I don't know why, but I just assumed that everybody knew how to solvent weld plastics like styrene. I guess it's something I've known for so long that I forgot I had to learn it somewhere. So, in the spirit of teaching and sharing what I've learned, I'l pass on this tip and a little explanation of why it works. Hopefully you'll never again feel the need to reach for ACC or Super Glue when you want to bond two pieces of styrene.
My "glue" of choice for styrene is not glue at all. It's a solvent, called MEK (which stands for Methyl Ethyl Ketone), and is sold in hardware stores in pints, quarts, and even gallons. In 20 years, I've used less than 2 quarts, with a fair portion of that being lost to evaporation. Many excellent modelers also recommend lacquer thinner. I have found MEK to be a little more aggressive at dissolving styrene than lacquer thinner, and also to evaporate faster. Usually, those are both useful properties, but there are a few cases where I prefer lacquer thinner for the gentler action or greater working time. Acetone will dissolve styrene and acrylic (like Plexiglas), making it useful for some situations as well.
There are also a number of hobby glues, cements, and plastic welders on the market. Many of them are based on MEK, some use other solvents. Some contain a mix of solvents, making them suitable for a wider variety of plastics. Some contain fillers, making them better at filling gaps between parts. I have used a few of the commercial products, but I have never felt the need to keep a supply on hand, because MEK, lacquer thinner, and acetone have generally met my needs just fine.
The way these solvents work is by dissolving a layer of plastic on either side of the joint. That dissolved plastic then fuses into a single piece when the solvent evaporates. Two pieces of styrene literally become one, with no seam, no weak point, and no dried glue to make a mess. The technique is called solvent welding, which describes the situation quite well. The joint is as strong as the base material. However, because there is no glue to fill the gaps, you do need the joint to be reasonably tight before making the weld. Fortunately, the solvents are quite thin, and will wick themselves into the joint nicely. My usual technique is to hold the two pieces together, then apply MEK to the outside of the joint, using a long handled artist's paint brush (which I keep with the MEK and never use for painting) to apply it wherever I want it. I will sometimes apply a little pressure to the parts after applying the solvent, which forces a little styrene to squeeze out. That fills and minor gaps in the joint, and can later be sanded off for a perfectly smooth and seamless joint.
Another advantage of solvent welding is that, with care, it is possible to use it on painted models without damaging the paint. I remember one particularly challenging build, a Proto 2000 Mather stock car, where I was able to glue the styrene grab irons to the painted body of the car, without any sign of the glue around the joint. In that case, the MEK dissolved the paint and styrene, forming a mix which was strong enough to hold the grab irons securely.
Hopefully this will help you save some money, and build neater, stronger models. I can't really think of a down side!
