Grout looks like a single product at the home center, but it’s actually a family of formulations with very different chemistry. Knowing what is grout made of matters because picking the wrong type — sanded portland cement in a tight shower seam, unsealed cementitious grout in a coffee-prone kitchen, or cheap pre-mixed grout in a heavy-traffic floor — leads to cracks, stains, and rework within a year. This guide breaks down every common grout type, what’s actually in it, and where each one earns its keep.
The Three Main Grout Categories
Almost all grout sold in North America falls into one of three categories: cementitious, epoxy, or pre-mixed urethane/acrylic. Each has a distinct composition and a distinct use case.
Cementitious grout is the original and still the most common. Epoxy grout is the premium performance choice for tough conditions. Pre-mixed grouts are convenient but compromise on hardness and longevity. Picking between them comes down to where you’re tiling, your skill level, and how much maintenance you’ll actually do.
Cementitious Grout Composition
Standard cementitious grout is roughly 70-80% portland cement, 10-20% fine silica sand (in sanded versions), 5-10% color pigments, and 1-5% chemical additives like polymers, water-retention agents, and accelerators. Brands like Mapei Keracolor, Custom Building Products Polyblend, and Laticrete PermaColor all sit within this general formula.
Sanded grout uses silica sand sized 50-100 mesh and works in joints 1/8 inch and wider. Unsanded grout omits the sand and works in joints under 1/8 inch — typical for polished marble or glass tile where sand would scratch. Mixing them up is the most common DIY mistake: sanded in tight joints leaves voids, unsanded in wide joints cracks as it cures.
Polymer-Modified Cementitious Grout
Most modern cement-based grouts include polymer additives like vinyl acetate or styrene-butadiene latex. These improve flex strength, freeze-thaw resistance, and stain resistance compared to traditional unmodified portland grouts. Mapei Ultracolor Plus FA and Laticrete PermaColor Select are leading examples — they look like standard cementitious products but perform much closer to epoxy on water resistance.
Polymer-modified grouts are the right default for most residential installs. They cost $20-$35 per 25-pound bag versus $15-$25 for basic Polyblend, and the performance bump is worth the upcharge on a job that needs to last 20+ years.
Epoxy Grout Composition
Epoxy grout is fundamentally different — a two- or three-part system with epoxy resin, a hardener, and silica filler. There’s no portland cement involved. When mixed, the chemical reaction creates a near-impervious solid that resists virtually all common chemicals, stains, and moisture.
- Laticrete SpectraLOCK Pro Premium: Three-part system, $90-$120 per kit
- Mapei Kerapoxy CQ: Pre-blended sand and pigment, $80-$110 per kit
- Custom Building Products CEG-Lite: Easier to clean during install, $70-$95 per kit
Epoxy is the right choice for commercial kitchens, shower floors, pool surrounds, and any tile installation where staining or chemical exposure is a real concern. The downside is working time — about 45-90 minutes from mix to unworkable, which punishes anyone slow on the float work.
Pre-Mixed Urethane and Acrylic Grouts
Bucket-mix grouts like Mapei Flexcolor CQ and Custom Building Products Fusion Pro arrive ready to use. The base is typically a urethane or acrylic resin with silica filler and color pigments. Skip the water-mixing step, skip the sealing step — the manufacturer’s pitch is “all-in-one convenience.”
Reality is more nuanced. Pre-mixed grouts perform well on backsplashes and dry walls but struggle with extended water exposure on shower floors and kitchen floors. They also haze easily during cleanup if you let the residue sit more than 20 minutes. Use them where convenience justifies a slight performance hit — never in a primary shower or a high-traffic floor.
How Color Gets Into Grout
Cementitious grout colors come from iron oxide pigments (red, brown, yellow tones), chromium oxide (green), titanium dioxide (white), and carbon black. Quality color consistency requires precise pigment ratios and dry mixing before water hits the powder. Cheap grout shows color variation across a single bag — premium grout doesn’t.
Epoxy grout colors come from pigments suspended in the resin component. Color stability is essentially permanent because nothing leaches out of the cured matrix. That’s why epoxy grout from 10 years ago still looks the same as when it was installed, while cement grout often fades and yellows.
Additives Worth Knowing About
Modern grout often includes mold and mildew inhibitors — typically silver-ion or zinc-based antimicrobials. Mapei Ultracolor Plus FA includes BioBlock technology that resists mold for 5+ years even in damp shower environments. Look for these additives on shower and steam room installs.
Water-reducing admixtures let manufacturers ship grout that needs less water at mix time, which produces a denser, stronger cured product. Look for terms like “high-performance” or “rapid-setting” on the bag — they usually indicate these additives are present.
Matching Grout Type to Your Project
For a standard bathroom backsplash, sanded polymer-modified cementitious grout in a color matched to your tile is the right default. Budget $30-$50 in materials for a typical 30 square foot backsplash.
For a shower floor or steam shower, epoxy grout is worth the cost and effort. The waterproofing benefit is real, and you avoid the every-2-year resealing cycle that cement grout requires in wet areas. Budget $90-$150 in materials for a 40 square foot shower floor.
For a kitchen backsplash where convenience matters more than absolute durability, pre-mixed urethane grout works fine. Budget $50-$80 for a 30 square foot backsplash.
Sealing and Maintenance
Cementitious grout must be sealed within 72 hours of installation and resealed every 1-3 years depending on exposure. Penetrating sealers like Aqua Mix Sealer’s Choice Gold or Miracle 511 Impregnator work better than topical sealers because they don’t film over the grout surface.
Epoxy grout requires no sealing — ever. That’s part of the appeal despite the higher cost and harder install. Pre-mixed urethane and acrylic grouts also typically don’t need sealing, though some manufacturers recommend a coat after 30 days of cure.
