I recently (last summer) made a round table from pie-shaped pieces of oak. The table is 4′ in diameter and the pieces have begun to shrink. I thought I had taken all precautions to avoid that, but I am now thinking it might not have been avoidable. Is there anyway to deal with the shrinkage, (filling in with wood filler for example? or adding a humidifier?) Is this just a case where I should have veneered? Any ideas on how to salvage what I have done?
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Replies
BigBob,
The only way I know of to keep wood from moving with seasonal weather changes is to completely encapsulate it with a water-impervious layer. The only such product (again, that I know of) that you might find reasonable is epoxy.
The idea is to completely seal off the wood from the air, so that no moisture can enter or leave the wood. That means, of course, that every part of the table would have to be coated with epoxy. Once the weather, or your humidifier, has caused the wood to resume its "proper" dimensions, two or three coats of epoxy would ensure the wood will not move again with the seasons. You can then varnish, or apply any finish you like.
I realize this may not be the answer you're looking for, or it may be impractical for the particular design of your table; but it's the only thing I can think of. Perhaps some of the others have other suggestions.
Alan
Alan,
Even with encapsulating in epoxy, wouldn't barametric pressure still effect the moisture in the wood and thus cause movement?
Don,
Not in my experience. Once encapsulated the moisture content of the wood hasn't varied--or if it did vary it didn't vary enough to cause movement. If you're familiar with the Gougeon brothers' book, they say the same thing: once sealed the moisture content remains constant.
I've not before heard the notion that barometric pressure could force moisture through an otherwise impermeable layer. Have you experience with this?
Alan
Alan,
No I don't have any experience with this in this context. Just was thinking that BP was along the lines of gravity. Just one of those things that is darn difficult to escape from.
Don
Alan-Don-BigBob:
I got into a similar discussion days ago concerning some testing I did back in mid-80's (no luxury of moisture meter at the time). I just started re-checking the theorys I formed back then. I've started an experiment that will last all 4 seasons here in Ga. I just purchased Bruce Hoadleys's book by Tauton Press, Understanding Wood. I highly reccoment it as Hoadley is a leading authority on wood technology. I have learned much so far as I'm very interested in some of the secrets that surround this subject.
Pg. 207, Slowing Moisture Exchange: "Although a primary objective of finishing treatments is to prevent moisture exchange, no finish is totally effective at doing so. Given enough time, moisture will be absorbed into wood from a humid atmosphere through any finish." Goes on to state finish retards rate of exchange enough to buffer between high and low extremes. Some finishes do it better that others. Affected by # of coats applied and amount of time of exposure to a different humidity level.
Get back to you in a year if I'm still around with results of what I might dig up. This book is excellent as it has already answered some questions that I knew from observation were happening, but not sure why with pure speculation.
Hope this helps as it's a tricky subject. Have a great day!
Sarge..
Sarge,
I don't disagree with what Hoadley says. I would be surprised, though, if he included epoxy as a "finish." Using epoxy as the ultimate finish layer would not be real attractive. It has a very plastic look to it, sort of like poly, and doesn't rub out at all well. About the only way to make epoxy presentable is to put another film "finish" on it, such as varnish (to which I alluded in my first post). When it is flattened and coated with a film finish that is then rubbed out as usual, the work piece can be very pretty.
I don't know the science of this. I'm taking other peoples' word for it and matching it to my own experience. I've used WEST epoxy along with other brands I've forgotten; the poop sheet on them advertised the finish was impermeable to moisture and most everything else (epoxy coated wood can be used for potable water, fuel tanks, refrigerator/ice-box liners, etc.). I've made a boat with the wood-epoxy system, tonneau covers for pick-up trucks (for which I also marketed plans) and several other smaller outdoor products. There were some very tight tolerances in both the boat and the tonneau covers. After several years outdoors I could discern no movement whatever. I received no complaints from my customers.
I'll be interested to see the results of your tests. It will be interesting to see if all those folks know what they're talking about (and if I know as well).
