Effect of humidity on wood

Discussion in 'Off-Topic' started by AlbertHall, Jun 4, 2019.

  1. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    I have asked this on a woodworking site but got no replies and I know you lot know everything about everything so I decided to ask in here.

    I have a wooden clock. The pendulum rod is shaped rather like a question mark, the curved part giving clearance to the mechanism.
    The clock needs to be carefully aligned on the wall so the pendulum action is centred but this setting seems to change with humidity sufficiently to stop the clock.

    The wood is hardwood veneered MDF. Would changing humidity change the curvature of the curved part of the pendulum rod?
     
  2. wayneh

    Expert

    Sep 9, 2010
    16,099
    6,212
    Yes, almost certainly. You've got yourself a hygrometer.
     
  3. jpanhalt

    Expert

    Jan 18, 2008
    7,233
    1,605
    Wood (dry) swells with moisture. The increase is considerably greater cross grain than along the grain. That's why the recommend wall clearance on walls parallel to the grain is more then walls perpendicular to the grain. Surely the same applies to your pendulum.
     
  4. Berzerker

    Active Member

    Jul 29, 2018
    512
    86
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    9,691
    2,341
    The with-grain/cross-grain difference mentioned in post #3 probably won't apply to MDF, since the wood particles have essentially random grain orientation. However, it could apply to the veneer. Regardless of grain direction, the wood dimensions will vary with humidity, though I'm surprised the variation is great enough to stop the clock.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    18,185
    5,577
    MDF is a medium density fibreboard composite, whereas it might swell with excess moisture, this would cause separation of any veneer on the surface, the veneer will typically be of a hard wood and would swell according to the direction of the grain, but this generally results in peeling of the veneer.
    Max.
     
  7. JohnInTX

    Moderator

    Jun 26, 2012
    3,674
    1,902
    +1 Having seen it damp around the house, it looks like it's just pressed sheets of paper. Get the end wet and it delaminates into mush. We have it all through our place and it's seriously humidity sensitive. Good woods are as well (ask any guitar player) but not like that stuff.
     
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    5,000
    1,903
    How is the pendulum sealed?

    Since humidity affects the operation of the pendulum, it needs a coat of waterproof sealant to minimize the effects of moisture. Several coats of good quality spray lacquer sealant might resolve your problem.
     
  9. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    So, general opinion is that this might well be the cause.
    I knew you'd come up trumps.
     
  10. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    It is not sealed, nor is any part of the clock. I suspect it would be problematic for the mating surfaces to be coated so I thought it best to leave it all naked.
    Do you know, that hadn't occurred to me as a solution. That can be done without interfering with the function at all.

    Are all spray lacquers waterproof?
     
  11. jpanhalt

    Expert

    Jan 18, 2008
    7,233
    1,605
    That depends on how mangled the term,"lacquer," has become. An epoxy might be better. Shellac is probably the worse. Why not make a new one out of ash, oak, or whatever real wood you have available? Or, maybe a composite foam sandwich? Model airplanes, particularly sailplanes, use such sandwiches.
     
  12. wayneh

    Expert

    Sep 9, 2010
    16,099
    6,212
    Polyurethane certainly is. The water-based version is really easy to apply. I've also used a sanding sealer product that was very similar - it puts a nice smooth and waterproof coating on wood without feeling like plastic.
     
  13. BobTPH

    Senior Member

    Jun 5, 2013
    1,721
    438
    How thick is the MDF? It is not normally sensitive to humidity like wood is, but if it is veneer over a thin later of MDF I could see the veneer swelling and warping the whole panel.

    Bob
     
    shortbus likes this.
  14. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    The rod is about 1cm square. The veneer is perhaps 0.5mm.
     
  15. Wolframore

    Active Member

    Jan 21, 2019
    687
    180
    What about using wax? thinned down with denatured alcohol it would penetrate and perhaps help reduce friction.
     
  16. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    5,000
    1,903
    As others have noted, all are not waterproof. But, check the can label. Most are.

    What do you mean by “mating surfaces”? Whether or not is problematic depends on your answer. If the surfaces are to be glued, then it depends on the adhesive. Wood glue may not bond strongly. A polyurethane glue or epoxy joint won’t be a problem. And, one can seal the assembly, after joining.
     
  17. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    There is no friction (other than air resistance) associated with the pendulum. It has two screws points on which it sits.
     
  18. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    By mating surfaces I meant the bearing surfaces, gear teeth and the like.
     
  19. wayneh

    Expert

    Sep 9, 2010
    16,099
    6,212
    I think just about any coating would make a sizable difference. It just depends on what you have on hand, or wouldn't mind having around for other projects. I've read of people using thinned-down wood glue (PVA) as a 'varnish'. Wax, oil, Thomson's water seal, paint, deck stain, whatever. Any of these would dramatically reduce water migration. I'd use the polyurethane varnish because it's perfect and I always have some around.
     
  20. AlbertHall

    Thread Starter AAC Fanatic!

    Jun 4, 2014
    7,750
    1,903
    Using PVA would be appropriate as it is glued together with PVA.

    I have ordered a small tin of polyurethane 'yacht' varnish.
     
Loading...