Tips for seasoning wood

[Joe Fabbri]

Hi everyone,

This is my first time seasoning green wood. It's for my bench project, which seems far off at the moment, but I have to start somewhere. The wood came from a birch tree that came down during the winter. I suppose that's beneficial, as it will be slightly on the dryer side. But I hewed the logs, and split them in half. The ends have already been painted with multiple coats of latex paint. Some ends got an epoxy floor paint coating--but for others I just used the latex.

Anyway, right now the slabs are sitting in my unheated garage, propped up on some 4x4s. I was looking at the slabs the other day, and I noticed that on one or two pieces I'm getting some stress cracks/checks. It's not from the end's drying out, I don't think. I think what's happening is that when I hewed the logs, I naturally squared some of the logs' bows. So the pith is probably still in that section. This section also has a fair amount of knots.

My plan was to rough out the slabs into my leg and stretcher pieces, cutting out these checked areas (since there's a lot of knots anyway), in hopes that the checking doesn't travel across the board. Then, I'd sticker these pieces individually. Does this sound like a good idea? I'm not sure, though, if it's best to let the boards sticker in as long of pieces as possible to minimize bows or twists?

Also, are there any tricks to minimize cupping, so I can save as much thickness of wood as possible (I'm thinking of my bench top here specifically). If the cupping happens mainly because the outer layers of the wood are drying faster, would it be a good idea to keep the bark side close if not on the concrete floor for some time, so the drying is balanced out? Or is there really no way to slow down or avoid the outer layers from drying faster?

Any help is advice is appreciated.

Thanks,

Joe

[Joe Fabbri]

No wood dryers on here? Come on, I know there must be one or two, haha.

My main question is would it be better to cut the green slab into leg and stretcher sections, leaving a few inches longer to allow for checking, or to leave the slabs whole and cut it up when it's dry? I don't want the stress and cracks in some parts of the slab to travel throughout and potentially ruin the whole piece, so I'm leaning to cutting it up roughly now.

Joe

[Rob Fisher]

I am no wood drying expert. But my general understanding is that the smaller the pieces, the quicker they will dry. Also the smaller the pieces, the less stress they should have and therefore less checking. Professional wood driers often weight down stacks of wood they are drying in an attempt to help prevent excessive movement. Also I would get rid of the pith ASAP. It's going to move and is generally the least stable bit of the log.

[Gary Herrmann]

When you say you split the logs in half - did you remove the pith? Do that if you haven't. Pith being in the wood will promote cracking.

I'd also recommend you cut them a bit oversize of final desired thickness, rather than leaving them in log form. They'll dry faster and will be easier to cut to size now. If you want 16/4 ready to work wood, cut them around 18-20/4 - depending on species. That will give you room for movement and final jointing/planing.

Stack and sticker them. Put a sheet of plywood on top and put weight on the plywood to prevent cupping. The usual rule of thumb is 1 year per inch to dry plus 1. Which means 20/4 could take up to 6 years to dry - but the thicker the wood, the harder it gets to predict. I've dried 8/4 and it took between 2 and 3 years to be furniture dry.

Maybe look into building a electrically powered or solar powered kiln. I've been meaning to do the same.

Not an expert, but have done this some and want to make my own kiln.


Gary

[Tony Shea]

Weighting them down may help things out. I would not suggest laying a face directly on the concrete floor, always have an equal amount of air flow above and below each peice. Air drying can be tough and sometimes disheartening. There are some trees that just will not cooperate no matter what precausions you've taken. I also agree that the pith needs to be taken out or that board will most likely not survive the long proccess.

[Joe Fabbri]

Thanks for all the advice.

I'm going to make sure there's no pith remaining, and I'll cut the legs and stretchers out of the slabs before I let it dry.

I was curious, though, if there's anything that can be applied to the slabs that would balance out the drying or make sure it doesn't take place too rapidly. I've coated the ends with many coats of latex paint, but other than that, I wonder if it would pay to coat the bark side with anything, or the bark side at the ends of the boards, to balance the drying with the center? I read somewhere about creating a mixture of salt, water, borax (for fungal growth, I guess), and some other stuff and applying it onto the wood.

The reason I'm thinking of such measures is the size of the slabs I have right now are pretty close to the dimensions (thickness mainly) that I'm hoping to end up with. For instance the slabs I intend to use for my top are around 3 3/4" to 4" thick, and I'd like to end up with a top that's around 3 1/4 - 3 1/2". I know that might be very hard to accomplish, but I'd be willing to slow the drying time down in order to try to keep more of the wood.