Alan
Alan:
Thanks for reply. The original dis-agreement was question answered http://www.woodbay ?? (new to computers) that was suggested in post. Said dry wood wouldn't warp no matter how stored. Yep!! been there, done that. Humidity will most certainly as I have had it happen many times before I took evasive measures years ago after thinking about it.
I have now become curious if what we assemble as kiln-dry which should be 8% to 12% moisture content is really that. Not that suppliers would take any short cuts to the cash register. Maybe we get wetter lumber sometimes that we end up assembling and I say finishing (I also use sealing). What bugs me is what's going on inside that seal. Is is shifting, escaping or is the seal really breaking down chemically and allowing more moisture in. I don't understand how it would get in either. Common sense (I though). Example.......
I built two night-stands years ago. Both from same batch of wood and checked moisture content at aproximately 10% as I keep my wood wrapped Saran wrap b-4 assembly and finish. One on both sides of bed. On one side is an AC/Heater vent that blows almost directly on it. A year ago, the one by vent separated about 1/64 an inch at table-top glue joint. The other is un-moved. Both were matching batch and started out as 10% content. The one that separated is below 6% after running moisture meter over surface. The other is about 9%. I don't know either, but I'm sure curious. Probaly wont matter to me 40 yrs. from now but it's sure sparked my curiousity for the moment. Maybe I should just take up crochet. Ha..Nope, been at this to long. I remember back in grade school when that guy came up with the assumption that the world was round, not flat. I though he was nuts too. I'll give it a shot!!
Thanks, and if there's anything else you might deem a clue you know or run across; I'm as close as your nearest computer. All input would be helpful.
Sarge..
PS: The 6% reading came immediately after I noticed crack. Not a lot of time for escape. But it doesn't take long I am guessing.
About three years ago I took some cutoffs (plain sawn red oak) from a table top I was making and glued them up into a 4 inch by 4 foot board and then proceeded to measure the moisture content and the length for about two years. The moisture content in my shop varied from 5.5% to 15% through the seasons and the length of my board changed 1 5/16 inches over this range, or about 5/16 inches / foot. This was with no finish so I would expect the excursion to be less with a finished product. FWIW, Art
Art:
Thanks for input. I have run similar projects raw wood. I have let flat boards sit overnite in sudden changes of weather in my shop which has similar humidity as yours.I have seen much as 1/16" in a 24 hour period. No doubt in my mind on unfinished wood.
I have become interested in does moisture locked in escape and does humidity from outside get in after you apply the finish. I have run digital moisture meters over various areas of finished pieces and detected moisture shift from one area to another by charting daily. It's a mystery to me why! I'm going to check all areas of the wood I'm about to finish to see if it has un-even degrees of moisture distribution. Then I will chart it to see if it moves around inside and if I lose moisture or gain over a period of time. I suppose the answer ( if I find one) won't be a great revelation. Everyone I speak to about this has their own theory from conclusions they've made with experience, as you and I. I have not read about any proven facts on this subject. Most wood technologist seem to derive their answers from people like you and I in the shop and from studies done by forestry people. I'm not sure they know the total truth or we will ever know. I got the time and patience to spend on the subject, so why not?
Thanks again and anything you notice in future projects let me know. By the way, what does FWIW mean. I only been on computers about 4 weeks and not familar with terminology.
Sarge..
Sarge,
I don't own a moisture meter, so I don't know actual numbers. (how would one measure through finish?). I have no idea what is the moisture content in the wood I use. More important, I think, is after the wood is thoroughly dry--by the method of your choice--to then let it acclimate for as long as possible in the environment where it will live. So far, so good; I've had no problem with wood movement, even after many years in upstate NY.
Shane,
I must have different literature than you. After this discussion began I looked in The Gougeon Brothers on Boat Construction, I also looked at the label on some WEST epoxy (the Gougeon brothers' brand) that I have, and I looked at product descriptions of various brands of epoxy on a couple web sites. They all said pretty much what I remembered: properly prepared and applied (meaning at least two coats) once fully cured epoxy forms a layer that is impenetrable by water, and nearly all other liquids and gases.
