Render Respraying Doncaster: Changing the Render Colour

Is the render sound enough to recoat?

Tap the render all over before choosing a colour. A solid note means the coat is bonded; hollow-sounding areas need cutting out and repairing first, and if they cover most of a wall, a new coating is money spent on a surface that is about to fail. Look at any existing paint as well. Flaking or powdery paint has to be removed or stabilised, or the new coat will lift with it.

Most cement-based renders can take a masonry coating; K Rend, for example, says its render is a suitable surface for masonry paint if a colour change is wanted later. Lime render is different. Mike Wye and SPAB both advise limewash or a breathable silicate paint on lime rather than ordinary modern paint, which can trap moisture.

Preparation: cleaning, algae and repairs

Green and black staining on north-facing walls is usually algae, and it has to be killed and washed off, not painted over. K Rend's instructions for its finishes describe a warm wash with a suitable detergent at carefully adjusted pressure, so the surface is not damaged, plus a fungicidal wash on walls prone to algae. The wall then needs to dry before coating.

Cracks are raked out and filled, blown patches are cut back and rebuilt, and the repairs are left to cure as their product requires. Pipes, lights and alarm boxes are taken off or masked. Windows, doors, sills, paths, plants and cars nearby are sheeted, because spray drift travels further than people expect; K Rend's own monocouche sheet asks for polythene over doors and windows during spraying.

1. 1

   Tap-test the render and inspect the existing paint.

2. 2

   Kill algae, wash the walls and let them dry.

3. 3

   Fill cracks and rebuild any hollow patches; let repairs cure.

4. 4

   Remove or mask fittings and sheet glazing, doors, paths and planting.

5. 5

   Prime where the coating maker requires it.

6. 6

   Spray the coating in the specified number of coats, finishing each elevation to a natural break.

Spraying the coating

Spraying gives an even film over textured or dashed render faster than a roller, and the sprayed coat is often back-rolled to work it into the surface. Follow the coating maker's limits on temperature, damp and drying time, and avoid rain and frost while it dries. Each elevation should be finished from corner to corner or to a downpipe in one session, because a coat that has dried and is then overlapped can leave a visible band.

Choose the coating for the render, not only the colour. A standard masonry paint suits sound cement render; a breathable mineral or silicate coating suits lime. Ask what the product's data sheet says about recoating and cleaning before you commit.

Choosing the colour

Paint a sample on the wall itself, at least a square metre on a face that gets ordinary daylight, and look at it in the morning and evening. Colour on render reads differently from a chart because texture throws small shadows. Compare it with the roof, frames and any brick that stays visible. If the house is in a conservation area, check with the council before a strong change of colour.

For example, a hypothetical post-war semi with magnolia render gone grey and green on its north side would be treated for algae and washed first, then have its cracks filled and two small hollow patches cut out and rebuilt. Only after the repairs had cured would the walls be masked and sprayed, so the new colour sits on a clean, sound and dry surface rather than over the old staining.