Can you paint concrete and besser block walls?

Short answer: yes, once it's cured, clean, dry and sound

Concrete and block take paint well once the prep is done. Haymes counts concrete walls and concrete blockwork as masonry, and says masonry is porous. It soaks up moisture and lets it go again over time. So most of the work on a concrete wall happens before the paint tin is opened.

• Cured. New concrete and block need at least 28 days. More on that below.
• Clean. Dulux says to wash bare masonry down with water and a stiff brush to shift loose material, then hose down and let it dry.
• Free of salt. White, powdery salt comes off before any paint goes on.
• Dry and sound. Haymes says leaking gutters, damaged flashing or structural cracks should be fixed before any prep or painting begins.
• Sealed if it needs it. Haymes says a primer or sealer undercoat helps most on porous, repaired or previously painted masonry. Some topcoats, such as Dulux Weathershield Low Sheen, are self-priming on most surfaces.

Get those right and you can choose from ordinary exterior paints. Dulux lists concrete and masonry among the surfaces for Weathershield Low Sheen, and Haymes says its Solashield range suits render, masonry, brick and concrete. For render walls, our guide to painting rendered walls covers the same ground for that finish.

New concrete and block: wait at least 28 days, longer if you can

Fresh concrete and block need about four weeks before paint goes on. Dulux's Weathershield Low Sheen instructions say unpainted masonry should cure for 28 days. Its 1Step Prep page says freshly laid masonry and cement-based surfaces need a minimum of 28 days. Resene says concrete may take up to 28 days to fully cure, and shouldn't be painted before then unless its Limelock product is used.

Some advice runs longer. Dulux's Render Refresh instructions say new concrete, mortar and render need four to eight weeks, depending on how thick the concrete is and how it dries. Dulux's PRECISION Sealer Binder page says to let new masonry dry for at least one month after it's built. Dulux's trade advice says at least 30 days, and ideally a full year if you're using a solvent-based paint. If you can't wait that long, it says to use an alkali-resistant sealer or water-based primer, then a 100% acrylic exterior paint.

Part of the wait is about lime. Dulux explains that fresh masonry is likely to contain lime, which is very alkaline. Until that lime reacts with carbon dioxide in the air, it can attack the paint film.

Two more things on new work. Resene says curing and release agents have to be removed from concrete before painting. And if the builder can't wait, Dulux makes Acratex Green Render Sealer, a water-based primer and sealer for fresh masonry that cuts the usual concrete and render waiting time and helps stop salt coming through. Dulux says it's sold through trade outlets only.

Moisture and white salt: check before you paint

Check a concrete or block wall for damp and salt before you buy paint. Haymes says moisture is often a contributing factor when paint fails on masonry. Water getting in through cracks, damaged sealants or building defects can affect how well the paint holds. Its checklist of things to look for includes damp areas, chalking and white salt deposits.

White salt (efflorescence). Taubmans describes it as white, powdery deposits on render or masonry. It comes from moisture moving through the porous wall and carrying salts to the surface. Taubmans calls it a frequent issue in coastal or poorly ventilated properties. Dulux's Render Refresh instructions say it must be treated before painting. To clean it off:

• Taubmans says a wire brush or a pressure wash.
• Dulux says a wipe with Dulux Concrete and Paving Etch & Clean, or a 5% acetic acid solution (white vinegar). Then hose down and let the wall dry.

Going by that description, salt that keeps coming back after cleaning means moisture is still moving through the wall. Find where it's getting in before you paint.

Chalk and powder. Haymes suggests running your hand across the wall. If a powdery residue comes off on your fingers, the surface may need sealing first. Resene says old unpainted concrete is usually powdery and carrying windblown salt, moss and mould, so it starts with a good wash.

Besser block: fill the pores first

The face of a besser block is full of small holes and voids. Resene's blockwork guide says unpainted concrete blocks usually need waterproofing with its X-200 coating. Resene recommends three coats, so that all the voids and holes in the blockwork are filled.

Here's how Resene's concrete painting guides set out a block wall:

1. Wash it down. Old block gets a scrub or a waterblast to shift dirt, salt and moss.
2. Prime old block. Resene uses its Sureseal primer on old blockwork. On new block, it says a primer isn't usually necessary.
3. Fill cracks. A brushable crack filler for cracks under 1mm, and an exterior gap filler such as Selleys No More Gaps for cracks over 1mm.
4. Finish. If waterproofing is an issue, Resene uses three coats of X-200 to fill the voids. If it isn't, two to three coats of Resene Sonyx 101 or Lumbersider. Resene says two is generally enough over a primer.

Other makers' sealers do a similar job on porous block. Haymes says its Ultraseal sealer undercoat is typically used on porous masonry and helps equalise porosity, so the topcoat looks more even. Dulux says to thin the first coat of Weathershield Low Sheen with up to 100mL of water per litre on very porous surfaces.

Thinking of a clear sealer so the block still shows? Resene warns that moisture trapped behind a clear film on blockwork will make it cloudy, because blockwork has so many holes and voids. For roller choice on a rough face, see our guide to painting textured walls.

Sealers and topcoats for masonry walls, as the makers describe them

A concrete or block wall gets an exterior topcoat, often over a sealer or primer when the surface is porous, repaired or previously painted. The table sets out what each maker says its product is for. It doesn't rank them, and the right pick depends on whether the wall is new, old, powdery or salty.

Pick your day too. Haymes says exterior paint should generally go on between 10°C and 35°C, out of direct sun, with no rain or heavy dew expected within 24 hours. Once it's painted, Dulux recommends washing Weathershield every 6 months in coastal areas and every year in sheltered or inland areas. For when a primer is needed on other surfaces, see do you need primer. For salt air, see the best exterior paint for coastal homes.

Retaining walls and damp walls: when paint isn't the fix

If water is getting into a concrete or block wall, fix the water first. Haymes says paint should never be used as a substitute for repairing building defects. Leaking gutters, damaged flashing or structural cracks should be fixed before any prep or painting starts.

Retaining walls are the hard case. A retaining wall has soil packed against its back, and you can only paint the front. For cement walls that are cracked or leaking, Resene's system adds two to three coats of X-200 where waterproofing is an issue. The Haymes rule still applies, though: find where the water comes from before you coat over it.

Old paint on a sound wall is the easy case. Resene says repainting a sound paint system over concrete is straightforward, because the concrete underneath is inert. Do the tape test Dulux describes: cut a small X through the paint, press tape firmly over it and rip it off. If paint comes away, it's unsound and has to come off first. For more on that, read why exterior paint peels.

Wide cracks, stepped cracks, a leaning retaining wall or water coming through a wall are a job for a builder or engineer to look at before anyone paints. If the repair counts as building work, the QBCC says a contractor needs a QBCC licence for work valued over $3,300.

Getting a concrete or block wall painted on the Sunshine Coast

Painting a concrete or block wall is mostly prep: waiting out the cure, cleaning off salt, sealing the pores and filling the voids on besser block. Taubmans names salt as a frequent issue in coastal homes, and Dulux's coastal washing advice is twice as often as inland. So on the Sunshine Coast, the cleaning and sealing steps matter.

We've painted Sunshine Coast homes since 1985, and we hold QBCC licence 1281728. For what an exterior repaint costs by wall type, see exterior house painting cost. We work right across the Sunshine Coast. Get a free quote through our contact page.