That Annoying Gap Beside Your Step: How to Block It Properly (So It Never Washes Out Again)

The Scenario

A homeowner recently asked:

"How to fill this gap?"

The GardenOwl Diagnosis

The Assessment

You’ve got a small front garden, a concrete step, and a short brick wall. Between the brick pillar and the edge of the concrete slab, there’s a nice big hole — a void where the soil has dropped away. You want to stone over the garden bed behind it, but if you just dump soil and rock in there, it’s going to bleed right through that gap and dribble onto the lower area. Every rainstorm will steal a bit more, and you’ll be out there sweeping gravel off the path like it’s a part-time job. This chronic issue, a textbook example of The Scour & Void Pattern, severely impacts your curb appeal by failing to provide mechanical containment for your garden's substrate.

This is one of those “small” details that makes the whole entry look half-finished.

The Trap: Why This Gap Is More Than Just Ugly

Most people do one of three things here:

1. Stuff it with loose soil or rubble.
   That works for, oh, about a month. Then water finds the path of least resistance, washes your fill out, and you’re right back where you started — just messier.

2. Stack random rocks in front.
   Looks like a campsite fire ring, not a front entry. Rocks shift, small stones still escape, and you’re always tweaking it.

3. Ignore the height difference and let the stone roll.
   You end up with decorative gravel on the path and bare spots in the bed. Worst of both worlds.

The real issue isn’t cosmetic. It’s containment and structure:

• You’re changing that bed to stone, which is heavier and more mobile than soil.
• That gap is a pressure point. When you backfill behind the old concrete edge, all that weight wants to push forward.
• The old step edge was never designed to be a miniature retaining wall.

So you need something that:

• Actually holds back soil and stone.
• Ties visually into the existing brick and concrete.
• Doesn’t require you to become a master mason in a weekend.

The Solution (Deep Dive): Build a Real Edge, Not a Patch

You’ve got two good routes here:

1. A simple timber sleeper/4×4 edge set snugly in the gap.
2. A small brick/block infill wall that lines up with the existing pillar.

Both will do the job if you build them like a tiny retaining edge instead of a cosmetic plug.

Option 1: Treated Timber Sleeper – Fast, Forgiving, and Clean-Looking

If you’re not excited about mixing mortar, timber is your friend.

What you need:

• Treated timber sleeper or 4×4 / 6×4 post (exterior grade, ground contact rated).
• Shovel and hand trowel.
• Crushed gravel (not pea gravel — you want angular stone that locks).
• Short level.
• Saw capable of cutting the sleeper square (circular saw, handsaw, or mitre saw).
• Rubber mallet (optional but handy).

Step 1: Measure the Gap

Measure from the inside face of the brick pillar to the edge of the concrete slab at the tightest point. That’s the length of your timber.

• Cut the sleeper slightly oversize (2–3 mm) so you can friction-fit it.
• Dry test it before you start digging. You want it to slide in with a tap from a mallet, not flop around.

Step 2: Dig a Small Trench

You’re going to bury the bottom third of the timber so it behaves like a mini retaining wall.

• Dig a trench 4–6 inches (10–15 cm) deep along the gap where the timber will sit.
• Make the trench slightly wider than the timber so you have room to adjust.
• Scrape out any loose, organic junk — roots, old mulch, soft soil.

Clay soil? Loosen and rough up the bottom a bit to avoid a slippery layer. Sandy soil? You still need the gravel base — sand alone won’t lock the timber in place.

Step 3: Add a Gravel Base

This is the step most people skip, and that’s why their edges heave and tilt.

• Add 2–3 inches (5–7 cm) of crushed gravel in the trench.
• Tamp it down with the end of a 2×4 or a hand tamper.
• Check that it’s roughly level and slopes very slightly away from your house so water can drain.

The gravel keeps the timber from sitting in a wet mud bath, which dramatically slows rot and movement.

Step 4: Set the Timber

• Drop the cut sleeper into the trench on top of the compacted gravel.
• Tap it sideways into the gap so it bears firmly against the pillar on one end and the concrete on the other.
• Use a level: the top should end up just below (5–10 mm) the level of the concrete slab.

