Frameless shower glass at the floor plane: why the 15mm threshold reveals water-seepage risk in a Hennur ensuite

A Hennur ensuite spec sheet landed on the atelier desk last month: frameless enclosure, 10mm low-iron glass, floor-to-ceiling wall. The architect had dimensioned a 12mm threshold. On paper it looked elegant—minimal joint line, clean sight line from the bedroom. On site, during monsoon, water was migrating sideways into the subfloor within six weeks of handover. The threshold was too shallow. The sealant joint couldn't hold back capillary rise.

The capillary problem at 12mm

Water doesn't only move downhill. In a narrow gap—anything under 15mm—capillary action pulls moisture horizontally and upward through micro-fissures in grout, sealant, and the stone or tile substrate itself. The Cauvery water in Bangalore carries TDS of 200–300 ppm; hard water deposits accelerate this migration. A 12mm threshold gives capillary pathways direct access to the subfloor structure.

The physics is simple: the narrower the gap, the stronger the capillary pull. At 12mm, water finds its way. At 15mm and above, the capillary rise is interrupted by gravity and air-entry points. This is why the 15mm threshold became the atelier standard for frameless enclosures in Bangalore projects—not an aesthetic choice, but a structural one.

Floor slope and threshold geometry

Why slope alone is not enough

Many architects specify a 1:100 floor slope (1mm per 100mm of depth) inside the shower pan, assuming gravity will handle water management. It doesn't. Slope moves bulk water toward the drain, but capillary action operates in the micro-gaps at the threshold—the joint between the glass and the floor plane. A well-sloped pan with a 12mm threshold will still seep.

The threshold as a capillary break

A 15mm threshold functions as a capillary break. The extra height creates two effects: first, it interrupts the continuous micro-path from the wet side to the dry side; second, it allows air to enter the sealant joint, breaking the capillary bridge. Below 15mm, the joint stays saturated and the pull continues.

The threshold should be chamfered at 45 degrees on the wet side (the shower side). This detail sheds water rather than pooling it at the glass base. Many Bangalore projects skip this chamfer to save cost or because the glass supplier didn't detail it—and then the threshold becomes a water trap, not a barrier.

Sealant joint depth and tolerance

The sealant joint between the glass and the threshold is where the capillary risk is managed—or ignored. A joint that is too shallow cannot accommodate the thermal movement of glass (4mm per metre in summer heat) and will crack, opening pathways for water. A joint that is too wide allows capillary wicking across the full width.

Specify a 6mm sealant joint minimum, filled with a polyurethane or silicone rated for wet-area use. The joint must be tooled flush or slightly recessed—never convex or proud. A convex bead traps water at the edge. The sealant should be applied in a single continuous bead, no gaps, no skip-troweling. Joint tolerance on site should be ±1mm; anything wider requires a backer rod before sealant application.

Hard water in Bangalore degrades standard silicone sealants within 18–24 months. Specify a polyurethane sealant with mildew resistance and UV stability. It costs 40–50% more than silicone, but outlasts it by three years in a humid ensuite. This is a spec decision, not a cost-cutting one.

The floor-plane detail: glass-to-threshold junction

The junction between the glass and the threshold is a construction detail that often goes undrawn. It should not. Here is the sequence, measured from the wet side:

1. Shower pan floor, sloped 1:100 toward the drain.
2. Threshold stone or tile, 15mm minimum height above the pan floor, chamfered 45 degrees on the wet side.
3. Backer rod (10mm diameter, closed-cell foam) in the joint between glass and threshold.
4. Polyurethane sealant, 6mm wide, applied over the backer rod.
5. Glass base, resting on the threshold, with a rubber or neoprene shim (2–3mm) to allow for micro-movement.

This detail is critical. If the glass sits directly on the stone threshold without a shim, thermal expansion will crack the sealant. If the sealant is applied without a backer rod, it will compress unevenly and fail. If the threshold is 12mm, capillary rise will overcome the sealant within the first monsoon.

