Outdoor Wall Tiles: 0.5% Absorption and a 100% Adhesive Bed

Outdoor wall tiles fail for three reasons: the tile soaks up water and splits in a frost, the adhesive bed has gaps where water collects, or the wall moves and nothing lets the tiling move with it. Fix those three and a tiled garden wall, porch or outdoor kitchen will last as long as the wall behind it. This page covers which tiles to buy, which walls you can tile, the adhesive and grout to use, and the fixing rules from The Tile Association that most DIY guides leave out.

We are a tiling firm working across Bromley and south east London, so the advice below is what we follow on our own outdoor jobs. If you would rather have it done for you, our Bromley tilers page has the details.

Which tiles can go on an outside wall?

The single number that matters is water absorption. Porcelain classed as Group BIa under BS EN 14411 absorbs 0.5% of its weight in water or less. Water that cannot get in cannot freeze inside the tile, so a BIa porcelain is the safest choice for a British winter.

Look for two lines on the manufacturer’s data sheet before you buy:

Water absorption: 0.5% or less (sometimes written as E ≤ 0.5%, tested to ISO 10545-3).
Frost resistance: “resistant” or “pass”, tested to ISO 10545-12.

If a tile has no data sheet, or the sheet does not mention frost, treat it as an indoor tile. A lot of decorative wall tiles sold for kitchens and bathrooms are ceramic with a soft, porous body. They look fine outside for one summer, then the glaze starts to lift after the first hard frost.

Natural stone, brick slips and patterned tiles

Slate, granite and dense limestones can work outdoors, but stone varies from quarry to quarry, so ask the supplier whether that specific stone is rated for external walls and whether it needs sealing. Encaustic cement tiles and handmade terracotta are porous and are usually sold for interiors only. Brick slips are made for outside walls and are a better fit if you want a brick look on a rendered or block wall.

Which walls can you tile outside?

The wall behind the tiles has to be strong, stable and not prone to swelling when it gets wet. Good outdoor backgrounds are:

Sound brick or blockwork, clean and free of paint, moss and loose mortar.
Sand and cement render that is well bonded and fully cured. The Tile Association‘s guide puts no general weight restriction on properly installed cement and sand render, which makes it the best base for heavy stone or large porcelain.
Concrete, once it has cured and any release agent or laitance has been removed.

Walls to avoid or prepare first:

Timber and plywood. The Tile Association says plywood and other wood-based boards should not be used for direct wall tiling, because they move as their moisture content changes. Outdoors, that movement is much worse.
Painted masonry. Paint is the weak link. The adhesive bonds to the paint and the paint lets go of the wall. Strip it back to the masonry.
Cracked or hollow render. Tap it with a trowel handle. If it sounds hollow, cut it out and re-render before tiling.
Walls with damp coming through from behind, such as a retaining wall holding back soil. Water pushing through from the back will lift tiles and leave salts on the face, whatever the adhesive.

Adhesive: improved, flexible and a full bed

Use a cement-based adhesive that the manufacturer states is suitable for external use. In practice that means an improved class C2 adhesive under BS EN 12004, usually with an S1 deformable rating so it can take some movement. Ready-mixed tubs are out: The Tile Association says they suit a maximum bed of 3mm and are not suitable for fixing porcelain.

The fixing rule that matters most outdoors is coverage. The Tile Association’s guide says that in exterior locations, 100% adhesive coverage of the tile should be achieved with no voids. A gap behind a tile fills with rainwater, the water freezes, and the tile pops off. To get a full bed:

Comb the adhesive in straight lines with a notched trowel, not swirls, so air can escape as you press the tile in.
Back-butter each tile with a thin coat of adhesive, filling any ribs or keys on the back.
Press and slide the tile across the ribs, then lift one now and then to check the back is fully covered.
Never use dot and dab. The Tile Association calls it unacceptable on walls and floors, and outside it leaves exactly the voids you are trying to avoid.

Our page on how to apply tile adhesive has more on trowel sizes and open time.

