Adhesives, also known as glue, cement, slime, is a non-metallic substance applied to one or both surfaces of two separate parts that combines them with each other and is resistant to their separation. The use of glue offers some advantages over other joining methods, such as sewing, mechanical joining, or welding. These include the ability to bond different materials, more efficient stress distribution in combination, cost-effective ease of mechanical process, and greater design flexibility. Wood adhesives are generally classified as synthetic or natural. Synthetic adhesives contain prepolymers (oligomers or polymers that can be obtained from materials such as petrochemicals). The glue should be applied in liquid form to evenly distribute over the surface of the wood and moisten it. Adhesive prepolymers can be used if they are liquids, or can be used as a solution, usually water-based.