Content area
[...]within one annual growth ring (the rings we count to determine the age of a tree), with some species, especially pine, there are the more or less wide open cells that the tree makes during the early part of the growing season (sometimes called springwood or earlywood) and then there is a transition (abrupt or gradual depending on species) from this wood to the late season growth. Studies that look at wood strength and other properties tend to ignore wood in the first 15 years of growth in the log because the wood in this region, often termed juvenile wood, is not as strong, can warp more easily in drying as well as warp more after drying when the MC changes (side bend and twist seem more common), and may have a different color and absorptivity during finishing. Because of faster growth of a plantation tree, the juvenile core will be larger in volume, so it is more likely that lumber sawn from the plantation log will have this juvenile wood and behave poorly, as noted. To search a full list of Wood Doctor's Rx question and answers, go to woodworkingnetwork.com/author-works/genewengert "Today we are seeing more plantation grown wood in the marketplace.
Plantation wood concerns.
QWhat is causing uneven stain absorption? Specifically, we can see, within each growth ring, good and sparse absorption. This is with pine. Also, maybe it is the same thing, but why doesn't varnish and paint stick well to pine plywood when exposed outside?
A Good question. Indeed both questions are dealing with the same thing. So to understand what is going on, let's go back to the basics of wood. Wood is made of small, skinny cells, which are small, hollow tubes similar to a soda straw, but only 1/4 inch long (plus or minus). However, within one annual growth ring (the rings we count to determine the age of a tree), with some species, especially pine, there are the more or less wide open cells that the tree makes during the early part of the growing season (sometimes called springwood or earlywood) and then there is a transition (abrupt or gradual depending on species) from this wood to the late season growth. The late growth, sometimes called summerwood or latewood), consists of cells that are mostly wall and have very small opening-analogy is a plugged soda straw.
So, now when we apply a stain or any sort of finish that tries to penetrate the wood cells, we find that the stain or finish goes into the earlywood cells quite deeply with not a lot of excess on the surface of the wood. On the other hand, a finish or stain on the latewood is not absorbed well, but stays mostly on the surface, giving a different appearance, especially with the first coat or two.
Note that if we were to sand the wood after the finish has dried, light sanding would first remove the finish from the latewood and then sand into the unstained, light-colored latewood. But the earlywood would sand into more stained or finished wood, as the finish would have penetrated deeply. So, after light sanding, the color contrast would be quite intense,
Now, let's consider the question about plywood. For wood exposed outdoors, with this lack of openness in the latewood, oftentimes we find that the finish does not adhere well to the latewood itself. So when we have some movement of the wood (normal swelling when more humid or in contact with rain; or drying and shrinking from low humidity or heating with the sun, for example), the finish detaches itself easily from the wood; that is, we come to the conclusion that the finish does not stick to the wood well, as you noted.
Although this contrast between earlywood and latewood is common in most pine species, it is not common, or so troublesome, with most other commercial species. With hardwoods, however, we do have blotchiness caused by tension wood, which we have discussed before in this column.
QWe have some concerns about plantation grown wood, especially regarding color and stability. Is there a difference between "wild forest wood" and plantation wood?
A Today we are seeing a lot more plantation grown wood in the marketplace, and you may not even know about it. It processes and looks like normal wood. But, from time to time, there are a few differences that we should be aware of and check for.
We know the growth rate in a plantation is much faster than in a competitive forest. In many species, this means stronger wood. However, there is a "catch" to this statement. Studies that look at wood strength and other properties tend to ignore wood in the first 15 years of growth in the log because the wood in this region, often termed juvenile wood, is not as strong, can warp more easily in drying as well as warp more after drying when the MC changes (side bend and twist seem more common), and may have a different color and absorptivity during finishing.
Because of faster growth of a plantation tree, the juvenile core will be larger in volume, so it is more likely that lumber sawn from the plantation log will have this juvenile wood and behave poorly, as noted. We may therefore have to change processing slightly to help moderate any problems, compared to "normal" wood.
One area that is a bit unclear is that some species with natural decay resistance (including cedar, cypress, redwood) seem to have less decay resistance in today's growth compared to the older growth of 50 or more years ago (called "old growth" wood). Speculation is that we will see certain properties change when looking at "old growth" compared to plantation growth, but the properties affected and extent of this effect is not well studies today.
Summary: Be aware of the sources of your wood supplies and the potential for some changes in properties or characteristics that may, in turn, require some small modifications in processing.
QWe ordered some stacking stickers for stacking and they are supposed to be from a plantation in Central America. They arrived wet, so we dried them and they warped like crazy. Did we do something wrong? They came in a full 1-inch in thickness, so we have to plane them too.
AI suspect that you got these stickers because the price was right. What they are is likely offal from a lumber operation and represent lower grade that has crossgrain; crossgrain from knots nearby and from the juvenile core which is the first 15 years of growth...a common event, especially with plantation hardwoods.
In the future, I suggest you only buy kiln-dried stickers, as they will be straight and the correct thickness. Many people today also get a profiled sticker that has grooves on the faces to help drying where the sticker contact the lumber.
QWe have recently switched to a water-based finish. When we use it on hard maple, the wood from one supplier seems to cause the sugars in the wood to come through the finish and appear as a white frost on the surface. What is it and why on just one supplier?
A We probably would have to run an expensive chemical test to know for certain, but I do think I can provide a likely explanation.
A couple of facts about hard maple. First, we know that the wood contains sugars and that these sugars are soluble in water. We also know that in most hard maple lumber, the kiln schedule reaches 150F and hotter, which seems to modify the chemical structure in the wood so that the sugars do not bleed out of the wood when the wood is dry.
However, there are some drying operations that reach only 110F maximum temperature, which would possibly mean that the sugars are more mobile in the wood if water (waterbased finish) is added to the dry wood.
So, check with the one supplier that is producing the troublesome wood and see if they are using an unusual drying system and what maximum temperatures they are using during drying.
My guess is that they are not reaching 150F or hotter. Let me know if I am incorrect. +
Copyright CCI Media Feb 2018