UV protection vs. clear layers

[MikeS]

I understand about UV protection the clear coat provides and according to the SPI tech manual there should be at least 2 mils after buffing. But I was curious about if that is at the total thickness level or spray session layer level.
As an example: in cases where one would spray a few coats of clear, block to level then spray a few more flow coats then sand and buff, is the UV protection capability the sum of all remaining clear coats of both sessions or just the more recent session sprayed and in this example being the flow coats.

Thanks,
Mike.

 

[Barry]

Great question.
Certain UVs tend to float over time, so if first three coats are allowed to dry and you re-clear, the UV's in first application are going nowhere and if nothing else your base will be well protected.
A common question is I have 3 coats and I want to wetsand and put down one coat of clear as a flow coat----Can't be done as now we are starting over and the 2 mil of left clear applies to last coat, so clear could start breaking down, speaking of the last coat.
In short yes, 4-8 coats of clear will help with UV protection for the base if nothing else.
By the way, the 2 mil left deal is a Ciba statement going back many many years ago as they are or were the largest manufacturers of UV adsorbers, not sure if they still are as BASF bought them about 3-5 years ago and it only took me 6 months to buy another brand at that point, mainly the stupid chemical rep agency's they hired..Fine with me, I will spend my $ 18,000-28,000 a month elsewhere.

 

[MikeS]

Hi Barry,

So if I understand it correctly this is a two part answer (being UV protection applies not only to BC but also to CC) in that the sum of all the clear layers combined will protect the base color and to protect the clear layer itself, the top most recent coat should still be a minimum of 2 mils thick after all the cut and buff is done.

Thanks,
Mike