# Paint Repair, Sunken Paint?



## Mr.Buff (Aug 5, 2011)

Hi guys, has anyone got any advice on what I call (and heard it off of others) "sunken paint". This may be called something different to the trade/bodyshop folk.

Its basicly when a panel has been painted at some point in time as this only occurs on paint repairs, not on factory paint.

It usualy appears on a panel looking like a patch of cross hatch within the lacquer surface. Cross hatch is the best way to discribe it as it has multiple lines in a pattern.

My understanding of this is that the area I describe of is where filler has been applied to the panel, which has "sunk" the following layers of paint/laquer into it. Or a different description is the filler has sucked in the following layers during/since its drying period.

Hopefully someone will understand my description as im intruiged to know the reason it does this? What actualy happens to form this strange looking paint defect?

Ive wet sanded these areas a fair few times and had some good results, although Id like more of an understanding of how to fix the issue, and the best method.

Hope someone can help me.

Mart


----------



## EliteCarCare (Aug 25, 2006)

Paint sinkage is usually caused by topcoating before undercoats have thoroughly dried/cured or inadequate flash time between coats (this can vary on the type of paint used). It can also be caused by painting over filler that hasn't thoroughly cured.

Alex


----------



## Graeme1 (Dec 9, 2006)

As you have tried best way is to wet flat a good amount and then polish back up. 

Would give it a good 1500 flat. If it doesn't go away only way is with painting again.


----------



## Mr.Buff (Aug 5, 2011)

Cheers guys!

So would I be correct in saying that the pattern I mention within the paint is in effect uneven lacquer?

My theory behind the wet sanding was litterealy to level out the paint by sanding it back so it is flat? As I say ive had good results doing this but wasnt 100% why.

Is it best to use a hard block first when trying to level the area (assuming the above sentence is correct!)

Cheers fellas


----------



## Sh1ner (May 19, 2012)

It can also caused by using too coarse a paper to sand the filler and then using a filler primer to try to make good the surface or filler having been applied on top of paint rather than the base material of the panel. Filler primers look smooth at first but as the paint cures fully over time everything shrinks and you can see the lack of preparation beneath.
The filler needs to be properly set and as well finished as you would expect a top coat to be, before painting, otherwise the paint dries at different rates because it is in varying thicknesses, due to the surface scratches and edge shrinkage and you end up with the problem you have.
In my experience with a laquered finish you will never get rid of it, because effectively it affects the base coat and can be seen through the laquer. With a solid colour you might be able to flat it out for a while but it usually reappears again as the exposed paint layers dry again.
The only way to fix it is to strip it/sand it off and prepare the whole panel correctly from the ground up. Re painting the panel will usually just reactivate/soften the old paint and you end up with the same problem after a while.


----------



## Andyb0127 (Jan 16, 2011)

Problem you will get if you keep flatting and polishing it, eventually it will drop back again resulting in polishing it again.

Reason for it sinking/dropping back is due to poor previous filler work, most likely filler finished of with a coarse grit paper, and the primer/colour/laquer are all dropping back into it. So no matter how many times you polish it, eventually you will end up going through the lawyer, as you don't know how much laquer is actually been put on, unless you have a paint depth gauge. 

probably not what you want to hear, but only real cure is to have all previous paint/filler removed and start again making sure its done correctly this time with correct prep work and drying times.


----------



## Porkypig (Jun 20, 2012)

As above dude, mainly down to poor or inadequate prep. They are marks in the filler left by sanding and the only way to rid them completely is to take it all off and start again.


----------



## Aaran (Sep 18, 2007)

a spray jobs only as good as the prep that went before the paint 

dont get this problem with lead (though it has its own drawbacks), also in extremes of temperature this same effect can show up due to conflicting thermal expansion rates between filler and metal. (you will be able to see a poorly feathered in edge in the repair area)

epoxy surprisingly is very very good at blocking any filler shrinkage/drop back as it basically isolates the filler from the primer/base . but again it adds to the time on the job and the cost. things most people dont like paying for :lol:


----------

