Hi all,
I am in Indonesia, pretty much on the equator. It’s very hot and humid all year. We are currently chainsaw milling an absolutely huge windfall mango tree. Slabs are 3 in thick. We have the ends sealed and slabs air drying in a-frames. (The wood is amazing)
My question is about further drying requirements. This wood or the furniture I make from it is not for export, and will end up being used here or by nearby friends etc. So it’s never going to end up in a dry climate, or a heated home.
Does this mean I don’t need to think about kiln drying? Air dried MC bottoms out at about 12%. Even for tables I made 5 years ago, which seem fairly stable and don’t seem to expand or contract noticeably any more.
I’m pretty sure I already know the answer, it’s just I may end up selling some tables, and don’t want people to come back in a year with an ugly mess.
Thanks in advance.
Replies
You can just let it air dry. It's just going to take a while. The rule of thumb repeated most often is one year for every inch of thickness.
In a place as warm and sunny as yours, it likely would not be hard to put together an economical solar kiln if you do not have the time to let them air dry and have the space etc.
I do have the time to air dry, but will perhaps look into a solar kiln in a few months. If nothing else it might be a fun project.
The goal in drying wood is to get it to approximately the level of moisture content it will have in its long term, in-use environment. Here in the US, folks generally use kiln-drying to take it down from air-dried (~12%) to 6-8%, which is what it will be at inside a house that is heated in the winter and air-conditioned in the summer. (Desert areas may have different values.) If your slabs will be used in homes that mimic the outdoor environment, you only need to air dry the slabs till they are at a stable moisture content (including the inner areas.)
I don't recommend kiln drying thick slabs to hurry the process, unless you really know what you are doing (which your questions indicate you don't. No disrespect; I wouldn't put those slabs in a dry kiln either, because I don't have lots of experience kiln drying less valuable thick slabs.) In fact, you need to be a bit careful air drying them. Keep them out of direct sunlight, as that can cause surface checks. I assume you have stickered them to allow air on all sides. Coating the ends was an important first step.
If the drying proceeds too quickly, the two most likely defects will be either surface checking, or worse, what is called honey-combing. This looks like lens shaped cracks inside the wood, that are only visible when you cut into it. They occur when the outside of the wood dries quickly, compressing the interior of the wood past its point of elasticity (so the compression is permanent, and can't spring back later.) Then when the interior of the wood dries, it shrinks and cracks. I have just had to deal with this issue on a 10/4 oak slab that I wanted to use for a wedding kneeler for a church. The 10/4 x 10" x 9' slab was useless. The cracks appear in random places in the interior.
The "1 year per inch" rule of thumb is likely for places like the US and western Europe. Observations have shown that air drying proceeds most quickly in the spring and fall, and almost not at all in the humid winters and summers. Your drying time will likely vary from that "half a year of drying time per year" situation, but I can't predict how. A good moisture meter (with long pins that are insulated except at the tips, for driving into the center of the wood) will be your best friend.
Take your time, and enjoy the beautiful wood.
Harvey
Thanks so much for this. No disrespect was received! I'm a hobby woodworker who happens to have a huge tree fall over on my land, and very little knowledge of how to properly dry it. The locals don't stack slabs with stickers they stack upright in a-frames, which I'm currently doing, with a makeshift tarp roof to keep rain and direct sunlight off. I am in no hurry to use the wood, but I may look into a simple solar kiln in 6 months or so from now. Transporting to the nearest proper/commercial kiln would be unfeasibly expensive I feel. There is a hell of a lot of wood. Many thanks again
Ok, this is going to take a long time to dry to 12%. The 1" per year rule of thumber is for lumber in the 1 to 2" thickness range. A timber-sized piece like you have, with the ends sealed, is going to take a lot longer... in 3 years, I bet those centers are near the same moisture as they are today.
I would say why are you keeping them at 3" slabs? Thinner would make drying faster.
I would also say - GET THE HEARTS OUT of these pieces - that is the part that is going to check on you. Produce as much free of heart lumber as possible.
The solar kiln idea is good. Still will take a long time but will speed up considerable. Honestly however, I would not stick them in there day one; let them air dry as long as possible.
Do NOT dry them in the sun. Do not try and use direct sun to speed up the process. It will check badly. Get these things OFF the ground - higher off the ground = better. Keep air circulating - natural wind good. Use lots of stickers between the slabs. These things are thick enough that they are unlike to warp that much, at least if the grain is fairly straight - which is one good thing of thickness.
Finally, different tree species dry differently. For example, pine = easy, not a problem. Hickory = very challenging to keep it from warping/checking/destroying itself. I have no idea on how easy or hard mango is too dry. Here is a bit on the wood, might be helpful to you: https://www.wood-database.com/mango/
Drying timber is a real art form. Done well product is amazing. Best of luck.
Any pictures of these slabs would be appreciated!
Thanks very much. We are milling some thinner slabs which will be used for flooring. I run a little eco beach resort and plan to make a bungalow exclusively from mango wood.
Here's one photo, which doesn't really do it justice. There's so many colours in there.
Yes, you do know the answer.
"Here in the US, folks generally use kiln-drying to take it down from air-dried (~12%) to 6-8%, which is what it will be at inside a house that is heated in the winter and air-conditioned in the summer."
This isn't really true unless maybe you live in AZ desert. No house is ever going to get that low in humidity.
The main purposes of kiln drying is to rapidly bring the MC down and to kill insects.
All that said, we shoot for 8% b/c the would is most stable at or below 10%. Once it gets in a house, it adapts to that environment, which is in the 30-60% range depending on where you live.
Many thanks. Yes killing insects is another reason I'm asking about kilns. I'm not sure a solar kiln would do this though?
We spend 4-5 months here in the North East where the equilibrium moisture will be around 6% in the winter with the heating and 8% in the summer with air conditioning. When I lived in the southeast US, 10% was a good number year round.
Many thanks. Seems EMC here is roughly 13, with little seasonal variation.
The EMC of the wood and the RH of the home, work in concert with one another, but are two different values.
Also, many tropical wood species have a lower FSP than the typical 30% used in most calculations here in the states. This is the level where the wood is considered stable.
This article might help some people better understand
https://www.wagnermeters.com/moisture-meters/wood-info/what-is-equilibrium-moisture-content/
Thanks so much for this, and for the link. It's complicated stuff! Fortunately people here don't heat or cool their homes, except for electric fans. So the outside and inside temps and humidity are very similar.
Ian Bishop,
I live in Hawaii and do a fair amount of mango (among other tropical hardwoods). Mango is a beautiful wood after it stops producing the fruit and starts making the dark heartwoods. I am currently working on one that is black and orange. Very stunning. As for drying, one of Mango’s advantages I have found is that it does not require kiln drying or a below 12% moisture content prior to working. This is great as it makes turning the wood into furniture much easier. The one issue with mango I have found is that the bugs absolutely love it. Termites (subterranean and dry wood) and the powder post beetle here will bore 1/4 inch thick holes entirely through it, not just the areas near the cambium and softer wood. They do this so aggressively that I often choose to stay away from mango unless I come across a rare find such as the one you have in your photos. The only way I have found to keep them away is to spray with borate and or put inside a walk-in freezer to kill them. If your furniture is staying in Indo then you can rest assured that the moisture content loss will not be a huge issue in the future. Be sure to utilize the tight grain as mangos cross section has no visible grain, beautiful patterns emerge when making curves and other shapes that include end grain. You can also make spalted mango which is beautiful, by leaving some half logs in the rain to start and decay. Rip them open with a chainsaw when the ends start to split, and you surely think they are ruined. You will find beautiful spalting and if treated with borate, no bugs.