That slight drop does two things:

• Keeps the step edge visually dominant.
• Prevents a trip lip for anyone stepping off the concrete.

If the timber wants to lean, pack more gravel in front and behind the base and tamp tight.

Step 5: Backfill Behind the Timber

Now treat it like a mini retaining wall.

• Backfill behind the timber with soil or, better, gravel up against the wood and soil above that.
• Tamp in thin layers so it doesn’t settle later.
• Stop backfill at the height where your landscape fabric and stone will sit.

Then:

1. Lay landscape fabric over the soil behind the timber (up the bed).
2. Bring your decorative stone in on top, to the desired depth.

Result: the stone can’t sneak under or around the timber, and the front path stays clean.

Option 2: Small Brick/Block Infill – The “Built From Day One” Look

If you’re comfortable with mortar (or ready to learn), this is the most seamless visually. You basically continue the wall to meet the concrete.

What you need:

• Bricks or small blocks that match or complement the existing wall.
• Concrete mix or mortar mix.
• Shovel, bucket, pointing trowel.
• Crushed gravel for a base.
• Level, rubber mallet.

Step 1: Prepare the Base

Same logic as the timber:

• Dig a shallow trench from the pillar to under the edge of the slab, 4–6 inches deep.
• Add 2–3 inches of compacted gravel for drainage and stability.

Step 2: Create a Bond With Existing Structures

You don’t want a free-floating toothpick of masonry.

• Clean dust and loose bits from the side of the pillar and underside/edge of the slab where your new bricks will tuck in.
• If you can, key the first brick into the pillar with mortar so they’re physically linked.

Step 3: Lay Bricks/Blocks

• Mix mortar to a peanut-butter consistency.
• Butter the first brick and press it into place against the pillar on your gravel base.
• Build across toward the concrete in one or two courses (you don’t need height here, just a solid face).
• Check level and alignment frequently so the top course ends just below the concrete.

If there’s a messy underside to the step, you can tuck the back half of the brick slightly under it for a tighter look.

Step 4: Backfill and Cover

Once the mortar sets:

• Backfill behind the new brick edge.
• Lay fabric and then your stone bed.

This makes it look like that wall-pillar-step combo was always continuous, and the gap never existed.

Why Gravel and Fabric Matter Here

Two quick technical bits that separate a pro job from a weekend regret:

• Gravel base: supports your edge (timber or brick) and handles water. Without it, freeze–thaw cycles or plain old soggy soil will shift things. University extension soil experts are constantly hammering on drainage and structure for any soil-related fix; a simple compacted base is your version of that on a tiny scale (see the University of Minnesota’s guidance on soil health and drainage).

• Landscape fabric under the stone: this isn’t for weed control magic — it’s a separator. It keeps stone from sinking into the soil and soil from pumping up through the stone, which keeps that clean edge over time. You’ll still get the odd weed, but you won’t lose half your decorative gravel into the subsoil.

If you’re going with stone over a wide area and want low maintenance, you might also like how we handled a similar “ditch and edge” problem in a front rock yard project: “Flat, Beige, and Boiling: How We Turned This Rock Yard Into a Welcoming Desert Front Entry”.

Visualizing the Result Before You Start Digging

The tricky bit in a tiny front garden is scale and style. A sleeper edge, a thin brick return, or even a small concrete edging block all work functionally — but which one actually looks right next to your house and wall?

This is where the GardenDream web app is your safety net.

• You take a photo of this exact corner — pillar, step, and bed.
• Drop in a virtual timber edge, then try a brick return, then a slim concrete block.
• Adjust heights, colors, and the stone finish behind it.

You’ll see fast whether:

• The timber adds a nice warm line…
• Or whether a brick infill makes the wall and step read as one solid unit.

Same idea we lean on when fixing awkward hardscape transitions in front entries, like in the project here: “Fixing an Awkward Porch Gable: Simple Updates for a Modern Cottage Front Entry”. We test visually before we commit to materials, so there are no “I wish I’d…” moments after the concrete dries.

Using a tool like GardenDream is cheaper than re-buying the wrong materials and way cheaper than living with a daily eyesore. Visualize your fix now using our Exterior Design App.