Published August 7, 2026 · By Concrete Pro Grand Rapids · ~9 min read
Exterior concrete in West Michigan carries 5 to 7 percent entrained air, and air-entrained slabs cannot be hard troweled without risking delamination. That leaves broom texture as the default and exposed aggregate as the durable upgrade. Smooth troweled finishes belong inside the building line.
Homeowners pick a finish from a photo. Contractors should pick it from the mix ticket. In West Michigan those two decisions collide, because the same air-entrained mix that survives our winters is the mix you are least allowed to trowel smooth.
Here is the chain. Exterior flatwork in this climate needs entrained air, generally 5 to 7 percent, so the paste has somewhere to push water when it freezes. Grand Rapids runs 40 to 60 freeze-thaw days in a typical winter, which is enough cycling to shred a non-air-entrained slab in a decade. That air is not optional. And that air is exactly what makes a hard-troweled finish fail.
So the finish question answers itself for most exterior pours before anyone opens a sample book. What is left is the choice between a broom texture and an exposed-aggregate surface, and knowing when the standard answer does not apply.
A broom finish is a bull float, then a hand float or light steel troweling to close the surface, then a stiff-bristle broom dragged across the slab while it is still plastic. The grooves run perpendicular to traffic. That is the whole method.
It gets specified on nearly every driveway, sidewalk, and patio we pour for three reasons. It gives real texture under wet feet and winter boots. It hides minor variation in color and flatness, which matters on a 40-foot driveway placed in one morning. And it does not require the slab to be closed tight, which is the point.
Broom texture is not a single thing, either. A soft-bristle broom pulled early gives a fine, almost velvet texture that suits a covered porch. A stiff broom pulled later gives deep grooves that hold traction on a sloped drive but collect grit and are harder to shovel. On any slab steeper than a gentle pitch we go coarser and tell the owner why.
The one honest drawback: broom grooves hold water and de-icing residue. That is a sealing conversation, not a finish problem, and our guide to sealing concrete in West Michigan covers timing and product class.
This is the part that costs people money, usually two winters after the pour.
A hard-troweled finish is what you see on a warehouse floor: dense, closed, slightly glossy, made with a power trowel working the surface repeatedly until it burnishes. Owners ask for it outdoors because it looks clean and sweeps easily. On an air-entrained exterior slab, it is a defect waiting to surface.
ACI 302.1R states plainly that entrained air is not recommended for concrete to be given a smooth, dense, hard-troweled finish, because blistering and delamination may occur. The American Society of Concrete Contractors takes the same position in its Position Statement #1 on hard-troweled finishes on air-entrained concrete.
The mechanism is simple. Troweling too early or too aggressively seals the top few millimeters while bleed water and air are still trying to rise. They get trapped in a thin plane below the surface. Nothing looks wrong on day one. Then the slab cycles through a winter, and the trapped plane lets go in sheets the size of a hand. The NRMCA technical bulletin on delamination of troweled surfaces walks through the same failure.
Delamination is not the same as the surface scaling most people picture, though the repair conversation ends the same way. If you want the freeze-thaw version of that story, we covered it in why concrete spalls in Michigan winters.
The rule we hold to: if the mix has entrained air and the slab is outside, it gets broomed or it gets exposed. It does not get burnished.
Exposed aggregate strips the top layer of paste to reveal the stone underneath. Two methods do it. A surface retarder sprayed on the fresh slab holds the top paste soft overnight so it can be washed off the next morning, which gives the most control. Or the crew washes and brushes the surface as it sets, which is faster, cheaper, and less uniform.
What it buys you: excellent wet traction, a surface that hides staining and minor spalling far better than a broom finish, and a look that ages well next to brick and stone. What it costs you: more labor, a tighter timing window, and a rougher surface underfoot. It is the wrong choice for a pool deck where people walk barefoot and a very good choice for a sloped driveway or an entry walk.
It also depends entirely on the aggregate in the mix, which means the sample you approve has to come from the same plant and the same gradation as the pour. Approving a photo from a different supplier is how expectations go wrong.
For where exposed aggregate sits against decorative work in cost, our cost guide and the patio cost breakdown put a plain broom finish at the bottom of the range and full stamped work at the top, with exposed aggregate in between.
