Ill answer ur second question first lol...in my opinion whats the point of paying extra for #42, a special gun to use the cartridges, and the cartridges when you can just buy #40 and shoot it out of all different kinds of applicators specific to each job. I use larger type syringes, squeeze bottles in a range of sizes and even just pour seams right out of a mixing container. Yes #42 may be neater in the aspect of not making a mess on ur acrylic and for cleanup but as for performance theres no difference with the right tools/applicators than can be found around the house or a dollar store.
Now back to why its not always best to use #40-42 on other types of plastics for lol...will it work? Yes....how well does it work is the real question. it does not give you the same results and strength as when you use it on acrylic. There are different solvents and methods like heat welding used to bond these other types of plastics for a reason. Ill try to find a data sheet from the weldon website for different materials. For example, say acrylic to #40/42 bond is 100% adhesion. #40/42 to a.b.s. or p.v.c. may drop as low as 40-60% adhesion. Thats a huge difference when were dealing with water pressure and making a water tight seal. If you tried to use a.b.s. sheet and #40 to construct a tank it would explode. Heat welding is used for most all plastics other than acrylics/polycarbs because it literally melts the sheets togehter. Cheap plastics like glass tank trim are just that, cheap plastics. Sometimes there not worth fixing. Its very possible the heat created when the weldon #40/42 starts to cure can warp, distort, or even melt the trim.
Just getting the point across the glue is not full strength on other materials. It may work for a certain case, it may not. More for non structural applications. I think u could get away with fixing some tank trim. I also think u could probably pull it back apart very easily lol...
Getting 2 things to stick together is easy, scotch tape will do that lol...physically melting them together permenatly with solvents/epoxies/heat can be harder and there are different ways to permenatly bond different materials. Just like putting regular silicone on acrylic. Yes it will stick, but u can also pull it right back off.
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