if the tint that is installed is in good condition, i would tint over it. i have 2 layers of tint on my car with absolutely no issues at all. keep in mind that the second layer of tint will require 7-10 days to fully dry, instead of the normal 2-3 days, and thats in the Florida sun.
most cars from the factory have the "tinted" option...for the most part, this is a 70% tint, which looks almost like no tint at all. heres a quick formula:
Layers multiply. If you start with the factory tint of 70% and add a 35% layer you get 25%. 0.7 x 0.35 = 0.245 which is what you currently have. Adding another layer. of 70% would of course lower the light reading, 0.7 x 0.35 x 0.7= 0.1715 or 17% tint.
Like begood stated in his post, 0.7 x 0.35 x 0.20 = 0.049 or 5%
The only problem i see is trying to find a tinter that has a 70% tint, and then spending the $$$ for such a light tint. If you are trying to get in the 15-20% range then adding the layer of 70% would do it for you (17%)...on the other hand, removing what you have, and installing a 20%, would give you roughly a 14% tint overall, with less drying time and no issues of bubbling. A lot depends on the tinter and his abilities. If he messes up the tint of the second layer, both layers have to be removed in order to fix it.
In my case, 0.7 (70% factory) x 0.2 (20% first layer) x 0.05 (5% second layer)= 0.007 less than 1%...1% is the light meter reading or how much light is coming through...and i had the pleasure of paying a ticket to the Casselberry Police Dept when they decided to check my tint.
