Why does my paint need so many coats?

Coverage figures on a tin assume a sound, sealed, similarly-coloured surface. Nearly every real wall breaks at least one of those assumptions. Knowing which one is broken is the difference between a third coat that works and a third coat that looks exactly like the second.

Step by step

1. Test whether the surface is porous.Flick a few drops of water onto it. If they soak straight in and darken the surface, the wall is porous and is pulling the binder out of your paint as fast as you apply it. New plaster, filler repairs and old distempered walls all do this.
2. Seal a porous surface before painting it properly.New plaster wants a mist coat — the same emulsion thinned as the manufacturer directs. Filler patches want the same treatment or they show as dull spots. Sealing is not a wasted coat; it is what makes the following coats work.
3. Look at the colour change you are asking for.Pale over dark, or any colour over a strong red, orange or yellow, needs more coats however good the paint. This is physics, not quality.
4. Use a tinted undercoat for a big colour change.A grey or mid-tone basecoat gets you to the finish colour in fewer topcoats than white does, because the topcoat has less contrast to bury. Many manufacturers offer this specifically.
5. Check you are not spreading it too thin.Trying to make a tin go further is the most common self-inflicted cause. If the roller is dragging and the wall looks translucent as you work, you are under-applying. Reload more often.
6. Use the right roller for the surface.A short pile on a textured wall bridges the peaks and misses the hollows, which reads as poor coverage. Match the nap to the texture.
7. Accept that some pigments simply cover badly.Strong yellows, bright reds and some oranges have inherently poor opacity. Three coats is normal for those colours and no amount of technique changes it.
8. Let each coat dry fully before judging it.Emulsion looks patchy while drying and evens out considerably. Judging coverage on a half-dry wall leads to unnecessary extra coats.

Tips

• A patchy result concentrated over filled areas is porosity, not coverage — those patches need sealing, not another full coat.
• Cheap trade white on a large job is often false economy: the extra coat costs more in time than the better paint would have cost.

Common mistakes

• Adding water to make the paint go further. — Beyond the manufacturer's mist-coat guidance, thinning reduces the pigment per coat and makes coverage worse, not better.
• Painting straight onto new plaster with full-strength emulsion. — The plaster pulls the moisture out unevenly, and the paint can peel later because it never bonded properly.

Questions people ask