For most amateur boatbuilders Resorcinol is an echo from the past. They might have heard it mentioned in an old book, or some crusty woodworker might have raved about it. Few have ever seen it on sale and fewer have used it. Here is some information.
If I were to say I have a glue that can glue wood. Is immensely strong. Can withstand immersion in salt and fresh water. Does not soften in high heat and become brittle in low temperatures. Has proven its long term effectiveness. Is chemically resistant to acids solvents and oils. Can glue Oak and oily woods. It is harder, slightly stronger in sheer joints, and more permanent than epoxy. You would be overjoyed and would ask what this wonder glue is called.
I would answer it's Resorcinol Glue!!
Many of the boats restored by Howard Percival Johnson were built using resorcinol. Check him out at Old Time World Some eye candy for old motorboat lovers.
What is ResorcinolResorcinol is a simple molecule of benzene with 2 Hydroxy bits. It's produced either by using a natural resin such as a distillate of brazilwood and combining it with potassium hydroxide, or by several synthetic methods. This resorcinol is then further treated to produce the wonder adhesives.
THIS IS NOT A CHEMISTRY ARTICLE. If you are interested in the chemistry, check out the Wikipedia Resorcinol Chemistry Article. This is the basis for Resorcinol glue
There are variations as to the exact content of different brands. Aerodux 500 calls itself Resorcinol-Phenol-Formaldehyde, whereas Cascophen refers to its glue as Resorcinol-Formaldehyde. Since the claims from all manufacturers are similar in major traits I will not differentiate and when I say resorcinol or resorcinol formaldehyde I am not saying anything about a specific brand. Differences occur in the setting times, and ideal moisture content of the substrates, for example. All brands claim to be superior waterproof, structural adhesives. All brands have similar warnings and procedures.
In practical terms resorcinol contains a significant amount of naturally occuring phenols and is similar in action and waterproof qualities to the synthetic phenol formaldehyde glues. Here is my page on Phenol formaldehyde glue.
Grasp Resorcinol Adhesive Data Sheet is typical. Available in Australia, it's worth having a look. Others data sheets can be found fromt he links on the left.
What are the Advantages of Resorcinol Glue?
- It is Waterproof with a capital W. Passes the boil test with flying colours, AND has been keeping boats together for a great many years. It is one of the few adhesives around that stay strong when wet for extended periods. Outside conditions are not a deterrant for using this glue.
- Chemically stable after it has set. It resists Acids, salt water, solvents, oils and most other things. It is sensitive to alkalis.
- It is strong. Currently one of its main use is to put together plywood, laminated support beams and other wooden structural elements. Wooden airplanes frameworks have long been glued with resorcinol formulations.
- Because it has been around for a long time it has been tested under countless different conditions, and it has passed the long term reliability test.
- Resorcinol can withstand a wide range of useful temperatures when cured. It is safe for outside temperature anywhere on this planet. Unlike epoxy it does not soften when it gets warm. It shows no creep and does not get brittle in sub zero conditions
- After curing it can be used in a wide range of humidity condition including varying conditions.
- Resorcinol can be used as an adhesive for oak and oily woods. Epoxy is noted as a poor oak glue.
- Pot life after mixing can be several hours. This is dependant on ambient temperature.
- Some formulations can glue wood with quite high moisture content. Best results are at about 12% but satisfactory results have been achieved in the 6-25% range with specialized brands. See technical sheets for more information.
- Metal surfaces can be bonded with appropriate preparation and primers.
What are the Disadvantages of using Resorcinol Glues?
- It has very poor gap filling capacity. Your joints must be good.
- Joints and laminations must be tightly clamped or pressed, often for several hours at room temperature, to be successful. Resorcinol does not like a thick glue joint.
- Unmixed Resorcinol has a short shelf life of about a year. Less if kept in a warm place. (This is similar to Polyurethane glues.)
- It comes in 2 parts, a powder and a resin which must be measured either by volume or by weight. These must be carefully mixed.