Has anyone successfully done anything along these lines?

Joe

[Prashun Patel]

Wax is usually a better choice than latex paint. You can wax the ends and the face if you wish, but this will slow down the drying process.

I dry a decent amount of green wood for turning, and I've found that storing split-prone wood in plastic bags or packed in shavings helps regulate the loss (in your case a tarp might work as well). I've found it necessary, though, to take things out of the bag every few days to allow air exchange and to avoid mold. As the wood matures, you can take it out the bag altogether.

Also, to the extent that you can take the blanks to the basement, do. High airflow and big temp differentials are a killer.

[Izzy Camire]

I have a ssawmill so I dry wood regularly.
I would break down the pieces as small as you can. I would also support them every 24" maximum.

[Joe Fabbri]

Prashun,

I've tried wax on some smaller cut-offs (which might become planes one day), and I can't get the wax to stick very well. I melted it and tried pouring some on (as the pieces were a little too big to dip them), but it ran all over the place. Then I tried taking a small brush and brushing the liquid wax. Some areas stuck, but a lot pealed right off from moving the pieces around. Maybe I'm doing something wrong, I don't know.

The wood is black birch, and I don't think it's very prone to cracking. In fact, it's very difficult to split with axes/wedges. Right now, they are in my garage, which isn't opened too often. I have the pieces close to each other, so I think the airflow is minimal. These pieces are 8 1/2' or so, which means trying to bring them into the basement, through the window would be tough. I'm not sure what to do when the warm weather comes around, though. Maybe I'll try a tarp on it, or at least wrap the ends in something to even out the drying somewhat.

The base of the tree has some spalting in the sapwood, as the tree had a rot spot at the base. The rotted area was cut out, but some spalting remains, so I have to be careful about trying to dry some pieces too slowly.

[Joe Fabbri]

Izzy, what's a good height for the spacers? And, to weight the top, would a bunch of bricks spaced every couple of feet work?

Joe

[Charlie MacGregor]

Joe,
For end coating: http://www.uccoatings.com/products/anchorseal As others have said get the pith out and more weight is better. Every species has an optimal rate for drying. Also the rate will change depending on current moisture content of the wood at the time.


Regards,
Charlie

[Scott T Smith]

Joe, regarding your original question, take a few minutes to read a post that I made a while back. Start with response #6 on this thread:

http://www.sawmillcreek.org/showthread.php?180522-Air-drying-vs-kiln-this-wood-I-bought-yesterday

That will help provide you with some background on drying wood.

Many of the ideas that you have mentioned in your posts are not the best ones to use when it comes to drying lumber. Do not tarp your lumber, nor should you dry it in an enclosed area w/o airflow. What part of the country are you in? What is your expected average outdoor temperatures and RH% for the next 120 days? Most likely you should stack and sticker the lumber outside where the prevailing winds can flow through the stack. Your targeted daily MC% reduction will be around .5% - .75% for a 4" birch slab.

Stickers should be between 3/4" to 1" thick, and made of dry lumber. The closer spaced that they are, the better chance you will have of ending up with flat slabs. I would suggest that you shoot for 16" - 18", no more than 24".

The best product to use on the ends of the slabs is a commercial end sealer, such as Anchor Seal Classic or Baileys End Sealer. A 5 gallon pail of either will set you back around $80.00

Typical weight to use on a stack of lumber is 250PSF. So, if you have 24" x 96" of stacked and stickered slabs to weight down, you need to come up with 4000 lbs of weight to place on top of the stack if you expect to yield any benefit from the weight. Some folks have successfully used ratchet straps, tightening down the straps a click or so every week.

Scott

[Joe Fabbri]

Hi Scott,

Thanks for the link to that old thread. I'm glad you chimed in here.

I live in Long Island NY. The tree fell down in the winter, sometime in January. I spent a few weeks off and on hewing the log sections. During that time, they remained outside, and it rained and snowed mildly occasionally and was pretty cold. I didn't seal the ends right away as I should have (though I did pile some leaves up against the log ends until I could get to hewing them). So I got some end grain checking. I did wind up freshly cutting some of the ends, though (about a foot in).

