Where the
world gathers for metal finishing
Q&As since 1989


-----

Powder primers cured with or before top coat?

We manufacture aluminum railing systems. some systems are installed near the ocean and require a primer, my question is should the primer be cured fully before the top coat is applied?

Dave McNulty
- Seattle, Washington
2006

---

Hi,
You do not state what type of primer you anticipate using, powder (epoxy) or a liquid (solvent or waterborne). The thing you must anticipate is damage to railings in situ. Powder primers are normally used to cover up imperfections in the substrate and may not prevent rust creeping under the coating system; in this case a zinc phosphate treatment would be required. For your purposes a liquid primer i.e. wash primer or a good waterborne primer both which can be air dried prior to the application of the powder film would be our recommendation. Of course you could go for a more expensive option, zinc rich powder primer. This type of coating requires application of the top coat within 24 hours. To green bake (partial bake) or full bake, you should follow the guide lines of the powder supplier, as any deviation from their recommendations would certainly invalidate any warranties they offer should things go wrong.

Terry Hickling
Birmingham, United Kingdom
2006

---

Please accept my apologies for some reason I read iron railing instead of aluminium, which of course is another ball game. For the best results I would suggest you investigate chromating ALL your aluminum items.
Sorry for the wrong info it must have been a bad day.

Terry Hickling
Birmingham, United Kingdom
2006

---

Dear Dave
Assuming you are using an epoxy powder primer, we cure ours at about 150 °C. If you fully cure the primer, it is too hard and smooth for the topcoat to adhere to. It is better if you can re-establish a thermoplastic situation, so that the two coats combine to form one coat. This will achieve better inter-coat adhesion.

Dale Windridge
coatings - Kent, UK
2006

---

Dear Sirs,

Presently we are using an Alkyd Melamin, water based paint, as a primer for powder coating of Polyester coatings.We are using electrogalvanised sheets for manufacturing purpose.wherever we do welding & grinding, we are applying this water based primer and then do powder coating over that.We are allowing 6 to 8 hours for air drying of the paint.If needs to be coated immediately,we force dry the primer.

For all our SS sheets as well Aluminum sheets, we are spraying full coat of about 10 microns primer.

Can some one suggest me any other suitable paint in this regard.Presently the manufacturer who has supplied the primer has stopped manufacturing the same.I also need some details regarding manufacturers of these kind of primer.

Thanks

SELLAPPAN THIAGARAJAN
- Dubai, UAE
2006