A project with wood log slices... Some questions.

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davedoublem

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I'm fairly new to working with wood, and am starting to use it more with some of my crafts, particularly when I work with gypsum plaster.

I particularly want to use some large wood slices approx 250mm diameter that incorporates a small 150mm mirror within it and has a plaster frame around it which is attached to the log slice. The wood in question is paulownia.

I've heard that wood slices can randomly crack depending on humidity. Obviously wood is porous and plaster is wet and takes a few days to dry out. I've giveny wood a couple of days and will continue to give it a few more to dry. At the moment all seems OK. My worry is something happening to the wood further down the line, say after a customer has purchased a piece. These log slices are for indoor use only but the fact these could naturally crack at any time would result in the plaster possibly cracking and maybe the mirror becoming damaged. The thickness of the log is approx 20-25mm and the overall weight of the plaster and mirror included is fairly minimal.

Am I over worrying or could this wood disintegrate or crack over time and in turn affect what is attached to it? Is there a recommended type of tree that might be more suitable to use... If anyone can give some advice it would be greatly appreciated.
 
A picture could paint a thousand words here to show how the parts of your artefact fit together. Wood moves as it dries out, and moves some more with changes in atmospheric humidity. Good wood product design is based on cutting components in such a way and fitting them together so that the effect of the movement is accommodated.
Log slices are just about the least stable way to prepare wood, and generally only used for rustic results where the cracks and movement are a feature. If you're incorporating rigid and brittle components like plaster and glass then your design needs to isolate these from the wood and it's movement. Think oversized rebates and careful used of flexible mounting so the wood can move without damaging the other parts.
On a small item using very well seasoned wood which is well sealed and kept in a stable environment you might 'get away with it' for a long time, but I wouldn't risk it on a customer product.
 
'Disintegrate' is a bit extreme but your rounds, as they are known as, will almost certainly crack radially as they dry out.
What condition are they in at present? How old is log? Has it been sliced already?
To avoid cracking the log should be seasoned in a very controlled way which could take several years from felling to usage.
If your rounds are already sliced I would recommend they be air dried, ie, outside but protected from the weather but with good airflow for at least a year. Then bring them indoors for a few months, ideally in the environment they will end up in.
By now they will have cracked if they are ever going to. After all this you will not want to throw them away so it's time to celebrate the cracks. Make a feature of them by filling with a coloured resin. Finish by coating completely with clear resin which will keep them isolated from that nasty wet plaster.
Brian
 
I'm fairly new to working with wood, and am starting to use it more with some of my crafts, particularly when I work with gypsum plaster.

I particularly want to use some large wood slices approx 250mm diameter that incorporates a small 150mm mirror within it and has a plaster frame around it which is attached to the log slice. The wood in question is paulownia.

I've heard that wood slices can randomly crack depending on humidity. Obviously wood is porous and plaster is wet and takes a few days to dry out. I've giveny wood a couple of days and will continue to give it a few more to dry. At the moment all seems OK. My worry is something happening to the wood further down the line, say after a customer has purchased a piece. These log slices are for indoor use only but the fact these could naturally crack at any time would result in the plaster possibly cracking and maybe the mirror becoming damaged. The thickness of the log is approx 20-25mm and the overall weight of the plaster and mirror included is fairly minimal.

Am I over worrying or could this wood disintegrate or crack over time and in turn affect what is attached to it? Is there a recommended type of tree that might be more suitable to use... If anyone can give some advice it would be greatly appreciated.
If the log is sliced at an angle of about 30% it greatly reduces radial cracking. Same principle as slicing French bread, you'll end up with ovals rather than circles though!
 
As you are new to this, and to save you asking, there is no known way to prevent the cracking and wood movement! Well, maybe (just maybe) if you encase the wood slice in thick resin.

Bear in mind also that, even when your slices have dried as much as they are going too, they will still react to changes in atmospheric humidity. The cracks will close a little when it's humid, and open again as the air dries out (eg if the central heating comes on).

Dee J's suggestion of isolating the frame from the wood, so that when the wood moves it doesn't exert any force on the frame, seems the only likely way you might succeed.
 
I have never used this but I believe wood can be stabilised using polyethylene glycol (PEG) which replaces the water in the wood.
Natural wood will always move with changing humidity. It is fundamental to understand and allow for this in design and construction
 
If I avoided using a log slice and went with say a poplar or birch wood panel, or similar, like those used in arts and crafts, for example the types used for plaques or painting onto, would this be more suitable or is it the fact every piece of wood will eventually crack?

Im only wanting my pieces used indoors (away from damp/humid areas). I need a wood that is at least 9mm thick and wanted circle, square/rectangle cut shapes to use as a backing board for my plaster pieces. I've seen many plaster arts put onto certain types of wood but not sure where people are buying such boards.

Any help would be appreciated.
 
If you use a fully seasoned straight grained panel there's a good chance it won't crack BUT there is every likelihood it will expand and contract across the direction of the grain. This is why panels in panel/frame doors are not glued into position; they are allowed to move in reaction to changes in humidity. Atmospheric humidity changes all the time, there is no escaping.
Basically you are attempting to bring 2 incompatible materials together; wood which will move and plaster which is brittle - not a good design basis. You could consider moisture resistant MDF but I would want to go thicker than 9mm.
Brian
 
Laburnum is often cut into slices, mainly because its really narrow most of the time, so to get usable timber, sliced and joined together to make a parquetry type pattern called oyster.
See if I can find and example....

Anyway. You slice them thin, then layer them with paper in a stack,and set aside to dry. Elastic bands help hold the stack together while it slowly season.
https://en.wikipedia.org/wiki/Oystering
Rolvenden,_St_Mary_'s_font_3273.JPG
 
Removing the centre areas ( where the pith is ) from your rounds will give them a smaller chance of cracking, ( cracking is due to uneven drying rates of the different parts of the log ) but all wood will crack a bit.I've got some 1 metre diametre oak rounds an some 10 cm diametre oak rounds , air dried by me..They all crack a bit, the ones with the centres removed crack less. Sometimes even removing a core from the centre of 5% of the total diametre will be enough to reduce cracking to a minimum.
You could always separate your plaster from your wood by "floating it" on a plastic or cork disc smaller than the plaster and secure the plaster to the rounds with a version of "mirror hooks" or similar home made "hooked pins" ( pin part into the wood, hook part cradling the plaster part ) with a few mm of "play".
 
You may have more success using plywood or MDF with a glued on veneer.

This will have normal rather than "round" grain showing but likely to be much more stable.
 
I was given 8 slices of Ash, around 250mm diameter and and about 35mm thick - I season quite a lot of timber for turning and had them stacked outside with good separation between them - after 2 years only 2 of them hadn’t split - and when I cut through the split ones the middle was still over 15% moisture.

The last two made a decent small round boards - until they split a couple of years later!

Personally I would buy some kiln dried bowl blanks for your project
 
In June 2021 I was tasked by my daughter to creat log slices from a silver birch trunk recently felled and sliced by her about-to-be husband as bases for table decorations at her wedding three months later. Not wanting the unseasoned wood to split I liberally coated them with Pentacryl Preservative (from Turners Retreat). I still have one which hasn't cracked in two years. Mind you at £26 for 909ml (32oz) it don't come cheap. That was enough to do 16 slices though not fully to the manufacturer's instructions - I skimped a bit!
 
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