Then, I brought the beams to my unheated garage and sealed the ends with multiple coats of latex paint. Then a week or so later, I split the beams in half. I then left them sitting on 4x4s in the garage, occasionally repainting the ends of the slabs. Right now, it's been cold and raining a lot outside. I expect the temperatures to remain in the 40s and 50s for a while. The garage is fairly large, so it's not in a cramped space, but would you say move them outside nevertheless?

On another note, just the other day I cut down a cherry tree that broke it's top last year. I painted the ends of the log right away, and the next day I hewed it. It sat outside in the rain for the past few days. I figured that until I can get to sawing it in half it would be better to keep it on the wetter side. Would you say that this was a good thing to do initially?

Joe

[Scott T Smith]

Joe, in general it is not a good idea for drying wood to become rewetted. The exception is if the wood is still very green, which it sounds like yours is.

I would suggest moving your wood outside so that it can start drying. Stack and sticker it where it can get some air flow. Cover the top of the stack to prevent rain from going inside the stack, but leave the sides exposed.

You took the right tract by cutting off the old, split ends and starting fresh. End checks are similar to cracks in glass - once the crack starts it tends to keep growing. The best option is to prevent the crack from starting in the first place.

Because of the relatively slow drying rate that you need to achieve for your planks, you will probably get some minor surface checking. There is not much that you can do to prevent it unless you can put the planks in an environment where you can control the RH% for the next 10 weeks. That's probably a long shot...

[David Keller NC]

To echo some of Scott's comments:

You want to air-dry green wood s-l-o-w-l-y. The stress cracks happen because of the moisture gradient in the wood between the wet inside and drier surfaces. That's why you don't want to dry the wood inside - indoor relative humidities are almost universally much lower than outdoors, so the outside will dry much more quickly that it would outside (out of the sun, obviously!). This is generally true even in an unheated space.

One other tip - if you stack wood over a bare concrete floor, even with stickers between the floor and the wood, there's going to be a good deal more humidity under the stack than on the outside, which leads to those moisture gradients and checking. This is true even if the concrete floor looks and feels dry. If you want it inside because of space limitations or code issues, you'd be best served to put down a layer of thick painter's plastic sheeting on the floor, then put your stickers over that, and the lumber stack on the stickers.

[Joe Fabbri]

Thanks Scott and David for the information.

One of the reasons I put the wood inside right when I got it was to be able to work on it, as it was freezing outside at the time. But also, I figured that the less air flow inside would be more beneficial initially than leaving it outside, where strong winds would dry it faster. But, I guess the more humidity outside would be better.

Regarding the concrete floor, my intention was to try to balance the drying of the bark side of the wood with that of the center. I figured that would help prevent the bark side from drying out too quickly compared to the center of the tree. Or do you think the dampness caused by the concrete would nevertheless outweigh the faster drying of the bark side of the wood?

Either way, I will be bringing it outside as soon as I can. I still have to flatten the boards out, as they are rough still from cutting them in half. One other question I have, though, is what's the best approach with boards with sides that aren't parallel or only have one flat side? Since the wood was hewed, rather than sawn, I was thinking of only flattening the tops and leaving the bottom somewhat rough, and only truing the joint areas later. Since I'm dealing with only a few large slabs, could I put the flat side down and dry the slabs individually, rather than stacked? Other than weighing it down, which I could do individually, is there any benefit of actually stacking them?

Joe

[Scott T Smith]

Benefits of stacking are 1 - weight, and 2 - the narrow gaps between the layers keeps too much air from flowing past the wood, and thus potentially over-drying the surface. With thicker slabs and your need for a relatively slow drying rate, you need to manage this closely.

You don't want your wood to dry from the bark side to the pith side - you want it to dry from the face side of each board / plank.

Wood will dry more quickly (and check less) if the surface is smooth, so if you smooth one side and leave the other side rough, you will experience uneven drying.

Unless your planks are quartersawn, you will experience some movement as it dries; thus if you flatten it green you will need to go back and flatten it a second time after it has dried.

On large slabs / planks, the use of a router sled is a great way to flatten large areas rather quickly. I recall that a recent issue of FWW had a great article about it.

[David Keller NC]

Joe - I wouldn't get too paralyzed by analysis here. There are certainly some "do's and don'ts" when it comes to air-drying wood, but some degree of checking and warping are unavoidable. The key items are, as Scott has noted:

1) Stack and sticker the pile - this is essential. With no weight on the slabs, they will more freely, which you don't want.

