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I am a very amatuer DIYer and am trying to paint some beige Dulux matt emulsion in my lounge. It appears the previous owners of my house have used both regular white matt emulsion and also something more shiny, possibly eggshell, on the walls where they have "touched up" - it is a right mess! I have no idea whether the paint they used is water or oil based but when I paint the beige over the top I am getting a really patchy result which is much lighter in some places (where it is painted over the eggshell I think). I have spent the last few hours searching forums for what to do but cannot get a definitive answer. My understanding is that I need to use an oilbased undercoat to "correct" what is there already and once I've done that I should be okay to get a non patchy topcoat with my Dulux Matt emulsion. Is this correct? Any advice would be very welcome.

Hi Spooniemoonie

Yes you're correct, you do need to use an oil based undercoat 1st to cover up the previous paint layers

Start by lightly rubbing down the walls with 180 grit paper just to provide a key for the undercoat and to remove any little imperfections

Wipe the walls down with a damp cloth, rinsed frequently in clean water to remove all dust

Use Dulux Trade White Undercoat from either Dulux Decorators Centres or Screwfix. Apply using a medium or short pile roller for a nice smooth finish and follow instuctions on tin. As this is an oil based paint and you are using on a large area, ie walls, you must allow plenty of ventilation whilst using

One coat is usually sufficient however use your judgement once the 1st coat has dried and if still very patchy, apply a 2nd coat
This will leave a great surface for your topcoat and should give a good result

Good luck and let us know how you get on

Hi, I don't think I would go that far as to put oilbased undercoat on a wall unless it was really necessary. I would do as toplondonchef says and give the walls a good rub down etc. Then give the walls a wipe down with sugar soap and wash this off. Sugar soap will give the walls a bit more keying. Then give the walls a mist coat or 2 and allow to dry properly. After this give the walls 2 good coats of Dulux emulsion whatever type you want ie, Matt, Silk etc and it should be a good finish. The shiny stuff on the walls could just be vinyl silk emulsion which will give a similar finish to eggshell so there would be no need to put on undercoat to cover this up. If it was an oilbased paint on the walls the mist coat will take ages to dry usually so that will give you some idea as to which it is. Good luck.

I doubt i would undercoat the walls either, Good prep and a misscoat in white then 2 coats of colour should be fine, I recon its silk BTW,

The easiest way to tell if they used an oil based paint is the emulsion you used over top would go crazed (cracked)... I guess this sounds more like Silk

I agree with londonchef, shedman & JRS the best course of action is to always give it a good sanding down. I would then just wash with hot water (I only use sugar soap on grease, filler etc) hot water should do the trick on this.

I would then give it 2 miss coats (a drop of water in your white paint), let it dry properly maybe another quick sand and then cover in your colour.

also use a decent quality paint - my recommendation would be Dulux Trade. if you are using a cheaper paint then you are much more likely to encounter this problem.