Something is VERY wrong!!

Sat Jul 20, 2013 9:08 am

OK, what did I not do correctly :? This was my first use of a gravity feed compressed air paint gun and with these results, there may just be a sale on a lot of unpainted metal parts :evil: Your suggestions are most welcome. Parts had been treated with phosphoric acid soln to inhibit rust after E Tanking.
Image
Image
Image

Used an acrylic lacquer primer with lacquer thinner at recommended mixing ratio.

Re: Something is VERY wrong!!

Sat Jul 20, 2013 9:54 am

When painting bare metal it should be coated with a etching primer, then your regualar prime rover that.. Usesing many thin coats. After the primer cures then you can top coat. But depending on weather and paint you may heve to use a slow reducer. especially when its hot a humid. From your pictures it looks to me like the paint and or both paint and primers dried way too fast causing the pealing.

Re: Something is VERY wrong!!

Sun Jul 21, 2013 4:57 pm

Bill:

What was the temperature and the ambient humidity? That is important. But more important is a good primer base. Usually a thin first coat of etch, then a thin hi-bild primer coat lightly sand, a second thin coat .. lightly sand then the top coats. As Clark said, a number of thin coats are better than a thick coat. It appears that 2 things are happening here. No etching primer and too much primer coming out of the gun. Turn down the proper adjustment screw on the gun that controls the product feed rate. Also, make sure that your air pattern is correct.

Re: Something is VERY wrong!!

Mon Jul 22, 2013 8:30 am

Rudi wrote:Bill:

What was the temperature and the ambient humidity? That is important. But more important is a good primer base. Usually a thin first coat of etch, then a thin hi-bild primer coat lightly sand, a second thin coat .. lightly sand then the top coats. As Clark said, a number of thin coats are better than a thick coat. It appears that 2 things are happening here. No etching primer and too much primer coming out of the gun. Turn down the proper adjustment screw on the gun that controls the product feed rate. Also, make sure that your air pattern is correct.

Thanks Rudi :!: Temp 77 F Humidity 52% used acrylic lacquer primer thinned with lacquer thinner. These parts have been sitting around for 3+ years with a phosphoric acid type coating for rust inhibition. (which is supposed to provide proper etching)
They were rinsed and dried before painting. During painting, noticed the flaking, so wiped the piece down with thinner and started over--same results. Parts shown above are forged steel pieces of Univ. Mounting frame, did notice the cast pieces of the frames also wanted to flake. Have since used liquid soap and water with SS scrubber to remove all remaining paint and hopefully rough up the metal a bit.
Don't know if that was the problem, or as you said, too much paint, wrong thinner, not enough flash between coats........and so on--So many variables :? :shock: Will stay with it and see if I can figure out the problem. Further suggestions solicited :wink: Got 4+ inches rain yesterday, so painting will be on hold till humidity drops--current 70-90% :(

Re: Something is VERY wrong!!

Mon Jul 22, 2013 3:48 pm

I would say the parts were dirty. Etch is nice for clean sheet metal but I am not sure it adds anything on sanded or rusted metal. The phosphoric acid already etched the metal if any was needed. From the photos looks like the paint did not stick and I would guess the metal was dirty from something. The problem with phosphoric acid is it will etch deeply and leave dirt and other nasty things in those deep etch pockets.

I never use etching primer since nothing I paint is untouched metal. It has been sanded, derusted, etc....

Does not hurt to use etching primer but the lack of etching primer was not the problem in this case.

Re: Something is VERY wrong!!

Mon Jul 22, 2013 8:49 pm

Bill:

Yup, wait until the humidity and temp is down to what the manufacturer stipulates for your particular product. Pay attention to what they recommend for surface prep, primer, wait times and of course top coats.

Etch is not required .. it is just what I have been using when my parts come out of the tank -- I use etching primer then hi-bild primer. A good primer is required though. Practice, practice and more practice will help with ironing out issues when painting.

Keep us posted on your progress .. :D

Re: Something is VERY wrong!!

Tue Jul 23, 2013 9:12 am

Thanks for the information gentlemen. After considerable research, I'm down to the following variables:
Air/paint ratio
coating thickness
flash time
precleaning parts
So, I will find some scrap and practice, practice,practice :!: Have also learned acrylic lacquer primer tends to shrink during drying process, so will give primed parts plenty of cure time before top coat. Since I have $$ tied up in the primer, will use it for implements/tractor castings and reserve the epoxy primer for the sheet metal. Pics as I progress--right now in rainy period with high heat and humidity so will be on hold.
Not too many good painting days in Ok. :(