Outdoor Concrete Floors

What fails outdoors

Four finishes and coatings go wrong outside.

• Standard epoxy

  Yellows

  Rust-Oleum says its 8000S epoxy "will yellow upon prolonged exposure to sunlight".

• High gloss

  Slick

  A glossy film sealer is slick when wet unless grit is added.

• Rock salt finish

  Warm climates

  Rarely seen in cold regions, where water can freeze in the pits and spall the surface.

• Hard troweling

  Avoid

  Finishing air-entrained concrete too early traps bleed water: delamination and blisters.

Exterior slabs "typically require a textured finish," says NRMCA CIP 14, usually a push broom after floating; it says to "avoid steel troweling air-entrained concrete."

Freeze-thaw and de-icing salt

Water expands about 9 percent as it freezes (University of Illinois), and in a saturated slab that pressure flakes off the surface, which NRMCA calls scaling.

• Entrained air

  6%

  Total air for 3/4 or 1 inch aggregate, per NRMCA CIP 2.

• Strength

  4,000 psi

  Where slabs stay wet, freeze and get de-icers; 3,500 otherwise.

• Banned de-icers

  Never

  Ammonium sulfate, ammonium nitrate or magnesium-based salts.

A sealer helps but doesn't replace air. It cuts how much water the slab soaks up. If a slab went down without entrained air in a freeze climate, sealing it is damage control.

Which sealer for outdoor concrete

Use a penetrating silane or siloxane, which NRMCA recommends; acrylics trade a shorter life for gloss and color. Lifespans below are from Foundation Armor.

1. Wait for the right cure. Quikrete's acrylic cure and seal goes on 4 to 6 hours after placing; penetrating sealers want a cured slab, so check the label.
2. Pick a dry spell above 50°F. That's Quikrete's minimum; NRMCA calls late summer, after a few dry days, the ideal time.
3. Apply two thin coats at right angles. Quikrete's acrylic covers 150 to 200 sq ft a gallon depending on texture; check your product's label.

Material is about $0.10 to $0.20 a square foot for acrylics, per the ASCC sealer guide. Application is covered in the concrete floor sealing guide.

Grip, and how to get it

Build texture into the pour with a broom, swirl or exposed aggregate finish, or add grit to the sealer on an existing slab.

Use 1 lb of grit per 5 gallons of sealer. That's Euclid Ultra Grip's dose, a colorless polypropylene powder. Polymer grit stays nearly invisible where silica sand changes the look; roll it on rather than spraying.

Stain or paint outdoors

Stain soaks in and can't peel; paint sits on top and lifts when moisture gets under it. Seal stained concrete outdoors to protect the color; see the stained concrete guide.

• Stain

  200 to 300 sq ft

  Per gallon for acid stain, per Sika's Lithochrome Chemstain Classic.

• Paint

  1,750 psi max

  Pressure-wash limit on DRYLOK floor paint; tape down a 1 ft plastic square for 24 hours first to test for moisture.

Pool decks

Pool decks need a cool, textured surface for wet bare feet: cool deck coatings like Mortex Kool Deck are textured cement surfaces that "significantly lower" surface temperature.

• Resurface

  $3 to $12

  Per sq ft, HomeGuide; Kool Deck about $4 to $6.

• Reseal

  Every 2 to 5 years

  Per Concrete Network, with a slip-resistant sealer or additive.

What outdoor concrete work costs

Sealing costs least; stamped overlays and stenciled stain cost most, according to Angi, HomeGuide and Concrete Network.

• Seal

  $1.35 to $2.50

  Per sq ft installed, Angi; about $1,500 for 1,000 sq ft.

• Paint

  $1.50 to $3

  Per sq ft, Angi.

• Stain

  $3 to $11

  Basic to intermediate, Concrete Network; stenciled work $16+.

• Resurface a patio

  From $3

  Plain $3 to $7, stamped $7 to $20, HomeGuide.

A 10 by 20 foot patio overlay runs $600 to $1,400, per HomeGuide; resurfacing a concrete patio covers the products and bags. For a new pour, size it with the concrete floor calculator or the concrete slab calculator, and tell the supplier it's exterior so the mix comes air-entrained.