2) Do the initial drying from dead-green to somewhat dry outside.

3) Keep the stack out of the sun and strong winds. There are many articles and many methods on the web about how to do this.

4) Put a ground cloth down under the stack (whether actual ground or grade-level concrete) to prevent large moisture gradients.

5) Be patient. Most hardwoods take about a year for every inch of thickness. Softwoods will dry faster.

[Joe Fabbri]

Scott, David, thanks for the tips, I appreciate them.

Scott, that's a good point about the uneven drying on the rough side of the wood. I didn't think about that. So, I'll smooth out the hewing decently. I won't remove all the chops/gouges, but I'll try to get a good part of it smooth.

If I still do decided to dry the slabs individually, I'll make sure that there isn't a lot of surface area exposed that would allow it to dry too quickly. And of course I'll weight it down as much as I can.

Scott, to insure that the slabs dry from the face side, it woud be a good idea to stack or dry the slabs with the bark side down, and the face more exposed to the air, right?

Joe

[Scott T Smith]

Scott, David, thanks for the tips, I appreciate them.

Scott, to insure that the slabs dry from the face side, it woud be a good idea to stack or dry the slabs with the bark side down, and the face more exposed to the air, right?

Joe

Joe, "bark side" is one of those terms that can have multiple meanings. When referring to the potential of flat sawn lumber to cup while drying, "Bark Side" referrs to one face of the board - even though it does not have bark on it.

When referring to "live edge" slabs/boards, "Bark Side" refers to the live edge side.

When air drying lumber out of doors, if I am worrying about cupping I prefer to stack the boards "bark side down" which means that when viewed from the end the growth rings create little "smiles". Lumber tends to cup towards the bark (the growth rings try to straighten out), so by placing the boards face side down it creates a little "hump" on top of the boards, which allows them to shed water if they get wet. If you go bark face up, then the cup will retain water, and you'll have degrade in your lumber.

With quarter and rift sawn lumber, growth ring orientation is a non issue. Also, when air drying inside a large shed, the bark orientation of the board is a non-issue.

In drying terms, a board has two faces, two edges, and two ends. Using a 2" x 12" x 10' board as an example, the faces are the 12" wide portions of the board. You want to dry lumber from the faces, not the ends or the edges, which is why you put end sealer on the ends of the boards. Thus, the boards are stacked and stickered so that air can flow through the stacks and wick the moisture away from the faces of the boards.

[Joe Fabbri]

Oh, okay. I didn't realize that "bark side" in rough lumber meant only the sides left with bark on it (seems simple enough!). I thought it always referred to the orientation of the growth rings in the tree.

Anyway, yes, I understand the way the ring orientation will cause a board to cup. I didn't think of it in terms of avoiding the catching of water. I was thinking in terms of allowing the boards to dry more evenly. Isn't it the faster drying of the actual bark side (not the live edge "bark-side") that causes the cupping to occur? If so, wouldn't keeping somewhat less air exposure on that side aid in even drying.

I was just curious about possible ways to avoid a lot of cupping.

Joe

[Ken Parris]

Joe, after you have done all of this and your wood is as dry as it is going to get, you may be disappointed that your top lumber has some twist and maybe a split or two that are unsightly. Remember that when you thickness your top only the top side needs to be near perfect. The bottom side might have a couple corners that are a little thinner when you get to the thickness you would like to have. I have seen several single board top benches that were this way. If the thinner corners bother you, you could put a 8/4 piece on each side either matching or contrasting wood, then the thinner corners are hidden. This would keep the thicker top that you desire. Also, if you have followed Chris S. bench builds, you know that one was built of cherry that had serious checking issues. He took care of them with black epoxy that look close to the dark streaks that cherry often has. My big Roubo bench has a couple splits because the pith is in both of the 11" wide boards that make up the top. The wood was free so I am not to concerned about the splits, they cause me no problems. I do wish I had put a couple lengthwise saw kerfs on the bottom of each piece to possible relieve the stresses. So just saying, follow all this good advice, give it your best shot, then build your bench with what you end up with. My smaller Roubo planing bench with the maple top, works no better than the big one with the pine top that has the two splits.



