Resurfacing a Concrete Patio

Check the patio before you buy anything

A resurfacer renews the top of a slab. It cannot change its shape, and on a patio the shape is half the problem.

Slope. Water has to run off and away from the house. The IRC, in section R401.3, requires that "Impervious surfaces within 10 feet of the building foundation shall be sloped a minimum 2 percent away from the building," quoted here from the California adoption, and the Department of Energy's Building America guidance says the same for patios. Two percent is about 1/4 inch per foot. A resurfacer goes on at a feather edge to half an inch, so it cannot fix a patio that slopes toward the house or holds a puddle. Lift it, or replace it. The concrete slope calculator tells you how much fall you have.

Movement. Cracks where one side is higher, or panels that rock, mean the base has moved. A resurfacer will crack in the same places.

Depth of damage. The ready-mix industry's scaling sheet treats moderate scaling, about 1/8 to 3/8 inch of surface lost, as fixable with a thin bonded resurfacing. Holes deeper than half an inch get patched first with a repair mortar.

Old sealer or paint. Quikrete's Re-Cap sheet says to apply it "only to bare concrete." If water beads on the patio, something is on it, and it has to come off.

Which resurfacers are rated for outdoors

All of the common bagged resurfacers are sold for outdoor slabs, but their data sheets say very different things about freezing.

From the SikaQuick, Flo-Coat, Re-Cap and NewCrete data sheets.

Note what is missing. None of these consumer sheets publishes a freeze-thaw test result. The only overlays we found with one are professional products: Brickform's SM Pro Plus reports a durability factor of 93.3 after 300 cycles to ASTM C666. So in a cold climate, "rated for outdoors" on a consumer bag is a description, not a test, and the sealer you put on afterwards does more of the work. Quikrete's own rain figure is not stable either: its data sheet says protect from rain for 8 hours, its project sheet says 6. Plan for the longer one.

Pick a day with a forecast that stays above 50 degrees F for the next 24 hours, with no rain, and work in the shade or early. Flo-Coat's sheet says to mist the surface for 24 hours above 90 degrees F, and Re-Cap's to moist cure for 24 to 48 hours.

How to resurface a concrete patio

1. Repair first. Patch holes deeper than half an inch and chip out loose edges. Re-Cap's sheet says repairs "must be made before resurfacing can be initiated."
2. Clean to bare concrete. Pressure wash at 2,500 psi, the figure on the Re-Cap and Flo-Coat sheets, and remove moss, sealer and paint.
3. Protect the joints. Re-Cap: "It is essential that control joints and expansion joints be maintained." Flo-Coat: do not let the material spill into them; tape them.
4. Dampen the slab so it is wet through with no standing water.
5. Mix and spread in sections with a long-handled squeegee, building to your thickness. For Re-Cap, no more than 1/4 inch per pass.
6. Broom it. See the next section; this is the step that matters most on a patio.
7. Cure and keep off. Keep it moist, keep rain and frost off for the times in the table, and stay off it for at least 8 hours with Re-Cap.

Grip: broom it, every time

A troweled resurfacer is slick when wet, and a patio is wet often. Every maker gives the same answer. Quikrete's project sheet: "For a slip-resistant professional finish, follow within five minutes with a large push broom." Re-Cap's data sheet: broom "when surface is thumb print hard" with all strokes in the same direction. Flo-Coat: broom in complete strokes after it stiffens but before it sets. The ready-mix industry's finishing sheet gives the same advice for new concrete.

No resurfacer publishes a slip-resistance number for its broomed finish, and no standard sets one for a residential patio. A medium broom texture across the direction people walk is the practical answer. If you seal afterwards, a glossy film sealer can undo it, which the outdoor concrete guide covers along with grit additives.

Stamped and textured overlays on an old patio

If you want the patio to look like stone or tile rather than new gray concrete, a stampable or spray-down overlay is the route. These are thicker, need a primer, and are less forgiving than a bagged resurfacer.

From Sika's SikaCem-172 sheet and Euclid's Thin-Crete Grout and Spray-Deck sheets.

Two things carry over from the plain resurfacer and matter more here. The joints have to come up through the overlay: Euclid says "Existing construction joints must be honored," and a stamped pattern laid across a joint cracks on the joint line. And the overlay needs a surface profile a pressure washer usually will not reach, so plan on grinding or shotblasting. The resurfacing hub has more on stamping existing concrete and what the profile numbers mean.

What it costs to resurface a patio

Take a 12 by 16 foot patio, 192 square feet, at the bag prices in the calculator:

• Bagged resurfacer at 1/8 inch: 2 cubic feet, 6 bags of Re-Cap, about $222
• Bagged resurfacer at 1/4 inch: 12 bags, about $444
• Stampable overlay at 3/8 inch: 6 cubic feet, 12 bags of 55 lb overlay, about $672 before primer, color, release and sealer

Those are bags only, with no waste allowance; the calculator adds waste. A contractor's price is mostly labor and preparation. The consumer cost sites put basic resurfacing at about $3 to $10 a square foot and stamped overlays at $4 to $20, so roughly $600 to $1,900 for basic resurfacing of this patio. The resurfacing cost section explains where those numbers come from, and the concrete patio cost guide prices a new patio if you are weighing replacement.

Sealing it afterwards

Quikrete's project sheet says its sealer can go on "no sooner than 24 hours after application" and also that "No sealer is required." In a freeze-thaw climate, sealing is still the better bet: NRMCA's scaling sheet recommends a breathable silane or siloxane sealer for exterior concrete, and keeping de-icing salt off it in the first winter. The outdoor concrete guide compares sealers, and the sealing guide covers how and when.