Didgeridoo Design, Make and Play
This part of the process can be the trickiest. The better the bond the longer the didge will last, and the less you will see the join.
I have tried a number of glues, all of which did the job, and have not had any problems with the joins coming apart on any of them (touch wood), but it must be said that all the glues behave differently from each other, having different composition, consistency and drying or setting times.
This is what I first used. PVA is known to me as I have used it from my days as a school boy, through to college and beyond. It is cheap, easily available and non-toxic. It is water based and soluble until set when it becomes waterproof. It takes additives well such as sawdust (for gap filling), and colourants such as acrylic paint or gouache. If a non-water proof paint such as gouache is mixed in small quantities then the mixture will still be waterproof when set. I have used PVA to seal the wood, both inside and out, normally in a 1:1 ration, however used even thinner, it can be applied as a protective layer, covering existing artwork. I have examples of work that I glued at college over 15 years ago and the glue is still sound.
Seems ideal, it almost is, with one or two exceptions. Firstly, when using it to glue the join, a small amount of the glue will expand and create a ridge on the join which can mar the finish. This will happen over a number of days after the gluing has taken place. Secondly, it gets everywhere when gluing and although can be prised off most metal surfaces (such as the clamps) when set, it tends to clog stuff up and get everywhere. I spent an awful long time cleaning when using PVA as a joining compound. Thirdly, it has a low melting temperature, so if sanding with power tools, the abrasive paper will clog very quickly.
PVA can be waterproof and resistant to wear and tear. Different grades and levels of chemical resistance are available, as are quick drying PVA glues. I put this glue to use a lot in my workshop but not for joining two halves of a didgeridoo together.
This is a two part compound that when mixed together cures or sets into a solid mass. It is extremely resilient to chemicals and water. The time it takes to cure (set) depends on the type of epoxy resin you have purchased. Epoxy resin has great strength with a very high breaking strain, again different varieties and brands over slightly different products. The chemical compounds are in gel form, and until mixed and fully cured are toxic and corrosive. The compound sets exothermically, that means that when mixed together heat is generated and it is this heat that bonds the chemicals together. The greater the mass of the mixture, the greater the heat generated (leave it as a mix for too long and the heat can be to hot to hold so be careful).
For bonding purposes, sawdust (very fine sawdust) can be added, to make a thicker paste. Colourants can also be added such as inks and acrylic. Too much paint, especially acrylic, can soften the surface of the mixture when it has set, so if in doubt experiment first. Colours additives can be purchased that have been made specifically for the epoxy resin; however they can be rather expensive. Unlike other mixtures comprising of two parts where a hardener is added and the more hardener that is added, the quicker the setting time. This is not so with epoxy resin. Mix the resin according to the instructions of the manufacturer and stick to them. I have had problems in the past of mixing resin incorrectly whether in amount or when it was to cold, on the se occasions, the resin did not set and was difficult to remove and redo. I took ages. Once resin is set, it is set so do be careful where you get when working. Make sure the area you work is well ventilated due to fumes and be aware that spontaneous combustion can occur in mixed uncured resin.
I always wear protective rubber disposable gloves when working with resin. Ben Hicks in the book 'The Didgeridoo Phenomenon' states that vinyl gloves are better than latex when working with resin. I haven't tested this out but it just so happens my disposable gloves are vinyl. I do not use epoxy resin for joining didgeridoos as I am distracted with the mixture, its setting time and toxicity which have resulted in a couple of bodged joins. I do use it extensively to protect the mouthpiece and bell, set and seal weak parts of the wood, especially knots. As resin cures it has a strong surface tension. When set the surface will be very smooth, like glass. I (and this is a personal feeling) that when applied to natural wood it can look similar to plastic, so I will always add a little depth underneath with a coat or two of Danish oil or a stain of some variety. I also use it in the workshop to repair tools, especially handles that come off files, chisels, etc.
This is the glue I currently use for joining didgeridoos together. It is a urea formaldehyde powdered resin. Water is added to the powder in the correct ratio forming a paste. This paste is then applied to one surface and sets fairly quickly. It sands well when set, bonds joints well and does not stick to the metal clamps I use. When mixed it has the consistency of thick cream. The mixed but unset mixture can be an irritant to the skin so, as with epoxy resin, I wear rubber gloves.
Mixing the glue in a small plastic pot with a small strip of wood the size of a lollipop stick, I use the stick to apply the glue to the didgeridoo. Any glue that is left in the pot will set, and if you leave the stick in the glue in the pot, once set the whole lot will pop out so the pot can be re-used. I do not use this glue for anything other than joining didgeridoos.
The disadvantages I have found with this glue is that when using it in hot weather, the glue will set very quickly, even if more water is added making the join very thick, visible and messy. To get round this I ask a friend to put the glue on one side, while I do the other, making the application process twice as fast.
P.U. or Polyurethane glue has become increasingly popular over recent years, primarily due to advanced in technology in combination with a a strong water proof bond with incredible strength. There is quite a variety of brands (and cost) on the market with availablity in almost every decent hardware store.
The glue is easily applied with only a thin coat required on one surface. When the surfaces are placed together the glue expands (and therefore filling any small holes in an uneven surface). The glue expands when in contact with air and any excess will grow to a consistancy like that of gap filling foam. When fully cured the excess can be removed (carefully) with a knife or similar sharp object.
P.U. glue is generally fast setting with the majority of brands having a 20 minute window for bonding befure it starts to set. I use two types, the 20 minute glue for normal applications and a 5 minute glue for awkward or simple jobs. I DO NOT use this glue for didgeridoos though though I know of didgeridoo makers that do. I do use it for other items such as Cajon Drums and Flutes as well as being the glue of choice in my day-to-day carpentry/joining work.