Where did you read that water vapor could get through epoxy? In the Gougeons' book? My copy is at least twenty years old, I'm sure there have been revisions since then.
Alan
Alan:
Opps, I didn't go back and read our original post to each other but I see a mis-understanding last sentence of recent post. Where did you read water vapor can get thorugh Epoxy?
I didn't! I was referring to regular finish. Sorry if I mis-lead or you mis-understood. If you have time read some other post. I had just recieved Bruce Hoadley's book Understanding Wood. I referenced pg. one of post. Howie has and big bob is getting. Highly recommend. Printed Taunton Press 2000.
With that said, I am interested in your apoxy. I am semi-retired and work part time Co. here in Atlanta called YEAR ONE. They have been supplying 60's to mid 70's muscle car parts all over the world (Chevelle-GTO-Camaro-Firebird, etc.) for 20 years. We just added 67-87 Chevy-GMC truck about a year ago. Sell all parts, also wood floor beds as I'm guessing you have encountered when you mentioned tonneau covers! We have a traveling show team and we built a show truck that is included. From what you reccomend on West Apoxy is it what we need to finish bed-floor. Sounds like it is! If we wanted a clear-finish can it be done over apoxy or does some type of stain have to be used to cover it's appearance? Any help you can give I would appreciate. Guess who gets to advise that project.heh...I have been afraid that even 4 or 5 coating marine spar won't hold up with the exposure it will get. That's why you caught my attention on the epoxy deal. I have been around the auto market for awhile so familar with epoxy for uses there, but totally un-aware of the wood deal. If you have the time I would appreciate any thought this suject. Hope I have made myself clear this time. I owe you one.
Again, sorry for the mis-understanding and the digging you did. Still recommend Haodley's book as it is a recent wealth of information.
Sarge..
While reading this thread I was reminded of an article I think was in FWW back in the early 80's. It was about a woodworker in the New England area I think, but he took all his wood and buried it until it was ready to be used. I think some things were buried for years. Anyone remember this?
Don
Don C.:
Thanks for the post as probaly not evereone would be interested in this subject. A shame though, as set-up and preparation are a vital part of finished product. You just tipped me off you've been around a while. (early 80's) I'm new to computers and forum. If you're like me you spend a much larger time with prep and check-list of machine alignment than you do with the actual cutting,etc. It eliminates most mistakes b-4 they happen. To me what happens long down the road to that finished piece is important. I won't be around forever, but my work at least has a chance if I took the time to produce a quality product. I am a red-white-blue American that tries to abide by the slogan that hangs in my shop. " MADE WITH PRIDE IN THE USA ".
Point: I have been working alone 30 and new to this cyber thing. I'm looking for little things others have discovered that I have missed. These computers gives us a golden opportunity to network those things. " If ", we are person (hi FG-hi-splintie) to admit no-one knows it all. I certainly don't and I'm always open for a better mouse-trap. I love wood and everything about it. I promote it to the masses (men,women and children) as it belongs to everyone that has been taken over by it's "spirit". No one owns the right to it, NO ONE SHOULD! There are many little aids and solutions out there that may be a better way than I've concluded so far. I Want To Know what they are. If a 8 year old child gives me a better way, I will adopt it and teach it to the many new-comers that pass through my shop.
I will look for that issue as I started reading FWW about 6 issues after it came out in black and white. As you probaly know there wasn't a lot of teaching and learning sources back then. Had to learn most from locals and trial and error. I now have the opportunity with networking to examine some theories I have formed and see if they stand tall or I might need to adjust on the fly. Who knows? There might be some buried wood out there as you suggested. There also may be some buried SECRETS about this craft that haven't surfaced yet. I've got a shovel in my hand and my attitude is : TIME IS WASTING--LET'S ROLL....
Hope I haven't bored. Remember I have been doing this without any people to talk to for awhile. With exception of my shop foreman Lucky (the cat). He has been been very agreeable so far; but I highly suspect it's because he is too smart to dis-agree with the hand that feeds! heh..heh...
