How do you know when a product needs reapplying?

[DanFreemanPhoto]

Some more really basic questions!:

If, for example, I wax to do a full clean of my car, ie SRP, EGP and then a couple of layers of wax, how would I know when I need to redo this process?

Is it a simple case of the looks starting to deteriorate?

Also, how do I know that applying other products wont remove any products already on the car. So if I wax my car, then wash it, I presume this wont remove the wax?
But will polish remove the wax?

Thanks

 

[MRBILLYUK]

Polish and seal once a year with SRP and EGP , or something easier to use like the Jeffs Acrylic worksatt sealant .

Add layers of wax just to top up as and when you feel the need or have the time .

SRP will remove previously applied wax .

 

[Guppy]

Clayed, SRP'd, EGP'd and natty's paste Wax yesterday and my paintwork is smooth as silk now