Big tiles, height and mechanical fixings

Large porcelain looks smart on a garden wall, but weight and wind change the rules. The Tile Association’s guidance is that tiles larger than 0.1m² fixed more than 3m above floor level should be secured with mechanical fixings, not adhesive alone. 0.1m² is smaller than it sounds: a 300 x 330mm tile is about 0.1m², and a 600 x 600mm tile is 0.36m².

For most garden walls, outdoor kitchens and porch walls this never comes up, because the tiling stays under 3m. If you are tiling the face of a house, a gable or anything above head height on a ladder, get a specification from the adhesive maker or a façade engineer before you start. External tiling is covered by its own British Standard, BS 5385-2:2015, which sets out design and installation for external ceramic, natural stone and mosaic wall tiling in UK conditions.

Movement joints on outside walls

An outside wall heats up in afternoon sun and cools fast at night, so it moves more than any bathroom wall. The Tile Association’s general guidance for wall tiling is to put movement joints:

Over any structural movement joint in the wall behind.
Where the tiling meets a different material, such as a window frame or a timber post.
At junctions between different backgrounds, such as brick meeting render.
At vertical corners.
At 3m to 4.5m centres, both across and up the wall, in large areas.

On a sunny south or west facing wall, or with dark tiles that soak up heat, we work to the shorter end of that range. The minimum joint width in the British Standards is 6mm, filled with a flexible sealant rated for outdoor use, not grout. Our guide to tile movement joints explains how to cut and fill them.

Grouting and sealing outdoor wall tiles

Use a cement-based grout the manufacturer rates for exterior use, preferably a flexible one. Let the adhesive harden fully before you grout so you do not disturb the tiles. Pack the joints full so there is no hollow for water to sit in, and keep the joint depth as close to the tile thickness as you can.

Practical points we see go wrong:

Weather. Do not fix or grout when frost is forecast before the products have set, or in heavy rain. Check the temperature range on the bag; most cement-based products have a minimum of around 5°C.
Capping. Water running down the top edge of a tiled wall gets behind the tiles. Fit a coping, a sloped top or a trim so the top edge sheds water.
The bottom course. Stop the tiling clear of the ground or patio so it is not sitting in splash-back and standing water.
Sealing. Glazed and BIa porcelain do not need a sealer. Natural stone usually does, and some grouts benefit from one. Follow the supplier’s advice for the exact product.

What a tiled outdoor wall involves, step by step

Check the tile data sheet for 0.5% absorption and a frost resistance pass.
Check the wall: sound, clean, unpainted, no damp coming through.
Plan the layout and the movement joints before the first tile goes on.
Prime if the adhesive maker asks for it on that background.
Fix with an external-grade C2 adhesive and a full, void-free bed.
Grout with an exterior grout and fill movement joints with outdoor sealant.
Cap the top edge and keep the bottom edge off the ground.

Frequently asked questions

Can you use indoor tiles on an outside wall?

Only if the data sheet says the tile is frost resistant and absorbs very little water. Most decorative ceramic wall tiles are not, and they crack or lose their glaze after a few frosts. Porcelain with water absorption of 0.5% or less is the safe choice.

What adhesive should I use for outdoor wall tiles?

A cement-based adhesive the maker states is suitable for external walls, usually class C2 under BS EN 12004 with an S1 flexibility rating. Do not use ready-mixed tub adhesive outdoors or for porcelain.

Do outdoor wall tiles need to be sealed?

Glazed tiles and porcelain do not. Natural stone usually does, and the right sealer depends on the stone, so ask the supplier. Sealing does not make up for a poor adhesive bed or missing movement joints.

Can I tile over render outside?

Yes, if the render is well bonded, fully cured and sounds solid when tapped. Sand and cement render is one of the best backgrounds for outdoor tiling. Cut out any hollow patches and re-render them first.

Why are my outdoor tiles falling off?

Usually because water got behind them. Gaps in the adhesive bed, a porous tile, a painted background or no movement joints are the common causes. Re-fixing the loose tiles with a full bed rarely helps for long if the others share the same problem, so check a few that are still on.

Do I need planning permission to tile an outside wall?

Usually not for a garden wall or a tiled feature. Cladding the outside of the house itself can need permission in conservation areas and some other protected areas, so check with your council before tiling the front of a house.

020 8058 5574

contact@bromleytilers.co.uk