Plastic cement

Plastic cement is not glue in the way white craft glue is. It is a solvent that softens the surface of styrene plastic on contact, and when two softened surfaces are pressed together they fuse as the solvent evaporates, effectively welding the parts into one piece of plastic rather than sticking two separate pieces together. This is why a well-glued styrene seam can be sanded and painted as if it were never a joint at all.

Plastic cements come in a few thicknesses. Thicker, tube-style cement gives more working time and gap-filling ability for larger or slightly uneven parts, while thinner, brush-applied cement sets faster and suits precise seams where you do not want excess squeezing out. Choosing between them usually comes down to the size of the parts and how much time you need to align them before the joint sets.

A common mistake is applying too much cement at once, which can soften more plastic than intended and leave a sunken or melted-looking seam once it dries. Another is assuming plastic cement will bond resin, metal, or photo-etched parts the way it bonds styrene, when those materials need a different adhesive entirely since there is no plastic surface for the solvent to melt.