Firstly, Hello my name is Tom and according to my friends I have a sanding addiction....
Secondly congratulations on being to forum I have selected on which to ask stupid questions.(you lucky buggers you!)
ok so here is my issue.
( please feel free to help in any way appropriate including sarcasm although please make it obvious as it can be hard to pick up on over text.)
I am painting a shell for the 20th time due to learning through trial and error and using cellulosed based paints when I started.
I have since stripped everything off to bare metal and started over with 2K isocyanide coatings.
so my process is thus,
bare metal,
rage ultra skim coat blocked to 180,
pro xl etch primer over any bare metal AND filler, this is a few coats as I then block it with 180 to double check I haven't missed anything obvious. (I believe it is a cellulosed based etch, it comes in rattle cans and I have found it to basically be about as non porous as I can find which is why I chose it)
hella sonne 2k surfacer followed by more blocking

at which point i have an issue

i accidently put a run / sag / over accumulation of paint in a gutter type swage line in the roof. this is a kind of channel basically triangular in cross section about 30mm wide by 5mm deep.
as i was blocking this over applied paint out i found that as i broke through the 2k surfacer there was a kind of speckled effect as the surfacer met the etch. its almost like the first coat was big blobs 1mm ish in size and they have melted into the etch primer so they show as im sanding through the interface between the surfacer and etch primer.
i also noticed the adhesion between the etch and surfacer wasn't that great in that area. Now as i mentioned iv painted this a few times due to errors on my part and one time i did apply the surfacer too thick and trapped solvents which led to me having to peel it all off and go back to filler. this run however was not in the first lot of coats as this was a second application after i found there were some areas that needed more surfacer.
so my question is, where did i go wrong? was it my up bringing and poor parenting or have i just bunged it on too thick again? i ask because there seems to be very good adhesion to bare filler on an area of the roof where i missed a low that was too much for surfacer and i didn't etch prime over the filler after.
it seems that where the surfacer is thicker it hasn't stuck to the etch that well.
when you peel it off with a metal filler spreader it takes some of the etch primer with it so its almost like the surfacer is sticking to the etch but the etch isnt sticking to itself.
yet in other areas i have tested such as the rear pillars it has stuck to the etch well enough that it takes etch and a bit of filler off with it when i scrape at it.
the etch was all on there for a few days before it was blocked and coated with the surfacer so i don't think its an issue of the etch being soft still.
is it possible the thinners in the surfacer have gotten into the etch from being trapped due to over application?
i have let each coat get touch dry before applying the next.
I'm using fast hardener and fast thinners.
iv probably forgotten some key info but im an amateur so if you feel like saving me from a mental breakdown then please ask any questions to help me get to the bottom of this before i die of old age (im currently 35 but the rate im going i may be 135 before i get this right).

thanks in advance,

Tom (king of relentlessly persistent failures).

Welcome to the forum, Tom.

Ok, first problem is the etch primer. Should only go over bare metal, never filler or previous paint.

Put the lid on the etch primer and take it to the nearest paint recycling place. Throw complete tin in the largest bin and don't even wait for it to hit the bottom. Proceed to your paint supplier and buy a tin of epoxy primer. This sticks to the metal better than etch, stops moisture and adheres beautifully to fillers. It also provides an excellent substrate for topcoats or even high fill primers. It can also be used as a sealer and/or surfacer.

If you want, you can do the whole car in epoxy primer and then do any panel beating or filling over the epoxy. This way you get rust protection while you're doing the bodywork. Alternately do bodywork first and then epoxy over that. Either way is acceptable.

Hi Tom

I fully agree with what Chriss said !!!!!

Etch primers are Tricky, Like Chriss said best to trash it a 1K spray bomb of Etch is Trash any way loose it along with any and all 1k products!

Their are legit Etch Primers that are mixed BUT their use is Tricky cant be applied over Fillers has to be sealed with Regular 2K primer before adding any filler any sand thorough have to be resealed with 2k primer its just a pain for the beginner to play with better to use Epoxy!

My suggestion is as Chriss said strip it again Start over with Epoxy over bare metal.

Post some pics we like Pics!