How to Tile a Balcony: 1.5-2% Fall, Drain Mat, 150mm Upstand

How to tile a balcony comes down to one thing most indoor tilers never have to think about: where the water goes. A bathroom floor gets splashed; a balcony gets rained on, frozen, thawed and baked, then rained on again. Water that sits under the tiles freezes, expands and pushes them off, and on a balcony above someone else’s flat it also finds its way into their ceiling. This page covers the order of layers that actually works, the fall you need, which tiles and adhesives survive a British winter, how to finish the edge and the door threshold, and when the job is not one to start at all.

Most balcony failures come down to three things: no fall, no waterproofing under the tiles, and an edge that traps water. All three are cheap to get right at the start.

Before you start: is the balcony yours to tile?

On a house, a balcony over a ground floor room is part of your roof. On a flat, the balcony slab, its waterproofing and its edges are usually part of the building’s structure and belong to the freeholder, even if the lease gives you the use of the surface. Read the lease and ask the managing agent before you lift anything. Lifting old tiles or screed can damage a waterproofing layer that keeps water out of the flat below, and you could be liable for the repair.

Three more checks before buying a single tile:

What is underneath? A concrete slab with a screed can be tiled. A timber deck, a felt or asphalt roof covering, or a fibreglass (GRP) finish is a different job: most roofing membranes are not designed to take tiles bonded straight onto them, and the membrane manufacturer has to approve whatever goes on top.
How much height do you have at the door? Every layer adds height. If the finished tile would sit at or above the door sill, water will be driven under the door in heavy rain.
Does it drain now? Pour a bucket of water on it. If it ponds, correct the fall before tiling.

The fall: 1.5 to 2 per cent, built into the screed

The single most important number on a balcony is the slope. Schlüter states that an adequate slope of 1.5 to 2 per cent is required for drainage, and every one of its cantilevered balcony build-ups puts that fall into the screed underneath the waterproofing. In plain terms, 1.5 per cent is 15mm of drop for every metre of balcony; 2 per cent is 20mm per metre. A balcony that runs 1.8m from the house wall to the outer edge needs to be 27mm to 36mm lower at the edge than at the wall.

Two rules follow from that:

The fall goes in the base, not the adhesive. Trying to create a slope with a thick bed of tile adhesive gives you voids under the tiles that fill with water. Correct the screed first, let it dry, then tile at an even thickness.
The fall runs away from the building. Towards the outer edge, a gutter or an outlet, never back towards the door.

The layers, from the slab up

Schlüter’s balcony assembly A.2 is a good model of how a tiled balcony should be built, and most competing systems follow the same logic:

Concrete slab. Sound, clean and free of old paint, moss and loose material.
Sloped screed at 1.5 to 2 per cent.
Bonded waterproofing. In the Schlüter build-up this is KERDI, a polyethylene sheet set in thin-bed adhesive, with the joints and laps sealed with KERDI-COLL-L sealing adhesive. A trowel-applied waterproofing compound from a tile adhesive maker does the same job if it is rated for external use.
Drainage and uncoupling mat. DITRA-DRAIN 4 or DITRA-DRAIN 8 is bonded to the waterproofing in thin-bed adhesive. Its studded underside lets water that gets through the grout run off to the edge, ventilates the underside of the tiles and lets the tile layer move independently of the slab. Schlüter lists DITRA-DRAIN 8 for large areas and staircases. On the edge profile data the 4 version adds 4mm and the 8 version 10mm to the build-up.
Tiles fixed in a water and weather resistant thin-bed adhesive.

Grout is not waterproof, so without a drainage layer rain sits in the adhesive bed. Our page on decoupling matting explains the uncoupling part in more detail for indoor floors; outside, the drainage function matters even more than the uncoupling.

Which tiles survive a balcony

Use fully vitrified porcelain. Porcelain in the BIa group under BS EN 14411 absorbs 0.5 per cent of its weight in water or less, which is why it does not soak up rain and split when it freezes. Even so, check that the specific tile has passed the frost resistance test (ISO 10545-12) and that the maker rates it for external floors: low absorption alone is not a guarantee.

Standard ceramic wall tiles, and many cheaper glazed floor tiles, are not frost resistant and should not go outside at all. Terracotta and porous stone need sealing and are a specialist choice over a habitable room.

Slip resistance matters more outside than in, because a balcony is wet for much of the year. Pick an external grade finish rather than a polished or lappato face. Our guide to outdoor tiles covers finishes and thicknesses.

Adhesive and grout for outside

Use a cement based adhesive classed as C2 (improved) under BS EN 12004, and ideally S1 (deformable), because a balcony slab heats up and cools down far more than an indoor floor. Check that the bag says it is suitable for external use and frost resistant once cured. Use the adhesive the waterproofing and mat maker specifies for their system; with Schlüter that means a dry-setting thin-bed mortar.

