Plenty of Brisbane townhouses and courtyard blocks share the same problem: you want a fence or privacy screen, but the boundary is a concrete slab, a paved path or a driveway edge: and there is nowhere to dig a post hole. There are two proven ways to put fence posts on concrete: bolt-down base plates and core drilling. One is a weekend job with a hammer drill; the other takes more effort but holds like an in-ground post.
The quick answer
Base-plate (flanged) posts bolted down with masonry anchors are the fastest option and suit most courtyard fences and screens in sheltered spots.
Core drilling a hole in the slab and grouting the post in gives far more holding power: the pick for tall or exposed runs and gate posts.
Chemical anchors out-hold sleeve anchors (dynabolts) and are the safer choice near slab edges.
Check the slab first: you want roughly 100 mm of sound concrete and about 100 mm from any anchor to the nearest edge.
The courtyard problem: a fence with nowhere to dig
On a normal boundary you dig holes, drop the posts in and concrete them. On a townhouse courtyard or a slab poured right to the fence line, that is off the table: you either fix to the surface or drill into it. Both methods work with DIY bolt-together aluminium panels; the right one comes down to fence height, wind exposure and the condition of the slab. Set out and measure the run exactly as you would for a dug-in fence: our guide on how to measure for aluminium fencing walks through it.
Method 1: base-plate posts with masonry anchors
A flanged post is a standard fence post welded to a flat base plate with four bolt holes. Instead of going into the ground, the plate bolts flat onto the slab. Here is the process:
Set out the post centres. Run a string line along the boundary and mark centres to suit your panel width.
Mark through the flange. Stand the post in position and use the plate as its own drilling template. Check every hole lands at least about 100 mm from the slab edge.
Drill the holes. Use a hammer drill with a masonry bit matched to your anchor (a 10 mm sleeve anchor takes a 10 mm bit), roughly 10 mm deeper than the anchor’s embedment.
Clean out the dust. Blow or vacuum each hole thoroughly: a dusty hole is the main reason anchors pull loose, especially chemical ones.
Fix the post. Tap in sleeve anchors or inject chemical anchor and set threaded studs, plumb the post both ways with a spirit level, then tighten down.
Hang the panels once every post is down and plumb: see how to install aluminium fence panels.
Tools you will need: a hammer drill, masonry bits, a blower or vacuum, string line, tape, spirit level, socket set, and safety glasses and a dust mask. Nothing exotic: which is why base plates are the go-to DIY method on slabs.
Method 2: core drilling and grouting
Core drilling uses a hired diamond core drill to cut a clean round hole through the slab: typically 75 to 100 mm across for a standard aluminium post. Where the slab sits over soil, drill right through and dig out a little below for extra depth. Stand the post in the hole, brace it plumb, then fill around it with non-shrink grout or a rapid-set concrete mix. Once cured, the post behaves much like one set in the ground.
When is the extra effort worth it? For 1.8 m privacy screens, exposed or windy sites and gate posts, which cop swinging and slamming loads that work bolt-down plates loose over time. The trade-offs: core rig hire, a wet and messy cut, and a result that is permanent rather than unboltable.
Base plates vs core drilling at a glance
| Base-plate posts | Core-drilled posts | |
|---|---|---|
| Holding power | Good: relies on four anchors resisting leverage | Excellent: behaves like an in-ground post |
| Height suited | Low-to-medium fences; taller screens only in sheltered spots | Tall privacy screens, exposed runs, gate posts |
| Tools | Hammer drill, masonry bits, anchors, socket set | Hired core drill, diamond bit, grout, bracing |
| Reversibility | Unbolt and patch four small holes | Permanent: the post is grouted in |
| Cost | Cheapest: anchors cost a few dollars a post | Rig hire and grout add real money to the job |
A general guide only: wind exposure, slab condition and fence style all shift the balance.
Sleeve anchors or chemical anchors?
Sleeve anchors (dynabolts, in Aussie shorthand) expand against the sides of the hole as you tighten. They are cheap, quick and fine for most base plates on thick, sound concrete, but that expansion force stresses the surrounding slab, which is why they misbehave near edges and in older, cracked concrete.
