Masonry & Concrete Fixings Explained: Plugs, Frame Fixings, Resin & Concrete Screws

Match the fixing to the substrate, not the other way round. Dense concrete takes concrete screws and throughbolts. Solid brick suits nylon plugs and frame fixings. Soft aircrete blocks need resin anchors or specialist plugs, because expansion fixings crush them. And in cavity or hollow walls, it's cavity anchors or nothing.

That one principle sorts out most fixing failures before they happen. This guide walks through each fixing family, what it's for, and the decision table that puts it all in one place.

Which fixing for which wall: the decision table

Substrate	First choice	Also works	Avoid
Dense concrete	Concrete screws, throughbolts	Resin studs, shield anchors	Undersized plugs for heavy loads
Solid brick	Nylon plugs, frame fixings	Concrete screws, resin	Expansion anchors near edges or joints
Aircrete / lightweight block	Resin anchors, specialist block plugs	Long concrete screws at reduced loads	Throughbolts and shield anchors - they crush the block
Hollow block, cavity walls	Metal cavity anchors, resin with mesh sleeve	Spring toggles	Any expansion fixing
Plasterboard on dabs	Corefix-type dot and dab fixings	Long fixings reaching the masonry behind	Standard plugs - they spin in the void

First, work out what you're drilling into

Thirty seconds with a drill tells you everything. Drill a small test hole away from where the fixing will go and watch the dust. Red or orange dust means brick. Fine grey dust with hard going means concrete or dense block. If the bit suddenly pulls in with pale, powdery dust, that's lightweight aircrete block, and it changes your fixing choice completely. If the bit breaks through into a void, you're in a hollow block or a cavity, and you need an anchor designed for it.

Wall plugs: the default for solid brick

The nylon wall plug is still the right answer for most everyday fixings into brick: shelving, brackets, radiators, cupboards. The rules that make plugs hold are simple. The plug must sit entirely within the masonry, not in the plaster, so add the plaster depth (usually 10-15mm) to your drilling depth. The screw needs to be long enough that its full thread passes through the plug, and thick enough to expand the plug hard against the hole. A brown plug with a 5.0mm screw is the everyday workhorse; step up in plug and screw size as loads grow, or move to a masonry screw driven straight into a plugless pilot hole for a quicker fix. You'll find the full range here.

Frame fixings: windows, doors and battens

A frame fixing is a long plug and screw supplied as one piece, and its trick is that you drill through the frame and into the wall in a single operation, so the fixing positions itself perfectly every time. That makes them the standard for window and door frames, and just as useful for battens and stud sole plates against masonry. Common sizes run from 8.0 x 60mm up to 8.0 x 300mm for deep frames and packers. Keep fixings around 100mm clear of frame corners, and don't overtighten - the frame should be held, not bowed.

Concrete screws: no plug, high load, removable

Concrete screws (also sold as masonry screws or multi-fix screws) cut their own thread into a pilot hole in concrete, dense block or good brick. No plug, no expansion pressure, and they can be removed and re-driven, which makes them the go-to for temporary works, formwork and anything you might adjust later. The critical detail is the pilot hole: a 7.5mm screw typically wants a 6mm bit, drilled deeper than the screw's embedment so the cut thread has somewhere to shed dust. Get the pilot size right and a single screw replaces a plug-and-screw fixing at a higher load; get it wrong by half a millimetre and the screw either snaps or strips. Lengths run from 40mm up to 200mm to cope with packers and thick fixtures.

Throughbolts and shield anchors: heavy kit, dense substrates only

For plant, racking, gate posts and structural brackets on dense concrete, expansion anchors carry serious loads. A throughbolt drops through the fixture into the hole and expands as you torque the nut; a shield anchor does the same with a heavier sleeve for bigger loads. Both depend on the substrate resisting the expansion force, which is why they belong in dense concrete and nothing softer, and why edge distance matters - expand one too close to an edge and the concrete spalls away. As a rule, if you're within about ten bolt diameters of an edge, look at resin instead. Sizes from M6 through M20 are stocked under engineering fasteners → /fixings/engineering-fasteners and the concrete bolts range.

Resin anchors: the answer when everything else is wrong

Chemical resin bonds a threaded stud into the hole rather than expanding against it, and that solves every awkward case at once: soft aircrete, old crumbly brick, fixings close to an edge, high loads in questionable substrate. In hollow materials, a mesh sleeve keeps the resin where it's needed. The one thing resin will not forgive is a dirty hole. Blow it out, brush it, blow it again - in our experience, nearly every failed resin fixing traces back to drilling dust left in the hole, not the resin itself. Studs, resin and sleeves are all under resin and accessories → /fixings/masonary-cavity-fixings.

Cavity walls and hollow blocks

When the fixing zone is mostly air, you need an anchor that spreads its grip behind the face material. Metal cavity anchors expand a set of legs behind plasterboard or hollow block and take respectable shear loads. Spring toggles suit lighter jobs where you can feed the toggle through. For plasterboard stuck to masonry with dot and dab adhesive, dedicated fixings bridge the gap and transfer the load to the masonry behind - the single best upgrade for radiators and TV brackets on dabbed walls.

Safety-critical fixings: what BS 8539 asks of you

Where a fixing failure could hurt someone - barriers, handrails, anything overhead, plant with dynamic loads - anchor selection and installation falls under BS 8539:2012+A1:2021, the code of practice for post-installed anchors in concrete and masonry. The short version of a 90-page standard: select the anchor for the actual substrate and load, install it exactly to the manufacturer's instructions, and proof-test where the design calls for it. For trade jobs in that category, buy anchors with published performance data rather than the cheapest box on the shelf.

FAQs

Do concrete screws need a wall plug?

No. They cut their own thread in the pilot hole. That's the whole point - the plug is what they replace.

How do I fix into old, crumbly brick?

Resin anchors. They bond rather than expand, so they don't ask weak brick to resist any bursting force. Drill oversize, clean the hole thoroughly, and let the resin cure fully before loading.

Can I use a throughbolt in lightweight block?

No, and it's one of the most common failures out there. The expansion force crushes aircrete. Use a resin anchor or a specialist block fixing instead.

What's the strongest masonry fixing?

In sound, dense concrete, a correctly torqued throughbolt or a resin stud at full embedment - properly installed, both hold more than most applications ever need. In anything softer, resin wins because strength depends on the substrate, not the fixing.

Why does my plug spin in the hole?

The hole is oversized, the plug is sitting in plaster rather than masonry, or the substrate is softer than the plug expects. Go deeper into the wall, size up, or switch to resin.