Replies

1. 
   ClancysBro | Mar 11, 2004 03:44am | #1

    In my experience white oak these cracks only showed up in very old lumber. 8/4 mostly. What is with that? The drying process or grain of the wood? I pay good money for this lumber and hate finding cracks after I plane a board. Is the tubular grain of white oak hardened over time PJ, I think so to. Rift sawn white oak doesn't show as much cracking or maybe it's dried differently. Fill the cracks with a well matched colored wood filler very carefully not over doing it to fill any side grain pours. Mask it off to be sure. Should blend in a little better that way. What worries me is if I have to shape white oak and run into this wild grain. White oak is like hardened tiny straws. I try to back cut my way out of it then- Prota

2. 
   AlbionWood | Mar 11, 2004 08:26pm | #2

   I get this quite often as well.  It's certainly not restricted to old wood, and I don't know that it's just a function of kiln-drying either; I think it is the nature of the wood.  We're getting relatively young, fast-grown trees which probably have a lot of internal stress, which kiln-drying probably exacerbates.  Maybe Jon can explain it scientifically?

   This problem seems much worse in thicker stock, especially 8/4 and up.

   For the lifting-rays problem on the QS faces, I keep a bottle of CA glue and accelerant handy, and just glue them back down as soon as I spot them.  Usually have to do this repeatedly, as new checks develop every few days.

   I do the same thing for open cracks on rift- or flat-sawn faces: fill them with gap-filling CA glue. 

   To prevent new cracks from opening up after everything is finished, consider using a penetrating epoxy sealer/primer, like CPE Multiprime.  Kind of a pain, but it should hold the wood together.  Especially useful on end grain, which can crack badly.

   "Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net

3. 
   jonsherryl | Mar 12, 2004 12:58am | #3

   PJ, I know it's fashionable to lay this off in the lap of poor kiln drying practices...and I'm sure it's made worse in heavier stock as a result of case hardening stresses that tend to be worse in thick material...But I think most of the blame rests with the anatomy of the wood itself.

   First of all, white oak (Quercus alba) has a very high average volumetric shrinkage, green to ovendry, of 16.3%. This is almost half again as much as a moderately stable wood such as cherry (11.5%) and more than twice as much as an exceptionally stable wood like genuine mahogany (7.8%). White oak's T/R ratio (the relationship between its tangential shrinkage of 10.5% and its radial shrinkage of 5.6%) is only 1.87 : 1, which would normally suggest a low tendency to cup or twist...But the absolute amount this wood shrinks as it dries, in combination with its rather high density, means that even when carefully dried it is bound to contain the potential for some serious stresses as it is placed in an environment with fluctuating humidity.

   White oak is futher handicapped by its ray dominated anatomy. The rays in this species are very large (thick and strong enough to be very rigid) and the ray tissue runs perpendicular to the other vessels and fibers in the wood. As wood dries, the cells shrink mostly in their radial and tangential dimensions and hardly any at all in the longitudinal dimension...so, the lignin bond between the ray tissue and the virtical vascular tissue is placed under extreme stress as a result of this diffenetial in shrinkage. Surface checks can appear anywhere as these two directionally opposed tissues fight it out, but the typical symptom on the radial surface is that the ray bands tend to lift.

   ...wish I could offer a sure cure for the problem. On occasion, I've gotten away with simply gluing down some of the worst lifts, but otherwise I simply try to bury the minor surface checks with a heavy layer of varnish.

1. 
   PhilipOrr | Mar 12, 2004 01:08pm | #4

   Thanks for the info guys. I agree with you Jon in that we now tend to blame the drying process for wood which is not perfect. I have just glued the rays down in the past but this last piece just seamed to be much worse which I attributed to the drying.

   Albionwood, is there any difference in the type of glue to use for glueing theses rays down as I normally just use Titebond and a waxed strip clamped to the piece.

   Once again, many thanks for the scientific and practical advice.

   Philip

1. 
   AlbionWood | Mar 12, 2004 08:17pm | #5

   For me, the gap-filling CA glue is more convenient and does a better job of filling/hiding the cracks and lifting rays than PVA glue does.  CA glue has extremely low surface tension, so it will run deeply into the cracks and splits, whereas PVA has to be pushed in.  As you probably noticed, those lifted rays can be pretty fragile, and trying to stuff glue under them can result in breaking them off - now you have tearout to deal with.  With CA I just put a drop at one end and it will work its way far back into the wood; less chance that the ray will lift again when I sand or scrape later.  Also, with the accelerant, CA sets up in seconds; you hardly need clamps at all.  (I use spring clamps - the glue doesn't adhere well to plastic jaws.) It sets up hard and sands off easily.  Doesn't seem to mess up the finish later as PVA can, although if you get a lot into the wood it can darken it.

   Disadvantage:  The noxious fumes.  The accelerant is extremely volatile, and the reaction with the glue gives off a nasty fume.  Do this outside if possible and even then, maybe wear a respirator; you can easily develop a chemical sensitivity to this stuff.  (The accelerant isn't always necessary, it's just convenient and helps prevent runs and drips.)  Also it sticks to everything, but was originally formulated to stick human tissue together and that is what it does best.  Wear nitrile gloves and be extremely careful about spills and drips; it's really easy to glue yourself to the bottle, a tool, or the workpiece.

   For me, the effectiveness and convenience makes CA glue the hands-down winner for this particular job.  But if I had to do this every day, I might look for something less volatile/irritating to work with.  PVA wouldn't be very far up the list, though; it is just too difficult to get it into those narrow cracks."Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net

1. 
   PhilipOrr | Mar 13, 2004 12:12am | #6

   Thanks Albionwood, I see the advantages and will try CA glue the the next time.

   Philip.