The Brief
A large open-plan kitchen extension in Orpington, approximately 45 square metres. The client wanted a grey porcelain tile in a herringbone pattern across the full floor, running from the kitchen through a dining area to bifold doors opening onto the garden. The floor had underfloor heating installed by the builder. The subfloor was a mix -- original suspended timber in the existing house transitioning to a concrete slab in the new extension.
The Challenge
Two substrates meeting in the middle of one continuous floor. The timber section flexes with foot traffic and seasonal movement. The concrete slab is rigid. Where the two meet, differential movement would crack any tile that bridges the junction without proper treatment. On top of this, the underfloor heating meant the entire adhesive specification needed to be UFH-rated -- standard adhesive goes brittle under thermal cycling. The herringbone pattern added a further layer: any error in the starting angle compounds with every row. Over 45 square metres, even half a degree off-square at the start becomes visibly crooked by the far wall.
The Solution
I installed a decoupling membrane across the entire floor -- essential over the timber section, and advisable over the UFH on both substrates. At the junction between timber and concrete, the membrane absorbs the differential movement. The adhesive was a C2S1 flexible product rated for underfloor heating. Expansion joints were placed at the perimeter, at the threshold of the bifold doors, and at the timber-to-concrete transition (hidden under a flush metal strip). The herringbone was set out using a laser level from the centre line of the room, with the pattern running parallel to the longest wall. I dry-laid the first three rows to verify the angle before any adhesive.
The Result
The finished floor runs seamlessly from the kitchen through to the garden doors. The herringbone pattern is straight across the full 8-metre run. The grout joints are consistent. The transition between old house and new extension is invisible under the tile. The underfloor heating runs evenly. The client has had the floor for over six months with no cracking, no movement, and no grout failure at the expansion joints.
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