Rock salt finish, where coarse salt is pressed into the surface and washed out to leave pits, is a Michigan mistake. Those pits hold water. Water freezes. The pit becomes a spall. It is a fine finish in Phoenix.
Smooth or "sacked" finishes on exterior steps and landings are the second one. They look sharp in October and put someone on their back in January. Steps take the most traffic in the worst conditions, and every one we pour gets texture.
Heavy stamping on a north-facing slab with poor drainage is the third. Stamped concrete is a good product, covered in our stamped pattern guide, but deep texture plus standing water plus freeze-thaw is a demanding combination, and it needs drainage designed before the pour, not after.
There is a published standard for this. ANSI A326.3 measures dynamic coefficient of friction on hard-surface flooring, and its 2022 revision sets category minimums: 0.42 for interior surfaces expected to be wet with water, and 0.55 for exterior wet conditions. Higher is more traction.
Two honest caveats. The test was written primarily for tile and manufactured hard surfaces, and the standard itself says the measurement is useful for comparing products, not for predicting whether a slip will occur. It is a specification tool for a commercial owner writing a scope, not a guarantee for a homeowner.
What it is useful for: if you own a restaurant patio, a retail entry, or an apartment walkway, the exterior 0.55 figure is the number to hand your contractor, and it rules out the burnished finish immediately. On commercial flatwork we spec texture against that threshold rather than against a photo.
Driveways: broom, pulled coarse if there is any grade. Standard for residential work in Grand Rapids, Wyoming, Kentwood, and the surrounding townships, and what our driveway crews place unless a client specifically wants exposed aggregate.
Sidewalks and public walks: broom, grooves across the direction of travel. Municipal specs generally require it.
Patios: broom for the budget-conscious, exposed aggregate for durability under trees and staining, stamped when the look drives the project and drainage is handled.
Steps and stoops: texture, always. Never smooth.
Garage floors and interior slabs: this is where a hard-troweled finish belongs, because interior slabs generally do not need entrained air. That is the whole reason the rule reads the way it does. A garage slab is the one place a homeowner sees a smooth finish and it is correct.
Commercial parking and loading areas: broom, with control joint layout and reinforcement designed to the load, not to the look. Our post on control joint spacing covers that side.
A broom finish. Exterior slabs here need 5 to 7 percent entrained air to survive freeze-thaw cycling, and air-entrained concrete cannot be hard troweled without risking delamination. A broom texture also gives traction on wet and icy surfaces, which matters more on a sloped drive than any decorative consideration.
You should not if the mix is air-entrained, which exterior mixes in Michigan are. ACI 302.1R states that entrained air is not recommended for concrete given a smooth, dense, hard-troweled finish because blistering and delamination may occur. The surface can let go in sheets a winter or two after the pour.
Generally yes, because the exposed stone gives a coarser profile than broom grooves. It is also rougher underfoot, which makes it a poor choice for pool decks and barefoot areas. For commercial exterior walkways, ANSI A326.3 sets a wet dynamic coefficient of friction minimum of 0.55 to design against.
That pattern is delamination, and it usually traces back to finishing rather than to the mix. Troweling an air-entrained slab too early or too hard seals the top few millimeters while bleed water and air are still rising, trapping them in a plane just below the surface that later separates.
No. Rock salt finishing leaves small pits in the surface by design. Those pits hold water, the water freezes, and the pit becomes a spall. It is a reasonable finish in a dry, warm climate. In a region with 40 to 60 freeze-thaw days per winter it shortens the life of the slab.
Usually yes. Interior slabs including garage floors generally do not require entrained air, which removes the delamination risk that rules out troweling outdoors. A smooth troweled garage floor sweeps clean, resists staining, and takes a sealer or coating well. Just keep the finish inside the building line.
Concrete Pro Grand Rapids places residential and commercial flatwork across West Michigan to ACI and ASTM practice. We spec air content to the exposure class before the truck is ordered, match the finish to the mix rather than to a photo, hold finishing crews to ACI 302.1R guidance on air-entrained slabs, and lay out control joints and reinforcement to the load. We serve Grand Rapids, Wyoming, Kentwood, Rockford, Holland, Muskegon, Kalamazoo, and Lansing. Call (616) 228-7544 or request a free bid.