" Hey, I'm interested in any considerations that you have towards using green douglas fir. I'm on the
west coast too, and all the larger wood (> 2x4) is usually green. I've wondered to myself how green
wood works with glue, and what will happen as it dries.
Have you built with green lumber before, and if so, how did the wood react as it dried out.”
So, I received a great question the other day from Marty about working with Green DF and I thought it was good enough to write a blog post about. Here is Marty’s question:Table top made from 1x3 DF edge glued pieces.
The easy part to Marty’s question is about the use of glue on GDF. I have seen nothing that would lead me to believe that wood glue works any differently with GDF than it does with any other wood out there. I use mainly Titebond wood glue and have never had a problem with its ability to hold DF together. I have made outdoor tabletops with just a glue bond edge (meaning no biscuits, dowels, dominos, or anything else in-between) and they have held up to this very day. One table I made sits on my front porch and goes through seasonally changes from below 30 to above 110 and the top is still dead flat. There has been no bowing or twisting that has overpowered the tabletop over the past two years.
As far as how the wood reacts as it dries. Well, the easy answer is that if it is nailed in place, like inside your walls of your house, it dries (seasons) very dimensionally. Meaning it will stay nice and straight because it is held in place. However, that is not how I use GDF for projects in my shop.Sawbench made from GDF.
Now on to the long answer for special considerations I use when working with GDF.
First I would like to say that Green Douglas Fur is a great wood depending on what you are building. I wouldn’t build all the furniture in my house out of it, but it is great for outdoor furniture (with a good finish on it) and a good choice for workshop appliances like a sawbench, workbench, stool, assembly table or lumber racks. I have one and soon to be two sawbenches made from GDF and I don’t see why I would use anything else. GDF is cheap, easy to get, and if I make a mistake it isn’t the end of the world.
However, GDF does have a dark side and it is right in its name, “Green”. Green means wood that has not been kiln dried. When the wood is cut it has a moisture rating of 40% or greater, which is what puts it in the category of Green wood. This wood has not been kiln dried, and actually even if it has, that doesn’t mean a whole lot. Construction lumbers such as GDF and KD DF are treated a lot different than wood you might buy from a hardwood dealer. Douglas Fur is a soft wood and can soak up moisture very easily and dry out very quickly; this means that it has the potential to move a lot. An example of this rapid wood movement can be observed in just a couple of days in a trick called the impossible nail in wood trick.
In this trick the wood is cut, then one end is placed in boiling water. Once the end prong soaks up the water it is placed in a vise for a couple days, the nail is then inserted. After the nail is in the wood the smashed end is re-boiled and the wood expands back to its original shape. Many woods can be used for this but DF is one of the best because it is a soft wood. Though that is a cool example, a real bad one is something that once happened to me. On my first workbench I cut out all the parts I needed for the build. I built the entire bottom of the bench in one day. No problem with the DF, everything stayed nice and straight because it was attached. But, the outside trim for the bench top was cut to 1 ½ ”x3”x8’ pieces and left for a few days. When I came back to add them to my multi-layered plywood top, they had bowed so bad that no power on Earth would make them line up with the edge of the bench top. They were actually bowed, twisted, and cupping in just 3 days. Why did this happen? This happened because the wood was not dry and once I cut the pieces out of a larger piece of lumber they were free to move about without anything holding them back. So, move they did.
Some wood I have on stickers in the back of my house.
Now with all that said, there are many things that someone can do to prevent bad things from happening to their projects. First, when looking at GDF do not buy any that is wet to the touch, if you can help it. And I mean actually dripping; I have seen GDF actually drip off the pallet. If wet GDF is all you can get then you just have to lay it out and sticker it. This mean placing some small strips on the ground and then one of the boards on top of these strips, repeating the process until all of your pieces are separated and surrounded by air. This will help them dry out evenly over the next several weeks. Drying your lumber like this is important because DF is rapidly cut, milled, and palletized. With all the DF tightly wrapped together the wood cannot breath but on the ends. The ends get lighter in color and crack very bad because they have dried out on the ends and not in the middle. I would let wet GDF sit for 6-8 weeks, at least, and normal GDF to sir for 4-6 weeks. Why not longer? Well if you have the time go for it, but in my experience any longer than the above times and it is just a waste of time. The wood will only get so dry because it is a soft wood that has either not been fully kiln dried or left to air dry for over a year. The normal time period for air drying lumber is one year per inch. Or so they say, it really depends on where you live. I live in a dry hot area of the US so for me things move along a little quicker. What you do with the DF after you work with it is more important.
When working with GDF only cut out the pieces of lumber you need for the task at hand. This helps prevent early wood movement (the almost immediate movement of wood after it has been separated from its support structure). The early wood movement is the worst, but can be prevented by assembling the project. By nailing, screwing, or gluing the DF in place it helps prevent the wood from moving as it dries out over time also called “seasoning”. If you ever talk to a carpenter they will tell you that as soon as a pallet of 2x4s is cut open they try to nail up the walls quickly because the boards will only stay straight for so long. All woods move even the most expensive hardwoods out there. But I will say that my sawbench was made from GDF and all the legs and the top are just as straight and square as the day they came off my hand planes. The reason for that is in the finishing process, which I think is one of the most important things to do to a DF project.
Everything that I have made for my shop out of GDF has had either a couple coats of boiled linseed oil, coats of an oil varnish blend, or oil followed by polyurethane. Why? Well it goes back to the fact that DF is a soft wood and will soak up moisture quickly and can dry quickly. When it dries out that is when it bends and cracks the worst. I prevent that from happening by keeping the wood stable with boiled linseed oil (BLO). BLO is in all the finishes I listed above and it keeps the wood from drying out and therefore prevents it from moving as much as it normally would.
I know this is more information on DF then most people would ever like to know. I think that most of this information applies to any wood we use to build things from, and shows that DF is really not too different than any other softwood. I do believe DF is greatly underutilized and shunned because of how common and plain it is. There is a ton of more information out there about GDF construction lumber and what the milling standards are for it. If you are looking for more information you can visit WWPA and find out more.