You're welcome to drop by any any time..just knock, wipe your feet on the welcome mat and come on in. The door is always open.. Did I mention, I Love Woodworking ??
Sarge..
Sarge,
What a long strange trip it's ben since the early 80's, huh? I've been on the computer for a while, but didn't know of this site. I was already logged in when I got here though because it's a delphi site. Go figure.
Anyway, a lot of memories have been brought back in my short time here. I have that issue around in a box somewhere along with other FWW materials that I see are still available. Unfortunately because of that long strange trip they are in a box in a storage unit. I didn't get the house! I'll see if I can stop by soon and come up with that article myself. The older issues use to highlight a woodworker every month, again if I remember right. I do remember the guy was a big burly guy whose shop was in a big barn. Seems he had a particular log buried right in front of the barn door so he was reminded of it every time he walked over it. Hey, just memories here now! ;^)
Don
Don:
I think you are remembering right if I'm remembering right..heh..I'm only 55 (in Oct., if anyone might want to send b'day gifts,OK OK) but sometimes think I have that disease OLE-TIMERS on occasions. Yep, it does bring back memories and I think that is maybe a good thing. Entry-level persons I'm sure take for granted all the info available at this point and the high-tech way it can be pulled-up and communicated rapidly. I do miss some of the old days but I also have adapted to the new. I always say CHANGE IS INEVITABLE ( except from a vending machine )..heh..I'm hoping to see Sam Maloof for the third time in Oct. Now there's a craftsman that doesn't tell you he's an expert. He doesn't have to!! You just look at his work and the way he presents himself and You Know!! The aura just radiates from him when he's not saying a word as he sits in that rocker and rocks.
I encouage you to dig up that old issue. Memories, like laughter are good for the soul. Get back on what you find. Remember that the door is open and if you happen to get in late---I'll leave the porch light on for you!!!
Sarge..
Sarge,
I think you're right about the bed liners: spar varnish wouldn't hold up to rough use. Epoxy might be just the ticket though. The only problem I can foresee would be making it presentable; though that's less of an issue on bed liners than it is on other projects.
Also, you can fiberglass with epoxy, and that would make the bed liner extremely resistant to abrasion, and other damage. As I'm sure you know, fiberglass fabric comes in various weights, the heavier the fabric the more protection it provides. If I recall correctly (I make no guarantees about my memory...now, where did I put that ginko biloba? or did I take it already today? hmmm.) I used 8 oz. fiberglass cloth on the tonneau covers and 16oz. cloth on the parts of the boat that might get to know various abrasive surfaces real well, and 8oz. cloth everywhere else.
For a great primer on the use of epoxy with wood, and even how to fiberglass with epoxy, I still highly recommend The Gougeon Brothers on Boat Construction. They also do wonderful woodwork and explain how it's done.
Alan
Alan:
Thanks for the reply. First I forgot to answer your question about moisture meter and read-out after finish. I use a dielectric ?? (wide open for the EE guys and gals). It doesn't have pins. I also have a pin-type that can be used under table tops,etc. Just have to remember to touch up holes with a little poly. Keep in mind I never had a problem until nite-stands 5 years ago. That bugged me and got my interest up. I'm not sure how effective meters are through finish except for manufacturers claims, even though I got within 1% using both. They have been extremely useful for various reasons and I reccomend unless you simply feel no need. I am of theory what works best for you is where you need to be.
The show truck is hauled by enclosed car trailer as a race car would be. Nothing will actually be moved across the floor as it is strickly show. The main concern is exposure during a show weekend from UV rays and possible rain. If the epoxy does not have a presentable finish the floor could be stained b-4 applying poly over stain. Can you stain over the apoxy and then seal again with poly is the question?? It has to be an attractive finish. The truck has 8 coats of GM white and is a frame-up restoration down to same stamping on hose clamps and spark-plug wires. We supply parts that are as correct to the way it came down the assembly line as possible. We've been doing our home-work for almost 21 years. I had my own business in those days and saw this go from a 20 page catalog on Firebird from a basement to 15 car lines of classics present. Customer base just under a million all over the world. As you see it has to be an eye-catching finish as the rest of the truck is show-quality.....
