Re: winshield haze

[Theo Thepen <thepen@pi.net>]

Toby Erkson wrote:
>
> About the anti-fog product and summer:  Just in case, you apply the
> anti-fog then buff the haze off once it dries, just like the Rain-X.  Now,
> as for the hazy stuff you ONLY see in the summer -- it is vapor from the
> dash that is deposited on the windshield.  Although more noticeable on

Hello,
Sorry guys, the story about a 'vapour from the vinyl' is very unlikely.
If you like I can calculate the amount of softening agent (plasticizer) 
solvents
remaining after production of vinyl, but I can assure you it's extremely 
low.
Also, this doesn't quickly evaporate from the vinyl. Remember that the 
vinyl in
our cars is at least 20 years old, so the amount remaining after that 
long a time
is absolutely extremely low, that's why the dash cracks. 20 years of 
hazing up your front screen by vapour
from the dash would require a lot of softening agent and solvent. Also 
the
cracking of the dash is not mainly caused by UV. Glass absorbs over 90% 
of UV
radiation from sunlight, only in a convertible in California that would 
play a
major role. The dash cracks because of drying out of the vinyl (yes 
indeed the
softening agents and solvents evaporate from the plastic, but as I said 
before, a
very low amount at a very slow rate), and temperature differences. Black 
dashes
that absorb more heat from sunlight (that means infra red, but also 
normal
visible light which is not absorbed by glass), crack faster and more 
severe than
lighter coloured ones. The stuff you use to make your dash shine again, 
adds only
little softening agent, if any, although the manufacturers of that stuff 
like you
to think so. It mainly contains solvents that remove the very thin top 
layer of the vinyl
and a kind of wax that seals the vinyl and prevents further drying and 
makes it
shine again.
The haze on the inside of your front screen is most probably mainly you ! 
It's your own sweat,
and yes, also smoke from cigarets, that precipitates on the (colder) 
glass. Sweat
is not just water but is used by the body to excrete waste products (and 
also
pheromones which is a very interesting subject btw). The effect is made 
worse by
the fresh air vents in our VW's which let most air circulate over the 
windscreen
as they're under the screen blowing 'fresh' air and air from the 
compartment over
the windscreen. The effect can even be worse in modern cars that have an 
airco
that recirculates the air in the car and only draws in little air from 
outside.
However, modern cars have more oulets, directing air from the dashboard 
to the
interior.

Cheers
Theo