Aim for full contact under every tile. Outside, a tile laid on five dabs of adhesive leaves cavities that fill with water and freeze. Back-butter large tiles. Our page on applying tile adhesive shows how. For grout, a flexible cementitious grout rated for external use is the normal choice; it will need cleaning more often than an indoor floor.

Edges and drainage

The outer edge is where most tiled balconies fail. Water running down through the drainage mat has to get out, and the edge of the screed has to be protected. Purpose-made balcony edge profiles do both. Schlüter’s BARA-RAKE, for example, is a colour-coated aluminium profile with a drip lip, for balconies with an existing sloped screed. Its vertical leg has drainage openings so water can leave and air can get under the tiles, and you choose the profile height to match the full edge thickness including the drainage mat.

Terracotta mosaic tiles on a balcony floor beside a slatted rail — A tiled balcony floor at its outer edge | terra cotta balcony flooring by Studio Sarah Lou (CC BY 2.0), via Flickr, https://www.flickr.com/photos/86665756@N00/4110163998

Whatever system you use:

Keep the drainage openings clear during tiling. Adhesive squeezed into the slots blocks them for good.
Leave a joint between the tiles and the edge profile and fill it with a flexible sealant, not grout.
Put a gutter under the edge if the balcony drips onto a path, a door or the balcony below. Schlüter’s BARIN gutter clips onto its edge profiles.
Use a movement joint at the house wall, not grout, so the tiled area can expand.

The door threshold and the 150mm upstand

Where a balcony meets the house, the waterproofing has to turn up the wall. NHBC’s standard for flat roofs and balconies says the waterproofing should generally form a minimum 150mm upstand, measured from the balcony drainage layer. That is easy against a plain wall and hard at a door, because a door sill rarely sits 150mm above the balcony.

NHBC’s clause 7.1.16 covers thresholds lower than 150mm where level access is needed: these need special detailing, and an accessible threshold should have a maximum 15mm upstand at the door position. On an existing balcony, the practical rule is simpler. Measure the height from the screed to the door sill before you buy anything, add up the thickness of waterproofing, mat, adhesive and tile, and make sure the finished tile still sits comfortably below the sill. If it does not, you need a thinner build-up, a channel drain across the door, or a conversation with a roofer.

Step by step: tiling a balcony

Clear and inspect. Remove old tiles and loose material, check the slab for cracks and the existing waterproofing for damage.
Correct the fall. Screed to 1.5 to 2 per cent towards the outer edge or outlet and let it dry fully.
Fix the edge profiles, bedding the anchoring leg in thin-bed adhesive at the correct height.
Waterproof. Lay and seal the membrane or apply the liquid waterproofing, with upstands at the walls and sealing bands at every joint, corner and pipe.
Bond the drainage mat, tucking it under the edge profile and keeping the drainage openings clear.
Tile with a C2 external adhesive and full contact, leaving movement joints at the walls and the edge.
Grout and seal joints with an external grout and flexible sealant at the perimeter.
Keep off it until the adhesive and grout have cured to the maker’s times, and keep it covered from heavy rain and frost while they do.

Do not lay cement based adhesive or grout when frost is forecast; most bags give a minimum working temperature.

Frequently asked questions

Can you tile directly onto a concrete balcony?

You can fix tiles to a sound concrete slab or screed, but tiling straight onto it without waterproofing and a drainage layer is the most common cause of tiles lifting and leaks into the room below. Rain gets through the grout and has nowhere to go.

What fall does a balcony need?

Schlüter specifies a slope of 1.5 to 2 per cent in the screed under its balcony systems, which is 15mm to 20mm of fall per metre. The fall should run away from the building and be built into the base, not the adhesive.

Can I tile over the felt or asphalt on my balcony?

Not directly. Most roofing membranes are not designed to have tiles bonded to them, and doing so can void the roof’s guarantee and damage the waterproofing. Ask the roofing manufacturer what can go on top, or consider a raised paver system instead.

Are porcelain tiles frost proof?

Fully vitrified porcelain absorbs very little water, which is what makes it suitable outside, but frost resistance is tested separately. Check that the tile’s data sheet shows a pass for frost resistance and an external floor rating.

Do I need permission to tile a balcony on a flat?

Usually you need the freeholder’s consent, because the slab and its waterproofing are normally part of the building’s structure. Check your lease and ask the managing agent before you start.

If you are in Bromley or nearby and want a balcony or terrace tiled with the right build-up underneath, Bromley Tilers can survey it and tell you honestly whether it is a tiling job or a roofing one first.

020 8058 5574

contact@bromleytilers.co.uk