With this in mind, is apoxy the answer as the base seal? Or can I not get a presentable finish over it ? I never thought about marine products. Just slipped my old stagnant mind. I'm glad you posted as this may be a break-through for our customers. Maybe not. Depends a lot what your answer to above question is.
Again, thank you for all your help and sorry for the mis-lead on previous subject. I have already begun on that project. Sure appreciate your help on this one!!
Sarge..
Sarge,
Epoxy would make an excellent base coat for all the reasons we've written about.
I don't think applying a stain over the epoxy would be a very good idea. IMHO it would be better to either stain the wood the color you want, or to use a toner between the epoxy and whatever finish you might apply.
Uncoated epoxy is not ugly, but it has a more plastic look than varnish, shellac or even lacquer (I've always thought lacquer had a very plastic look to it--and I won't even mention poly; IMHO epoxy looks better than poly). Also, epoxy by itself does not filter out UV as much as other products, such as spar varnish for example. So I would apply a good spar varnish over the epoxy (that is what I did on the tonneau covers).
BTW, you probably know this already, but if you do not... Be careful when buying spar varnish. Despite some nautical names and salty descriptions a lot of products called spar varnish don't offer much UV protection. As always, read the label.
Alan
Alan:
Thank you for this info. Very well written and described. Even a dummy like me got you loud and clear. I put out a request another thread for opinion also. They also had some experience with epoxy. Haven't recieved answer yet from that source. I will watch the label UV concerns. I was not aware as I don't often have any need for spar. ( Mailboxes etc. ) I think I will test several variations of ways you recommended and see what I feel will be the most attractive as thousands will view the truck over the course of a show season.
Again thank you immensely as this is extremely useful information not only for this project; but for any future that might relate. Any way I can return favor, don't hesitate to ask!
Have a great week-end...
Sarge..john
big bob:
If you will go to message #6 from me to Alan you might get a little insight on your question. The damage has already occured so you might add humidifier to slow further. If you read mess 6 you see that I have been interested in this subject for a long time. I just started a new test to last the course of 4 distinct seasons of humidity changes here in Ga. Need your help for insight, please!
You did table in summer. Questions.. What state? Did you check wood with a moisture meter and was it between 8%-12% after assembly b-4 finish? What finish & how may coats? Does your house stay at a pretty constant humidity or is there often sharp changes and for short or long periods.
I know this is a mouth-ful of answers, but if I need some help with relation-ship with various areas and conditions. I also need type finishes and # coats, what wood to determine if grain structure is a factor (my theory is yes from I've done so far).
If you don't have the time, completely understood! I'll get there, it just will take a little longer. Fortunately I have the patience. Thanks for any insight in advance.
Sarge..
Great questions! Right along the lines of what I have been reading. I am in Northern NJ: very humid and warm last summer. Wood was kiln dried when ordered from Hearne Hardwoods, (6-7%). But I am sure it sat too long in my garage. This was my first go around with sort of furniture piece. I did not have a moisture gage, and so did not have an adequate measure of moisture content before I started. Unfortunately, I am not sure what I could have done even if I did have one, I was not going to order new wood.
Using the Jeff Jewitts' Wood Finishing, I elected to seal the wood with a mixture of Tung Oil and turpentine. The finish coat was blond shellac cut to 1 lb.. I put on somewhere between 8-10 coats by hand. All done according to his instructions.
finally, the table is used in our dining room, sits in the sun and shares the room with the heater, (steam heat). Sounds pretty bad, I think. I had hoped to be able to seal it adequately. But based on your other comments, it would appear that it is impossible to do that completely.
I am of the opinion that I will now wait until winter again, and fill the cracks with epoxy. If I use a humidifyer, it should mitigate the range of movement, I hope.
