How do I fix into a hollow or perforated brick?

Most bricks made in the last few decades have vertical perforations through them, which reduce weight and fuel use in firing. They are perfectly sound bricks, but as a fixing substrate they behave more like a hollow wall than a solid one, and a fixing chosen for solid brick will not perform in them.

What you'll need

• Chemical anchor resin and perforated sleeves
• A studbar or the screw the fixing takes
• Masonry bits and a hammer drill
• A blow pump and a brush
• Purpose-made cavity or hollow-substrate fixings (optional)

Step by step

1. Recognise it while drilling, not afterwards.The bit meets resistance for the first few millimetres of the outer web, then drops through into open space, then meets a web again. The dust output stops between webs. A wire pushed into the hole confirms it — it will go deeper than the hole you drilled.
2. Understand why an ordinary plug fails.In a void it has nothing to expand against and simply spins. On a web it grips, but a web is only a few millimetres thick and the outward pressure of the plug is exactly what a thin clay wall cannot resist, so it cracks.
3. Use resin with a perforated sleeve for anything of consequence.Push a mesh sleeve into the cleaned hole, inject resin until it just begins to show, and insert the stud with a twisting motion. Resin bulges through the mesh into each void and forms mechanical keys in several webs at once.
4. Clean the hole thoroughly first.Blow out the dust from the hole and, as far as you can, from the voids. Resin bonding to dust is the standard way a chemical anchor fails.
5. Do not overfill.Resin escaping into a large void is wasted and can weep out of the face or into the cavity. The sleeve exists to prevent that — use one rather than trying to fill a void.
6. Consider a purpose-made hollow fixing for lighter loads.Nylon or metal fixings designed for perforated brick and hollow block work by folding or knotting behind the inner face of a web rather than expanding against it. They are quicker than resin and fine for moderate loads.
7. Go deeper rather than wider.In a perforated brick, engaging three webs rather than one is what gives capacity. A longer fixing outperforms a fatter one.
8. Let it cure and then load it.Follow the cure chart for the actual temperature. Perforated bricks in an external wall are colder than the room you are standing in.

Tips

• Perforated bricks are frequently used for the inner leaf as well, so an internal wall in a modern house may be exactly the same problem.
• The mortar joint between perforated bricks is solid and continuous — which occasionally makes a joint fixing the better option here, the reverse of the usual advice.
• If a whole item can be fixed to a resin-anchored timber batten, do that: it converts several unpredictable fixings into one predictable set.

Common mistakes

• Hammering a plug harder when it will not seat — It is passing into a void, and force will not create material that is not there. Change fixing type.
• Injecting resin without a sleeve into a voided brick — It runs into the cavity, leaves an under-filled anchor, and can appear as a stain on the outside face. The sleeve costs very little and is the whole technique.