You often see cans of solvent finishes, including lacquer, and alkyd and polyurethane varnish, with instructions not to thin them. Manufacturers include these instructions in order to comply with VOC laws in some areas of the country, such as California. Adding thinner could take the finish out of compliance with the local or state laws, and manufacturers might be breaking the law if they advocated thinning.
But they then sell these finishes everywhere so they can avoid printing a separate label. It’s most likely that you live somewhere that these restrictions don’t apply.
The instruction can be confusing, however. It may lead you to think that you might be doing some harm to the finish if you thin it. Just to be clear, you can’t do any harm to any finish by adding thinner. In fact, you can add all the thinner you want to solvent finishes, even 99 percent, without causing any harm. You’ll just get a thinner build with each coat, which may result in your having to apply more coats to get the look and protection against liquids that you want.
The advantage of adding thinner (five to thirty percent is usually adequate) is better leveling – that is, reduced brush marking and orange peel.
Keep in mind, however, that if you are in an area of the country with strict VOC laws, you could be taking the finish out of compliance if you add thinner.
— Bob Flexner
Clamping Pressure on glued joints.
So, let’s review the role of pressure in gluing. A glue joint should be 0.002 to 0.006 inch thick for maximum strength. Obviously, this preciseness requires very flat surfaces, especially for the denser wood species that do not compress easily. Flat surfaces mean perfect surface proportion, plus we need to apply the glue before the surfaces have a chance to pick up moisture from the air (if the are a bit dry, such as in the summertime) or lose moisture if they are a bit wet (true in the dry wintertime air). If the wood surfaces change MC, they will swell or shrink a little bit, but this can make the 0.002 to 0.006 inch impossible to attain along the entire joint. Obviously, the surfaces cannot be dirty, or burnished from saw heating, etc.
Now here is something that you may not have thought about. In the wintertime, the plant is cooler than in the summer. The glue itself, if the plant is really cool at night, will be really cool in the morning. And on those hot summer days, the glue will be really thin. So, it should make sense that it will take a little more effort (pressure) to squeeze out the glue in the wintertime than in the summertime. So, think about using two different pressures. It might also be prudent to think about storing the glue at a constant temperature year-round.
So, how much pressure? The starting guide is the glue manufacturer and your clamp manufacturer. We always want to see good squeezeout along the joint. Then after the joint is cured, with a small magnifying glass (15 or 20X) you can examine the dried joint and determine or estimate its thickness. Make sure you check multiple locations along the joint’s length.
Greetings from central Nebraska beaming to the world wide web. This is my very first blog, so hopefully it comes across sounding ok. I’m doing this blog to try to help out anyone who is interested in learning more about woodworking. This is a journey of discovery for myself also. I have wanted to start woodworking for almost 20 years, but never got around to it. Kids, work, commitments etc, so I have finally decided to just dive in and learn as I go. Naturally, I’ve spent lots of hours reading and watching some really awesome YouTube video’s on the various aspects of woodworking. I would like to share my experience in the craft, with whomever wants to come along and follow my blog. (more…)