Windex works okay for applying all types of adhesive backed material, however you can make a little concoction that works better.

Add 4-6 drops of liquid dishwashing detergent (Dawn, Ivory, etc.) to 4 ounces of tap water in a spray bottle. Shake up a little then test spray some on a smooth, vertical surface (tile countertop, refrigerator, etc.) and watch it's action. If it beads up and runs, add more detergent until you get a solid wet surface.

Windex contains ammonia and alcohol for deep cleaning and rapid evaporation and can negatively affect some adhesives. Plus it doesn't allow much "move around" time and will stick in some spots while floating in others. Dish detergent contains neither but does have a wetting agent (thats what causes it to leave a "sheet" of wetness). The decal floats on the wet surface and does not bond until you squeege out the liquid, starting from the center out. This "sheeting" action eliminated 95 to 100% of any trapped bubbles. Plus, once squeeged out, you still can easily lift the decal if you don't like the position.

It takes longer to dry than Windex but is better to work with. This is why I apply decals in the evening, turn out the lights and go to bed. Resists the temptation to keep checking the decals for adhesion.

I supply a small spray bottle full of sign grade application fluid to my decal customers with large size decals. However the dish detergent works well too, just takes longer to dry.

Drop and email if any questions about applying decals.