blue78rs

iTrader: (1)

I'm about to start some body work on my car and my question is. If I am using urethane primer will it absorb moister. I was told if I put primer on spots of my car I will have to paint right away. However I see a lot of cars driving around in just primer. can someone please make this clear to me.
This is the primer I would be using.http://www.eastwood.com/media/catalo...e95/p40795.jpg

blackbmagic

Primer does somewhat absorb moisture. Which is why you need to seal before paint, unless the primer instructs otherwise.

The reason you must paint asap is because over time the primer can accept contaminants like dirt, oil, silicates, ect and they will also absorb into the coating. If moisture is continuously allowed to bleed through your primer coat it could could lifing and poor adhesion.

You see people driving in primer for a few reasons. Mainly lack of knowledge. Other reasons being the "primer" coating you see may be a matte paint. Also there are some primer surfacers out there such as polyesters that act as a sealer as well and are much more resistant to the elements because of their properties.

You shouldn't really drive your car with a primed coating, not necessarily because of just moisture but because of oils and grime which can get caught in the primer and create an unsuitable surface for your basecoat to adhere to. I have had primered cars I have painted succumb to the elements and get wet, its fine. Just make sure they have had a day or so of sunlight and are completely dry before base.

Slayze

iTrader: (1)

I have been an automotive painter for years and the best primer I have come across is Diamont DP20 Primer http://absap.com/rmtech/DP20.htm. I would take a look at the Tech data sheet for your primer to see what you should and shouldn't do with your particular primer. Theres usually a window of time that you have in order to get some paint applied to the primer. If your past that time then you usually have to scuff/sand and reapply primer. Like the DP20 its 12 hours I think. yup just looked it up. (Do scuff, clean and reapply one light coat of DP20
before topcoating if the initial application dried
longer than 12 hours.). Its important to get a good bond as blackbmagic pointed out.

Slayze

iTrader: (1)

I just looked your primer up and here is yours
Urethane Primer Surfacer may be topcoated after approximately 30 minutes, or up to 18
hours (at 70 °F with sufficient cross-ventilation), with no additional prep required. After
18 hour recoat window, primer MUST be sanded prior to topcoat application for adhesion purposes

http://www.eastwood.com/images/pdf/50240INST.pdf

Yours says it just needs to be sanded prior to paint where the DP20 says to reapply, but I have also done that with the DP20 with the same results. Our paint rep. from BASF told us that it would be ok to just scuff and topcoat after the 12 hours, but if someone is leaving it on for weeks at a time and driving with it on I would definitely reapply some primer. Oh and if you have some bare metal I would use an epoxy primer for the bare metal areas as a pretreatment primer.