Xylene (mixed isomers)
The medium-evaporating aromatic solvent that has thinned epoxies, urethanes and primers for generations.
Commercial xylene is a mixture of the three dimethylbenzene isomers (ortho, meta and para), usually with some ethylbenzene. It boils at roughly 137–144 °C and has a flash point near 25–30 °C, so it is flammable at ordinary temperatures.
Xylene is used as a thinner and cleanup solvent for epoxy and polyurethane coatings, in primers and alkyds, and as a cleaning solvent for equipment. “Urethane grade” xylene has very low water content for isocyanate systems.
As an aromatic hydrocarbon, xylene dissolves epoxy, alkyd and many acrylic resins well and evaporates at a moderate rate (about 0.7 relative to n-butyl acetate), giving films time to level. It contains no reactive hydrogen, so it does not react with isocyanates when dry.
Xylene is flammable and its vapor can cause headaches, dizziness and central nervous system effects. It is listed as a hazardous air pollutant in the US. Ventilate, ground containers and use organic-vapor respirators where needed.
Use urethane-grade xylene with low water content, and only if the product data sheet allows it. Water and alcohol contamination react with isocyanate.
PCBTF has a similar evaporation rate and is VOC-exempt under US EPA rules, though it costs more and has its own hazards.
