In my last column, I talked about the basic techniques used to veneer furniture. This week, I’d like to explore hammer veneering with hide glue, a method used by ebenistes or veneering specialists for centuries.
Today, hide glue can be purchased off-the-shelf in pre-mixed form, similar to white or yellow glues. This, however, is an expensive way to purchase hide glue, especially if you plan to veneer large surfaces. In my experience, the most cost-effective way to buy the adhesive is in the form of water-soluble granules or pearls, available at Lee Valley or on the Internet.
The granules form a stronger bond, but they also have a short open time. On the other hand, the pearls have a weaker bond, but they have a longer open time, which is important when you are working on areas where extra fitting time is required.
There are two methods to dissolve the granules or pearls, both of which require a source of heat and some method of controlling the temperature as hide glue loses bonding strength when overheated, and it really stinks. If you are a DIYer who does not want to invest a lot of money in a commercial electric glue pot, a double-boiler and a candy thermometer will suffice. To maximize open time and bonding strength, hide glue should be maintained at about 140°F to 150°F.
I prefer the pearls because of their longer open time. When you purchase a batch, there should be an instruction sheet included that explains how to mix them with water. Example: pour two ounces (measured by volume in a standard eight-ounce measuring cup) into a plastic container, covering the pearls completely with cold water. After a few hours, the pearls will have expanded into a large gelatinous mass. Pour off any excess water and empty the glutinous mixture into your glue pot.
My electric pot, which cost $135, takes about a half hour to heat a batch of glue.
If the mixture is lumpy, add very small amounts of hot water and stir the mixture until it is the consistency of hot caramel. A double-boiler may take longer to heat the glue to working temperature. Keep your eye on the candy thermometer so that you do not overheat and destroy the working properties of your batch.
As a rule of thumb, I allow one ounce of glue per square foot of a substrate such as MDF, which is ideal for this purpose because it does not expand and contract like wood, eventually cracking the veneer. If you have not worked with hide glue, it is advisable to prepare some six-inch by 12-inch test pieces of MDF and sheets of veneer that allow for a 1/8-inch overhang on all sides of the MDF. Use a cheap bristle brush to spread the hot glue onto the substrate, and then place the veneer over the substrate to ensure there is sufficient overhang to be trimmed off later.
Unlike contact cement, hide glue is forgiving in that it leaves you some wiggle room and adjustment time. When the veneer is properly registered, work from the middle of the substrate, smoothing excess glue toward the edges with a veneer hammer. (A veneer hammer is a block of wood fitted with a solid brass strip that stands about a quarter-inch proud of the block or head. The head has a handle to allow it to be pushed across the surface of the veneer with sufficient pressure to adhere the veneer to the substrate.
Veneer hammers can be purchased on the Internet or made from scrap wood and a solid brass hinge. Do not use brass plated or steel hinges as they will stain some veneers like oak which have high tannin content.
If your batch of glue is properly mixed, it should only take a few passes of the veneer hammer to smooth the veneer onto the MDF. Some people like to lubricate the brass tongue with a little glue to help it glide more easily over the surface of the veneer. I avoid this, if possible, because it can create a mess that has to be removed with a cabinet scraper once the glue has set.
One advantage of hide glue is that it can be reheated with a household iron, allowing bubbles in the veneer to be removed with a couple of passes of a veneer hammer. Luthiers, who restore stringed instruments, still use hide glue because of its forgiving nature and is especially useful when a restoration job goes awry.
Though hide glue is technically dry when it cools and gels, I always wait 24 hours for any adhesive to completely set. If you have prepared several samples of MDF and veneer, wait until the following day before trimming the overhanging veneer from the edges of your samples. The quickest and most precise method to remove the overhang is with a flush trim bit and a router. Work slowly at the corners so as not to tear out bits of veneer.
Another method is to flip the sample over on a flat surface so that the veneer is facing down, and then score the overhang with an X-acto knife, using the edge of the MDF substrate as a guide. A couple of light passes with the knife is always preferable to trying to remove the overhang with one heavy-handed pass, especially on end grain which tears out if roughly handled.
A trick to prevent end grain tear out is to run a strip of masking tape across the face of the veneer’s end grain before flipping the sample. The tape prevents the veneer from tearing out while you are in the process of trimming the overhang. Before removing the tape, rub a bit of varsol or paint remover onto it, allowing the tape to sit for about five minutes to soak up the solvent. The tape will then lift off the veneer’s surface without pulling away bits of material when it is removed.
I mentioned in a previous column that Lee Valley sells a large pizza box of veneers for about $50. For first-time hide glue DIYers, this is the best value for their buck as it lets them experiment with a large selection of veneers from curly maple and black walnut to exotic rosewoods and eye-catching burls.
Once you feel confident working with hide glue, it is possible to create all sorts of jewelry boxes and plaques with dazzling colours and figures by combining veneers or by just using a single sheet of zebrawood. There is enough material in the Lee Valley pizza box for a person to create many small objects.
If you decide you are ready to tackle a table, there are many sources for large sheets of veneer on the Internet.