Development and use for plywood

Tego film was developed in Germany around 1930 as a glue for waterproof plywood. It comprised a paper sheet pre-impregnated

Pre-preg

Pre-preg is a term for "pre-impregnated" composite fibres. These usually take the form of a weave or are uni-directional. They already contain an amount of the matrix material used to bond them together and to other components during manufacture. The pre-preg are mostly stored in cooled areas since...

 with a resole phenolic resin. When heated, assembled between wood veneer

Wood veneer

In woodworking, veneer refers to thin slices of wood, usually thinner than 3 mm , that are typically glued onto core panels to produce flat panels such as doors, tops and panels for cabinets, parquet floors and parts of furniture. They are also used in marquetry...

s and then compressed, a strong and waterproof laminated plywood was formed. Most plywood at this time used other adhesives, such as casein

Casein

Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....

. These adhesives were generally applied as aqueous solutions, which caused warping of thin veneers and made it difficult to achieve a solid laminate without risk of voids. As Tego film was used dry, it gave a high integrity result, solid and without risk of hidden weaknesses. This became an important factor in time, when it was applied to use in aircraft construction.

This adhesive was unique at its time and was only available as the Goldschmidt product line from its makers Goldmand AG of Wuppertal

Wuppertal

Wuppertal is a city in North Rhine-Westphalia, Germany. It is located in and around the Wupper river valley, and is situated east of the city of Düsseldorf and south of the Ruhr area. With a population of approximately 350,000, it is the largest city in the Bergisches Land...

. By 1932 it was being exported worldwide.

Use for aircraft

The de Havilland Albatross

De Havilland Albatross

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 airliner of 1936 had a fuselage

Fuselage

The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

 of wooden sandwich construction: wafers of birch plywood

Plywood

Plywood is a type of manufactured timber made from thin sheets of wood veneer. It is one of the most widely used wood products. It is flexible, inexpensive, workable, re-usable, and can usually be locally manufactured...

 were spaced apart by a balsa

Balsa

Ochroma pyramidale, commonly known as the balsa tree , is a species of flowering plant in the mallow family, Malvaceae. It is a large, fast-growing tree that can grow up to tall. It is the source of balsa wood, a very lightweight material with many uses...

 sheet and glued by Aerolite

Aerolite (adhesive)

Aerolite is a urea-formaldehyde gap filling adhesive which is water and heat resistant. It is used in large quantities by the chipboard industry and also by wooden boat builders for its high strength and durability. It is also used in joinery, veneering and general woodwork assembly...

, a casein

Casein

Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....

 adhesive. This same construction achieved fame with its wartime use in the Mosquito

De Havilland Mosquito

The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...

 fast bomber. As well as being a construction of light weight and high performance, it also avoided the use of aluminium, a strategic material during wartime, and could use the skills of woodworkers, rather than those of specialised aircraft metalworkers.

When Germany attempted to copy this aircraft as the Moskito

Focke-Wulf Ta 154

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, it used Tego film. Flight testing and development of the first Tego film-bonded prototypes from Summer 1943 to 1944 was highly successful. However RAF bombing of Wuppertal in February 1943 (incidentally one of the first Oboe

Oboe (navigation)

Oboe was a British aerial blind bombing targeting system in World War II, based on radio transponder technology. Oboe accurately measured the distance to an aircraft, and gave the pilot guidance on whether or not they were flying along a pre-selected circular route. The route was only 35 yards...

-equipped Pathfinder squadron

Pathfinder (RAF)

The Pathfinders were elite squadrons in RAF Bomber Command during World War II. They located and marked targets with flares, which a main bomber force could aim at, increasing the accuracy of their bombing...

 bombing raids) had already destroyed the only Goldman factory producing Tego film.

For the production aircraft, an ersatz

Ersatz

Ersatz means 'substituting for, and typically inferior in quality to', e.g. 'chicory is ersatz coffee'. It is a German word literally meaning substitute or replacement...

 cold adhesive was used, produced by Dynamit AG of Leverkusen

Leverkusen

Leverkusen is a city in North Rhine-Westphalia, Germany on the eastern bank of the Rhine. To the South, Leverkusen borders the city of Cologne and to the North is the state capital Düsseldorf....

. During a test flight on 28 June 1944, one of the two aircraft broke up in flight. Investigation showed that the glue left an acidic residue after curing, which in turn damaged the structure of the timber. Mass production of the aircraft never took place after this.

Another case of an aircraft design whose existence was threatened by the acidic replacement adhesive was the largely wood-structure Heinkel He 162

Heinkel He 162

The Heinkel He 162 Volksjäger was a German single-engine, jet-powered fighter aircraft fielded by the Luftwaffe in World War II. Designed and built quickly, and made primarily of wood as metals were in very short supply and prioritised for other aircraft, the He 162 was nevertheless the fastest of...

 Spatz, the winner of Nazi Germany's last significant aircraft design competition, for a so-called Volksjager "people's fighter" single engine jet-powered fighter-interceptor as part of the Jägernotprogramm in the concluding months of the war.

Modern use

The term 'Tego film' remains in use around plywood manufacturing today, although it has become generic. It is now used to refer to the phenolic resins still used for the manufacture of exterior plywood, although no longer indicates manufacture in Germany. Most of the plywood produced of this type is now from Indonesia

Indonesia

Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

.