An epoxy resin is a compound that contains the reactive epoxide group. These groups can react by cross-linking with other compounds called hardeners or curing agents to form rigid three-dimensional networks. Many types of curing agents can be used to impart different properties to the finished product. Among these curing agents are aliphatic amines, aromatic amines and cycloaliphatic amines.

There are two main types of epoxy resins:

• Bisphenol A: Formed by the reaction of Bisphenol A and epichlorohydrin
• Epoxy Novolac (also called epoxy phenol novolac): Formed by the reaction of phenol and formaldehyde.

Epoxy Novolac resins have higher functionality than Bisphenol A resins, which means they have more sites available for cross-linking with hardeners. This higher cross-link density results in products with higher chemical and temperature resistance.

Furane resin (also called furan resin) is formed by condensation of furfuryl alcohol and furfural at elevated temperatures using an acidic catalyst.This resin is mixed with an acidic hardener to produce a hard, cross-linked solid with excellent chemical resistance.

Vinyl ester resin (also known as epoxy vinyl ester) is made by reacting acrylic or methacrylic acid with epoxy. Vinyl esters are an improved version of standard unsaturated polyesters with greater strength, higher chemical and heat resistance, reduced shrinkage and less susceptibility to moisture during curing.

Vinyl ester resin hardens by polymerisation, using a promoter (accelerator) and a catalyst (hardener). The catalyst is generally a peroxide.

Silicates are solutions of sodium or potassium silicate (also called water glass) that react with an acidic hardener in a condensation reaction to produce a hard silicate gel.

Potassium silicate is now used in preference to sodium silicate. Sodium silicate can have adverse reactions with sulphuric acid under certain conditions.

Halogen free potassium silicate denotes a product that does not use a fluoride hardener. There is a theory that fluorides can react with acids under certain conditions to form hydrofluoric acid.

There are many different types of polyurethanes ranging from soft, elastomeric compounds to rigid materials and polymer concretes.

• One-part polyurethanes are polyisocyanate compounds that react with moisture.
• Two-part polyurethanes consist of a polyalcohol and a polyisocyanate which react to form a cross-linked polymer.

The properties of the end product can be modified by altering the type of polyalcohol and isocyanate used, the mix ratio of these components and the fillers incorporated in the system.