Can you render over pebbledash? What’s involved

Pebbledash covers a substantial share of British housing stock, most of it applied between the 1920s and the 1970s. Much of it is now failing, and almost none of it suits current taste. The question that comes up on nearly every one of those properties is the same: does it have to come off?

Usually, no. Rendering over existing pebbledash is a standard and well-proven approach, provided the existing finish is sound and the build-up is specified correctly.

Why removal is the expensive option

Hacking off pebbledash is slow, filthy work. It generates a large volume of waste, needs skips and disposal, and adds days or weeks to a programme depending on the size of the elevation. On a terrace or a housing scheme, multiply that across every property.

Worse, removal frequently damages the substrate underneath. Pebbledash was often applied to poor-quality brickwork precisely because it hid poor-quality brickwork. Take it off and you may find soft bricks, eroded mortar joints and previous patch repairs, all of which then need making good before anything new goes on. What began as a render job becomes a masonry repair job.

Overcoating avoids all of that. The existing render stays where it is, doing its job as a substrate.

When you can overcoat

The existing pebbledash has to be sound. That means:

• Well bonded. Tap across the elevation. A hollow sound means the render has debonded from the wall behind it, and anything applied on top will come off with it.
• Free of significant cracking. Fine crazing is usually fine. Cracks that run through to the substrate need investigation, because they normally indicate movement that will simply reappear through the new finish.
• Dry and clean. Organic growth, salts and general grime all have to go before anything is applied.
• Structurally stable underneath. Overcoating hides the substrate. It does not fix it. Damp problems, failed lintels or movement need resolving first.

Where sections are debonded but the majority is sound, those areas can be cut out and made good rather than stripping the whole elevation. That is a much smaller job than full removal.

The problem with the surface

Pebbledash presents two difficulties to whatever goes on next. It is heavily textured, and its suction is unpredictable, varying across the elevation depending on the original mix, the exposure and how much weathering it has taken.

Both are solved at the preparation stage. The elevation is thoroughly cleaned. A primer regulates the suction so the base coat cures evenly rather than drying out fast in some patches and slowly in others. Then a levelling base coat, applied with reinforcing mesh embedded in it, bridges the texture and produces the flat, consistent plane the finish needs.

That mesh-reinforced base coat is doing two jobs at once: flattening the surface and distributing stress across the elevation so that movement in the old render below does not telegraph through as cracking in the new finish.

Choosing the finish

Once the base coat is on, the finish options are the same as on any thin coat system. Silicone render is the usual specification: highly water repellent, breathable, and available across a wide colour range. On an older solid wall property, breathability matters more than most people appreciate, because the wall needs to be able to dry outward.

Grain size determines how the finished elevation reads. A finer grain gives a tighter, more contemporary surface. A slightly coarser grain is more forgiving of minor variation in the substrate beneath, which on an old pebbledash wall is worth considering.

Doing it alongside insulation

If the property has solid walls, and most pebbledashed housing does, overcoating is the natural moment to insulate. Rather than rendering directly onto the existing finish, external wall insulation boards are fixed over it and the render system applied on top.

The cost difference is smaller than people expect, because the scaffold, the preparation and the render finish are all needed either way. The additional cost is the insulation, its fixings, and the labour to fit it. The gain is a warmer property with lower running costs and a considerably better U-value.

On funded retrofit work under the Warm Homes Plan and similar programmes, this is normally the specification anyway.

What to check before you price it

Three things determine whether an overcoat job runs smoothly:

• Adhesion testing on a representative sample. On a housing programme, test each property type rather than assuming the whole street behaves the same way.
• Reveals and details. Adding thickness to a wall affects window reveals, sills, verges and any services fixed to the elevation. This needs drawing before it needs pricing.
• Ground levels and DPC. The new finish must terminate correctly above damp proof course level. Getting this wrong causes problems that take years to appear and are expensive to fix.

Getting a specification

Every pebbledash elevation is slightly different, and the condition of the existing render is what governs the specification. Send us photographs, the property type and what you know about the wall construction, and our technical team will confirm whether overcoating is viable and what the build-up should be.

Contact the technical team or browse the render systems to see the options.