I think that answers all your questions. Thanks for your interest.
Big bob
big bob:
Thanks much. I never used a moisture meter before I had the experience with dupicate nite-stands mentioned above. Never had a problem in 25 yrs. at that time. Could I have missed a spot on glue seam and moisture escaped there? That's possible. I have found with meter, wood my area has a tendency to shrink below 6% and expand from 13% up when not sealed (stored lumber). I clamp my raw storage in wood rack in stable basement waiting for 9% to 11%. This is when I pre-cut for my design and wrap with plastic wrap. Then re-clamp and wait for co-ordination of shop humidity to come within range of pre-cuts. Like I said, no problems till nite-stand top separated 5 years ago.
You have a lot of seams on the pie-shape you mentioned. That and you left your raw sit in un-stable area without moisture check before you preceded. Hmmmm!! Sounds like Howie might add from his post as he seems to have some previous expirience with your pie-shape. I will continue to explore as I realize these things happen, I'm just not sure what the combination of reasons are..
Thanks again for your input and good luck with the repairs. Hey, even if it's horrific after you do repair; and your wife still is happy with it.....Well, you just got past the only critic that really counts!!! Even a dumb country boy like me has already figured that one out!! he..he..
Happy woodworking..
Sarge.
As you have found out, it is impossible to make a table from pie shaped segments if you use solid wood. The wood movement from moisture content changes will always cause the seams to open and/or cracks to develop.
To do make a table like you have, you need to use a plywood, particleboard or MDF material that has been veneered with the wood you want. However, the way these types of tables are made is to use a full circular piece of one of the above as a substrate, then veneer pie shaped pieces of the veneer you want.
There is little you can do now to recover from the problems you are seeing.
Howie:
I agree. I got interested with this years ago. I have charted things I have observed since the first time I started looking for answers on this subject. Have seen some written word from sources recently that conflict with my current conclusions. I just recieved UNDERSTANDING WOOD by Hoadley. Plan to read several times as I usually catch something I missed if I'm not totally concentrating.
Obviously you have experience with subject from your post. If there is any pertinent info or sources you might pass along to me, I would be eternally grateful. I realize I'm not going to un-lock all the secrets without scientific equipment or extensive testing. I'm just one person with a pretty accurate moisture meter against a tough objective.
Sorry to take your time. If you can think of anything, again I would appreciate. It's a big jig-saw puzzle as to Why? now. Any piece of the puzzle would hopefully help me get to the big picture.
Have a great day..
Sarge.
I did not have the tools to make the veneer when I decided to make this table. I have just ordered a band saw, and may try again with MDF and my original jig for the pie shapes. However, my wife loves the current table, and I wanted to see if I can salvage it to whatever extent possible. It was an experiement on my part to work with wood-bending. That part worked fine. it is the contraction I should have focussed on avoiding!
Big Bob and Sarge,
The moisture content of the wood will eventually reach an equilibrium with the water vapor in the air. Of course, water vapor is moisture in the air and is known as humidity. Over a long enough period, relative humidity (RH) of 25% will result in an equilibrium moisture content(EMC) of the wood of 5-6%. 50% RH will cause wood to go to 9% EMC and 75% RH will cause wood to go to 14%. Unfinished wood will react faster than finished wood. The more impervious the finish to water vapor, the slower the wood will gain or lose moisture. Short of completely encapsulating the wood, there will always be some transfer of moisture between the wood and air in the environment.
Where I live outside NYC, I need to plan on RH ranging from 75-85% in the summer to 15-25% in the winter. Heating dry air makes it even drier and nothing is worse for furniture than a force hot air heating system without supplemental water vapor injection. Air conditioners also dry air as it is cooled so AC air blowing on a piece of furniture will cause it to be in a different environment than a piece of furniture on the other side of a room.
Finally, there are many factors causing uneven moisture absorption in wood. The biggest is where it came from on the tree but, how it was cut, how porous it is in various spots (porosity varies within a board) and if it has been sitting on another piece of wood. That's why, you measure the MC at various points on both sides of the board as well as at varying depths. Then, don't get paranoid about things. Just be aware that wood moves (see Hoadley's book) in any number of ways depending on any number of things. Build within the limitations and in the knowledge that it will move and allow for it.
