If you have a home woodworking shop, you no doubt have glue in it as a part of your shop inventory. Many actually like to keep a variety of glues on hand and which one is chosen for use is determined by what you are bonding.
Even if the pieces of wood being joined are being nailed or screwed, glue is still that extra measure of bonding that adds life to the project. Of course, glue is indispensable when the joinery involves biscuits, dowels, and tenons. Clamps are used to hold the workpieces joined while the glue dries, and you have a strong bond.
We all know the widely used wood glue Elmer’s, but in fact, Elmer’s makes a variety of glues. The most familiar is the yellow glue we grew up with, but there is also white glue, school glue, and carpenter’s glue. Are they all different?
Yellow Glue vs White Glue
Wood glue is merely a classification of glue rather than glue itself. Aliphatic resins are chemicals used in the composition of the yellow glue or carpenter’s glue we know and use. It is a bit stronger than traditional white glue and dries quicker. Yellow glue takes sanding well and can be painted over but not stained.
Wood glue (yellow glue) and white glue have in common their origin – both are derived from animal products. Waste byproducts from animals, including bone, hooves, and tails, are boiled with zinc oxide, and the reduction produces a glue-like substance that is cooled, bottled, and sold as white glue.
The difference between the two is the chemicals added during the manufacturing process all for the purpose of producing adhesive strength.
- Yellow glue is an aliphatic resin, a synthetic adhesive that has a light yellow color and a creamy texture. We all know yellow glue and likely have it in our shop as it is a common glue used to bond wood pieces. It has little odor and a low flammability, excellent bonding strength, and moderate moisture resistance.
- White glue is a PVA glue, the hobby and craft glue, the school glue. It’s non-toxic, cheap to buy, and easy to use. It’s also the most commonly used wood glue. Like most glues, it does not adhere well to itself, so joints that were PVA-glued are difficult to repair as they loosen over time. More on PVA glue below.
As an added note, so-called superglues are made from chemical components, and not animal derivatives. Laboratory designed chemicals were designed to give them the combined benefits of both wood glue (yellow glue) and white glue which has the ability to bond just about anything so that you don’t have to choose between them.
What is PVA Glue?
Polyvinyl acetate (PVA) is a water-soluble synthetic polymer used as a thickener and emulsion stabilizer in the making of adhesives. It is used as a sizing agent in the making of textile yarns that enhances strength, and in paper making, it helps the paper resist oils and grease.
In the manufacture of glue, it is one of the base compounds in synthetic adhesives. It is specifically designed to be absorbed into the surface of wood, thus enhancing its adhesiveness. PVA wood glue can be used to bind wood, paper, cardboard, and other craft materials.
PVA is not waterproof, and it isn’t even water-resistant, but it is water-soluble as we noted above. If you need the joining to be waterproof, there are other adhesives better suited for that purpose. It is colorless and odorless, and that was its appeal as a component of glue, along with the fact it is cheap.
Elmer’s glue is very well known, of course, but glue is not the only product made by Elmer’s. Craft, home repair, and office supply products also come from Elmer’s Products, but Elmer’s Glue-All is its most well-known product. The name has acquired the status of brand name used as generic product as Coke refers to soft drinks.
To be clear, though, Elmer’s Glue-All, white glue, is a PVA-based synthetic glue. Among the qualities of PVA glue:
- Discovered by Fritz Klatte, 1912
- Can be used on solid wood, plywood, and MDF
- Dries quickly with a solid bond strength
- Flexible, permanent, will not harm the skin but is toxic if you eat it
- Water-soluble and can be thinned by adding a little water and stirring well
- Can be cleaned away with warm, soapy water
- Susceptible to fungus, algae, and bacteria that can cause breakdown and weakening in adhesive strength
- Freezing will break the polymer
- It can be painted over but not varnished
- Full adhesive strength is achieved after 24 hours of drying and curing
PVA Glue Uses
Woodworking projects are not the only uses to which PVA glue is put. Other common uses of PVA glue include:
- Paper, fabric, and leather adhesion
- Arts and crafts
- As wood filler with sawdust mixed in, something we have mentioned in past articles, including here.
While this article addresses Elmer’s Glue specifically as a PVA glue, it’s not the only PVA glue on the market. Yet, Elmer’s offers several PVA glues, and here is a video that discusses both Elmer’s line of PVA glues, and two competitors.
If you’re an experienced woodworker, you know the routine for gluing workpieces. Clamps to hold the workpieces together; wipe away excess glue before it dries; adequate air circulation to enhance drying; adequate drying and curing time before unclamping and continuing on with work; follow these guidelines for the most effective joinings.
One last mention and that has to do with the right glue for the right job. PVA glue can be painted, but in most instances can not be stained. Stain penetrates wood to provide it with color; glue prevents the stain from penetrating.
And yet, there is an exception. Elmer’s Products offers Elmer’s Stainable Wood Glue Max, a glue made specifically for this purpose. It contains wood fibers and thus can be sanded and stained.
If you’re like us at Obsessed Woodworking, your shop has several different types of glues on your shelves, but you do have and use glue. We all do. While it’s not necessary to understand the chemical composition of glues to know which glue to use in which situation, knowing glue applications is important. The rest is just detail, but interesting nonetheless.
The glues we have discussed in this article are for indoor use, too. You would not use a PVA glue in an outdoor project – it’s not waterproof, and t’s chemical composition breaks down when it freezes.