I work with a startup community forestry company in the Choco Wet Forest of Ecuador. We have recently considered expanding into the slab market, and have had splitting issues with certain species.
We have little knowledge on many of our wood properties (we're compiling data as we work with unknown trees) and I was wondering about general tips to prevent cracking. We're slabbing the logs at 8'x8"x23/8" in the woods, and cabling the slabs to a drying facility. They will be unstickered, in the forest, from two weeks to a month. The area is humid, generally 70 - 90% all year.
I have read about wax sealants and Johnson paste - is this to be applied immediately, and do you cover the slab or only apply on the ends?
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Where are the splits? We do have excellent commercial end coatings to prevent most checking and splitting (except for splits due to stress in the tree). If you are concerned about face checks and splits, then we have to slow down the drying rate so the wood does not dry so fast. This subject is covered in most texts. You can consult Drying Hardwood Lumber
What are the species giving you the most trouble? As the Doc said, you won't be able to do much about the stress cracking, but the checking due to rapid moisture loss is easy to control - except of course in some species. We have species up here that present drying challenges almost no matter what you do. Pecan and sweetgum come to mind.
Wood doesn't begin to shrink until it's reached the FSP (fiber saturation point), which for most species is roughly 30%. A month is a long time to leave them lying in the forest at 70% RH, and even at 90% if they aren't sealed at least at the ends and anywhere that figure, knots or other open grain characteristics exist, then the water will leave those areas much faster than the other parts of the wood and you'll see movement, i.e. warping/twisting/cupping/bowing/checks, etc.
Regarding the original question, the sooner you can get end coating on, the better. In fact, applying Anchorseal or similar in the woods is not a bad idea, especially with your month long storage of the slabs. Otherwise, as soon as the slabs get out of the woods, coat the ends. Of course, if in transit, the slabs are exposed to sun, high wind, and/or low humidity, you can get some face checking that will only get worse as drying continues. Try to prevent end checks and face checks from developing in the first place. Such checks will often develop within 24 hours after the surface is exposed. Once checks form on the ends, end coating is of limited value.
Appreciate the advice on the end coating. Not sure if Anchorseal is available in Ecuador, but I'll look for it or a similar product and apply it immediately after sawing, 2 to 3 inches in from the ends.
You would advise stickering the slabs/boards we process onsite? We are operating with a Peterson sawmill that we cabled in. The slabs are currently ripped by chainsaw, but we're considering the purchase of a slabber attachment. With the Peterson, it would be relatively easy to convert a low value tree to stickers.
Sun, wind and low humidity are rarities. It takes three to seven days to air-dry my socks. Which brings me to another question - how long would you suggest pre-drying our large slabs at 8' long, with a depth of 2 3/8" and a width of between 16" and 50"?
Thanks for the advice and I'll keep bothering all of you as I encounter new problems.
Incidentally, many species do cause allergic reactions (skin and nasal oftentimes), so be careful with these less common species.
If Anchorseal is not available, you could use paraffin wax, but there is a high fire risk. Some non-latex paints provide limited protection, but for thick valuable pieces, paint is not a good answer.
The wide pieces with face cracks are most likely due to the close proximity to the pith (center of the log) and perhaps some quality loss due to bacterial activity in the living tree. If it is indeed bacterial, you will notice a foul odor as well as the weakening of the wood.
Fungal staining is controlled by fast drying (which you do not have) or by chemicals designed for fungal control in freshly sawn lumber. Likewise, new insects are controlled with the same chemicals, but existing insects cannot be controlled. Hence, it is important to avoid long storage in the woods, as the insects will enter the wood and then you cannot control them and they can do quite a bit of damage internally.
Questions on any of these items?
We considered using a boro-borax solution for insect control. I've heard it easily washes off with rain. We can keep the wood covered, but it's likely to get rained on at some stage, in transit on the cables, etc. Do you have other suggestions for protecting fresh sawn lumber from insects and fungus?
Any suggestion for decreasing the chance of splitting when sawing slabs? Are staples or cleats effective in holding pieces together? As contributor T said, there will be some species that just won't work, but until we identify those I'd like to salvage what we can.
Cleats have been used with limited success.
Borate does indeed wash off in heavy rain, as might other chemicals too.
You can dry any species, but some may require a special effort or technique (such as covered shed drying). We never had success with tropical walnut. Be aware that some species have silica and quickly dull tools.
Can you find out how many kWh it uses per % MC removed?
I do wonder about the uniformity of incoming material... thick and thin, heartwood and sapwood, etc. Will a vacuum get all the material to a uniform MC? This was a problem with many kilns in the past decades.
The wood we're bringing down has bacteria and fungus. Is there something we should treat it with prior to putting it into pre-drying? Would planing it green be a good idea, or an unnecessary waste? We do not have a treatment pond - thinking of one for the future.