Big Bob, If you have Hoadley's book, it shows on page 84 exactly what happened to your table and why. He uses a miter joint as an example. A miter joint opens on the outside in the summer humidity and opens on the inside with the dry air of winter.
Howie:
I just posted and see exactly what you saying.(please read post to big bob as I was typing as you were entering) I just got Hoadleys book and scanned. From what I see so far I also highly recommend. I'm free this week and will read it at least twice. Thanks for your explanation as I (believe it or not) followed you to the letter. Hey, I'm beginning to think you are interested in much more than electricity. Ha.. Any time you see any theory I've concluded through my information gathering and observation and you don't agree; let me know. I am always open to construtive critisizm as it is a tool for learning what the truths are.
Thanks for your time and interest. Off to finish Hoadleys book to continue my life-long education.
Sarge..
Howie,
I don't have that book, but have looked at it in the advertisements on many occasions. This is the catalyst I need to finally order it. Thanks for the explanation, too. I understand what I should have done. Now I have to figure out if I can salvage the piece.
If I understand the WEST System guys correctly, they mean that the epoxy slows down the absorbtion of water vapor enough so that the annual variation in moisture within the wood is essentially eliminated. But there is enough movement of water vapor such that the wood will eventually reach an equilibrium with the average humidity in the region. So, if your region's humidity goes from 20% to 60% every year and averages about 40% you might not be able to measure a significant expansion and contraction month to month but it will eventually reach a moisture level thats in equilibrium with 40% average.
Shane
shaneyee:
Thanks for input. That is a good lead. With my current theory that just might make sense. Remember I said theory. I simply don't know and want to. I am going to conduct experiments over course of year so all distinct seasons are covered. I have the time and patience to not jump to any quick conclusions. I may come up with absolutely no answers. If I don't, I don't! My philosophy is better to have tried and failed than not to have tried at all. Most probaly wouldn't even be interested. I have just been searching for answers for years. Don't know why? I guess the answer to that is WHY NOT? Like I said, I don't know and I want to..
Have a great day and everyone's opionion is always welcome with me!
Sarge..
Interesting discussion. I would focus on how best to cover the separations and account for further movement without sacrificing the beauty of the piece. It is difficult to give much good advice in this regard without actually seeing the piece, but here goes. One might inlay a strip of contrasting wood over each separation, gluing one side only to allow for further movement. Additionally a v groove could be cut on each side of the inlay, after it is glued down to further disguise the movement. Another similar consideration, although more complicated, would be to inlay two strips of a contrasting wood over each separation, shiplapped in the center so as to disguise the movement and glue each one to their relative side of the separation. This fix would allow the wood to continue to move without showing the structure under the separation. The mating edges of the shiplap could be v grooved to further disguise the situation. All this would depend on whether or not the original piece had the joints equally distributed, whether the finished (fixed) piece would be aethestically acceptable and whether one had the time and patience to fix it.
Wayne
WAMARA,
You're right. It has been an interesting discussion. I have elected to wait before I try to fill gaps. That would include anything using your approach, or otherwise with a filler-type solution. The cracks are not very large, but large enough to be disconcerting. None larger than 3/16ths at the outside edge of the circle.
I want to stablize the humidity of the room to see if I can stabilize the piece before I start to fill gaps.
Because the pie-shaped pieces have contracted, it has also compromised the bent-wood edging. so I will HAVE to epoxy or reglue those joints around the circle portion of the table. I just got a bandsaw last week, and was experimenting with creating veneers over the weekend. I will most likely do this project again using MDF and the oak veneer in the pie shapes. I have several jobs on the "to-do" list before I can redo something, however!
Thanks for your comments. They make a lot of sense. I should probably post a picture of the table on the message. I am just not sure how to do it right now.
