What Causes Pitting in Exposed Aggregate Concrete?

You get pitting and small holes in exposed-aggregate concrete when something weakens the surface matrix or the stones themselves. Often, water and finishing choices leave a thin, fragile paste at the top, and freeze-thaw and salt drive scaling.

The frustrating part is that these problems can look almost identical from a few feet away. It is like judging a seawall by the paint. In a coastal North Carolina setting, you also get extra salt sources that speed up the damage, including ocean air and pool splash-out. In the sections below, you’ll use the damage pattern and the timing to separate popouts from scaling/spalling.

In coastal areas, salt exposure can accelerate surface wear on more than just concrete, especially where wind-driven spray and humidity stay on materials longer. Read more in our article: Signs Salt Air Wind Damage Shingles

Match the Hole to the Cause

A homeowner sees a handful of fresh craters and assumes the whole slab is failing, then spends money on patching that never had a chance to stick. The quickest way to stop the bleeding is to name the damage correctly first.

If you call every small hole “pitting,” you’ll buy the wrong fix for exposed aggregate concrete pitting. The devil’s in the details, not a This Old House recap. Start with the pattern, then work backward to what caused it (concrete bugholes vs pitting).

A popout looks like a small cone-shaped crater, often with a pebble still visible at the bottom or a matching fragment nearby (ACI’s description of concrete popouts). Scaling/spalling shows up as broader rough areas where the thin top paste flakes off and exposes more aggregate, often worsening after winter or salt exposure (concrete surface scaling causes). Bugholes/pinholes are tiny, uniform voids that were there from day one and usually don’t keep growing (pinholes in concrete surface). Corrosion spalls tend to be larger, localized blowouts with cracking or rust staining near embedded metal.

Use the Timeline to Narrow It

In real-world slabs, freeze–thaw scaling is often noticed within 1–3 winters, while salt-driven spalling is commonly described as showing up around year 3–5. Those windows can save you from blaming the pour when the calendar says otherwise.

The timing can be as diagnostic as the appearance. If you saw peppered voids right away or within the first few weeks, you’re usually looking at placement/finishing artifacts (bugholes or pinholes) rather than “weather damage.”

If the surface looked fine until it went through its first cold season, then started roughening up within 1–3 winters, freeze–thaw scaling is a prime suspect (freeze thaw damage exposed aggregate), especially if the slab didn’t have enough air entrainment for exterior exposure. And if it holds up for a few seasons and then you notice accelerating pitting and flaking around year 3–5, repeated salt exposure (de-icers or coastal salt spray) often fits better than a one-time finishing mistake (deicing salts concrete pitting). If you use it well, the calendar keeps you from chasing the wrong culprit. It can also make you drop the idea that any new hole means the pour was “bad,” or that sealer will reverse a sandcastle surface.

Freeze–thaw cycles tend to show their worst effects after the first cold seasons, which is why seasonal inspection beats guessing after the damage is already obvious. Read more in our article: Roof Inspection Frequency

Fix Now, Prevent Later

You keep the texture you paid for, the surface stays tighter through winter, and new holes slow to a crawl instead of multiplying every season. The biggest improvement comes from controlling water and salt before you touch a patch mix.

Start by treating this as moisture-and-salt management. It is not a cosmetics problem. Clean with a mild detergent and a stiff brush, and rinse well. If you’re on a pool deck, don’t let salty splash-out dry in place. Then add a penetrating silane/siloxane sealer to reduce water absorption (often cited up to ~95%) and plan to recoat every 3–5 years. You’ll slow new damage fastest by fixing drainage and drying time: keep downspouts off the slab and re-grade low spots.

Patching is where you need to reset expectations for how to repair pitted exposed aggregate concrete: fillers can hide small pits, but they rarely bond invisibly or last through more freeze–thaw and salt, especially on an exposed-aggregate surface that keeps moving water through the top layer. If the pitting is widespread but shallow, a professional resurfacing/overlay can buy time; if you’re seeing deeper scaling or loose stones, replacement usually beats paying to chase failing patches.

If you’re hiring, ask directly about air-entrained for exterior freeze–thaw (often ~6% air, roughly 4.5%–7.5%).

Water control is often the cheapest prevention step because downspouts and gutters decide where runoff concentrates and how long surfaces stay wet. Read more in our article: Clean Gutters Downspouts Trust the specs and documentation, not a shrug. Stronger isn’t automatically tougher at the surface, and in coastal North Carolina that detail often decides whether you’re fixing this again in a few winters.