Weld-On solvents are incredibly toxic -- like, causing brain damage toxic. (I've read similar warnings about MEK.) I've used Weld-On a lot, and the manufacturer recommends an AIR-SUPPLIED RESPIRATOR when working with it. That's the kind that has a hose bringing you fresh air from outside the area. It means a dust mask or even a regular paint respirator isn't going to be enough to protect you from the fumes. So, don't use this stuff indoors!
I actually went to the trouble of building a ventilated work booth so I don't have to breathe any fumes when working with solvents like this.
This stuff is extremely "hot" for use with styrene. It will work, but it quickly dissolves the plastic. It's really formulated for acrylic. I find it doesn't work well for ABS and doesn't always do a good job with bonding styrene to acrylic (it works but sometimes the styrene parts will pop off later). [BTW, The best glue I've ever used for joining acrylic to styrene/ABS/Butyrate is made by Plastruct. I wish I could get this stuff in larger quantities!]
A couple other tips:
1) Using any sort of open dish or bowl as a "well" to dispense solvent causes waste in the form of evaporation and helps toxic fumes get up in your face. A very experienced modeler friend introduced me to something called a Menda Pump. This is used to dispense solvents in tiny amounts and helps avoid excessive fumes and waste from evaporation. You can get it from Plastruct.
2) When using a brush to weld parts with solvent, it must be a natural hair artists brush. Many paint brushes have synthetic hairs made from plastic. These are likely to dissolve or stick together and become unusable when dipped in powerful solvents like Weld-On.
