Smooth uneven paint

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Wall was freshly plastered but was not a great job and was rather uneven, although this could not be seen under normal lighting conditions. The wall was painted and it was only when 2 wall lights were installed that it became apparent the wall was not smooth at all.

My first attempt to correct this was to use filler, then sand it smooth and repaint. Unfortunately the paint being used reacts differently when painted over existing paint than it does over mist coated filler and this made the problem even worse.

The second attempt was to sand the wall until it looked fairly flat which resulted in a surface that was partly bare plaster, partly mist coat and partly finished coat. This didn't work very well either, although better than the first attempt. I was able to remove some element thought repeated light sanding and repainting but not everything could be removed.

My third attempt was to sand back to bare plaster in the affected area, this is taking ages as the paint in Mylands marble emulsion, which contains ground marble! This dulls the sand paper within about 30 seconds so took about 3 hours to sand less than a 1m area.

The result has worked, but has just moved the problem, I now have a line around the area where along the transition from paint to bare plaster.

I've included 2 photos, 1 is under the light that I sanded back to bare plaster, then applied a mist coat of the mylands paint, the other is under the light that I filled, painted, then sanded lightly then painted again.

The first photo looks a little worse than it actually is, the seconds photo looks slightly better than it actually is.

IMG_2509.jpeg
IMG_2510.jpeg


Does anyone know how I can get rid of these lines in the paint? I feel like I'm going round in circles with this now.

Thanks
 
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At a minimum, you could feather the area with something like the powder Toupret Interior filler. Sand back with 180 grit paper and then prime with a cheap acrylic filler such as Leyland Trade Primer/Undercoat.

On the larger area, you may need to apply a few coats of the primer and then gently sand that back a tad. The Leyland Trade primer is the only waterbased primer that I have found which doesn't the abrasive when sanding. When you sanded through the skim coat you ended up with a surface that is less smooth than the polished plaster finish. Hopefully, many coats of the primer will serve to fill any microholes in the plaster.

I would recommend sanding using silicone carbide paper rather than rigid aluminium oxide paper, even better would be Abranet "paper" (available on rolls but more expensive).

The plastering is not great but those kind of wall lights that flood the walls are very, very unforgiving.
 
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Set up lights shining across wall.

Troupet wall smoother
400mm skim blade with stainless steel blade
Sand using large block of wood with 180grade sandpaper.

Then acrylic primer but I always spray primer over filler. Just any ridge or roller mark shows with critical light. A £30 hvlp will do but add 15% water. No more. 2 thin spray coats.
Then roll paint on with a 15+ inch roller.
Finish in same direction so for me last roll is up.
Load roller again, up and down apply with last roll up.
Don't go back on yourself with roller or that patch will show
 

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