Tile Trim: Sizes, Profiles and the One-Size-Up Rule

Tile trim is the thin metal or plastic profile that finishes an exposed tile edge, and choosing it comes down to three things: the profile shape, the material and the size. Get the size wrong and the trim either stands proud of the tile, catching sleeves and towels, or sits below it and leaves a sharp tile edge exposed. This page covers all three, how to fit tile trim on an external corner, and when a mitred edge or a bullnose tile is the better finish. It is the same advice we give customers across Bromley before a job starts.

What tile trim actually does

A cut tile edge is the weakest part of any tiled surface. The glaze stops at the face, the body underneath is exposed, and a knock from a vacuum or a door handle chips it. Tile trim does two jobs at once: it protects that edge, and it hides the cut.

You need it wherever a tiled surface stops without meeting another surface:

External corners, such as the edge of a window reveal, a boxed-in pipe or a chimney breast.
The top of a half-height tiled wall or a splashback that stops short of the ceiling or wall units.
The exposed edge of a bath panel, a shower niche or a tiled shelf.
Floor edges where tile meets a lower surface, such as carpet or a threshold.

Internal corners are different. Two walls meeting at an inside corner move slightly independently, so that joint is normally finished with a flexible sealant rather than trim.

Tile trim profiles: round, square and angle

The profile is the shape you see from the front. Most ranges come in three broad families.

Round edge (quadrant)

A curved face that wraps the corner. It is the most forgiving choice on walls where people brush past, and it is what most people picture when they think of bathroom tile edging. Schlüter’s RONDEC, for example, forms a symmetrically rounded outer corner with a 6mm radius.

Square edge (box)

A crisp, squared reveal that suits large format tiles, porcelain and modern bathrooms. Schlüter’s QUADEC is a well-known example. It looks sharper than a round profile, and it shows any misalignment more clearly, so the setting out has to be accurate.

Angle (L-shape)

A thin 90 degree strip where only a narrow line of metal shows. Schlüter’s JOLLY is the classic version for outside wall corners and edges. It is the most minimal look, but it offers a little less protection than a full round or square profile.

Tile trim materials: plastic, aluminium, stainless steel and brass

The material decides the finish, the durability and where the trim can safely go.

Plastic (PVC). The budget option. Bends slightly, comes in many colours to match white or coloured tiles, and cuts easily with a fine-toothed saw. It dents and scuffs more easily than metal, so keep it to light-use walls.
Aluminium. The everyday metal trim. Sold anodised or colour-coated, including matt black, brushed and bright silver finishes. Light, easy to cut with a junior hacksaw, and fine for most domestic walls.
Stainless steel. The hard-wearing choice for floors, commercial kitchens and anywhere constantly wet. Schlüter recommends its 316L grade (sold as V4A) where exposure is constant, such as swimming pools, rather than the standard grade.
Brass. Solid brass is sold chrome plated or in a brushed brass look, and suits period and high-end bathrooms. It is usually the most expensive of the four.

If you are matching taps and shower fittings, choose the trim last, once the brassware is in hand. Brushed brass finishes vary between manufacturers, and a trim that looked right in a showroom can read noticeably yellower or pinker next to your actual mixer.

What size tile trim do you need?

Tile trim is sold by depth, and the depth has to suit the tile. The trim sits on the wall with its perforated leg under the tile, bedded in the same adhesive, so the tile ends up slightly raised by the adhesive bed. That is why the usual rule is to go one size up from the tile thickness.

An 8mm tile takes a 10mm trim.
A 10mm tile takes a 12.5mm trim.
Common trim depths run 6mm, 8mm, 10mm, 11mm, 12.5mm and 15mm.

Measure the tile yourself with a steel rule or calipers rather than trusting the box, because thicknesses listed in a catalogue are often rounded. Floor tiles usually sit on a thicker adhesive bed than wall tiles, so allow a little more depth on floors.

The check that matters on the wall is where the tile face ends up. Schlüter’s own fitting advice is that the tile should finish flush with the top of the profile, or up to about 1mm lower. Never proud of it: a tile edge sitting above the trim defeats the whole point, because the edge is exposed again.