- Resorcinol glue is sensitive to temperature and will not set very well if your shop is below 70 degree F. It will set faster at higher temperatures, and plywood and other architectural structures are often pressed and clamped then put in a kiln to shorten and improve setting. Full structural strength is achieved sometimes after several days, although it can be worked after clamping period is completed.
- Setting takes some time, often in the order of 10 or more hours clamping time plus several days to attain full strength at room temperature. Most amateur failures are due to improper setting temperature. Brands vary with composition.
- The glue line is dark brown or reddish brown. This explains why resorcinol is sometimes called red glue.
- Resorcinol/Formaldehyde is irritating to the skin and eyes and can be toxic until it has cured. This is not unusual, Epoxy components, Polyester resins and hardeners or polyurethane are all irritants, or trigger allergic reactions, or poisonous.
I received an email from someone who used Resorcinol for years and several of his workmates died of Leukemia after years of exposure. All these glues are dangerous until they are cured. Use your respirator and wear gloves.
- Most places have restrictions on shipping because of the composition of the resin. It is flammable and toxic.
- Resorcinol based adhesives are not readily available to the general public having been mostly upstaged by epoxy for amateur boatbuilders. I have included a number of links on the left, listing Suppliers of Resorcinol based glues, in Canada, US, UK, and Australia. One area besides Architectural structure elements, where resorcinol is still in use, is the aeronautic applications. Amateur plane builders have not found a good substitute for it.
- Resorcinol contains solvents which evaporate. The resin has approx: 55% solids, This can cause problems during application if the open time is exended too long. It also means that it has a higher VOC than some other adhesives. The solvents are inflamable
- Before setting, resorcinol can be cleaned with water. After setting its hard to remove. It goes through a half cured period where the squeeze out can be scraped off easily.
- It tends to be expensive in smaller quantities.
Why is Resorcinol glue not used
much by amateur boatbuilders?
Even though Resorcinol is a superior adhesive which offers exceptional performance, this comes at a price. The main drawback of Resorcinol based glue is the exacting conditions of use. It is a fussy character to use
- Joints MUST BE TIGHT
- Glued parts MUST BE TIGHTLY CLAMPED or pressed
- Setting temperature is critical. It will fail if too low.
- 2 parts need to be measured and mixed.
- Water content of the 2 parts to be joined must be similar and around 12%.
- Glue cannot be left in the open too long otherwise the solvent evaporates.
Resorcinol is not readily available in hardware stores and is not well known. It is also pricy and has a relatively short shelf life. There is no doubt that some amateur failures using this glue was because old stock was used.
Resorcinol is very poorly understood and practically unknown in the amateur boat building world. It is not marketed to these people and so suffers from being severely misunderstood and improperly applied.
Resorcinol Brands and Where to find it.
I've put a link on the sidebar for the Amazon.com listing. It's good for the US.
Weldwood from Dap Products used to be available but is now a discontinued brand. It was made by Hexion, who still makes Cascophen also called Penacolite. Confused yet? ResorsaBond comes up but I can' find any suppliers. Aerodux-500 is now called Prefere and is available in pint size. Grasp is available in Australia as is Resobond. I've included links on the left for suppliers in various parts of the world I could identify.
Since it is still in common use by amateur plane builders that is sometimes a good place to look or Google.
Would I use Resorcinol glues and where?.
I would not hesitate to use Resorcinol based adhesives. It has proven itself in marine applications and boatbuilders swear by it. It's the best adhesive for oak laminations. It needs gap free well made joints and tight clamping. The glue needs to be fresh and kept in cool dry storage. It's imperative to have a good warm (at least 20C workspace.)
With care and careful workmanship and planning this is a good choice. It is not as convenient and forgiving as epoxy but proven and reliable. I think it would be a great glue for a bird's nest mast.
I am currently building a Puddle duck Racer using chine logs glued to the sides. This would work very well with resorcinol glue.
Resorcinol is not able to bond polypropylene, polyethylene, pvc, teflon or waxy surfaces.
email me if you find mistakes, I'll fix them and we'll all benefit: Christine