double stickering suggested in an article.???

[tomsteve]

hey all. im more of a lurker here that just loves seeing all tbe work ya'll do. would love myself to be able to get into some hobby milling but thats not possible, but ya'll make up for that!
anyways, i was reading an article from wood magazine on air drying and tbe author says this:

At Anderson-Tully, Robert takes extra precaution so the green boards won't degrade in the drying process. "We dip them in an anti-stain sealer, and then put them on stickers [strips of wood that separate the board layers]," he says. "And we seal the ends."
Home woodworkers can do practically the same thing, notes Robert. "Paint the ends of all boards with latex paint [or a commercial sealant such as Sealtite 60 or Mobilicer-M]. Or, put double side-by-side stickers under them. The check won't go past that second stick.

my question is on the last 2 sentences.
does double stickering really help prevent checking and if so,how?

[Ianab]

Possibly...

What you are trying to do is slow the drying of the end few inches of each board.

End grain wood dries about 10X faster than side grain. So if you do nothing it's likely the end 6" of the board will dry out much faster than the rest of the board. As it dries it shrinks. So now you have the end of the board 5% smaller then the rest of the still green wood. Physics says you can't have that, so a crack opens up to allow for the difference.

Putting the stickers at the very end of the board helps slow the drying in that area, along with the end coating. So I can see the idea of having a wider (or 2) sticker slowing it even more.

It might also be overkill, and be extra work for little added benefit.

[Greyhound]

my question is on the last 2 sentences.
does double stickering really help prevent checking and if so,how?

Total rubbish.  It will absolutely crack as far is it needs to to release the tension and stickers provide no lateral resistence.  Seal the ends asap and sticker out to the very end of the boards.  If the wood cracks after that treatment, it "needed" to release the internal tension anyway.

[GeneWengert-WoodDoc]

It sounds like there is some disagreement in the previous postings, but they are talking about two different things.  That is, we have two types of end checks: 

1)Those caused by the drying and shrinking of the ends of the lumber faster than the wood further back from the ends.  The first two posters (Tomsteve and Ianab) are referring to these drying caused end checks or splits.

2)Those caused by stress within the tree and log that with a little shrinkage exceeds the strength of the wood.  These, which Greyhound is referring to, are not drying end splits, but are growth-stress, end splits.  These growth-stress, end splits are next to impossible to control with end coating, double stickers or other miscellaneous techniques.  Generally, these growth stress checks and splits will be wider than 1/4" after drying and may extend several feet along the board (mostly internally), and will worsen during planing.  In North America, eastern white pine, cottonwood and yellow poplar have this issue sometimes;  non-NA wood, eucalyptus has the issue much worse than NA species.

Drying end checks can be controlled buy limiting the drying on the end, which in turn limits the shrinkage and therefore limits stress development.

Many of the drying checks on the ends of a piece of lumber will go back to the first sticker.  This is well known.  Checks or splits that go further are tension created splits (growth stress) and not due to drying.  So, one or two stickers placed close to the ends of a pile will seem to control drying end checks somewhat.  However, any technique that slows the end drying will work even better.  Latex paints pass too much water to be very effective.  The commercial coatings (UC Coating's Anchorseal, Sealtite 60, Mobilcer-M, roofing sealer, etc.), if put on thick enough, do slow drying and do an excellent job of controlling all drying related end splits.  Sometimes for squares, paraffin wax will be used.  One property that the coating should have is that it either must get really hard or it must evaporate when the kiln goes over 130 F or so.  We do not want the coating residue to enter the manufacturing plant, so if it hasn't evaporated in drying, it needs to be cut off after drying

In my many visits to sawmills, probably half do not put the coating on thick enough for it to do to its job perfectly  A thick enough coating put on fresh ends will eliminate 99% of all drying related end checks at a cost of about $4 per MBF.  Some of the coatings can be sprayed on, which is really a plus for fast and good applications.  (Warming:  Do not park a blue pickup nearby when the wind is blowing and they are using orange Anchorseal end coating.  Two runs through the car wash using the "super wash cycle" cleaned it off.)  Probably 90% of the mills end coating their lumber use Anchorseal I or II; it can be sprayed or brushed and it has an antifreeze.  It is probably obvious that the ends must be fresh ends, as a coating will not stop preexisting checks.  Also, snow or ice on the ends will stop the coating from attaching to the wood under the snow or ice, so the coating does little good.

With two sticks at the end of the lumber, the check will not go past the second stick (about 4"), at least on the surface; we see this often.  However, most drying end checks do not go much further than that anyway, at least visible surface checks.  So, double sticker is very rare to see...an extra sticker that does very little good.  (The same thing if you put a second sticker at 12" in...the check will not go more than 4" and will never go past the second stick.)

But here is the problem...if a stack has stickers right at the end and then a lift picks up the stack and moves it, but hits a little bump or if the forks are too close together so the pile sags when lifting, the end stickers will fall out from time to time.  So, very few mills will stack with a sticker right at the end of the lumber; rather they put the sticker a few inches inward.  In this case, they will see that the single sticker, which is about 3 to 4" back, stops end checking from going any further.

So, in answer to the OP, if you want to control end checking related to drying, use a commercial, properly applied, end coating.  DO not use the stickers to try to prevent drying related end checking.

Incidentally, they do not dip the board in an anti-stain sealer; it is a fungicide chemical that prevents most fungal blue stain, but it does not do any sealing at all.  Some of the chemicals have optical brighteners too.  Very few control surface mold fungi or mildew fungi.  Some used to have insecticides, but not so often today.

[tomsteve]

that was very informative,gene. thank you greatly for your time!