Grout vs Caulk vs Silicone: Which Material Goes in Which Tile Joint

Use grout between tiles in a flat field, and use a sealant wherever tile meets a change of plane, another material, a tub or a countertop. For wet areas and real movement, 100% silicone (or urethane sealant on floors and exteriors) is the right sealant. Siliconized acrylic and sanded caulk are easier to work but suit only dry, low-movement joints.

Why the difference matters

Grout and sealant look similar in a finished job, so people treat them as interchangeable. They are opposites in one key property. Grout is designed to be hard, dense and stable once cured, so it can hold a profile, resist abrasion and lock tiles into a single surface. Sealant is designed to stay soft and recover after being stretched or squeezed, so it can absorb movement between two surfaces that do not move together.

Where a tub meets a wall, where a wall meets a floor, where a backsplash meets a countertop, the two sides move independently: settling, thermal expansion, a tub dropping slightly when filled, wood framing shrinking. Grout in those joints cracks, usually within the first year. TCNA EJ171 accordingly calls for sealant at changes of plane, at perimeters and restraining surfaces, and in planned movement joints. The rules for where and how often those joints go are on the movement joints page. This page focuses on the materials themselves.

The five materials

Cement grout

Portland cement, fine aggregate, pigments and, in ANSI A118.7 products, polymers. It cures into a rigid, slightly porous solid that bonds to the tile edges and the setting bed. Its job is the field joint: stable, abrasion resistant and easy to tool flush. It has essentially no movement capacity. Resin grouts (epoxy, urethane) are tougher or slightly more forgiving but follow the same rule. Even products marketed as flexible grout are not movement joint materials.

Siliconized acrylic caulk

Acrylic latex caulk with a small silicone additive to improve adhesion and water resistance. It tools easily, cleans up with water and can be painted. It cures by water evaporation, so it shrinks somewhat as it dries, and its movement capacity is low compared with true silicone. In a wet shower it tends to mildew and lose adhesion sooner. Its proper home is dry, low-movement joints: trim, baseboard tops, a dry backsplash edge against a painted wall.

Sanded caulk

Usually an acrylic latex or siliconized acrylic caulk with fine sand added and pigmented to match a grout maker's color line. The sand gives it the texture of sanded grout so a corner reads as one continuous grout line. Functionally it inherits acrylic's limits: modest movement capacity, some shrinkage, and less durability in constantly wet areas than silicone. The added sand also makes the surface rougher, which can hold soap scum. It is popular because it looks right, and in a wall-to-wall corner of a shower that rarely moves it can perform acceptably, but it is a compromise.

100% silicone sealant

A silicone polymer that cures by reacting with moisture in the air. It is highly elastic, water resistant, UV stable and stays flexible across a wide temperature range. Products sold for kitchen and bath often include a mildewcide. There are two common cure chemistries: acetoxy (acid curing, vinegar smell) and neutral cure (alcohol or oxime). Acetoxy silicone can etch or stain some natural stone and corrode some metals, so neutral-cure silicone is the usual choice on marble, limestone and other sensitive stone; many stone fabricators also recommend a non-staining silicone made for stone. Its main drawbacks: it is harder to tool neatly, it cannot be painted, and almost nothing (including new silicone) bonds well to silicone residue, so old silicone must be removed completely before recaulking.

Polyurethane sealant

A tough, elastic sealant that cures with atmospheric moisture. It bonds strongly to concrete, masonry and tile, resists abrasion and foot traffic better than silicone, and many grades can be painted. That makes it a common choice for floor movement joints, exterior joints and joints that see traffic or rolling loads. It typically has less UV stability than silicone unless the product is rated for it, and it is messier to tool. Self-leveling urethane sealants are made for horizontal joints in floors and patios.

Side-by-side comparison

Where each belongs

For shower-specific grouting decisions, see shower grout; for tiled counters, see countertop grout.

Color-matched sealants

The main reason people grout corners is appearance: a white silicone line in a field of gray grout looks wrong. Most major grout makers solve this with sealant lines pigmented to match their grout colors, in both 100% silicone and sanded acrylic versions. A few practical points:

• Match the grout you actually used. Cement grout dries lighter or darker than the bag swatch depending on water and cure, so compare the cured grout to the sealant in daylight, not the color chart. See grout color guide.
• Silicone looks glossier than grout. A matte or satin finish silicone is closer to grout. Lightly tooling with a dry tool gives a smoother, flatter line.
• Sanded caulk matches texture better, which is why some installers use it in dry wall corners and silicone at the tub and floor.
• Clear silicone is not invisible. It shows the dirt, gap and backer behind it. A color match usually looks better.
• When matching an old installation, bring a loose piece of old grout to compare. Matching faded grout is covered in matching existing grout color.

What makes sealant joints last

Material choice is half the job. Sealant joints fail early for reasons unrelated to the product:

• Grout cured into the joint. Corners must be kept free of grout during grouting or raked out before cure. A thin skin of sealant over grout fails.
• Three-sided bond. In wider joints, a backer rod or bond breaker tape keeps the sealant from bonding to the bottom so it can stretch. Details are on the movement joints page.
• Dirty or damp surfaces. Soap residue, old silicone, grout sealer and moisture all reduce adhesion. Clean with the solvent the sealant maker recommends and let the joint dry.
• Using the shower too soon. Silicone typically skins in minutes but needs about 24 hours or more to cure through, longer in deep beads or cool rooms. Follow the cartridge.
• Grout not cured. Many sealant makers recommend waiting for cement grout to cure before applying sealant against it so moisture does not interfere with adhesion. Check both data sheets.

Sealant is a maintenance item. Expect to replace silicone in a heavily used shower every several years as it discolors or loses adhesion, and replace it whenever you regrout a shower.