What happens after the first render removal test patch?

Where to place the trial patches

One opening describes one spot. Render that comes off cleanly by the back door can be welded on along the side wall, and the brick behind a dash can change completely around an old window. A useful trial is therefore usually two or three small patches, each placed to answer a different question about the wall.

Start with an ordinary stretch that represents most of the elevation. If the pebbledash separates cleanly there, taking its backing coat with it and leaving clean brick, the main stripping is likely to go the same way. Then place one where the house has probably been altered: beside a door or window that looks newer than the rest, or where a bay or extension meets the original wall. Infill brick, steel or timber lintels and patched joints tend to show up there.

Render on a gable or the most weather-exposed face deserves its own patch, because that wall has taken the most rain and frost and may be the wettest. A patch low down, just above the damp-proof course, shows whether the render was carried down over the DPC and whether the masonry at the base is damp or salty.

Keep each patch small, a hand's width or a few bricks across, and cut its edges cleanly with a disc or chisel so the surrounding render is not shaken loose. A neat square opening is also much easier to fill or cover if the main job does not start straight away.

Pebbledash removal ↗Wall rendering ↗

How a test patch is cut and what it shows

A test patch is usually small, a few bricks wide, and chosen so it tells you something useful: an area that sounds hollow, one that sounds solid, or a spot near a window where an old alteration is suspected. The render is cut round with a disc or chisel and knocked away with a bolster, slowly, so the behaviour of each layer can be seen.

Look at the edge of the opening, which shows the layers like a cross-section. On a dashed wall there may be stones in a 6–8mm receiver coat, which is how Structherm describes its own dash receiver, over a thicker backing coat on the brick. On an older wall there may be a lime render under a later cement skim, or paint between two coats. Each layer that comes away cleanly from the one below is a layer that has already lost its bond.

Then look at the masonry. Clean brick faces with intact joints mean removal is unlikely to damage the wall. Brick faces coming away stuck to the render, crumbling joints or soft, damp stone mean the wall will need more repair than expected, and on a traditional wall the SPAB's warning about damage from levering off large sheets applies directly.

Reading the findings

Hollow render that drops off cleanly onto sound brick is the easy result: the rest of that elevation is likely to strip easily, and the new system can go onto repointed brick with a meshed base coat. Render that is welded on, taking brick faces with it, tells you that full removal will leave a damaged surface, so either the stripping method changes, the area that comes off shrinks, or a full base coat is allowed for to rebuild the face.

Wet masonry, salts or soft stone point to water getting in somewhere, perhaps a gutter, a sill or render bridging the DPC. That cause has to be fixed and the wall given time to dry before new render goes on, and an older wall may be better suited to lime than to a cement-based system.

What a useful test-patch record contains

Keep a simple record: where the patch was, a photo of it with enough of the wall around it to find it again, a close photo of the edge showing the layers, and a note of what the masonry looked like. Note whether the render sounded hollow before it was cut, because that links the tap test to what was found.

For example, on a hypothetical end-terrace with a dashed gable, one patch beside the back door might show hollow dash dropping off clean brick, while a second on the gable shows render bonded hard to soft brick that comes away with it. Those are two different answers, and they lead to two different methods on the same house: a quick strip at the back and a gentler approach, or a full base coat, on the gable.

Agree how the patch will be left if the main job does not start straight away. An open hole in render lets water behind the surrounding material, so it is patched, covered or primed until the work begins.

Then use the findings to firm up the job. If stripping is confirmed, the repair allowance can be set against what was seen. If the backing needs a base coat to rebuild its face, K Rend's HP12, as one example, can be applied up to 12mm onto masonry, which shows how much unevenness a base coat can take up. If the wall is old, soft and damp, a lime approach may be the right change of plan.

The pebbledash removal page explains the full stripping and re-rendering sequence. Keep the trial photographs with the final specification; if the wall is repaired or altered later, they explain why different parts were prepared differently.

Related services

A test patch is often the step that settles which job a wall needs. The Wakefield rendering homepage sets out how repair, recolouring, stripping and re-rendering differ, so the findings can be matched to the right one.