Adhesives and glues can be conveniently divided into the following groups:
- Water Soluble
- Water thinnable (emulsions)
- Solvent based Air Drying
- Heat Sealable
1. Water Soluble
- Simple water soluble adhesives have limited use in modelling due to their lack of water resistance after drying.
- They are mainly used where water resolubility is required:
- Wallpaper pastes
- Paper Glues such as Prit-Stick, useful for sticking down templates
- Gums used in artwork or decoration
2. Water Thinnable Emulsions
- These are the main products used when waterbased adhesives are quoted.
- They come in 4 principle forms:
- Vinyl Emulsions
- Vinyl Copolymer Emulsions
- Acrylic Emulsions
- Reactive Emulsions
- Green Evostik Wood Adhesive or similar
- These can be used for track laying, ballasting and most scenic applications where limited water resistance is required but ease of removal is a factor.
- They are usually polymers of polyvinyl acetate and although giving some degree of water resistance they are not totally waterproof and are usually quite brittle when fully dry.
Vinyl Copolymer Emulsions
- Blue Evostik Weatherproof or similar .
- Can also used for tracklaying and ballasting but they may be difficult to remove when fully dry.
- These are copolymers of polyvinyl acetate and ethylene which are tough, flexible and waterproof when dry.
Water based Acrylic Emulsions
- Similar properties to Vinyl Copolymers although even more water resistant.
- No tendency to yellow. Useful when clarity and lack of colour are important .
- However expensive and unnecessary for most modelling uses.
Reactive emulsions such as Copydex
- Typically Copydex, based on Casein, they react after drying .
- Limited in water resistance and can be difficult to handle with a strong smell of ammonia.
- Can be useful for woodworking.
3. Solvent based Air Drying
- Traditional solvent based adhesives such as Bostik or Evostik.
- They oxidise with time rendering them more resistant but less resoluble .
- Solvent based Evostik is useful due to its versatility. It can be used in a number of ways.
Uses of Solvent Based Evostik
- Straight from the tube as an impact adhesive, allowing time to move items to be stuck before setting.
- Allowing the solvent to evaporate and using it as a contact adhesive.
- Thinning it with solvent (sold as Evostik cleaner) in order to brush it out evenly prior to using it as a contact adhesive.
- Its one drawback is that it is extremely stringy and dries very fast initially. These problems can be reduced by thinning it with solvent.
- Very useful for track laying.
- This category covers all the tougher adhesives used in modelling but also the ones which due to toxicity, require the greatest care in handling.
- This group includes Epoxies, Cyanoacrylates, Silicone based polymers and Polyurethanes.
- They react at different rates and produce different results, but two basic rules of reactivity are that the faster something reacts the more toxic it is likely to be and the more brittle is the resulting film.
- Epoxies are 2-part adhesives that must be mixed before use.
- They come in 2 types: 5-minute and 24-hour according to the time taken to react.
- Typically available as Araldite or Devcon.
- Useful for white metal kit construction in place of solder and for making split axles.
- Caution with all epoxies prolonged or repeated skin contact can cause dermatitis, so direct skin contact should be avoided.
5-minute Epoxy Polymers
- 5-minute Epoxy is useful where repositioning is required. It is very thin when first mixed and remains so for 4-5 minutes. It then thickens rapidly.
- Items can easily be repositioned and then held long enough for thickening to occur. Its film is more brittle than the 24 hour Epoxy but tougher and more flexible than cyanoacrylates.
24-hour Epoxy Polymers
- 24-hour Epoxy is adhesive of choice where toughness and a strong bond is required and you have the time to leave it to cure.
- It is the next best thing to solder and may be preferable to white metal solder.
- It is most useful for making paper gaskets in split chassis construction.
- For this use and others where a thin film is required both 5-minute and 24-hour epoxies can be thinned with cellulose thinners and meths or isopropanol, but it will then be necessary to let the film dry out.
- Typically Superglue.
- Cyanoacrylates are ideal for rapid curing and come in various thicknesses and reactivity from slow curing (about 30-40 sec) which are thick, to instant cure (less than 5 secs) which are very thin.
- The 20 sec variety is the most useful. However for instant bond the 5sec type is ideal but necessary to get it in the right place, first time!
- Cyanoacrylate films are quite brittle so they should not be used for load bearing applications. Avoid breathing the vapours as at even low levels they are very toxic.
Silicone based Polymers
- Silicone based polymers are very reactive and give off acetic acid.
- Mainly used as bath sealants they give a tough, waterproof and very flexible result.
- They are however, expensive, difficult to use and come in large containers which once open will not last.
- Polyurethanes require water to activate them and give you 5-10 minutes open time for repositioning.
- They then require 8-10 hours to fully cure. Once cured polyurethane films are tough, water resistant and very flexible. In use they are therefore similar to 5-minute epoxies but with a much more flexible film.
5. Hot Melt Adhesives
- These require a glue gun.
- They are useful where instant cure is required and the side effects of reactive polymers are to be avoided.
- In many ways they behave like solder but on non-metallic surfaces. In effect solder is a hot melt adhesive for metals..