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Williams & Co Paint Contractors

Exterior

How to choose an exterior paint system, properly

You are not buying paint, you are buying a system: preparation, primer, film build and the right product for that substrate. Get the order right and the brand almost stops mattering.

4 min readWilliams & Co Paint Contractors25 August 2026

The question everyone asks, and the one that matters

Almost every homeowner opens with the same question: which paint is best? It is the wrong question, and the trade is happy to let it stand, because answering it with a premium brand name sounds like a quality promise and costs nothing to make.

A coating is one part of a system. The system is preparation, then primer matched to the substrate, then the correct number of coats at the correct thickness of the correct product. Get all four right with a mid-range product and you outlast a premium product applied badly, every single time.

Start with what you are painting onto

SubstrateWhat it needsWhat goes wrong
Sound old PVA on plasterWash, sand back chalk, binding primer, two to three coatsCoating straight over chalk. The new paint bonds to powder and lets go in a few seasons.
New or patched plasterFull cure time, alkali resistant primerPainted too soon. Alkali burns through and the colour patches.
Face brickClean, sealer or breathable coating depending on the goalTrapping moisture behind a film that cannot breathe.
Textured or bagged surfacesHigher coverage allowance, brush work into the profileRolled only. The paint sits on the peaks and the hollows stay bare.
Timber trim and barge boardsSand, wood primer, undercoat, two enamel coats, end grain sealedTwo coats over old flaking enamel. Water gets into the end grain and rot follows.
Mild steel, gates and balustradesDegrease, wire brush, rust converter or removal, metal primerPainted over rust. It bleeds through within a year.
Galvanised steelEtch or galvanised-specific primerStandard primer, which simply does not adhere to zinc.
Previously enamelled surfacesSand to a key, bonding primerWater-based paint straight onto glossy enamel. It peels in sheets.

Choosing the finish

  • Matt on walls hides surface imperfection and suits plaster. It is the standard exterior wall choice for good reason.
  • Low sheen and satin on walls clean more easily and handle knocks better, but they show every undulation in the plaster in raking light.
  • Enamel or a high performance water-based enamel on trim, doors and steel. Water-based enamels have improved enormously and do not yellow the way solvent-based ones do.
  • Roof coatings are their own category and a wall paint does not belong up there.
  • Waterproofing is not paint. If a wall or roof is letting water in, that is a liquid rubber system and a separate decision. Painting it does not seal it.

Paint decorates and protects a sound surface. It does not repair a failing one, and it never waterproofs anything.

How to judge the specification you have been handed

  1. 1Does it name a primer, and does the primer differ by substrate? If there is one primer for the whole house, someone has not thought about the steel or the timber.
  2. 2Does it give coats per surface, not one number for everything?
  3. 3Does it give a litre quantity you can check against delivery?
  4. 4Does it state the dilution, or state that the paint is applied unthinned?
  5. 5Does it treat rust and bare timber as their own line items?
  6. 6Does it distinguish smooth plaster from textured areas in the rate? Texture drinks paint and any honest quote reflects it.
  7. 7Does it say what happens to the surfaces that are damp or cracked before coating starts?

What we specify

Substrate by substrate. Preparation written out, primer named per surface, coats stated per surface, litres allowed, no dilution beyond manufacturer allowance, and the weather-facing detailing dealt with before any decoration. One fixed price for the whole job.

Common questions

No pressure

If you would like a second opinion on your own property, we will come and look.

The inspection is free, you get the findings in writing with photographs, and you are under no obligation to do anything with them.

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