Adhesives are most commonly used in landscaping projects to bond porcelain paving slabs to concrete foundations, or to bond porcelain tiles or natural stone walling slips as cladding to raised planting beds, garden walls or features.

There are two distinct types of adhesives for external use; ‘S1’ Rapid Set adhesive and ‘S1’ Slow Set adhesive. Both are deformable from 2 – 5mm which allows for expansion and contraction of both the sub-strate and the slab or tile. There are several manufacturers in the market, offering different products. Always read and follow the instructions on the packaging before use, especially in regard to ideal temperatures and weather conditions.

When bonding to a concrete foundation, it is important to ensure the concrete has sufficiently ‘cured’ or dried – anywhere between four and six weeks from laying dependent on the weather and temperatures prevailing.

The concrete foundation must be free of dust and moisture, as both can affect the efficacy of the adhesive products. An exterior grade universal primer is then applied to the concrete, followed by Rapid Set S1 adhesive (together with an anti-fracture mat if deemed necessary). Once the adhesive has cured, the back of the slab to be laid is prepared by cleaning with a non-ferrous brush to remove any further dust which may affect the bond prior to fixing.

Apply the adhesive to the back of the slab and to the concrete foundation using a 10mm notch trowel. Gently tap the slab down with a rubber or nylon maul, giving it a slight wiggle to ensure the collapse of the peaks in the adhesive formed by the notches in the trowel, thereby creating a full contact bond between the slab and foundation. A battery powered vibrator may be used to collapse the peaks instead of the maul.

When installing porcelain tiles or natural stone tiles or slips to vertical walls, the back of the retaining wall must be tanked or coated in a thick layer of tanking slurry or bitumen paint to prevent water ingress into the concrete blocks. These have a propensity to absorb water and delaminate the tile in freezing weather conditions. Suitable drainage must be installed to the rear of the walls to prevent any water build-up, and relieve hydrostatic pressure.

In a similar manner to laying paving, apply primer to the wall before adhesive, using the same type of notched trowel to both surfaces, and gently apply pressure to collapse the ridges and ensure a full bond when pressing the tile into position.

When using large format sizes of tiles -especially thinner units – use a suitable sized board as a buffer to minimise pressure on any part of the tile when placing into position and pressing to achieve the full bond.

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