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Have a question about wood products? Termites? Lumber drying? Wood properties? Fill out the form below to send a question to the
faculty in Wood Science & Engineering. Please provide as much detail as you can so we can fully address your question.
Recent questions & answers: |
11/21/2009
Q: We have a new facility manufacturing wood plastic composites (WPC) in India. The products seem to be very good, however carpenters are not happy because when the piecies are joined with nails the WPC are breaking and are difficult to join. What are the best adhesives or fasteners to use?
A: From our experience in the US, the manufacturers generally provide installation instructions that describe what type of fasteners to use, how to predrill, the size of gap to leave between boards and at end joints, etc. You might look at installation instructions from other WPC manufacturers and/or contact the faculty at the Wood Plastic Composite Information Center at Washington State University to see what they recommend.
| 11/20/2009
Q: I have recently had fir trees on my property milled into lumber to build an outside structure (covered deck). Although it has been stickered and under tarps with lots of open areas for air flow, many of the pieces of lumber have developed black marks. I was able to sand off some of this but even when sanded the wood when moistens looks black in those spots again.
Can you suggest anything I can do to remove the black spots and prevent them from developing when the covered deck is built with them?
A: What you describe sounds like mold. Stacking and stickering lumber certainly helps to minimize risk of mold formation. However, if airflow is inadequate or the humidity is high for prolonged periods, it's hard to avoid mold, particularly when the wood is freshly-sawn.
The standard approach to remove the mold is to use a mixture of either detergent & water or bleach & water, depending on the severity of the stain. The Western Wood Products Association produced several publications on mold, including a 3-part series. Part 3 in the series (Cleaning Mold on Wood) is probably most relevant to you at this point. Of course, as you addressed, the challenge is also in keeping it from coming back. Keeping the wood as dry as possible and using a finish with a mildewcide will help keep the wood clean and bright.
Of course, this is all assuming that the stain you have is from mold and not a chemical stain such as from iron. The tannins in fir will react with iron (either from fasteners or in hard water) to create a black stain as well. Typically iron stain will form in streaks whereas mold will appear blotchy.
| 11/16/2009
Q: Are there risks to using ACQ-treated lumber for a raised-bed garden for growing vegetables? I have them for the posts only in a 4ftx12ftx16inch bed; rest is cedar, not pressure treated.
A: The primary concern with using pressure treated wood in raised-bed gardens has been with the arsenic in CCA- (chromated copper arsenate) treated wood. The publication Environmental Soil Issues: Garden Use of Treated Lumber from Pennsylvania State University does a good job describing the risks of using both CCA-treated wood as well as ACQ-treated wood. With regards to CCA, they state, "Although the plant and human health risks from garden uses of CCA-treated lumber appear to be extremely small, there are steps gardeners can take to further reduce any such risks." One of these steps they recommend is to use wood treated with ACQ - "This is an alternative wood-treatment chemical that contains no arsenic, chromium, or any other chemical considered toxic by the EPA."
| 11/02/2009
Q: How many bone dry tons are there in a ton of bark?
A: The moisture content of bark varies with the time of year, how long it's been since the tree was cut, and exposure conditions both before and after the bark was removed. That said, a good rule of thumb is 50% wet basis, which means the bark is half water and half bone dry bark. Depending on other factors though, a particular ton of "bark" could contain anywhere from a low of 0.3 bdt (bone dry tons) to as much of 0.85 bdt of bark. The only way to know for sure is to pull representative samples and measure their weight loss by drying for 24 hours in an oven set to 103 deg C.
| 11/01/2009
Q: I'm working for an NGO helping to set up a small bamboo enterprise to provide jobs for local people in a poor area of Bangladesh. As part of the pre-processing of bamboo we need to dry bamboo culms (trunk) and slithers (thin strips to weave with) down to 20% moisture content. Normaly we would do this in the shade over a period of 7 days, however we will not be able to do this during the rainy season where it rains every day and humidity is extremely high.
Do you have any suggestions for a low-technology, low-cost drying system that we could use to reduce the moisture content?
A: High humidity may be the primary challenge since the moisture content of wood (and I assume bamboo) responds to changes in temperature and humidity, but humidity is the primary driver. We have a publication that describes how to build a 'solar' (not photovoltaics but rather a greenhouse) dryer for firewood. However, I wonder how effective even that would be without some way to reduce the humidity and ensure airflow.
The solar wood dryer is the lowest-cost option I can think of. Another possibility would be a solar kiln such as is used for drying lumber. We have information and plans on solar kilns web page. To be effective, you'd need some way to power the fans inside the kiln. Again, I think that will be a primary concern - some way to ensure airflow within the kiln/dryer so that the moisture evaporating from the bamboo can be moved away.
| 10/30/2009
Q: Middlebury College, VT, grows willow to convert into wood chips to burn for electric power generation. Do you know of any wood farming programs in the West for power generation?
A: I am not aware of any similar efforts in the western U.S. The forest industry supply chain in the west differs from that in the eastern U.S. in that there are plantations in the Lake States and the southeast that grow trees strictly for paper - and now it seems, energy production as well. The industry in the west is primarily focused on solid wood products production (e.g., lumber and veneer-based products like plywood) and the residues/by-products from these operations are used for paper, fiberboard, particleboard, fuel pellets, boiler fuel, etc.
