Wood Movement

Chas Jones

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Location
Cotswolds, UK
Hi, as someone who does not suffer extremes of climate conditions at home base I've been wondering if you get problems with highly finished pieces if they migrate to different states with having big differences in temperature and humidity.

Having visited States up north and driven down through Texas I wonder about the ability of items finished with the high gloss multi layer poly finishes we see used by some turners to hold up if they travel to such extremes.

Got brought up here because of thoughts generated seeing lacquer finishes applied over oil base coats, not the best scenario for max adhesion without the wood movement, both physicaly and geographically, coming into the equation I would have thought.
 
Interesting question. I have a small segmented bowl that was made in Georgia and highly lacquered. Living in Arizona, a considerably drier place, has allowed the bowl to slightly shrink and the glue lines can be felt. It has not significantly changed its visual appearance but the surface certainly has a distinctive tactile change. I suspect a large object may exhibit greater changes.
 
Early on I used PVA for my pieces Carol and noticed glue creep at the joints, more due to wood movement due to differing moisture contents than climate difference I suspect, I've since changed to cascamite and been more careful with wood choice and that seems to have fixed it, at least for our local climate it would seem.
 
The piece I was referring to is in my collection from a friend in Georgia. I do not know what glue he used. I have not heard of cascamite and will have to research further. Thanks for the information.
 
You might find it under the brand name polymite, it changed names for some obscure reason for a while, maybe because of the parent company PolyVine.

sample details

If you try it and need to keep remainder more than a few months it's best to decant the contents of the supply containers into smaller airtight jars to avoid air moisture spoiling it. (may not be a problem for you)
 
The Cascamite glue looks like much like the "plastic resin" (ureaformaldehyde) glue sold here by DAP/Weldwood. I started using it on cutting boards to prevent the glue creep I was seeing with Titebond II.

Back to your original question...so far (touch wood), I've not seen any finish degradation issues on turned pieces where I used spray lacquer over BLO or over a wipe-on oil based varnish finish like Formby's Tung Oil Finish or Minwax Antique Oil. That includes pieces that were made and finished in Southern California then later given to relatives in New Mexico. Due to concerns about adhesion issues, I do make it a point to let the oil finish cure well before applying the lacquer.
 
On one of my trips to NZ I picked up a good sized blank of koe-koe a local timber good for turning. It had been stored for around 10years in a dry wood rack. Got back to Sydney put with the rest of my dry blanks on a shelf at the rear of the garage. Had a look two weeks later and it had pealed open, pretty well destroyed the blank I gave it a way to a pen maker friend.

So the bottom line is wood moves and will always move. some more than others.
 
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My understanding of this issue has more to do with how dry the wood is before finishing. I think the standard for dry wood is 6% or so. I have a radiator in my shop and if I am making something for someone who lives in a dry climate I will put the wood on the radiator to get the moisture content real low. The radiator can get as hot as 180 degree F. Then when you apply an oil finish first, it will soak into the grain and help keep moisture out if the humidity goes up for a time. I mostly have used a lacquer hand rubbed finish over the oil.

I have read that there is no finish that keeps moisture out completely. However, I think shrinkage will cause more problems with a piece rather than some swelling.

In Michigan where I live, we experience wide humidity swings Summer to Winter. I do check wood with a moisture meter before using it. This Summer, a friend and I hope to build a kiln. Kiln drying helps stabilize the wood because it changes the wood cells ability to take up moisture. For instance I have a pile of kiln dried q-sawn white oak that started out at 6% but now is around 12-15%. The non-kiln dried wood can be as high as 20% moisture.
 
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