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How does wood move with time.

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Forum topic by Carloz posted 01-27-2018 11:50 AM 1280 views 0 times favorited 6 replies Add to Favorites Watch
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Carloz

1147 posts in 592 days


01-27-2018 11:50 AM

I noticed the wood on very old furniture always shrinks and if not left enough room for movement, cracks. I’ve never seen that it would crack because of expansion.
Is it because the wood was not dried properly or generally wood shrinks with time? I am talking about very long time, like 20-100 years.


6 replies so far

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WDHLT15

1744 posts in 2476 days


#1 posted 01-27-2018 12:39 PM

Wood moves with changes in humidity. If left outside, it will reach about 12 – 15% moisture content because of the average outside humidity. Bring that wood inside a heated and cooled space where the humidity is controlled and much lower than the average outside air, and the wood will shrink in response to the lower humidity. Conversely, if you bring wood outside that was stored inside at lower humidity, it will gain moisture from the wetter air and the wood will expand.

A lot of old furniture was made with air dried wood, and in the old days, people did not have the humidity controls that we do today (modern heating and cooling). Also in warmer times of the year, the old houses would have the windows open to capture breezes for cooling, etc., bringing in more moist humid air. Plus, the old houses were not as tight as they did not have modern insulation.

It is all about the environment. Wood will seek stability with the environment whether it be inside or outside. Wood moves with time, either shrinking or expanding, depending on the humidity. The more stable the environment and the less variation in humidity, the more stable the wood will be.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln. hamsleyhardwood.com

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sawdustdad

354 posts in 885 days


#2 posted 01-27-2018 01:31 PM

Danny is spot on regarding wood response to humidity changes. Today’s homes are much drier than those of yesteryear.

To address your question about cracking/splitting, wood shrinkage usually only causes cracking when part of the board is constrained by another piece of wood fastened to it at right angle. Since wood expands and shrinks across the grain much more than along the grain, a wide board with another board fastened across the grain is likely to crack because parts of it are held tight and shrinkage has to “go somewhere.” If the perpendicular board is fastened with slotted screw holes, elongated mortises, or other appropriate fastening method that allows for wood movement, it is less likely to split. It’s amazing to me that some really nice furniture made by obviously talented people from the 19th century (and earlier) had no clue as to wood movement.

-- Murphy's Carpentry Corollary #3: Half of all boards cut to a specific length will be too short.

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bondogaposis

4728 posts in 2351 days


#3 posted 01-27-2018 02:04 PM

Not all antiques were constructed in such a way as to allow for wood movement. It generally shows up as a crack, when the wood shrinks in a dry environment. Expansion doesn’t show up as a crack but as a cup or warp.

-- Bondo Gaposis

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jmos

827 posts in 2370 days


#4 posted 01-27-2018 02:07 PM

Another wood movement phenomenon I’ve read about is where wood tries to expand, and if it can’t, the fibers can be crushed to the point where it will not expand when the humidity drops. The example was on turned chair parts, where they expand, are held by the round mortises, and then when the humidity drops they can be loose. It actually looks like the wood shrunk, when it was actually crushed.

-- John

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rwe2156

2926 posts in 1481 days


#5 posted 01-27-2018 03:09 PM

As noted, lots of antique furniture was built with little to no regard for wood movement, primarily because they didn’t have to. The environment inside the shop was the same as the home it was going in. So long as the wood was seasoned properly and reached equilibrium, no issues.

That being said, there is still seasonal movement that has to be considered – expansion in summer/shrinkage in winter. 200 years ago, drawers, panels, etc were made tight summer and loose in winter.

BTW, this principle still applies today, except its usually in anticipation of moving the piece inside rather than season.

In my own personal experience, until I started building furniture in a climate controlled room, I was continuously fighting and getting frustrated with wood movement.

But I still make drawers fairly snug regardless of season because I know they will loosen up once inside the home.

-- Everything is a prototype thats why its one of a kind!!

View a1Jim's profile

a1Jim

117095 posts in 3577 days


#6 posted 01-27-2018 04:15 PM

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