUAIQ

 

I also read that it is in various demestic cleaning agents, including Barkeeper's Friend. Not sure that it would have the same results as obviously the cleaning agents have other ingredients in them. Might be worth trying on a piece of scrap though!

[Mike Jordan]

Hi Rob

 

Your local chemist will sell you a half kilo of the crystals. I always leave it in the original box with the safety labeling because the crystals look just like sugar.

Edited February 1, 2015 by Mike Jordan

[Tonka]

How about Danish Oil rather then varnish. In a few years just apply more varnish

[chazzy]

When changing the perspex, I agree with Mike, my choice would be the 6.4 laminated glass. Toughened glass often called safety glass, is a job to clear up all the small bits should it break, but no way use float glass.

[Southern Star]

 

My own preference is for natural wood without stain, thinning the first coat of exterior varnish (or yacht varnish) 50% with white spirit to allow it to soak into the timber, following up with two full strength coats of gloss varnish.

 

Completely agree with thinning down any first coat of varnish with 50% white spirit, if it is practical to do so then I make up a very thinned mix, maybe 20% varnish, 80% white spirit, and soak the end grain in it for two hours each side before I even get out the paintbrush. Over 75% of the moisture which gets in to wood gets in through the end grain.

 

I personally reckon you need seven or eight coats of varnish on wood which is exposed to the weather, allowing 24 hours between each coat, and rubbing down between each coat with fine sandpaper, say 280-320 grit.

 

Other random advice I'd give is never to use varnish directly from the tin but always to decant a suitable amount into a glass or plastic container, empty food containers work well, always use a new, good quality paintbrush for the job, use another new, good quality paintbrush for the final coat, and dry-brush the final coat lightly with yet another new, good quality paint brush. You can still use these brushes for lesser duties afterwards. I use Harris Smoothglide brushes for varnishing, you can buy a set of four on ebay for less than the cost of two cheap and nasty own-brand brushes from one of the DIY sheds.

 

Personally, I wouldn't varnish wood at the moment unless I could do it indoors, it is simply too cold. I'd be looking at doing this sort of job in March or April.

[Ryeland]

I got oxalic acid from eBay!

 

Richard

[Cheshire cat]

I have found the Oxalyic acid needs to be rinsed off well otherwise it reacts with the varnish

[Rob L]

I have dismantled the cratch boards and brought them home whilst the boat is in the dock having some work done. So this project is being worked on at home in the shed. So soaking the end grain and varnishing indoors are all possible.

 

I still have quite a bit of sanding to do before I get started on any oil or varnish finishes. The front upright board appears to have faired worst of all due to weathering, but still looks recoverable.

 

I'll get some oxalic acid this week if I can, and probably have a go at the weekend.

 

Thanks everyone for the advice so far.

Rob

[Peter-Bullfinch]

If you decide to varnish be prepared to recoat it annually. Any minute cracks will let in moisture next winter and the black stain can reappear unless you recoat before the frost. Boats vibrate, wood flexes, sunlight and frost are harsh. Despite all this I still like my well varnished woodwork including boat poles, gangplank and cratch.

[Machpoint005]

Annually? I appreciate that it's a matter of taste, but that's why I favour paint!

[Ricco1]

I'd use normal glass personally. The position of this glass makes it extremely unlikely that anyone might slip and fall against it. Unless there's a regulation?