The largest 'fiber' plantations in the west that I am aware of are owned by GreenWood Resources. Again, however, as far as I know, these trees are sawn for solid wood products such as moulding and a portion of the residues (limbs, tops, bark, etc.) may be used for bioenergy.
| 10/28/2009
Q: Is there literature on the best way to clean a cedar roof? Afterwards is there a product that would help to preserve the shingles?
A: We have a couple publications related to maintenance of cedar and shake roofs on the Using Wood page of our website. Both publications talk about cleaning and preservative applications.
| 10/01/2009
Q: What suggestions do you have for drying eucalyptus wood in a solar kiln?
A: There really isn't much detailed information on drying any wood species in a solar kiln since you have such limited ability to control temperature and humidity. The most important thing is to closely monitor drying and take the appropriate steps when there is evidence that the wood is drying either too slowly or too rapidly.
If the species of eucalyptus is very dense and prone to warp and checking, high temperatures and rapid airflows (which are possible in a solar kiln) can dry the wood too quickly and result in significant degrade of the lumber. The common approach for 'difficult to dry wood species' is to air dry the lumber for 6 to 9 months. Even with air drying, when it is hot and windy, the wood may begin to warp and check. If so, you could place the wood in a covered location and/or cover it with a shade cloth to slow the drying rate. On the other hand, if the wood begins to mold due to drying too slowly, you need to take steps to speed the drying process (which can be difficult in cool, humid climates).
Once the wood is below about 20% moisture content, you can move it into the solar kiln. As with air drying, you will have to closely monitor the wood - if the wood is warping and checking you need to the slow drying rate. Often the way to do that in a solar kiln is to either open the doors and turn off the fans and/or cover the glass panels with a tarp to lower the temperatures.
| 09/08/2009
Q: I have some Douglas Fir logs that have been decked for two and a half years. I would like to use them in the interior of a new home I am constructing. I want to stand them up in the entryway of the house to create the feel of walking through trees to the center of the house. I want the bark to remain on the logs, but I am worried about bugs that may be living in the bark. Is there a way to rid the logs of bugs other than kiln drying them?
A: We have received this question a time or two in the past. And unfortunately, we really haven't been able to come up with a reliable solution.
It's surprising that the bark has remained on your logs. I know that some woodworkers say that harvesting standing dead timber or harvesting in winter (when the bark is 'tight' since the tree is dormant) will ensure that the bark stays on. However, bark and wood are such different materials and shrink at different rates that typically it's near impossible to keep the bark from falling off. Further, the layer that separates the wood and bark (called phloem) is the layer where the sugars produced by the leaves/needles flow down the tree - so there's lots of food there to entice insects. In fact, I know many rustic furniture makers that have had complaints from customers due to insects flying out of their furniture (with bark on) 2 to 3 years after the furniture is made. With the bark on, insects burrow in and lay eggs. If that food layer remains viable, the insects will have a food source whenever conditions are right for the eggs to hatch.
All that aside, people have done what you're wanting to do - and places like Yellowstone Lodge and Glacier Park Lodge are built with logs where the bark is still on them decades after they were built. From what I know though, it's a gamble. Kiln-drying (providing you can hold the temperatures high enough - 160 degrees or more for long enough) will certainly lessen the risk.
Lastly, I know a guy in eastern Oregon that did exactly what you're wanting to do; but he was a contractor, not the homeowner. He tried air-drying the logs and then put them in place. Slowly but surely the bark fell off and there were bug problems. He eventually went the painstaking route of cutting logs in spring (when the bark is easiest to remove), peeling off the bark in large sections and numbering the sections, drying the logs (they were only 10 feet long) in a solar kiln, and then glued all the bark back on.
| 08/30/2009
Q: I hired a contractor to supply and install oak baseboard and casement trim for my living and dining room. After applying the second coat of water-based finish, black mold appeared on the surfaces of the wood, even where I didn't apply finish. I had to hand sand the wood and still could not get all the mold off. The company that supplied the wood took it back and ran it back through their planer and it seems to have removed the mold on the detailed surface. I have had to sand all other surfaces. There is still some black spots on the wood that seem to go inside, and you would have to sand off quite a bit to get it all. They told me that my house was too damp when I put the finish on. I am thinking that the wood was still green when I received it. Who is right?
A: First thing we need to do is ensure that the stain is from mold and not perhaps something like iron stain.
If it is mold, my first thought was that the wood must have been in a pretty humid environment without much ventilation for mold to be able to grow on the surface. It's possible, of course, that the moisture content of the wood was too high or that there were small areas of bacterial wetwood (common in hemlock and red oak). My best guess though would be that the mold was due to high humidity combined with inadequate airflow.
If the wood was green when it was machined, you'd likely see some indications of that in the quality of the machining - when green wood is machined, it is common to see 'shelling' (areas where the growth rings separate) and/or fuzzing. Also, in small pieces like moulding you'll be able to see wet areas as you sink the nail heads. Can you get access to a wood moisture meter to check the wood before you install it? Home inspectors usually have such devices. Other than that, it might be best to either wait until it is less humid or use fans to ensure that there is good airflow.
Now if it is NOT mold it is possible that it is a stain caused by reaction of the tannins in the wood with iron. Of course, fasteners are one source of iron - in that situation, black stains form around the nails. However, it's also common for iron stains to form due to iron in hard water. See the US Forest Products Lab's publication Iron Stain in Wood for more information.
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