Most homes are full of breakable plastic items that sometimes need repair, but because plastic is a non-porous, smooth material, gluing the pieces back together can be challenging. Some adhesives that work with wood, such as polyvinyl acetate -- carpenter's glue -- don't adhere well to plastic, while others, such as epoxy resin, may not be flexible enough. Moreover, an adhesive that works well with one type of plastic may not work with another.
Know Your Plastics
The list of plastics you may find around your house is extensive. The plastic in your plumbing pipes is different from the composition of your plexiglass appliance covers, and both of these differ from the soft and molded plastics in toys and furniture. Before gluing one plastic item to another or a broken piece back together, therefore, it's important to know from what types of plastic the items are made. Some glues work by partially dissolving the material you spread them on, and they won't dissolve all types of plastic. Other glues form a purely mechanical bond, but adhere better to some types of plastic than others.
Gluing Plastic Pipes
Plastic pipe cement is a combination of plastic resin dissolved in a solvent, and because the solvent dissolves the materials you're bonding, it's called solvent-weld adhesive. Some types are designed only for use with PVC pipes while others are only for ABS pipes, and you can also buy an all-purpose variety that works on both types of plastic. Plastic pipe cement is volatile, and it momentarily softens the surfaces on which you use it so they fuse together. This pipe cement is only for use with tight-fitting plumbing joints and, when used correctly, produces leak-proof connections.
The solvent-weld strategy also works when joining acrylic plastic sheets, but the products are slightly different. These gluing products, usually identified as plastic-weld or weld-on plastic adhesives, soften the materials you're joining so they fuse together after you clamp them for several hours. In some cases, you can even weld acrylic by applying liberal amounts of acetone -- a powerful solvent -- to both parts that you want to join. Silicone caulk forms a strong mechanical bond on acrylic plastic and effectively holds sheets together. It also holds acrylic plastic to other materials, such as wood, concrete and glass.
All-Purpose Plastic Bonding
Silicone caulk forms a strong bond on virtually every plastic, but because it's very flexible and difficult to control, it isn't the best glue for rigid or small plastic repairs. Polyurethane glue is a good all-purpose choice; it's waterproof, flexible, permanent and adheres to most plastics. Cyanoacrylate glue, usually known as super glue, also bonds most plastics, but its lack of flexibility limits its usefulness to only the most rigid types. If you need a temporary bond, hot melt glue is a viable adhesive option. Objects stuck together with this material can usually be separated again without much effort.