Bangalore monsoon and hard-water deposit acceleration

June through September brings sustained humidity (often above 80%) and rain. In an ensuite with a 12mm threshold and a standard silicone sealant, hard-water deposits from the Cauvery begin to crystallize at the sealant-stone interface within four weeks. These deposits act as capillary wicks, pulling moisture deeper into the substrate. By month two, the subfloor plywood or concrete begins to absorb moisture. By month three, the finish is compromised.

A 15mm threshold with a polyurethane sealant and a proper backer rod resists this degradation. The extra height breaks the capillary chain. The sealant flexibility accommodates thermal cycling. The backer rod prevents sealant compression and maintains joint depth.

Projects in Hennur, Sarjapur Road, and Whitefield—all areas with high water table and summer heat—have shown this pattern consistently. Architects who specify 15mm thresholds and polyurethane sealants report zero seepage complaints. Those who cut the threshold to 10–12mm for a "cleaner look" face remedial work within six months.

Glass specification and frame detail

The glass itself should be 10mm toughened, low-iron or clear, depending on the aesthetic brief. Our 10mm frameless shower in clear glass with black hardware is specified by most Bangalore architects for its clarity and durability. The frame detail—whether you use a minimal U-channel or no frame at all—does not change the threshold requirement. The glass sits on the threshold; the threshold holds the water.

If you are specifying a grid-pattern frameless enclosure, the grid lines can complicate the floor-plane detail. The grid mullions should terminate 15mm above the threshold, not sit on it. This prevents the mullion from becoming a capillary bridge. The shop drawing must show this clearance; if it doesn't, flag it before fabrication.

As-built and handover: what to check

On site, during fit-out, inspect the threshold detail before the glass is installed. Confirm that the threshold is 15mm minimum, chamfered on the wet side, and level to ±2mm across its length. Check the sealant joint after the glass is fitted—it should be continuous, no voids, and tooled flush. Run water along the threshold with a hose; it should shed toward the drain, not pool at the glass base.

Request a shop drawing from the glass supplier showing the floor-plane detail, the sealant joint, and the backer rod. If the drawing shows a 12mm threshold or a sealant joint less than 6mm wide, reject it and request a revised spec. This is a handover risk, not a minor detail.

After handover, advise the client to avoid harsh chemical cleaners on the sealant joint during the first three months. The sealant needs time to cure fully in Bangalore's humidity. Standard bathroom cleaners are fine; bleach or acetone will degrade polyurethane prematurely.

Questions we get asked

Can we use a 12mm threshold if we apply a waterproofing membrane under the sealant?

No. A membrane helps, but it doesn't solve the capillary problem. Water will still wick into the micro-gap at 12mm, and the membrane can trap moisture against the subfloor, causing delayed failure. The threshold height is the primary control. Membrane is secondary—a backup, not a substitute.

Why does the threshold need to be chamfered? Can't we just use a square edge?

A square edge pools water at the glass base and concentrates stress at the sealant joint corner. A 45-degree chamfer sheds water and distributes stress across the joint. It also looks intentional, not like an unfinished edge. Chamfer is a spec requirement, not optional.

We specified polyurethane sealant, but the contractor used silicone to save cost. What do we do?

Document it and request replacement before handover. Silicone will fail within 18–24 months in a Bangalore ensuite. The cost of removing and re-sealing later far exceeds the upfront difference. Polyurethane is a structural spec, not a preference.

Is a 15mm threshold too high for a barrier-free ensuite?

A 15mm threshold is still ADA-compliant for residential bathrooms (the limit is 25mm). For a fully barrier-free design, you can slope the floor at 1:12 from the dry side to the wet side, eliminating a hard threshold altogether. This requires careful drainage design and a recessed shower pan. It's more complex and more expensive, but it's the right approach if accessibility is the brief.

Do we need to re-seal the threshold every few years?

With a polyurethane sealant and proper installation, no. A well-spec'd joint should last 5–7 years in a Bangalore ensuite before minor touch-ups are needed. Silicone sealants need refreshing every 18–24 months. The upfront cost of polyurethane pays for itself in reduced maintenance.

If you are specifying a frameless shower enclosure for a Bangalore project and the threshold detail is not yet drawn, commission a shop drawing from the atelier. The floor plane is where water management happens. Get it right at the spec stage, and you avoid remedial work during monsoon.