The Wall Has the Final Say: Fixings for Old Brick, Render and Blockwork

Anyone who has spent time on a McPhail & Sons counter will know the scene. A customer arrives with a handful of wall plugs, a photograph on their phone and a hopeful expression. The wall in the picture is old, probably painted, possibly rendered, and definitely not a clean test panel. The fixing has to work anyway.

That is the thing about fixings: the metal or plastic is rarely the weak point. The wall around it usually is. Since 1952 we have sold a lot of plugs, screws, anchors and drill bits, and the same lesson keeps coming back. You are not fixing to plaster. You are fixing to whatever lies behind it, and that material has the final say.

Start with the wall, not the box

The temptation is to choose a fixing by load rating on a packet. A better starting point is the substrate. In older UK housing stock that means asking a few blunt questions. When was the building put up? Is it solid brick, blockwork, rendered, cavity or something stranger? Has it been altered? Is the plaster thick, loose or just a skim over something hard?

A small test hole can tell you plenty. Drill slowly with a masonry bit and note whether the drill bites hard brick, crumbles through mortar, or sinks into something soft and grey. A magnet can sometimes find screws or services, though never rely on that alone. Tap the wall gently and listen for hollow patches. If a patch sounds hollow, do not assume it will hold a heavy bracket. It may only be plaster.

At the counter, bring a photo of the wall and a description of what is going behind it. A merchant cannot see through plaster from a shop stool, but a clear description narrows the options quickly.

Four walls you will meet

Victorian solid brick

Solid brick walls are often hard bricks with softer lime mortar joints. The brick can be unforgiving, and the mortar can be surprisingly weak. A plug that expands in a joint may feel tight and still pull out under load. Where possible, aim for the brick rather than the mortar, keep the hole clean and avoid over-tightening. It is easy to spin a plug in an oversized or crumbly hole.

A masonry bit and a steady hand matter more than brute force. Use the correct diameter, drill to the right depth and stop before you break through into a void you did not expect. For heavier loads, a resin anchor or a specialist masonry fixing may be more sensible than a general-purpose plug.

1930s render over blockwork

Render is a useful weather skin and a poor structural layer. It can be friable, painted, cracked or hiding a cavity. A short plug sitting mostly in render is a fixing waiting to fail. The trick is to reach the blockwork behind and use a fixing long enough to do real work there. Frame fixings can be useful because they pass through the render and anchor into the block.

Do not let a neat countersunk head convince you the job is done. Check that the fixing has actually gripped the structural layer, not just the render.

Post-war aerated concrete

Aerated concrete, often called aircrete or breeze block in casual conversation, is soft and crumbly. Ordinary expansion plugs can struggle because there is little for them to grip. Vibration makes things worse. Use a fixing designed for aerated concrete, keep the drill speed low, and clean the hole properly. In some cases a resin anchor or a specialist screw is the better route.

This is one of those materials where a test fixing is worth the trouble. Put one in, apply a sensible load and see how it behaves before you commit a whole run of brackets.

Later cavity construction

Cavity walls bring their own puzzle. The outer leaf may be brick or block, then a gap, then insulation and an inner leaf. A long screw that only bites the outer leaf is not the same as a fixing that bridges the cavity properly. Cavity wall anchors, toggle fixings and frame fixings all have their place, but the right choice depends on the cavity width, the load and what the fixing is holding.

Do not guess the cavity size by eye. If you are unsure, find out. A fixing that is too short, too long or wrongly seated is an expensive way to learn.

Bits, holes and the details that matter

The right drill bit is half the job. A worn masonry bit will wander and enlarge the hole. An SDS bit on the wrong setting can blow out soft material. For aerated concrete, a low-speed drill and less percussion is usually kinder. For hard brick, a decent masonry bit and a controlled hammer action may be needed.

Match the hole to the fixing. An 8mm plug in a 10mm hole is not a clever workaround. Clean the dust out, drill to the marked depth and avoid drilling close to an edge unless the fixing manufacturer allows it. Small details like washers, screw length and correct seating decide whether a fixing performs as intended.

The counter questions worth asking

Before you buy, ask yourself or the person behind the counter:

• What is the wall made of, and what is behind the plaster?
• What is the fixing holding, and in which direction will the load pull?
• Is there a cavity, and how wide is it?
• Is the area damp, hot, vibrating or exposed?
• Does the fixing need to come out again, or is it permanent?

A good merchant will not pretend to know everything about a wall they cannot see. They will help you choose a sensible fixing and tell you when to stop and ask a structural engineer. That is not a sales pitch. It is the difference between a tidy job and a callback.

At McPhail & Sons, we would rather sell you the right box of fixings once than the wrong box twice. The wall has the final say, so let it speak first.