Sika Pave Fix Plus: Why a Kiln-Dried Filler Resists Ant Nesting between Block Pavers

Colonies of Lasius niger, the common black garden ant, favour joint cavities between 4mm and 12mm. Loose sand in that range can stay dry enough for workers to move and deep enough for brood chambers. Conventional 0-2mm kiln-dried jointing sand gives them a workable material: dry, unbonded grains that can be carried away one load at a time. As the sand leaves the joint, the joint slumps, and the paver can begin to rock.

Sika Pave Fix Plus changes the behaviour of the joint fill by combining graded silica with a moisture-triggered polymer binder. The filler is brushed into the joint dry, then wetted with a fine spray. Once the polymer film coats the grains and cures, the sand forms a cohesive matrix. Individual grains stop travelling freely, while the cured joint remains permeable enough to pass surface water at roughly 0.5 litres per square metre per second on a correctly laid patio.

Void space gives ants the route in

A joint packed loosely with pure 0-2mm silica typically contains around 30 to 40 percent void space by volume. Those gaps create the route through the joint.

Workers carry the excavated material up to the surface, which is why fine conical spoil heaps appear on the paver faces after a dry spell. Each heap marks material removed from below, with joint depth lost a little at a time.

Sika Pave Fix Plus reduces the usable voids because the cured polymer bridges grain-to-grain contacts. The product is rated for joints from 3mm to 30mm wide and a minimum 30mm deep. That depth matters. A shallow 10mm fill cures as a thin biscuit, then cracks and delaminates under foot traffic, reopening the cavity that the filler was meant to close.

Depth is the specification many installers underweight. On block paving, the full 50mm to 80mm paver depth gives the joint the shoulder it needs. The filler should be worked down the entire flank of the block so the joint has a continuous bonded column from top to bottom.

The base decides whether the joint stays intact

A joint filler cannot compensate for a moving base. For a domestic patio or driveway, block paving sub-base preparation starts with compacted MOT Type 1. Pedestrian patios need a minimum 100mm thickness, while areas where a car parks need 150mm or more. The material should be compacted in layers no thicker than 75mm with a plate compactor.

The laying course above the Type 1 is sharp sand or 4-6mm grit, consolidated to 30mm to 50mm and screeded to the finished profile. If the Type 1 is under-compacted, the blocks migrate under load. The joints flex, the cured Pave Fix cracks along its weakest line within a season, and ants can enter again through the fracture.

The sequence is fixed for a reason: compact the sub-base to refusal, screed the laying course, lay the blocks, vibrate them with a plate compactor running over a rubber mat, then joint the paving. If jointing happens before final consolidation, vibration traps uncured filler and leaves a hairline map of cracks across every joint.

Drainage belongs in the same preparation stage. A permeable joint sitting above an impermeable base with poor fall holds water at the block base. That water softens the laying course, encourages settlement, and keeps the surface damp enough for algae to thrive. The base has to shed water through the planned fall.

Cross fall setting out

A patio needs a minimum fall of 1 in 80, equal to 12.5mm of drop per metre run, falling away from the house. On a 4 metre deep patio, that produces 50mm of fall from the wall to the outer edge.

Set the plane with string lines pegged at both levels before any sand goes down. Check it with a spirit level on a long straightedge or with a laser level. A fall below 1 in 100 leaves standing water. A fall steeper than 1 in 40 feels visibly tilted underfoot and sends furniture legs drifting toward the garden.

Porcelain slabs need priming slurry

Porcelain paving has almost zero water absorption, often below 0.5 percent. That low absorption helps it resist staining, and it also makes the slab reluctant to bond to a mortar bed by itself. A 20mm porcelain slab laid on a standard sand-cement bed with no primer can lift within months as a hollow, drummy unit.

The fix is a priming slurry brushed onto the full underside of each slab immediately before bedding. An SBR slurry bonding coat is the common approach: styrene-butadiene rubber latex gauged with cement and a little water to a thick, paintable consistency.

The whole back of the slab is coated so no dry patches remain. The slab is then placed onto a wet mortar bed while the slurry is still tacky. The SBR migrates into the mortar and grips the sealed porcelain face mechanically and chemically.

Marshalls and Sika both supply priming slurries formulated for this work. The working time is short, often 20 to 30 minutes per batch, so the slurry is applied to individual slabs as they are laid. Skip the priming coat and the most expensive part of the patio is the part that fails first.

The same SBR slurry principle also bonds new concrete to old and seals the interface on a mortar bedding course. That is why SBR earns its place on paving jobs well beyond porcelain laying.

Efflorescence and algae need different treatments

The white bloom seen on Marshalls Fairstone and similar sandstone or concrete units after laying is efflorescence. Soluble salts move to the surface as the unit dries, then remain there as water evaporates.

Marshalls Fairstone efflorescence removal usually begins with patience. Much of the bloom weathers off naturally over one to two seasons of rain. Where the surface needs treatment sooner, a proprietary efflorescence remover based on dilute acid can lift the salt when applied to a pre-wetted slab and rinsed thoroughly. Acid on natural stone can etch and dull the face, so a test patch on an offcut is the honest first move. Neat acid should never be applied to dry stone.

Algae is living growth with a separate treatment route. Green and black growth on garden paths thrives where the surface stays damp, which links it directly to cross fall and drainage. Algae treatment starts mechanically with a stiff brush and a controlled pressure wash below 100 bar, keeping enough restraint to avoid blasting joint filler out.

After cleaning, a benzalkonium-chloride-based path and patio cleaner kills the growth at the root. Sodium hypochlorite bleaches algae white and the growth returns. Quaternary ammonium biocides actually kill it, and reapplication every 12 to 18 months on a shaded north-facing path is realistic.

Using acid for algae leaves living growth in place. Using biocide on a salt bloom leaves the salts in place.

A 25 square metre jointing calculation

Take a 5m by 5m block-paved area with 10mm joints, an average 6mm effective fill width, and 60mm block depth. Sika Pave Fix Plus coverage depends heavily on joint geometry. Manufacturer figures for a joint of this width and depth sit in the region of 3 to 5 kg per square metre.

That puts the job at roughly 75 to 125 kg of filler. A 15kg tub covers only a few square metres at those dimensions. Underbuying is routine because the printed coverage on the tub assumes narrower joints than much block paving actually presents.

Brush the dry filler in fully, compact it down the joint, and top up before wetting. The specified fine water spray is part of the cure, and the joint needs to be workable-dry as the filler goes in. It is wetted precisely once.

Overwatering carries polymer to the surface and can leave a glazed skin over an under-bound core. Under-depth produces a similar failure: a thin cured crust above loose material that ants can still reach. Where ants reappear after a correctly deep and properly cured joint, lifting a block is the only way to see whether the break sits in the filler or in the laying course beneath it.

The surface can look finished while the loose core underneath remains available for excavation.