Ken

[Scott T Smith]

Isn't it the faster drying of the actual bark side (not the live edge "bark-side") that causes the cupping to occur? Joe


Joe, cupping occurs due to shrinkage associated with the orientation of the wood cells; all things being equal, both sides of the board typically dry at the same rate. During the drying process, cupping is the natural tendancy of flat sawn lumber.

Cellular shrinkage rates in wood occurs along two axis - tangential and radial. Tangential shrinkage rates are less than radial rhrinkage rates, which is why quartersawn lumber shrinks less in width than flat sawn lumber. Each species is different; in oak tangential shrinkage is about 1/2 the rate of radial.

Cellular alignment is different on each side of a flat sawn board, hence the different shrinkage rates. The bark side of flat sawn lumber will always shrink more than the pith side.

[Joe Fabbri]

Thanks for the information, Scott. I guess there's no real way of avoiding some degree of cupping it seems, other than perhaps a lot of weight. I thought I could manipulate the drying somehow.

It's interesting, like you've said, you practically always see cupping to some degree in boards. But I've had some exceptions. One I can think of is a piece of regular flat sawn 1x12 pine. It's very old, and was in my basement for years. It wasn't stored in any special way, just laying around (maybe leaning against a wall, I don't remember). But, the board is dead flat, with no cupping. (I'm keeping it for a possible tool chest top). Anyway, I'm curious, what for instance would keep one board flat, while almost every other similar board would be cupped in no time? This board has very tight growth rings, if that matters in terms of cupping. I can't remember exactly, but maybe it was cut directly from the center. Still wouldn't you expect it to cup with the center in it still?

[Scott T Smith]

Thanks for the information, Scott. I guess there's no real way of avoiding some degree of cupping it seems, other than perhaps a lot of weight. I thought I could manipulate the drying somehow.

It's interesting, like you've said, you practically always see cupping to some degree in boards. But I've had some exceptions. One I can think of is a piece of regular flat sawn 1x12 pine. It's very old, and was in my basement for years. It wasn't stored in any special way, just laying around (maybe leaning against a wall, I don't remember). But, the board is dead flat, with no cupping. (I'm keeping it for a possible tool chest top). Anyway, I'm curious, what for instance would keep one board flat, while almost every other similar board would be cupped in no time? This board has very tight growth rings, if that matters in terms of cupping. I can't remember exactly, but maybe it was cut directly from the center. Still wouldn't you expect it to cup with the center in it still?


Joe, if it was cut from the center the wood is quartersawn on each side of the pith. I would not expect a quartersawn board to cup, and in some species the pith does not crack.

[Roderick Gentry]

I have a big piece of beech drying in my garage right now, and it has the pith running through it, and since it was sawn there will be some grain run-out. My piece is standing on end, it's the top, though it was a few months horizontal. I covered the ends with wax emulsion, some of it is good, some of it is junk. I have had excellent results with Behr Super White int/ext latex. I do have a crack in the pith, but I will probably fill it with epoxy, or if it gets too horrible (no sign after 2 years) I will just saw an reglue.

What I normally do when flat sawing is saw right through the pith, I have a chainsaw mill so it takes a big kerf, and the result is that I get rid of a lot of pith. Then I run a circular saw kerl hald way through those boards (I mostly saw 2 inch or 1.5, and resaw later). That will basically disarm the kerf. If it is really bad I will just saw those center boards at the site. Even if you loose some of the widest pieces they are pretty much quarter sawn, and that is always valuable wood.

My other approach, particularly with 4" benchtop pieces, is to leave the kerf right in the middle, there is enough material to hold it together.

One thing that will cause checking is a heat difference. Nice dark cold garages are pretty good, but even a window casting a few hours of winter light can be too much.

If you have a good idea what pieces you will need for your bench, breaking them out will work great. Just be sure to leave a lot of material, you will tend to get a lot of drying distortion, and it will require you to do some heavy planing, so leave some room.

The general rule is that the grain lines try to straighten. The best way to hold wood flat is to cut it thick. That can cause trouble, with some species, but I have dried most of the common woods with little difficulty. So the center piece, pith and quartered wood, should stay straight, then the next piece with some riff and a tight ring at the center will dogleg, then the rest will cup a little. Stacking it well with the stickers on top of each other, and one every foot or 2, will help a lot. But basically you need to let wood be wood, you will loose a little, and have to plane a lot, but you should end up with some great wood if you aren't pushing everything beyond reason.

Oh, unless you need it, cut off any bark.