# Filler edges / sanding lines, tips and advice please



## Harry_p (Mar 18, 2015)

Ok, please bare in mind that I'm a novice, painting in open air and using solvent based 1k products ( as 2k scares me without proper aired equipment and filtered booth )

I've recently painted a mk2 golf bootlid, the paint was quite poor with lots of scratches and a few small dents, but zero rust, which was the reason for buying it.

I sanded it down, skimmed it with filler, upol feather lite I think, sanded it smooth with p120 followed by 240.

A decent coat of tetrosyl filler primer mixed at 1.5:1 with celulose thinners, left to dry 24 hours before adding a guide coat and sanding smooth.

A coat of the same primer thinned 1:1 for a standard primer coat to cover any areas left thin above, again left to dry 24 hours and sanded with p400.

At this point t it looked supers, no filler ghosting, no scratch or sanding marks, I was really happy with it.

Next, solvent basecoat, thinned 1:1 with basecoat thinners. Round the edges then a light coat allowed to flash for 5 mins before a second covering coat. The basecoat dried to a nice even satin finish, again, no signs of any filler or sanding marks, although harder to spot on a satin finish, I did look very closely and couldn't see anything.

Left to sit in the warm September sun for 20mins before hitting with clear. Upol 1k acrylic rfu ( can't remember the exact name, blue and silver tin ) again, a light coat allowed to flash for 5mins before a wet gloss coat.

Then, as the lacquer dries suddenly I can see sanding scores and filler edges. I'm confident they weren't there before the clear. After it is touch dry after half an hour I could slightly feel the marks with my finger tips 

I left it outside for a few hours and the marks did settle back down, but still visible if you know where to look.

I just don't know what's caused it and how to prevent in the future, could the solvents from the clear really be penetrating all the way through the basecoat and primer to cause the filler to swell?


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## rich9 (Jan 28, 2014)

I have used similar products in the past, however I waited 10-15 minutes flash time and 1 hour before clear. 1k products are a pain for these kind of reactions because they are so solvent laden.

I think your flash time was not long enough. You should have done more than 1 coat of lacquer as well, 3 coats really as 1k is so thin.

Did you wet sand at all? As this may also be a factor particularly with the filler.


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## Harry_p (Mar 18, 2015)

I stopped at one coat of lacquer as I could see the marks appearing and didn't want to lay any more over and make it worse, I'll see how it looks after a few more days.

The filler was dry sanded, the first filler/primer coat was wet sanded but left several days in a dry shed before the normal primer layer, which was again wet sanded then left outside in the sun, then overnight in a shed before the basecoat the next day.

I think I'll have to do some testing on spare panels. I didn't want to leave the basecoat too long before lacquer as I didn't want to risk it not bonding properly and peeling at a later date.

Like you say though, they're very solvent heavy products so I think it would get some sort of etch into even a fully dry basecoat layer. 

I will definitely let the basecoat harden longer as my first port of call.

I'm only doing bits and pieces here and there and don't have the budget to spend huge amounts on loads of different products and equipment, so far I've been very happy with the general painting and finish I've been getting, if only I can solve my prep / filler issues!


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## Sicskate (Oct 3, 2012)

I think you issue was with the sanding. 240 is too rough if your not using 2k primer. 

I'd have 320 it.


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## rich9 (Jan 28, 2014)

How much flash time did you give the primer? Was that only one coat?

With any 1k products it is much better to do several thinner coats than try for thick coats, as you can get solvent waiting to burst out when more layers are put on. This usually results in a bubbling up, but can also reveal edges like what you saw.


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## steveo3002 (Jan 30, 2006)

might want to let the primer sit longer too


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## squiggs (Oct 19, 2009)

Although what you used is described as a filler primer you really shouldn't rely on it to cover up lazy or bad prep work.
Getting stuff to the correct standard to accept the next product is the time consuming part of any job - and cutting corners will only come back to bite you.
Expecting the filler to be fully feathered in without going any further than 240 and then asking the primer to make up for this and cover the 240 sanding marks would seem to be the main problem.


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## Harry_p (Mar 18, 2015)

Fair comment, yes, I probably am expecting too much of my filler primer.

I'm just transferring what I've learnt over many years of playing with aerosols to materials which can be bought and sprayed in larger quantities. I was hoping filler primer would make the prep easier than needing a glass smooth finish on the raw filler. It's a substance I've not really played with before as aerosol filler primer is rubbish.


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## Scoobycarl (Aug 13, 2011)

Aerosol primer can be great if you know its limits and use a finer grade scratch for it to cover


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## Harry_p (Mar 18, 2015)

Well, a week on, and the vast majority of the marking has settled down all bar a couple of very fine scratch marks which are only visible from certain angles in certain lights.

I'll put it partly (mainly ) down to rushed prep, and partly solvent swell. I'm glad I left it alone though as I know know to leave at least a week before I attempt to wet sand and polish even in warm conditions. If I'd done it earlier to try and rescue the finish it would now have sunk back the other way.


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