Base not sticking

[Mirk]

Hi
First off, Thanks to who ever wrote the welding toturials helped me out.

Now..

I recently painted my engine bay. At first, all seemed good. But at sharp edges, it does not take much effort to peel the base/clear off the primer. also almost everywhere else, it does not take much impact befor it scratches/peels down to the base (if i dropped a spanner for example).

What went wrong..

Sanded the entire bay
primer was out of a spray can, an good quality one.
i let it dry plenty, cannot remeber how long.
Did not sand it... my mistake?, or... incompatible paints?
Sprayed water based metallic base. let it dry for a day.
then 2k clear.


Id love to pin down the problem, befor i continue to bigger areas on the outside body.. espesially dont want my windshield to fall out

 

[the snooper]

possibly 2 mistakes there

you didnt flat / key the primer

and

used water based base coat and possibly left it too long before laquer i wouldnt use water based unless i had all the right gear for it ie dryers
unless you have all the gear forget water based as you have found out

i know quite a few painters and non are using water based and i dont see the point as you still have to use 2k laquer solvent based every time here

 

[the snooper]

one other reason water an oil dont mix, is your filtration system on the compressor suficcient to remove any fine oil mist that may reach the gun

 

[Engineer]

Firstly not a good idea to use rattle can primer if you are able to spray 2K, as proper 2k primer is an awful lot better. Secondly water based paints must be cured in a low bake oven. Thirdly base coats need to top coated with clear as soon as they have dried (generally 10 minutes).

 

[steveo3002]

primer needs sanding

 

[Mirk]

Firstly not a good idea to use rattle can primer if you are able to spray 2K, as proper 2k primer is an awful lot better. Secondly water based paints must be cured in a low bake oven. Thirdly base coats need to top coated with clear as soon as they have dried (generally 10 minutes).

Yeah, should proberly had used some proper primer.
You sure about the 10min?, the water based paint dries with air, so if any small bit is not cured i will trap it under the clearcoat. thats why im under the impression, that the longer i wait, the better.

-----

anyway, the base and clear sticks well together.

Base and clear both from a real auto paint shop, who use it everyday.

Had both filter at compressor, and gun.


Could it really, just be all down to, not sanding the primer?.

 

[Engineer]

Water based paint of the type used for car body work generally needs to go in a low bake oven to cure properly. Primer does need sanding, but I would think rattle can stuff would be very thin, and easy to rub through?

 

[paintpot]

i use water base paint 8 hours a day .five days a weak ,Don't use etch aerosol primer ,and then put water base on.You did not key up your primer .

 

[Engineer]

Does the water base paint air dry without problems?

 

[steveo3002]

yes

 

[paintpot]

water base will air dry ,Your best bet with water base is dry each coat of ,by blowing ,each coat dry with your spray gun or air blowers.You will no if your water base was not dry enough .What happens is when you apply your clear coat ,and every thing is dry.Two or three days down the road,you will get tiny little pin holes in your clear coat .Were the water base was not cured ,and evaporating through your clear coat.The blowers we use ,blow warm air .These are built in the spray oven .

 

[Mirk]

i use water base paint 8 hours a day .five days a weak ,Don't use etch aerosol primer ,and then put water base on.You did not key up your primer .

Good hearing from someone who work with the stuff ..

Ok, try and avoid aerosol in future, and key the primer.

Hmm.. but already sprayed the other parts of the car, with the areosol primer.. have not had problems with this in the past, tho, then i used solid color also out of areosol. also keyed it, those times.

Going to paint some scrap metal, where i used different methods, one where i try to reproduce my one of my faults (not sanding)... and another piece where i sand, etc. See how it turns out.. then take it from there i guess.


A question, at paint shop they mixed the water based metallic base, so that it was "ready to spray".. i did not need to add anything later. Tho, project dragged out, and first got around to spraying about 2-3 month later. Could that had played any role aswell?. dont know how this water based stuff is mixed, if they would had giving me something in a separate bucket, had i said, i first was going to spray in some months on.

 

[langy]

Unfortunately you made a couple of errors, you used aerosol primer and you should of keyed the primer otherwise how would it stick ???
Why use aerosol primer when you were going to use 2K anyway

 

[langy]

Incorrect i'm afraid, some basecoats have up to a 36 hour window before they need overcoating.

Firstly not a good idea to use rattle can primer if you are able to spray 2K, as proper 2k primer is an awful lot better. Secondly water based paints must be cured in a low bake oven. Thirdly base coats need to top coated with clear as soon as they have dried (generally 10 minutes).

 

[Mirk]

Unfortunately you made a couple of errors, you used aerosol primer and you should of keyed the primer otherwise how would it stick ???
Why use aerosol primer when you were going to use 2K anyway

Used it because, well.. Have lot of places where i fixed it up, then it was just alot easier, rather than cleaning a gun each time, and never had any real problem with it befor.. usually sand my stuff, but in engine room, i thought, "oh i dont need it be perfect in here, and felt the primer, it seemed rough.. should be enough bite in that" i said to myself.. :-S.. D´oh.

 

[Engineer]

The reason nearly all base coat materials need to be clear coated quite soon after they are sprayed, is so that the clear coat chemically bonds to the base. If its left for any length of time, then the base coat will be fully cured, and will need keying with sanding to prevent clear coat flaking off at some time in future.