various problems with spray can paint job and self adhesive sticker, advices?

[add4]

Hello guys,

Today was my first try at finishing a box using car paint (acrylic primer, paint and varnish) and inkjet self adhesive stickers for labeling.

Here is the process i used :
- sand the box using very rough sandpaper
- rub it with vinegar to remoe dust and grease
- apply one first layer of primer (spray can)
- bake for 20 mins
- apply a second layer of primer
- bake
- apply a first layer of paint
- bake
- second layer of paint
- bake
- print the decals, spray varnish on them (2 layers)
- cut the decals, stick them into place
- i tried to make them less seeable by using vinegar (i read that it can be used as a softener for waterside decal so i thought i might try) but it didn't worked well at all no visible change, the vinegar didn't killed the labels because of the varnish layers
- spray a first layer of varnish
- bake
- second layer of varnish
- bake
- third layer of varnish
- bake

At this point i have a few remarks and question about this process :

- The primer seems to be regular and smooth after the 2 layers so i thought the paint job would be easy, but i have a visible area on the front face of the pedal on which the paint doesn't have the same texture as the rest, it seems 'liquid' when the rest looks like a solid coat. any idea? too much paint in this place?

- the self adhesive stickers leave VERY visible marks where they start and stop, theres a visible edge on the surface of the pedal ... Can i do something to avoid that or does that comes with this kind of stickers? i have waterside decals on the way so i guess it will be better next time if i use vinegar as a softener, right?

- I manipulated the box to screw the knobs on and i scratched the surface with a nail, not very hard, and the paint chipped down to the metal. How can i make it more durable?
i thought i had done everything for that...
more varnish? bake for longer? the paint felts like i was scratching something soft when it chipped, maybe it's just still too new to be durable?

Anyway, that's my second attempt at finishing boxes and it's much better than the first
Waiting for your advices to make a professional looking third one

[amptramp]

I doubt vinegar is what you want to remove dust and grease after sanding.  You may be getting the formation of metal acetates which have little adhesion to the metal.  You may be better off with acetone or some other such cleaner with no ionic content to poison the metal surface for paint.

If you spray the decals with varnish before softening them with vinegar, the vinegar may not be able to get through the varnish to soften them.

It is very difficult to get even coatings.  That is why many people put several light coats on, to avoid any wetness from excess thickness.  Also, how rough was the sandpaper you used?  You should aim to get a flat surface, but rough sandpaper should be followed by finer grades - say 220 or 320 before priming.  Use a flat surface like a table, put the sandpaper upside down on it and sand, so you get the flatness you need.

What does the paint manufacturer say about cure times and baking?  There is a difference between time to dry to the touch and time to build up hardness and adhesion.  Mny paints have a no-respray window where you can add another coat before, say 30 minutes from the last coat or after 48 hours but not between.

[add4]

Thanks for the advices!

I should add vinegar to the decals before varnish, even if they're inkjet printed?
the first decals i tired were not varnished, and the vinegar did not soften them also, but it did ruin the ink on the decals.
So I assume when you say that you talk about waterslide decals, or is the softener thing it also true for self adhesive decals? or only jaserjet ones?

I did not fine sanded, i will go and buy some finer sand paper.

how many layers of varnish do you usually use?

thanks

[robmdall]

Here is what I have found that is important to a good paint job. I coated in a production setting, paint and powder for the auto industry for 20+ years. YMMV

Adehsion is a direct reflection of proper prep, cleaning, film build and curing, etc. (I don't use an oven during the warmer months.)

Sand with varying grits 120 ~ 320, wash the enclosure with soap and water, dry and wipe with acetone. (I always drill before starting any coating project)

Prop the enclosure on something that fits inside it and allows you to turn the enclosure as you coat. Gun to target (or can to target) directly relates to film build - keep the distance equal at all times - do do swoop the can with your wrist - move the gun with your arm. Swooping causes a light film on the start and end of the target and a heavier center - very hard to fix later.

Apply primer, wet sand with 600, prime, etc. You want the primer to fill in and level any deficiencies in the substrate. Use light coats. I am also keen on using a tack cloth prior to coating to remove any dust.

Once the primer looks great - (primer is a lot easier to 'work with' vs a base coat color especially when using high gloss). Consider the prime coat your finished appearance, whatever shows up in primer will be 10 times more apparent after a gloss coat. The goal is to build up multiple coats of primer wet sanding between each until the sanded enclosure is completely coated with no metal showing. Remember these are light coats and follow the manufacturers cure time and re-coat window.

On to Color coat - again, the wet sanded primer coat should be tacked prior to applying color - use a few light coats a minute or two a part. Corners are tricky, too much paint and you may run and and have poor cure time. Do the same thing you did with the primer, coat, wet sand (higher grit now (1000 ~ 2000), tack...

If the primer was used correctly, you should only need a couple coats of color. Sand the final color coat before applying the clear. One coating of clear should do it as long as it looks ok.

Take your water slide that has been lightly clear coated, trim with a sharp blade and apply. I have used a mix of water and vinegar as the water to activate the decal. Pay attention to the directions for the decals - do not over soak or you take a chance of diminishing the adhesive. Using vinegar on the edges will not aid much if the decal has been cleared. However this is a trick I use, after a few clear coats on top of the decal-ed enclosure, take some painters tape and try your best to cover the decal leaving just the higher edge showing - a few quick build up coats on the edges and sides should build up the clear to the height of the decal. Remove the tape soon after the coating becomes tacky - you don't want the tape to become adhered to the enclosure. Once wet sanded, the edge will level and become less noticeable or disappear completely. add a couple more coats of clear until happy...

Try to stay with the same brand of paints if possible, at minimum try all paints on a sample before pulling the trigger on a good enclosure. I use this clear now without issue http://www.krylon.com/products/crystal_clear_acrylic/. Cures hard and really haven't had an issue coating over different paint chemistry.

Apologize for the loooong post, but I'm having a really slow day at work. Hope it helps and remember YMMV - attention to prep is the key!

[add4]

That's very interesting! i've been searching for detailed informations like this for a loong time!
I'll try to find finer grain sandpaper and try this method and i'll certainly come back with more specific question.
I assume that with spray can primer, paint, and finish, i SHOULD be able to get a durable paint job.

Just a quick question about wet sanding : water and regular sandpaper? or do i need special materials?
Thanks

[robmdall]

You want specific Wet sandpaper. Normally, when you get into the 600 and above grits wet paper is easy to find. One other thing I didn't mention, always use a block when sanding, sanding with just your bare hand can actually leave ridges.

[add4]

Thanks for this precision.
For your information, the box finish is now 3 days old and it's MUCH more durable. i guess when i cooked it, it was dry to touch, but not dry under the outer layer, that made it so easy to scratch.
i was going fast to show the pedal to my guitar teacher so i chipped the paint and when i brought it, the input jack had turned around and one of the lug was touching a potentiometer, just a huge buzz, no signal, AND the pedal popped when it was turned on and off ..
everything fixed now, except that i'll redo the whole paint job, but sometimes waiting is better :p