Painting Over A Failed Surface

Paint does one thing: it sticks to what is under it. When it fails early, the paint is almost never the problem.

Which is why a repaint that looks excellent for three months and then flakes, blisters or chalks is a preparation failure, and why a quote with more days of preparation in it is often the one that lasts.

Read the failure

Blistering and bubbling means moisture behind the paint film. The source is water from somewhere, and until it is found the surface will push off any coating applied to it. A wall blistering in one patch is a leak, not a paint fault.

Peeling in sheets, down to the previous coat, means the new coat did not bond to the old one. Usually a glossy, chalky or contaminated surface that was not sanded or sealed.

Peeling down to bare substrate, means moisture or an unsuitable primer.

Chalking, a powdery surface that comes off on your hand, is the breakdown of an old coating. Painting over it is painting over powder.

Cracking and flaking in a pattern, means too many coats over the years, a film too thick and too brittle to move with the surface.

Staining coming back through, means tannin, nicotine, water stain or rust that needs a blocking primer rather than another topcoat.

Mould returning, means a moisture and ventilation problem. Paint with a mould inhibitor slows it; an exhaust fan fixes it, which is the argument in [bathroom condensation, mould and the exhaust fan](/blog/bathroom-condensation-mould-and-the-exhaust-fan).

Find the water first

More repaints fail from moisture than from everything else combined.

So before any surface is prepared, the water gets traced. Which can be a roof leak, as in [roof tiles, ridge capping and the leaks they cause](/blog/roof-tiles-ridge-capping-and-the-leaks-they-cause); rising damp from raised ground levels, as in [damp in basements and ground floor walls](/blog/damp-in-basements-and-ground-floor-walls); a failed balcony or planter, as in [planter boxes and the leaks they cause](/blog/planter-boxes-and-the-leaks-they-cause); a plumbing leak in the wall; or condensation with nowhere to go.

Painting before that is resolved means paying for the finish twice. It is the same sequencing as the repair after a leak in [plaster repair after a water leak](/blog/plaster-repair-after-a-water-leak), where the plaster also cannot go back until the wall is dry.

What proper preparation is

Wash the surface. Not optional externally, and not optional on kitchen and bathroom walls where there is a film on everything.

Remove what is failing. Scrape and sand back to a sound edge. A feathered edge on sound paint is the base; a flake left in place is where the next failure starts.

Treat the mould, rather than painting over it.

Sand the gloss off anything previously enamelled, so the new coat has a key.

Fill and make good, then sand the filler flat, then spot prime it, because filler takes paint differently from the surface around it and shows through as a patch otherwise.

Prime for the problem. A sealer for chalky or porous surfaces, a stain blocker for tannin or water marks, a metal primer for rust, an alkali resistant primer on new render or masonry.

Replace the sealant at the joints rather than painting over cracked silicone, as in [silicone joints and when they need replacing](/blog/silicone-joints-and-when-they-need-replacing).

Let new substrates cure. Fresh render, new concrete and new patching all need time before they are coated, and the wait is part of the programme.

External work has its own rules

The failure modes are faster and the preparation is more of the job.

Render cracks have to be cut out and repaired rather than filled with paint, which is the work in [render and external wall repairs](/blog/render-and-external-wall-repairs). Concrete spalling has to be addressed structurally before any coating goes near it, as in [concrete spalling on balconies and facades](/blog/concrete-spalling-on-balconies-and-facades). And the whole question of timing is in [external painting and when to repaint](/blog/external-painting-and-when-to-repaint).

Weather is a constraint rather than an inconvenience: coatings have temperature and humidity ranges, and paint applied outside them fails regardless of the preparation.

Why it gets rushed

Because preparation is invisible in the finished result and visible in the quote.

A repaint priced on two days of preparation and one of painting looks worse on paper than the reverse and lasts years longer. Which is the whole reason we scope the preparation separately and say what it includes, so the comparison is between two known pieces of work rather than between two numbers.

And because the water source, the substrate repair and the finish usually sit across different trades, it goes in as one scope with one team holding the order. The paint goes on when the wall is ready, not when the painter is next available.

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