Enclosure Painting question

[Widows]

Hi all, first I'd like to say thanks to all of you who've answered my painting questions in the past as I've tried to gather some knowledge on how best to paint my enclosures.

I decided to put the knowledge to use today and have a question for you all:

Whilst painting the backs of the enclosures (the plate that comes off the enclosure) I noticed that there was a tiny area on each one where the paint wasn't taking and just seemed to collect in a small blob surrounded by a gap, as though the paint in this area were being drawn in on itself. The rest of the plate was fine, just these tiny bits on each one.

I'd sanded the enclosures and backs with 400 grade wet n dry paper, rinsed and repeated, then sprayed 2-3 layers of grey primer leaving 15 mins in between each layer, as per the instructions on the can.
I then gently sanded the backs with the 400 wet n dry again (before reading that I needed to leave 24 hrs before sanding), gave them a rinse and dried them off.
After this, I sprayed 3 layers of blue paint with 15 mins between each coat, as per the instructions on the can.
The paint n primer were both enamel spray paint from Halfords.

I didn't wear gloves; could this have been caused by some residual fingerprint grease on the metal?

Here's a pic of one of em:


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I'm not hugely heartbroken by the fact this is occurring on the base as nobody will see it, I'm just hoping I've not missed something that will casue it to happen on the face of the enclosure as that would be balls.

Can anyone offer an idea of what's caused this?

Cheers

[italianguy63]

Probably-- called a fisheye.

Paint won't stick to oil or grease... (could be caused by a fingerprint).

[tonyharker]

You're putting too many coats on too quickly, and not degreasing the surface before spraying.

This is my method.
I always degrease after initial sanding by wiping with a tissue containing IPA (Isopropyl Alcohol) (Isopropanol) before painting and thereafter DO NOT touch with my hands. Use gloves. After spraying the first primer coat I leave it overnight in a warm room to harden,  then a further coat of primer the next day.
Leave to dry for at least one hour. Then smooth off using 400 wet and dry, wet.  Wipe clean with a kitchen tissue and leave to dry.  At least 1 hour in a warm atmosphere. All spraying is done in the warm and dry. If the surface has been exposed by sanding I spray over an additional light layer of Primer. Once dry again after 1 hour, I spray 2 top coats of colour paint. leaving 1 hour between them. Then a final coat of varnish either gloss or I prefer satin finish.  
This I understand takes a long time but produces a blemish free surface.

Regards  Tony

[KazooMan]

Note to self:  Never eat chips while painting stompboxes.

I wrote "chips" since you are from Nottingham.  

I would have to agree with the fingerprint theory.  I usually do wear disposable gloves when spray painting, but that is more to keep the paint off my hands as opposed to keeping my hands off the paint.  Your process is much more elaborate than what I usually do and I don't have the problem you are seeing.  I usually sand the metal enclosure to get it reasonably smooth , wipe it with a cloth or paper towel, and then with a cloth and some acetone.  At this point I make certain that I do not touch the surface to be painted, only the back side.  Some primer and top coats and it is done.  I put the box parts on a "stand" that is just a block of wood.  That way I can rotate the piece without touching it.  A simple "spray booth" cobbled together from some cardboard keeps most of the paint in and most of the dust out.

If I were you, I would sand off the paint job and give it another go.  Wear some nitrile disposable gloves for the entire process if you want to be really certain that you are not contaminating the surface.

[davent]

For painting backs i create a hanger out of mild wire that goes through two of the holes, that way i never have to handle the piece just the hanger once it's ready for painting.

Same for the enclosure, make a little stand that you can stick the enclosure to with double sided tape so you can hold and manipulate the enclosure without ever having to touch the enclosure.

[johngreene]

Check this stuff out.

http://hgarts.com/water-transfer-printing-videos