Drying wood

[koenbro]

I am looking to buy freshly cut walnut or maple and was told by a vendor that it is possible to accelerate the drying process using a "solar kiln" (I am in Arizona btw). Not sure what to think of this, so here it goes.

Seal the ends with latex paint, wrap the slabs in transparent painter's plastic, allow drainage through two holes at the bottom, and lay the wrapped wood on the ground over some 2x4s. In 6 weeks the wood is allegedly dry.

I just wonder what the Fog hive mind thinks of this. 

 

[HarveyWildes]

A true solar kiln gives you a high degree of control over the temperature, and then you need to dry the wood according to standard drying schedules to avoid ruining it.

You're in Arizona where the relative humidity is low to begin with.  I would just sticker it, strap it (ratcheting straps every 2-3 feet), and put something over the top to keep the direct sun and rain off.  That works well for me in Colorado, and my 2" planks are dry to about 6-8% MC after a year - about the same as commercially bought hardwood in my shop after a couple of weeks.  I usually have some end checking and minimal twist, cupping, or bowing.  I normally get 1 1/2 to 1 1/4 inch thick boards out of rough planks that start out at 2" thick, over 8 feet.  You probably could do better than that if you built a true solar kiln.

I'd be leery of a total plastic wrap because it will heat the wood under direct sun during the day and then it will cool at night.  If you open it up more, then you end up with my solution, but I prefer tarps that breath a bit more to plastic.  Also, put plastic under the 2x4s that your wood is resting on so that ground moisture (such as there is in Arizona) doesn't affect the bottom layers - make sure all plastic/tarp layers drain, and make sure that none of the wood you are drying is in direct contact with moisture.

The latex paint will help, but I haven't found anything that totally eliminates end-checking.

 

[aloysius]

Sound like an ideal recipe for mouldy wood to me.  Excess heat & humidity will irreparably damage your timber.  Sealing the ends is always wise:  hardwood vessels are tubular, with sideways connecting rays.  Think of a bunch of drinking straws bound together.  Sealing the ends of the "straws" will even out the overall moisture loss along the planks' length whilst minimising end checking.

The surefire way to correctly season timber - in my opinion the ONLY way to do it reliably & safely - is airdrying in a low humidity environment.  If your accommodation (& your wife/family) will allow, then your planks need sticking & stacking under weight.  Sticks should be at about 300-450mm intervals, including & especially close to the ends between planks, & immediately perpendicular to each other vertically through the "stack".  The stack should have sealed ends, be elevated off the floor or ground (sticks will suffice for the former) & located in a dry, cool site with reasonable air circulation.

Some likely places are behind a sofa, under stairs, a spare room, under a carport (climate dependent) or in a shed or garage.  Allow 6-12 months per inch of thickness (humidity dependent) & check with a meter.

The stack should be straight sided, even with perpendicular rows of sticks.  I prefer to have one "straight" end as opposed to staggered ends of diminishing length.  The final "must do" is to weight the top of the stack well & evenly, centred around the rows of rack sticks.

If the stack is huge, & must be located in the weather the same rules apply, except that the ends of the stack must be weather protected from the wet/dry cycle, & sited to allow adequate cross ventilation THROUGH the stack.  It should be well elevated (CCA sleepers work well) to protect from rising damp & splash.  A water & windproof cover protects from whetting & warpage of the top layer/s.  Hope this helps.

 

[Rob-GB]

Drying too fast can cause what is known as "case hardening" where the cells of the timber collapse and make it useless.
Rule of thumb for temperate regions is one year per inch of board thickness for air drying. Given your location you may need to research kiln drying, which also takes time when done right.
Effectively shrink wrapping wet timber and letting it out to bake in the sun is a bad idea even with a couple of holes in the bottom as the perspiration will hit the top layer of plastic and drip back onto the wood.
For an example of this look at transpiration of living trees as a water source in a survival situation, the bag is left loose to let water drain to lowest point for collection. sample vid below



Don't seem to be able to embed the vid.
Painting the ends helps prevent end shakes occurring as the end grain will lose moisture at a higher rate than the long facets of the timber.

Rob.

 

[dltflt]

You might try calling Todd Langford at (520)561-0284. He is in the Peoria area and has two kilns plus he has an awesome selection of live edge slabs.