Every leathercrafter does, or at least should be using some form of glue, yet why does this one subject generate the most questions and the most confusion?
The intention of this blog isn’t to tell you which brand to use or which product to buy, rather I will be going over the basics of what types of glue are available, what they do best and their limitations.
But let’s get one thing straight, you don’t need to stick (here we go) to one type of glue in every project. Most projects see me using two or three types of glue for varying reasons. It’s these reasons I’ll be focusing on today.
Take the Bloomsbury attaché case video course. In that build I am using contact adhesive between the case board and the bridle leather for 100% contact, but also to provide a moisture barrier which prevents swelling and delamination inside.
For the lining, I am using a type of PVA glue that can be undone with time and a damp sponge. So if a case lock needs repair or replacement, a restorer can easily peel back that part of the lining to gain access without having to rip out the suede, preventing permanent damage and allowing the original lining to remain intact.
By far the most important factor of adhesion isn’t what glue to use, but rather the design of the piece. Every effort should be made to prevent relying on the mercy of glue.
PVA glue
Polyvinyl acetate is one of the most common glues available in the world. For that reason many people underestimate its strength and usefulness within leathercraft.
Common knowledge suggests the best glues are always hard to get, available to trade only, and the only people aware of them are those ‘in the know’ right? But sometimes, the most useful materials have been staring us in the face the whole time.
Water resistant, it is also available as waterproof and water soluble (school glue/washable PVA). So this covers you in case you make projects exposed to the elements (bag exteriors etc) or components that may need repairing by temporarily un-bonding leather parts (washable PVA).
PVA glue is also great if you want to burnish an edge after gluing and stitching. It will not roll up and come away as you burnish like rubber based contact adhesives do. So you can have a strong bond and a smooth traditional burnish. However, as it doesn’t have an instant grab, many seams will need clamping as the PVA dries. It is also not easy to remove from the surface of your leather should some dry on there.
Water based contact adhesive
Also known as solvent free contact adhesive, it is a white adhesive similar to PVA, but it relies on you applying a thin layer on both parts to be bonded, before allowing it to become touch dry (10 - 20mins). After this, both parts are carefully pressed together firmly for an instant bond on contact (hence the name). No clamping, no weights, no coming apart as it dries. Magic stuff!
Probably the most common glue in leathercraft, it lacks any solvents, so as well as being less harmful to your health, it is easy to remove with crepe rubber should you be a little over liberal with your application.
The down sides are a longer dry time, less penetration into the grain and a weak bond to anything that isn't porous (metal, plastics, ceramic, glass etc).
Being rubber based, once dry it becomes waterproof, so the additional benefit is that it creates a thin moisture barrier. Handy for some bags and cases.
These days it’s mostly made from neoprene rubber much like it’s solvent counterpart. Years ago it was made from latex and known as ‘rubber milk’ and applied with braided rope so that a new piece could be cut as the end became gummed up. It is still made by Copydex and famed for its strong ammonia smell.
Solvent based contact adhesive
The only thing stronger than its smell, is its bond. As contact adhesives go, nothing sticks stronger or dries quicker when used correctly. That’s physics folks.
However, this adhesive horsepower comes at a price. The solvents that keep the rubber in liquid suspension such as hexane, toluene and acetone, aren’t that friendly to your endocrine system with high frequent exposure. So it’s use should be limited to only when necessary, infrequently, and with plenty of ventilation.
Other issues include the need to purchase solvents separately for dilution. If not, then the adhesive will dry out over the weeks and become firm in your glue pot or tin. This makes it hard to spread, not to mention little if any penetration into the leather fibers.
But oh no, you can't just buy generic solvents, you have to buy the same solvents as the brand used to make the glue! Many brands don’t sell these to the public, ruling out their glue in the first place. Not a problem with solvent free, hence the popularity.
Great for oily/waxy difficult to bond leathers and materials such as synthetic interlinings and reinforcements.
The adhesive can also be cleaned up and diluted with solvent adhesive cleaner.
Wheat paste glue
Not so popular anymore outside of conservation work, traditional bookbinding and bespoke shoes. However this glue used to be the mainstay of leathercraft and it’s amazing to see antique pieces still held together with what is essentially flour and water boiled out for an hour.
The addition of clove oil also adds a pleasant smell and prolongs the shelf life before mould and bacteria set in.
It is essentially the most proven leathercraft glue as far as I can see. A damp cloth or a little steam can reactivate the glue for repairs, then once dry it will go right back to it’s bonded state.
Paste glue can be difficult to buy, but you can get a similar effect using high strength wallpaper paste with a high concentration of flakes to water. This is commonly used for bonding skins to writing desks.
Here's some common question I get asked about glue:
What’s the difference between glue and adhesive?
These days? Nothing. The names can be used interchangeably (watch me!). Originally however, ‘glues’ were natural or at least animal based, such as hide glue. ‘Adhesives’ were synthetic based such as rubber cement.
Today we see synthetic ‘PVA glue’ everywhere, so even the manufacturers prefer to be understood rather than historically correct.
What is the best glue for leathercraft?
There really isn’t a ‘best’ glue I’m afraid, much like there isn’t a best leather, best thread or best anything. There is only ‘most fit for purpose’. So it always comes down to what you want to do.
‘What is the best glue to bond waxy leather’, will likely get a different answer to ‘what is the best glue to bond leather if I want to burnish the edge after?'.
Is solvent based contact adhesive bad for your health?
With frequent use, yes, the human body is not designed to breathe in the solvent fumes put out by most SBCAs. The key is to have adequate ventilation from a window or a fan.
If I had to be using glue all day, every day, SBCA would not be my first choice for health reasons.
However, for bonding waxy/oily leather, or bonding leather to a non porous material such as metal, there is little better, especially if you require an instantaneous bond and a moisture barrier.
If you are going to use it, don’t use it all day every day, and make sure you have proper ventilation or an extractor fan nearby.
My PVA glue cracks when I bend the leather, what’s happening?
Some PVA glues are designed primarily for the construction industry. These can contain resins and other additives that make the glue more brittle. This is especially important with wood glues or ‘white glues’ as this brittleness reduces ‘creep’ in the joints (slow gradual movement given enough time and pressure).
Sometimes construction PVA finds its way into the craft aisle in your local hobby store.
As PVA glue is about as cheap as it gets, test a few to see if it has the flexibility to bend and resist cracking. The right PVA should flex as well as rubber based contact adhesives while providing as good or better bonding ability.
I'd love to hear your thoughts on what glues you have found to be the best for your work and what questions you have about adhesives in general. Comments below!
Philip