Adhesives, sealants and joint fillers

ADHESIVES, SEALANTS AND JOINT FILLERS

1. ADHESIVES

Adhesives are used to join two or more surfaces to form a single unit. Glue is a general term used for adhesives. Glue is used for joining the surfaces of timber, glass, plastic or even metal. However, there is no adhesive that can be used for joining all materials. The various types of glues are briefly explained below:

Natural Resin Adhesive: Asphalt, Shella and cresin are natural resins. They are used for joining papers.

Rubber Glue: This is obtained by dissolving rubber in gypsum. It is used for joining plastics, glass rubber, etc.

Synthetic Glue: These glues are based on resins used in the manufacture of plastics. There are many varieties like melamine resin, phenolic resins urea resins, polyvinyl resin, phenolic resins and nitrocellulose. These adhesives are strong, fireproof and waterproof. They are used in plywood and laminated products. They form permanent and high-class joints.

Starch Glues: It is prepared from vegetable starch. It is made by mixing wheat or rice flour with hot water. Acids or alkalis may be added to improve adhesive property. Such glues are available both in dry and liquid forms. They have a fair resistance to heat but poor resistance to water. They are quite cheap and are used for joining paper and an inferior quality of plywood.

Special Glues: They are prepared to join metals. For example, cycle-weld glue, which is ideally suited for joining aluminium sheets, is made by modifying rubber. Araldite is used to join light metals.

2. SEALANTS

Sealants are materials used to seal cracks or joints in a structure. They are used to close joints such as those between the wall and window frame, glazing and window frames or lap joints of roof sheets. Sealants are subjected to various types of stresses due to differential expansion and contraction of the materials they join. Hence, sealants should be soft, flexible and at the same time should bind the two materials. They should not allow water to leak.

Sealants are marketed in the form of performed strips, semi-elastic and elastomeric sealants. Elastomeric sealants are the most efficient. They are based on silicon, acrylic, urethrone or polysulphide. Among these polysulphide sealants are the most popular and efficient.

3.  JOINT FILLERS

Construction joints should be provided in wide concrete structures to avoid undue thermal stresses. The width of construction joints is usually 20-30 mm. Joint fillers are materials used to fill the sides of joints that are subjected to relative movements. They should be compressible and resilient. They are built in strips of metals, bitumen treated felt, cork bound rubbers and so on.