cracking planks

[fedor]

Hi folks,

A few weeks ago we moved to live aboard our boat - 1970 carvel mahogany on oak, with epoxied marine ply decks. We stay in marina where they do not meter the electricity consumption, so we happily use on of those electric heaters with small ventilator in it. It heats all boat in minutes, keeps it well ventilated and does not produce as much humidity as, say, paraffin or propane heater. Brilliant.
But a few days ago I noticed a worrying sign: oaken plank in doghouse wall on starboard developed a very serious crack in it. After investigation I found two more cracks - this time in mahogany planks on port, just above waterline.
Can it be that thesudden change in air humidity inside the boat from damp and cold to warm and dry caused it? What can I do to prevent wood from drying and cracking up? And, how would you treat something like that?

Thanks in advance for your replies!

Fedor

 

[ccscott49]

Oak does tend to crack, "Shake" but it is probably caused by too much heat inside, as for repair, you are probably going to need to put a spline in the planks, but I would reduce the temperatrue of the inside of the boat first and see if the cracks close up a little, I have the same problem, with my boat, taking it to the meddy, cracks appearing all over the place, it lived all it's life in the northern climes before. The humidty/temperature is totallty different in the med from where she was built and the timber seasoned.

 

[miket]

You often hear of the use of de-humidifiers, but you can also buy humidifiers.

Antique furniture used to suffer similarly when central heating became common. One way round this was to hang containers of water on each radiator.
You can buy pucka jobs too.

 

[Richard_Blake]

I suppose I'm asking rather than suggesting, but this is a problem I'm interested in too.
What about the various possible impregnation substances? I've heard of flexible things such as traditional oils, Deks Olie, Varnol, Burgess wood sealer or plain anti-freeze being used to re-swell wood and prevent it cracking through the heat/cold or wet/dry cycles by stabilising it with the oil instead of moisture. What do people think? Anybody found anything that will really swell planks again and keep them that way? And what about gluing and finishing afterwards?

I have also learnt from experience that mahog seems particularly sensitive to having things like bulkeads or ribs glued to it with the grain running at right angles to the mahog. plank grain. The original construction may be fine, but later additions too immovably fastened could be a source of problems. That's prevention, not cure though....

Good luck.

LowTech

 

[fedor]

I tried redusing temperature ( we do not heat the boat during the day) but cracks do not close. *sigh* I think it's more humidity than heat related, but if I start sprinkling walls with water, boat will quickly turn into sauna and become impossible to live in.

As for splines... I do not quite understand how you can put a spline into a long and winding crack. Could it be done with some kind of filler or it will be just asking for trouble when timber picks up some moisture again? (

 

[ccscott49]

Try re-humidfying the boat, but placing water in front of fan heaters etc. not to turn it into a sauna, but to bring the humidity back up, the cracks may well close some. Flexible filler would be best for now, something like a sikaflex, un til the cracks close, then you may well jave to condider a proper epoxy filler or similar. You are going to need an expert to put splines in, its not a easy job, if you've never done t before, several splines may be needed, if its a long wavy crack.

 

[Guest]

Do you have any advice on how you would create the spline ? I have a similar problem and I have spent the last month looking for suitable shaped routers or wedge shaped circular saws but to no avail. Someone suggested an oscillating saw but the only one I could find looked like a toy.

 

[chippie]

A visit to a saw doctor who sharpens tungsten tip saws may provide some suitable advice on re shaping an existing blade to suit. Just a thought.

 

[ccscott49]

You need a parallel, router bit, DO NOT use a wedge shaped spline or router bit, this will just force the crack open when you drive it in. They are available in virtually any tool shop. one about 1/4" wide would be adequate, then cut the spline to fit, just fit, without forcing the crack open. Apply plenty of unthickened epoxy to the crack and spline, then allow it to soak in, then thicken the epoxy with micro fibres and put on both the spline and crack, drive the spline home, gently, I finish off the ends of the spline, by drilling and inserting plugs, with the grain across, to try and stop the crack progressing. Thats a very simple explanation, it's not a hard job, but can be a bit fiddly. There is such a thing as a spline saw, or even a plunge saw will do. If you need any further help, PM me.

 

[Strathglass]

What Colin says is correct. Another important thing to do is to temporary fix a wooden straight edged guide to the hull. It needs to be parallel with the crack not the planking. This will help ensure that the router cuts a straight line and you only have to cut a parallel infill piece of wood, rather than a wavey bit.
Sorry about the GPS Colin, its on it's way up here, I just happened to be on the For Sale form earlier than you that morning.

Iain

 

[ccscott49]

No problem, I have a GPS, just wanted another one of the same type, as backup. You're welcome to it if you didn't have one! The straight edge is a good idea, it's the way I do it. The plugs at the ends work a treat aswell.

 

[fedor]

Thanks, Colin.

At the moment it looks like the cracking stopped - I presume that wood has stopped drying. I tried putting some water in front of the fan - it does not really have any visible effect on the cracks. Will see how it goes - the cracks are wuite thin, might be the case of simply filling them in and painting over just one more time.

Polysulphide/polyurethane fillers: I tried to use it last spring on one of her topsides ( there was a replacement plank fitted by the previos owner a couple of years ago with quite big gaps in seams ( 1/2" in some places)...they used epoxy filler to fill seams and of course when the wood started to move(dry-swell cycle) filler cracked and started to come out piece by piece) So, I caulked seams with cotton and topped it up with some sikaflex. The result I do not like: sikaflex moves too much and although the seam is well sealed, paint on the top cracked all over the length of the replacement plank.

Now I am thinking about putting in some splines in the seams and I've read your posts in this thread with great interests. Some parts of it still remain unclear to me, e.g. timber selection (should it be of the same seasoning as other planks?) and fitting in the end of the spline. Can you point me to some source of information on this job?

 

[ccscott49]

The spline must be of the same timber, leave it inside the boat for a week or two to acclimatise to it's new enviroment. I can't point you in the diection of any books, as I learnt this by watching and doing. I always find making the spline the most difficult bit, big hands, little splines!! If the cracks are very minor and thin, I would fill them with a flexible filler/glue, You will always see a caulked sikaflexed join in planks, they move, so cracking the paint, it's a fact of life I'm afraid, especially with a new plank, which hasn't and may never get like its mates. Hopw this helps, there must be some books, wooden boatbuilding or some such title, have a look on this sites book store. I wopuld also only be tempted top spline where it's structually neccessary, splits in non strutural areas, are just that splits! I live with mine!

 

[tillergirl]

I had to do this about 5 years ago. It's not as difficult as it seems. Basically I followed the curve of the crack in a series of straight routs, then glued and inserted the splines as others have described, That left me with some interesting but unattractive designs on the exterior of the coach. Remedy suggested by the Surveyor was veneering the coach. Again not as daunting as I thought although it's off with the portholes, removal of the varnish and the preparation of as flat a surface as possible. I got the veneers (thick ones obviously) from Robbins of Bristol and in eight strips did both sides from front to back. Everybody thinks she's been kept looking nice since 1964. The veneer remains stable and touch wood I've had no problems.