gapping boards laterally?

[wkf94025]

In our first few thousand board feet of 1x8 and 1x6 redwood, we rookies stacked, stickered and strapped the load with every board on the same layer abutted tightly to it's neighboring boards.  No lateral gaps.  1" tall stickers.  As I learn more about air flow, and instrument the bake of that load in process, I am realizing that my current airflow is way below ideal, in several aspects.  On our next load, also 1x8 and 1x6 redwood, we are gapping 1/2" between all boards laterally.  We are also not cramming the kiln to the hilt, for several reasons:  better access around the edges for placing sensors, recirc fans, DH appliances, and also to reduce the 13:1 ratio of the last load (bf : glazing_SF) to something closer to 10:1.  Curious if veterans / experts gap their boards laterally, or pack them tight?   Or perhaps it doesn't make a difference?  This next load should provide some good data.

I was pleased to find that the next load MC, based on a couple months air dry under tarp, with ends open, is generally in the 17%-18% range.  Current load in the oven was more like 30%+ when it went in.  

Fun with science.  And math.

[wkf94025]

Anyone?  Do you gap your boards laterally or stack them tight?  Or does it not make a difference in terms of quality air flow?

[beenthere]

Gaps between boards in a layer will be hard to avoid. I'd suspect gaps lead to some disruption of air flow, and also takes up more kiln space. Catch 22.
Drying will lead to wider gaps when the boards shrink in width.

I'd butt them edge to edge and distribute any gaps that result from maintaining the outside boards to end up with straight edges to the stack.

[petefrom bearswamp]

I seem to remember DR Gene posting about this some time ago.
If memory serves, in the old days of hand stacking and handling the piles would be as wide as 8' and the recommendation was spacing the boards, but with 4' pile tight stacking was OK

[Ljohnsaw]

My stickers are 42" long and either made from some 2"x2" material that I routed a grove to make them an H profile or 1"x2" stock from side wood.  I space them at 24" because my wall block give me a convenient reference.  I have less than optimal air flow so I don't crowd the boards together while maintaining a full 42" wide pack.  Anywhere from ¼" up to 1"+.  I just air dry which works well for my cedar and Ponderosa pine in the low humidity of Northern California.  I've given up on red and white fir.  It does whatever it want to do - usually twist.


 

 

[Crusarius]

Since I saw for myself and optimum yield I always have 1 live edge on my boards since I make a 3 sided cant and then boards from that. That little extra wood can come in handy sometimes.

[Don P]

I would have more biomass between boards than in the wood if I stacked against a block wall here  :D.

I don't worry about it. I usually stack 3' wide because anything here can pick up that width and make the bottom that width tight. Then I just try to roughly maintain pile width and quickly distribute any gaps that happen by tipping a board or two up and making them slide over.

[WDH]

All my drying pallets are 4 feet wide.  I never worry about gaps between the boards. If your stacks are wider than 4 feet, expect sticker stain and gray stain in light colored hardwoods like maple and yellow poplar unless you have a hurricane for air flow.  Southern yellow pine is more forgiving but it will blue with stagnant air in our brutally humid summers.   

[longtime lurker]

I was always taught that lateral gaps were to be avoided as much as possible because they create airflow issues in kiln. The only time I deliberately stack in lateral gaps is when air drying squares or other large end sections

[moodnacreek]

I am air dry only. In the case of boards I want them strapped tight as if they where clamped , end stickers all the way out, even overhung. Air flow through the side of the pile is the thing. On squares I drop T shaped sticks in between to space both ways. I think in the old time kiln drying heat rose from the floor so they spaced out a chimney in the stack.

[longtime lurker]

I am air dry only. In the case of boards I want them strapped tight as if they where clamped , end stickers all the way out, even overhung. Air flow through the side of the pile is the thing. On squares I drop T shaped sticks in between to space both ways. I think in the old time kiln drying heat rose from the floor so they spaced out a chimney in the stack.

Yeah there is that too.... lateral space between boards means you can't strap the pack tight and that's going to get messy when you start lifting them around. I'd never thought about having T shaped sticks for the squares... simple idea and it'll save me some swearing so thanks for that.

[GeneWengert-WoodDoc]

Gaps in narrow loads will not change drying much, if at all.  Gaps for lumber that will be air dried AND in packs over six feet wide will allow vertical air movement within the pile.  Internal air movement in a wide pile is usually poor.  The spacing problem is worse with softwood lumber, as they are uniform in width.  Hardwoods, being random width have quite a few natural, unavoidable gaps.

An air yard in a rat.her windy location does not need gaps between lumber.

You can defeat gaps if there is not a large open area at the bottom of the stack to allow the cool, moist air to escape.

Lumber going directly into a kiln needs no gaps.  Gaps are a negative as they reduce kiln capacity.  On the other hand, we do want about a 4" gap between piles, edge to edge.

[wkf94025]

Thanks Gene.  Very helpful.  Our next load of 1x8 redwood is stacked with 1" gaps laterally, and yes, we lose kiln capacity as a result.  For 1x or 2x softwoods (Doug Fir and Redwood), sounds like air dry setup would be good to have modest lateral gaps, though at the eventual expense of kiln capacity, as I'm not going to restack between end of air dry and beginning of kiln dry.  On the other hand, if coming off mill and straight into the kiln, no lateral gaps in the banded stack.  Sound right?

[GeneWengert-WoodDoc]

Sounds good.  Gaps help with low velocity at high MCs...air drying with packs over six feet wide.  In the kiln, the fans move so much air that gaps reduce capacity, as you noted, but do not help drying.  A gap for something like a 2x2 will help, as you will have twice as much surface area.  In fact, you may end up drying twice as fast, which could damage some species.  So, with hardwood squares, no gaps are important.  Pine is very forgiving.

[scsmith42]

Gene has addressed the gap question. With respect to load size in the kiln, when drying from green I prefer to size my load to the maximum load that  the kim will dry. 

As an example, if I put 4000 bd ft of 4/4 green wo in my L200, as long as the temperature stays within norms, I don't have to worry about it drying too quickly.

However, if I load only 2k bd ft of the same material, I have to be more careful with my management throughout the first 2/3 of the drying cycle.

I like the failsafe that the max load sizing provides.