Body filler over 2k primer

[RosharonRooster]

I've read in here a few times that it is not good practice to apply body filler on top of 2k primer. Can someone explain why that is bad?

 

[dhutton01]

It can lead to poor adhesion and/or bad mapping because the cure time for 2k urethane primer is very long.

At least that is my understanding.

Don

 

[Lizer]

I may or may not have applied filler over 2k primer many times without issue.

 

[JimKueneman]

Barry is ok with Dolphin or Icing glaze over 2k though.

 

[El Toro]

I don't and won't do it but if I think the longer the 2K has cured the better.

 

[dhutton01]

I am wondering if it would be ok over Turbo primer because it uses those hyper cure resins. Asking for a friend….

Don

 

[RosharonRooster]

So it has to do with cure times?.

 

[El Toro]

In short yes cure time will help. In the collision world done all the time but the type of job you are doing Rosharon Rooste I would not take the chance............small pit or like may be ok

 

[Barry]

Small spots done every day for ins work, never heard of problems but still risks involved.
Products like dolphin glaze, icing are made for this, so why risk it.

 

[Chris_Hamilton]

From the Evercoat Rage Ultra TDS

APPROVED SUBSTRATES:
Steel
Stainless Steel
Fiberglass
Galvanized Steel
Aluminum
Silicon Bronze Welds
Sanded OEM Paint

Notice no mention of Urethane primer. Also interesting that Epoxy is not mentioned even though OEM's have recommended/required it for 20 years or longer (Mercedes).

Even in Collision Shops putting body filler over Urethane primer is taboo. Although same shops, no one frowns on using polyester glaze over urethane. At least that has been the case at places I've worked at.

 

[crashtech]

Unreacted body filler contains styrene, which until fully catalyzed acts as a solvent that can penetrate materials that aren't solvent resistant. 2K urethane primers are somewhat solvent resistant, but this resistance develops over time, and even then the primer remains porous and subject to chemical attack. That's why 2K urethane is never suitable for a topcoat.

Sometimes it happens that filler needs to be placed over 2K urethane primer. The procedure that I recommend is to first make sure the primer is as cured as possible, with the maximum amount of heat and time that can be managed in the repair area. Second, use a heat source to cure the filler and to either cure or otherwise drive any unreacted styrene out of the primer. 120° for at least a half hour depending on the thickness of the fill.

After that, the area should still be given extra time and heat during priming stages, since it should be suspected that some solvent remains under the filler. As long as heat and time are used to make sure solvent is out from under the repair, there is a high chance of success.

 

[RosharonRooster]

I never knew any of this info. I thought it was common practice to smear filler over high.build.