How to fit tile trim on an external corner

Trim goes on as you tile, not afterwards. The sequence we use:

Cut the trim to length. Use a junior hacksaw and a mitre block, and file off the burr so the ends sit tight.
Comb adhesive along the corner. Spread it with a notched trowel along the full length where the trim leg will sit.
Press the leg in. Push the perforated leg into the adhesive and check it for plumb with a spirit level.
Cover the leg. Trowel a little more adhesive over the perforations so adhesive pushes through the holes and locks the trim in.
Set the tiles against it. Butter the back of the edge tile, bed it, and check the face is flush or just below the trim.
Leave a grout line. Keep a small gap between tile and trim, around 2mm in wet areas, and grout it with the rest of the wall.

Where two trims meet at a corner, either cut both at 45 degrees so they meet in a neat mitre, or use the matching corner pieces most ranges sell. Corner pieces are quicker and hide small errors; a mitre looks cleaner but shows every half millimetre. Our guide on how to grout tiles covers the finishing stage, and the tiling tools checklist lists the hacksaw, mitre block and file you will want to hand.

Tile trim, mitred edges or bullnose tiles?

Trim is not the only way to finish an edge. There are two alternatives worth knowing about.

Mitred tile edges

Both tiles are cut at 45 degrees so they meet in a sharp corner with no metal showing. It is the most expensive finish because it needs a good wet cutter or a mitring tool and time. It only really works with through-body porcelain, where the colour runs all the way through; on a glazed ceramic tile the clay body shows at the slightest chip. A mitred corner is also more vulnerable to knocks, so it suits feature walls rather than busy hallways.

Bullnose and edge tiles

Some tile ranges, particularly metro and traditional ceramic ranges, include matching tiles with a rounded, glazed edge. Where they exist they give the neatest period finish, but you are limited to whatever the range offers.

For most bathrooms and kitchens, a decent metal trim is the right balance of protection, cost and looks. We tend to reserve mitres for large porcelain feature walls where the client specifically wants no metal line.

Common tile trim mistakes

Buying trim before the tiles arrive. Order it once you can measure the actual tile.
Fixing trim after tiling. A trim glued or siliconed on afterwards has no leg locked under the tile and is far weaker.
Adhesive left on the face. Wipe it off the visible profile immediately; dried adhesive scratches anodised and plated finishes when you scrape it.
Standard grade stainless in a pool or steam room. Use the higher grade the manufacturer specifies for constant wet exposure.
Trimming an internal corner. Use flexible sealant there instead.

If you are also cutting around pipes and sockets on the same wall, our guide to cutting holes in tiles will save you a few broken tiles. And if you would rather have it done properly first time, Bromley Tilers fits trim as part of every bathroom and kitchen job. For the manufacturer’s full fitting notes, see Schlüter’s JOLLY profile page.

Frequently asked questions

What size tile trim do I need for 8mm tiles?

A 10mm trim. The extra depth allows for the adhesive bed under the tile, so the tile face finishes flush with the trim or just below it.

Do you grout between tile trim and the tile?

Yes. Leave a small joint, around 2mm in wet areas, and grout it along with the rest of the wall so water cannot get behind the edge tile.

Can you add tile trim after the tiles are fixed?

Not properly. A standard trim has a perforated leg that sits under the tile in the adhesive. Anything stuck on afterwards relies on glue or silicone alone. The sound fix is to remove the edge tiles, fit the trim and re-tile the edge.

Does tile trim go on internal corners?

Normally no. Internal corners are finished with a flexible sealant, because the two walls move slightly differently and a rigid trim or grout line there tends to crack.

Which tile trim is best for a shower?

Aluminium or stainless steel suit most domestic showers. For swimming pools and anywhere constantly wet, Schlüter recommends 316L (V4A) stainless steel over the standard grade.

Is round or square tile trim better?

Round edge trim is more forgiving to knocks and suits traditional bathrooms. Square edge trim looks sharper with large format porcelain, but needs very accurate setting out because it shows misalignment.

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