I agree with the others, I think your downfall was the turps!
Completely scrap using that for anything connected to your vinyl work mate.
Isopropyl alcohol or Industrial Meths is what i prefer to use.
dont buy from the likes of B&Q though, buy it from a Janitorial / Cleaning Chemicals type supplier. You will buy it in 25litre drums which will last you months and only cost about £30ish
Buying from local stories will cost you about £10 for a small hand size bottle.
Industrial Meths is Clear, domestic is purple. dont buy the domestic stuff, the purple in it can dye certain surfaces, including resprayed vehicles. i have that T-shirt from many moons ago.
Be careful buying either ISO or Meths thats clear, make sure you have a sealed container as you maybe buying watered down bottles, which is not uncommon. you can tell if it doesnt remove the likes of pen ink on first swipe, or if the fluid beads on the surface rather than evaporates very fast.
There are ways the vinyl can fail simply by the way the customer treats the banner. if the banner is folded rather than "rolled". this can create dog-earing of the vinyl, creases and so on.
also, you cannot roll it tight. loose or around an old card vinyl core tube.
You MUST roll the banner with the vinyl facing out, not inwards as again this can cause the vinyl to come off.
apply with a nylon squeegee rather than felt.
heat promotes adhesion also, but dont overheat one area or you can create gloss patches on the banner.
if you banner is stiched, dont cross the stitching with vinyl. to be honest if you do your too close to the edge with vinyl anyway.
