Hopefully this is the correct board, I was wondering if it is ok to use dupont flex additive in nason 421-19 high build primer. the msds says nothing but I have read where people do use it and have good results. my other option is to buy a quart of dupont high build, trying to save a little cash this way.

 

I would save the cash by not using flex additive at all unless you are doing something unusual with it. The only reason it is needed is if you handle flexible parts roughly before installation or if you want the part to be able to deform and rebound without visible damage. While the latter sounds good , I have found that only the most durable (not like anything on a third gen) plastic bumpers can actually do thus without damaging something besides the paint.
Also, while I can't speak for all paints, usually flexible additive is only needed for the clear coat as that gets very hard and inflexible after cure. If you are usng the high build primer on a bumper, maybe that's a place to use the additive , but I would prefer to yes a flexible filler in problem areas and regular epoxy primer everywhere else.

 

Thanks for the quick reply. Yes, only on the bumpers and front lip was i going to use the flex, because my instructor says I need it. I have heard both sides and am leaning to using it because I am painting them all off the car so they will be all floppy/droopy until I get them installed. But I have talked to numerous people who have not used it and had great results. Just curious if I do add the flex in my nason, should i use the recommended amount for the dupont high build?

 

Sorry, don't have any experience with either product so can't answer that. Some surfacers are more flexible than others so also can't say for sure the additive is necessary. Probably a good idea to follow what your instructor says since if you don't and it comes out poorly, it might affect your grade. It's always a risk mixing different types of product unless you can get the details of their composition.
Unless someone can tell you for sure it will work, I think I would go buy the correct additive or primer.

 

Sounds like a plan, Thanks!

 

To answer your specific question, it is OK to use the DuPont flex in the Nason High Build. I've only used generic and other brand flex agents for close to 40 years without issues. Who knows what will happen tomorrow.

I currently used a brand Bulldog as a flex additive. It is also an adhesion promoter for urethanes and plastics.

There is a continuing argument about the need for flex agent in modern paints. I've always been on the side that uses it in sealers, primers and clearcoats religiously. Several times, I've used flex on the complete vehicle. IMHO, flex...in addition to its flex characteristic...makes the paint much glossier and makes it easier to color sand and buff.

I recently ran across some comments on a manufacturer site that stated the newer flex agents DO provide long lasting flexibility and chip resistance. I bookmarked the site, but now I don't remember which one it was.

You can believe what you wish. I have a Corvette that I painted in 1989 and used flex on the entire vehicle. It still look like new and usually get a trophy in local shows.