Why does my paint not cover, even after three coats?

Hiding comes from pigment, and the brightest colours physically contain the least of what hides. Why more topcoats stop working, and the basecoat that solves it.

Difficulty: beginner
Time: 15 min
Read: 4 min

Short answer

Bright, saturated colours — strong yellows, oranges, reds and some greens — have weak natural opacity because the pigments that give the colour do not hide, and adding the white pigment that does would dull the shade. Stop adding topcoats and put down a tinted basecoat instead.

Opacity in paint comes almost entirely from titanium dioxide, a brilliant white pigment that scatters light. Every colour on the shelf is that white pigment plus tinters — except the strongest, most saturated shades, where the tinters have to dominate and the white has to be reduced or removed, because white is exactly what would make the colour pale. That is a physical constraint on the tin, not a defect.

Why some colours never cover, and what a tinted basecoat does about it

Step by step

Confirm it is opacity and not something else.Real opacity failure looks like the colour beneath ghosting through evenly across the whole surface. If instead you have dull and shiny patches, or a difference over repairs, that is suction and flashing. If it is a border round the wall, that is picture framing. Those are different problems with different answers.
Check what colour you are covering.Anything dark, anything strong, and anything red under a pale colour will show through for many coats. The bigger the jump in lightness, the more the basecoat matters and the less another topcoat achieves.
Stop after the third coat and change the approach.Each coat hides a proportion of what remains, so the visible improvement shrinks rapidly. By the fourth coat you are spending a full coat of paint and a day's work for a difference nobody can see. That is the point to change method rather than persist.
Put down a tinted basecoat.A basecoat or primer tinted towards the final colour does the hiding, and then two coats of the finish colour give the colour. Grey works under most deep colours; a warm pink or buff basecoat is the traditional answer under strong reds and yellows. Many merchants will tint a basecoat for you free.
Do not try to fix it by painting thicker.A heavy coat sags, dries unevenly, takes far longer to cure and does not hide proportionally better. Two properly laid coats hide better than one double-thickness one.
Make sure the surface underneath is uniform.Opacity problems and suction problems compound each other viciously. If the wall has bare patches, filler or old repairs, seal the whole surface first so the basecoat lands on one consistent substrate.
Buy for the system, not the tin.When choosing a strong colour, ask what the manufacturer recommends underneath it. Several ranges specify a particular undercoat shade for their deepest colours, and following that is far cheaper than four topcoats.

Tips

Yellows are the worst, then bright reds and oranges. If you are painting a wall in one of those, plan the basecoat before you buy the topcoat.
On woodwork, a properly tinted undercoat is doing exactly this job, which is why skipping the undercoat on a colour change means three coats of gloss.
A wall that looks patchy only in daylight and even under lamps may be a sheen problem rather than opacity — check it at several times of day before buying more paint.

Common mistakes

Buying a fourth tin of the finish colour — Returns diminish sharply with each coat. A single tinted basecoat costs less and does more than two further topcoats.
Blaming the brand — Weak hiding in a bright saturated shade is a property of the pigments that make that shade. Every manufacturer's version of that colour has the same constraint.
Applying the topcoat over a white primer for a deep colour — White under a deep colour is the hardest case there is. Tint the basecoat towards the topcoat and it covers in two.

If it doesn't work

Deep red or yellow still patchy after three coats

Cause: Low-opacity organic pigments in a saturated colour — Fix: Apply a tinted basecoat — grey for deep shades, warm buff under reds and yellows — then two coats of the colour.

Old colour showing through unevenly rather than everywhere

Cause: Suction difference across the wall, not opacity — Fix: Seal the whole wall so the absorbency is uniform, then two topcoats.

Covers fine on one wall and badly on another

Cause: Different substrates or different previous colours — Fix: Basecoat the problem wall only, then finish all walls together with the topcoat.

Questions people ask

Why do bright colours cover so badly?

The pigments that produce bright saturated colours scatter light poorly. Hiding comes from titanium dioxide white, and adding enough of it to hide would make the colour pale. It is a physical trade-off, not poor manufacturing.

What colour basecoat should I use?

Grey under most deep colours, and a warm buff or pink under strong reds, oranges and yellows. Ask the manufacturer or the merchant — several ranges specify a particular shade for their deep colours.

Will a more expensive tin cover in fewer coats?

A higher-solids paint of the same colour will hide somewhat better, so it can be worth it — but it cannot escape the pigment constraint. A tinted basecoat is a bigger improvement than a better topcoat.