Please note: I wrote this article some time ago for another site that I used to own. It's not really up to TG standards as it has no images to illustrate it. This is an issue that I hope to rectify as and when I have time to take suitable photographs but in the meantime I offer it here in it's original text only format:
Of all the materials that are used to make kits probably the biggest pain in the backside is vinyl. Thankfully we don't see a lot of vinyl kits in the genre of terrain making however the advantage of vinyl is that the tooling costs are low so we may well see specialist vinyl kits appearing in the future. Anybody with an interest in sci-fi or movie related kits will already be aware that there are a plethora of niche market kits for that genre that simply would not exist but for the low cost, small quantity production runs made possible by vinyl.
The reason I'm not keen on vinyl is because the parts are often misshapen and need correcting, and that various solvents, including those in oil-based paints, will attack the vinyl. The final straw is that if you put the finished model in an environment that's a tad on the warm side it'll probably sag!
As already mentioned, vinyl softens when warmed and this is a problem with a built in solution: The parts you will receive in the box will almost certainly be distorted but this can be corrected by warming the parts and reshaping them. The use of a hairdryer is often suggested for this purpose but as the idea is to warm the part, reshape it, and then cool it down so that it retains the new shape I'm inclined towards the use of warm water. Basically this entails placing the part in warm, not hot, water until it softens. You can then shape it and run it under the cold tap to cool it down and fix it in its new position.
There will also be quite a large amount of spare to be trimmed off vinyl parts. The best thing to use is a sharp knife and again the job can be made easier if the vinyl is warmed first to soften it. Save the pieces you trim off so you can use them to test glues and paints later on.
Note that at the same time you're mucking about with the warm water, you may as well get some soap in there and wash of the release agents that will no doubt be hanging around from the moulding process.
When it comes to assembly you will need super glue and probably a bucket full of P38 or similar epoxy filler. The reason for this is that the parts hardly ever match up well. Several rounds of dry fitting and trimming are usually par for the course before you put the glue anywhere near it and then you'll probably have a fair amount of filling and sanding to do afterwards.
Before you actually glue anything together there is another problem that you should consider: after you've built the model, if it gets warmed up again, it's likely to change shape damaging the paint job in the process. Part of the solution is to keep the completed model away from heat. Radiators and direct sunlight are definite no-nos. Another precaution is to pack the inside of the model with something so that it can't change shape. I've seen newspaper or metal foil suggested but my own preference is for papier mache or plaster. Plaster has the advantage that it's easier to use but is heavier and will warm up as it cures. Papier mache is somewhat lighter but more troublesome as you have to stuff it into the crevices. Either way, once your stuffing has set solid there is no way that your finished model is going to start moving about.
By now things are starting to take shape and you can apply a coat of primer but BEWARE. Vinyl will react to oil based paints. The answer is to do the priming at least with a water-based acrylic. I'll say that again 'a WATER-BASED acrylic' because acrylics aren't necessarily water based and you need to make sure particularly if you're using the spray can variety. If there's any doubt at all, test it on an off cut of vinyl. After the primer it is possible to use enamels (as they will only be coming into contact with the primer and not the vinyl itself) but it's probably safer to do the whole job with acrylic.
The application of primer will probably show up a lots of surface abnormalities which will require filling and sanding (super glue will effectively fill pin-prick air bubbles) before priming again. You can now proceed with painting in the normal fashion.