Warped chair advice needed

tvrgeek

Scott
User
The seat of this solid wood chair has warped and pulled out the corner screw. Sure I can drill a couple new pocket holes and pull it down, but I am afraid the seat will eventually crack. Any advice?
20210602_073948.jpg
 

chris_goris

Chris
Senior User
I agree with Jeff for one, it looks like it isnt finished on the bottom side. Did this just happen by moving it to an uncontrolled environment? outside of the A/C?.
 

FredP

Fred
Corporate Member
flatten the bottom and re-attach or rip into 3 sections, joint and re-glue,then seal all 6 sides. Pulling it down with screws will likely cause it to crack.
 

tvrgeek

Scott
User
It is finished. A factory finish I can't duplicate. My sister is waiting on feedback from the Amish factory where it was made.
 

tvrgeek

Scott
User
They said to sit it outside in he humidity for a few days and see if it relaxes, then re-attach. I am not optimistic as it will return to a house with about 50% again. I do wonder of their house was much drier than that.
 

FredP

Fred
Corporate Member
I would think more humidity would cause it to curl farther. The bottom is not sealed so drying would cause the bottom side to shrink allowing the seat to lay back down IMO.
 

marinosr

Richard
Senior User
You can read this exhaustive, very nice report by the Forest Service about how finishes affect moisture exchange. But I'll quote the take home message: "Only 11 finishes [out of 91 tested] were found to retard moisture vapor movement into wood with any degree of success over the relatively short time of 14 days, and then only when two or three coats were applied." The only finishes that were effective were a) paraffin dip b)multi-part epoxies and c) solvent-borne enamel paints. An unfinished seat bottom is very unlikely to be the cause of warping. Plus, as Fred points out, the warpage would have been expected in the other direction if it was indeed due to the unfinished bottom equilibrating faster to lower humidity inside.
 

FredP

Fred
Corporate Member
You can read this exhaustive, very nice report by the Forest Service about how finishes affect moisture exchange. But I'll quote the take home message: "Only 11 finishes [out of 91 tested] were found to retard moisture vapor movement into wood with any degree of success over the relatively short time of 14 days, and then only when two or three coats were applied." The only finishes that were effective were a) paraffin dip b)multi-part epoxies and c) solvent-borne enamel paints. An unfinished seat bottom is very unlikely to be the cause of warping. Plus, as Fred points out, the warpage would have been expected in the other direction if it was indeed due to the unfinished bottom equilibrating faster to lower humidity inside.
exactly. that is why it is important to seal all sides. when completely sealed the wood accepts moisture at the same rate on all sides and moves equally (somewhat). some woods just do what they do no matter what. ;)
 

marinosr

Richard
Senior User
Well that USFS report shows that most finishes have a negligible effect on the rate and extent of moisture exchange. Which myself and others have taken to indicate that it is not beneficial to finish a non-show side of a board. It's certainly not hurting anything though!
 

JimD

Jim
Senior User
I completely disagree that the paper shows finishes have a negligible effect. Did you look at it before making that statement? It clearly shows effects including a MEE (moisture eliminating effectiveness) of 83 for a type of shellac. That is not a negligible effect. Lacquer was low but still had an effect.

The test is interesting and was conducted reasonably, I believe, but it is time consuming to review mainly because they call all the finishes by number and you have to read the captions or look in the appendix for description of finishes. They were also evaluating paints and clear finishes with a wide variety of types. The test is kind of unique and severe. The wood started at 30% moisture content which is higher than I start with and then they exposed it to 90% humidity. It gets that high were I live (SC) but not inside my house. The relatively high initial moisture would slow the rate of absorption, I think, but the 90% would speed it up. So not real representative of furniture mositure environment but I think it is a reasonable way to see how permeable finishes are.

Last, I would say that a big reason to finish both sides is not that we are blocking all moisture changes. We are not. But we are making the rate of absorption similar on both faces. I finished the underside of my 10 foot long 42 inch wide dining room table so I did not have the bottom absorbing moisture at a significantly higher rate, expanding, and bowing the table severely. If I had left it unfinished, or put fewer coats of finish on it, it might reach equilibrium and flatten back out but I don't want to wait around with a warped table to see if that happens. Best to just finish both sides the same. That maximizes the chance the wood doesn't warp as it changes mositure level. I used Osmo which I doubt is great at blocking mositure exchange but so far it is staying flat.
 

JimD

Jim
Senior User
I will also say that I would not do anything about a little gap like that, particularly if it flatten out when somebody sits on the chair as I suspect. How many people get down and look under a chair to see if there is a gap? It is probably due to a less finished bottom absorbing moisture quicker but I don't think it affects the serviceability of the chair. Appearance is affected but not in a "in your face" kind of way. As we have all experienced, trying to prevent wood movement doesn't work and causes problems. When wood wants to move it will, it is usually best to try and minimize it and then live with the rest.
 

tvrgeek

Scott
User
Seat is warped. Yes it will flatten with force, but I can tell the amount of stress will crack the seat. If the manufacturer will not provide a new seat, then best choice may be to shim the opposite corner so as to split the difference and not put stress on the wood. Then put the screws back in so it won't spring, or worse, "pop" when someone sits on it.
 

marinosr

Richard
Senior User
I completely disagree that the paper shows finishes have a negligible effect. Did you look at it before making that statement?
Aye, I did.
It clearly shows effects including a MEE (moisture eliminating effectiveness) of 83 for a type of shellac. That is not a negligible effect.
Yes, it was a pigmented, flattened shellac that did this, not really a common finish and somewhat of an outlier. Everything that I would consider a typical furniture finish had a very low moisture excluding effectiveness.
The wood started at 30% moisture content which is higher than I start with and then they exposed it to 90% humidity.
The wood started at equilibrium moisture content for 30% RH, not 30% MC. But yes the test conditions are severe. Agree it's a useful test though. Moisture absorption by wood is a diffusive process, so reasonably approximated by Fick's law: diffusive flux = gradient x diffusivity constant, and changing the gradient to more realistic environmental conditions shouldn't affect the diffusivity constant (a constant), which is what the finishes are modifying.
Last, I would say that a big reason to finish both sides is not that we are blocking all moisture changes. We are not. But we are making the rate of absorption similar on both faces.
Yep, I certainly grasp your reasoning and it's a convincing argument from first principles. It's just my two cents that, with respect to the USFS report, the authors' data and their own stated conclusions (as quoted above) suggest that this reasoning doesn't really hold up. Also, for centuries handmade furniture was unfinished on non-show surfaces, and furniture manufacturers by-and-large don't bother to finish non-show surfaces.

Edit: Sorry Scott for hijacking yr thread. I'll let it be.
 

tvrgeek

Scott
User
The lesson from the Forrest Service is that moisture is a very small and given time, can permeate about anything. It does not have data on how perfect any of the coatings they tested was or even real dat on thickness. 1 to 3 coats is not a controlled thickness. That would require far more controlled testing.

I need to get a wood moisture meter. Sounds like the HF one is a good deal. I suspect my sisters house was drier than expected over the winder. If it relaxes back when it sits in my shop, controlled about 55%, that would be great, but I suspect it will not. What I do not know is what % wood stabilizes at when in a stable environment. I do not know know how long it takes for wood to stabilize. I kind of suspect the advice from the manufacturer is to delay as it takes months. Wood an inch thick mostly finished is not going to stabilize in a week or two.
 

FredP

Fred
Corporate Member
Try applying some dry heat to the bottom. Maybe a heating pad with something to block up the seat (not directly on it). It may draw the moisture out from the bottom enough for it to lay down. You got nothing to lose. It might not help but it certainly won't hurt.
 

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