Exposed aggregate vs broom finish concrete pool decks

A broom finish is exactly what it sounds like. After the concrete is placed, leveled and floated, the finisher pulls a wide broom across the surface while it is still soft. The bristles leave fine parallel grooves. The grooves give bare, wet feet something to grip, and they shed water in the direction of the brooming.

You can adjust it. A light broom with a soft bristle leaves a fine texture that is comfortable to walk on. A heavy broom with stiff bristles leaves deeper ridges that grip better on a slope but feel coarse underfoot. For a pool deck we lean toward a medium or light texture on the flat areas and a slightly heavier pass on steps and ramps.

The concrete industry treats a broom finish as the default for outdoor slabs for a reason. The National Ready Mixed Concrete Association's guidance on preventing scaling says plainly that for most exterior surfaces a broom finish is adequate, and warns against overworking the surface, because extra troweling knocks the protective air out of the top layer. A broom finish is quick to put down, so it avoids a lot of that overworking by design.

Every concrete slab is full of stone. Normally a thin layer of cement paste covers the top of that stone. Exposed aggregate removes that layer so the stones show on the surface.

Concrete Network describes the common methods. The oldest is simply washing and scrubbing the surface with water and a broom at the right moment during the set. Most contractors today spray a chemical surface retarder onto the slab right after finishing, which slows the set of the top paste so it can be scrubbed or pressure washed off later, sometimes up to a day afterward. That gives more control over how deep the exposure goes and how even it looks across a big deck.

You can also choose the stone. Standard gravel gives a rustic, speckled gray-brown surface. Some installers seed decorative stone into the top of the slab so the exposed layer is a chosen color or a small rounded pebble. The exposure depth matters too: a light exposure, sometimes called a sand finish, shows just the tops of the stones and feels much smoother than a deep exposure.

This is the question that decides it for a lot of families. A broom finish is fairly uniform, and a light broom is comfortable for most people. Exposed aggregate is more of a split decision. Concrete Network puts it bluntly: some homeowners have no problem walking barefoot on it and others find it too rough. Their suggestions are to keep the exposure light or use small polished stones in the mix instead of raw crushed stone.

Our advice is to walk on it before you commit. Stand barefoot on a sample or on a finished deck with the same stone and exposure depth. What looks great in a photo can feel like a gravel driveway to a seven-year-old running to the diving end.

Both give good grip compared with a smooth troweled slab, tile or polished stone. Concrete Network lists broomed and exposed aggregate finishes among the ways to add traction to a concrete pool deck, and calls exposed aggregate especially well suited to pools because it is highly slip resistant.

Sealers change the picture. A glossy film-forming sealer can make either surface slicker than it was bare. If a deck gets sealed, the product should be one made for pool decks, and many installers add a fine anti-slip grit to the sealer on walking areas. On steps and the first few feet around the pool, grip should always win over shine.

The finish on top matters less than the concrete underneath. The main enemy of outdoor concrete in Northeast Ohio is scaling: the top surface flakes and peels after the slab has been saturated and frozen over and over. Deicing salts make it worse because they keep the surface wetter and add freeze-thaw cycles. Pool decks here see snow melt, rain and pool splash, and in the snowbelt towns of Geauga and Lake counties, a lot more snow on top of that.

NRMCA's recommendations for slabs that stay wet, freeze and may see deicers are specific. Order air-entrained concrete, with a recommended total air content of 6 percent for mixes with typical 3/4 inch or 1 inch stone. Specify 4,000 psi strength for concrete that stays moist and sees deicers. Do not add water at the site to make it easier to place. Do not finish while bleed water is on the surface. Cure it properly with a curing compound or wet covering. The Federal Highway Administration's guidance on deicers points the same way, calling for air-entrained concrete with a low water-to-cement ratio wherever deicers are used.

Exposed aggregate has one small advantage here. The weak paste layer at the surface, which is where scaling starts, is the layer that gets removed. That does not excuse a bad mix, but it does mean a well-made exposed aggregate deck has less of that fragile top skin to lose.

Go easy on deicers, especially in the first winter, when new concrete is still wet inside and not at full strength. NRMCA suggests clean sand for traction on new concrete and moderate amounts of deicer when you do use it. It calls rock salt and calcium chloride acceptable for concrete, and says never to use ammonium sulfate, ammonium nitrate or magnesium-based salts, which attack the surface. Read the bag on any "pet safe" or "concrete safe" product, because some of them are magnesium chloride.

Most people do not shovel the pool deck at all once the pool is closed and covered. That is fine. The deck's real winter job is to drain. A deck that slopes toward the pool or toward the house collects meltwater and freezes in a sheet, so we set the pitch to carry water to drains or to the lawn. NRMCA also points out that poor drainage, which lets salty water sit on the surface, raises the risk of scaling.

A breathable silane or siloxane water repellent is the sealer NRMCA suggests for protecting exterior slabs from winter, applied when the concrete is reasonably dry. Late summer, after a few dry days, is their suggested window, which lines up nicely with the end of the swim season here.

A broom finish is the base concrete finish and the least expensive. Exposed aggregate costs more, because of the retarder, the washing step, the extra care needed to keep the exposure even and, if you choose it, decorative stone. Concrete Network sums it up as more than a basic finish but less than stamped concrete, and that matches what we see. Pavers and natural stone generally sit higher again.

Every Ohio State Pools fiberglass package, which starts at $68,400 installed, includes a 4 ft concrete wrap deck. That is enough to walk around the pool, but most families want room for chairs, a table and a grill, so extra decking is priced separately after the site visit. Mixing finishes is a smart way to spend: exposed aggregate or a decorative border where people see it most, and broom finish across the larger lounging areas. Deck and patio work on its own starts at about $15,000.

Pick broom finish if you want the lowest cost per square foot, a uniform surface that is kind to bare feet and a look that fades into the background so the pool and planting do the talking. Pick exposed aggregate if you want more texture and color from plain concrete, you like a natural, pebbled look and you have walked barefoot on a sample and liked it.

Whichever you choose, ask your builder about the concrete itself: the air content, the strength, the base under the slab, the joints and the curing. A beautiful finish on a bad mix will scale in a few Ohio winters. A plain broom finish on well-made concrete, placed on a compacted base and pitched to drain, will look the same for a long time. We show deck layouts and finish areas in the 3D design so you can see where each surface goes before we pour.