Chemical anchors glue a threaded stud into the hole with injected epoxy or resin. No expansion force, a stronger hold, and they can sit closer to a slab edge. The trade-off is discipline: the hole must be brushed and blown spotless, and the resin needs its full cure time before you tighten. For a 1.8 m screen, a gate post on a plate or any anchor within about 150 mm of an edge, chemical anchors are worth the few extra dollars.
Check your slab before you drill
Thickness. House slabs are usually 100 mm or more; garden paths can be 75 mm or thinner: too shallow for proper embedment. Drill one test hole and measure before committing.
Edge distance. Keep sleeve anchors about 100 mm from any edge or expansion joint; a chemical anchor buys you a little more room, but never crowd the edge.
Cracks. Do not anchor into a cracked section of slab: shift the post centre or bridge the crack with a longer panel bay.
Services. Slabs near the house can hide conduits and pipes. Check plans or scan before drilling deep.
And be honest about the limits: a bolt-down plate is a lever, and the taller and more solid the fence above it, the harder wind pries at those four anchors. For tall or exposed runs, core drill: or talk to us about professional installation, and get an engineer’s advice for anything unusual.
Privacy screening on a slab
Most courtyard jobs are really privacy jobs, and spacing matters twice over: a near-solid 1.8 m screen catches far more wind than an open picket fence. On base plates it pays to leave a small gap between slats: you keep the breeze, ease the load on the anchors and barely lose any privacy. Our slat-spacing guide covers the numbers, and the DIY aluminium slat fencing guide walks the whole job.
Flanged posts and panels from our Slacks Creek yard
You do not need to weld anything. Our Aluminium Flange Post is a powder-coated post on a welded base plate, ready to bolt straight to a sound slab, and it pairs with our bolt-together aluminium fence panels: just a socket set and a level. Buy supply-only and fit it yourself, or have us install it. We deliver across South East Queensland (Brisbane, Logan, Ipswich, Gold Coast, Sunshine Coast, Toowoomba and surrounds) or collect from the Slacks Creek yard or arrange your own freight. Return customers earn loyalty discounts, too.
Frequently asked questions
Can I install a fence post on a concrete slab without digging?
Yes. A flanged (base-plate) post bolts flat onto the slab with four masonry anchors: no digging at all. For more holding power, core drill a hole through the slab and grout the post in, which performs much like an in-ground post.
How tall can a fence on base plates be?
Base plates are happiest on low-to-medium fences and screens in sheltered courtyards. A taller 1.8 m screen can work on plates with chemical anchors in a protected spot, but for tall runs in exposed or windy positions, core drilling (or an engineer’s advice) is the safer call.
Should I use dynabolts or chemical anchors?
Sleeve anchors (dynabolts) are quick and cheap and suit most plates on thick, sound concrete. Chemical anchors hold harder, put no expansion stress on the slab and tolerate closer edge distances: the better pick for taller screens, gate posts and anchors near a slab edge.
How thick does the concrete need to be for a fence post?
Aim for around 100 mm of sound concrete, which covers most house slabs and driveways. Thin garden paths of 75 mm or less will not give anchors enough embedment. Drill a single test hole first to confirm the true thickness before you commit to the run.
Can I core drill an existing slab myself?
Yes: diamond core drills hire by the day from most tool-hire shops, and a 75 to 100 mm bit suits standard aluminium posts. It is a wet, heavy job, so allow a full day for a typical courtyard run and check for pipes and conduits before you cut.
Does FY Fencing supply flanged posts for slab installs?
Yes: our Aluminium Flange Post is made for exactly this job, alongside bolt-together panels and gates. Order supply-only with delivery across South East Queensland, pick up from our Slacks Creek yard, or ask about professional installation on (07) 3803 1098.
A quick note on wind. The heights and anchor figures here are a general DIY guide, not a site-specific design. Wind load climbs quickly with fence height and solidity, and every slab is different: for tall screens, exposed positions or anything you are unsure about, core drill or have an engineer or professional installer look at the job first.
Working out what your fence line needs? Tell us the run and the height and we will quote it, supply-only or installed.
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