Big Bob
Edited 8/26/2002 9:30:27 AM ET by big bob
I've been away from my computer for several days or I would have made my comments earlier. I have some credibility regarding wood as I received my Master's degree in Wood Science and Technology from Penn State. Like Hoadley, I consider myself to be a wood technologist even though I do not have a PhD. I worked at the Forest Product's department at Oregon State University for seven years and found the stated rule that 1 in 5 PhD's has an IQ of less than 100 to be appropriate (Hoadley is definitely NOT being among the <100 group -- his book being an extremely excellent text).
The first issue that needs to be clarified is that the equilibrium moisture content (EMC) of wood is dependent on both humidity level and the temperature. Unless both are controlled (as in a museum) these variables change throughout the day and with seasons.
The warmer the temperatue the more moisture air will hold. This however does not necessarily mean that the EMC will increase. For example (figures obtained from the Dry Kiln Operator's Manual - USDA Forest Service, Forest Products Lab) at a temperature of 70 degree F and an RH value of 64% the EMC will be 11.6%. At 80 degrees and the same 64% RH the EMC will be 11.5%. Not a whole lot of difference. However if the RH at 70 degrees drops to 44%, the EMC value will be 8.3% which is more dramatic of a change.
Daily changes (morning vs. night time variation) will not effect the entire piece of wood as moisture adsorption or loss in this situation is generally a surface phenomenom. Grain direction has a dramatic influence because moisture adsorption through end grain is about 10 times (+/- depending on species) than that of the tangential or radial directions. Seasonal changes are much more significant because extended periods of time allow the overall moisture content of the wood to change and to do so to a greater depth/degree of penetration.
To my knowledge, there is no finish that is completely effective in creating a total barrier to vaporous water. The molecular size of a water molecule is 18 (2 hydrogen atoms each with a molecular weight of 1, and 1 oxygen molecule with a molecular weight of 16) and as such is extremely tiny. If there is an opening in the coating of a size greater than the size of a water molecule, the water will penetrate and be adsorbed by the wood. With adsorption, the wood will swell and therein stress the elasticity of the finish. If the finish is brittle, cracking will develop and with that, the size of the opening will increase.
The effectiveness of a coating to exclude moisture has been researched at the Forest Products Lab in Madison WI. They have rated moisture excluding effectiveness (MEE) which compares the coating to an unfinished piece of wood for just about every commmon coating formulation (eg. latex, varnish, enamel, lacquer, shellac, oil and waxes), and they have published MEE numbers that are both a function of number of coats and time of exposure to specific temperature and humidity conditions.
The values for a modified butyl-acrylo-styro epoxy finish are as follows:
One coat MEE after 1 day = 71%; MEE after 7 days = 8%; MEE after 14 days = 3%.
Two coats MEE after 1 day = 90%; MEE after 7 days = 36%; MEE after 14 days = 2%.
Three coats MEE after 1 day = 94%; MEE after 7 days = 60%; MEE after 14 days = 16%
Test samples were Ponderosa pine sapwood and there were three replications at each level. The test conditions change was from 30% RH and 90% RH.
If you truly wish to stabilize wood, PolyEthylene Glycol (PEG) is extremely effective because this substance readily bonds to cellulose and bulks the cell wall thus minimizing the impact of expansion or shrinkage associated with changing moisture content. The bulking implies that the PEG (generally of Molecular Weight 500, 1000 or 1500) bonds between two adjacent cellulose molecules in the wood. As the PEG is of a very large size (compared to water) changes in MC will not significantly change the dimension between the cellulose molecules and the wood will remain relatively stable.
Unfortunately for your situation, PEG treatment of wood is generally done while the wood is green (certainly above the Fiber Saturation Point). PEG also interfers to various degrees with adhesive strength and finish adhesion.
I know of no easy or completely effective way to solve your top dimensional instability. Therein, welcome to the crowd of woodworkers who have made mistakes in design without fully accounting for dimensional changes due to varying moisture contents. It is a hard lesson to learn but I am certain that it will not be one you will repeat.
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