POOL PROBLEM SOLVER

Ants in Pool Joints? Here’s What It Means (and How to Stop It)

Ants love warm, dry pathways—failed expansion joints give them both. If you’re seeing sand, pinholes, or ant trails along the coping, your mastic isn’t sealing properly and water may be escaping.

Common Signs of Ant Activity in Pool Expansion Joints

Sand or grit along the coping edge

Ants push up soil from tunnels below the expansion joint.

Pinholes or seams in mastic

Tiny openings where ants enter/exit and moisture escapes.

Soft, spongy, or separated sealant

Failed mastic makes tunneling easier and allows water intrusion.

Sinking or cracking deck sections

Chronic moisture from failed joints undermines soil and causes settlement.

4-Step Plan to Eliminate Ants and Protect Your Pool Deck

Confirm Activity Safely

Look for fresh sand piles, live ants, and active pinholes.
Note wet areas after running the pool—water may be tracking through failed joints.

Treat Ants Correctly (Keep Pool Water Safe)

Use bait-based ant control around the deck perimeter—avoid broadcast spraying near water.
Do NOT apply chemicals directly into the expansion joint or into the pool.
If fire ants are present, spot-treat mounds away from the water line per label.

Fix the Root Cause: Failed Expansion Joints

Remove compromised mastic, clean and dry the joint, and re-seal to block moisture paths.
Use UV-resistant, flexible sealant sized to the joint with backer rod where required.
Proper preparation matters—adhesion to both coping and deck is critical.

Prevent Recurrence

Maintain intact mastic to keep water and insects out of the joint.
Manage irrigation overspray and standing water near the pool edge.
Schedule seasonal inspections—Texas heat and UV accelerate mastic wear.

Safety First Around Pool Water

Always follow label directions for any pest products and keep chemicals away from pool water. If in doubt, coordinate with a licensed pest control provider and schedule mastic replacement after treatment.

Why Ants Specifically Target Pool Expansion Joints

Ants do not tunnel into pool joints randomly. They are attracted to very specific conditions — and failed expansion joints provide all of them in one location.

Warmth. Concrete and coping absorb and hold heat from the Texas sun throughout the day. The expansion joint sits right at the edge of this thermal mass, and the narrow gap between coping and deck creates a warm, sheltered microenvironment that fire ants and other species actively seek out when establishing colonies near structures. In Dallas summers, this warmth is present almost continuously for months at a stretch.

Moisture. Pool expansion joints that have cracked or separated allow water to move through them. Ants need moisture for their colonies, and a failed joint provides a reliable water source. The zone just below the joint — the soil under the coping edge — stays consistently damp from this water movement, which is ideal for colony development and expansion.

An existing cavity. When mastic has cracked, shrunk, or been partially removed, the joint becomes an open channel running along the entire coping edge. Ants use this as a protected pathway and nesting corridor. Once a colony establishes itself in the soil beneath the joint, they continuously work the existing gap to expand their tunneling network in both directions.

In North Texas, fire ants are the most common species found in pool expansion joints, but carpenter ants and pavement ants are also documented in these environments. Visible mounds along the coping edge are a sign the problem is already established — not just beginning.

The Damage Ant Tunneling Causes to Sealant Over Time

Even after ants are treated and the colony is eliminated, the damage left behind in an expansion joint is real and cumulative. Here is what happens over time with an active or previously active colony:

Physical sealant degradation. Ant tunneling physically displaces or removes existing sealant material. Even if the mastic was not completely failed before the colony arrived, active tunneling accelerates deterioration by creating voids, pinholes, and channels through previously intact sections of sealant.
Sand and soil intrusion into the joint. As ants push soil out of the joint, sand and grit work their way into the gap. This material prevents new sealant from bonding properly and holds moisture against whatever sealant remains, which speeds up further breakdown.
Undermining of coping support. Extended colony activity beneath the coping can displace the compacted soil and sand that supports the coping edge. Over time this can cause the coping to shift or become unstable — a structural problem that goes well beyond the joint itself.
Expanded moisture pathways. The tunnels and pinholes left by ant activity become direct routes for water to reach areas behind the coping and below the deck. Each tunnel that reaches the pool shell’s bond beam is a pathway for water damage that did not exist before the colony established itself in the joint.

Why Pest Treatment Alone Does Not Fix the Joint

Treating the ant colony eliminates the active pest problem — but it does nothing to restore the integrity of the expansion joint. After treatment, you are left with a joint that has been physically degraded by ant activity, often has residual soil and sand packed into the gap, and still has every moisture pathway the colony created entirely intact.

Without joint repair, several additional problems follow:

New colonies can re-establish. Ants are highly motivated by the conditions a failed joint provides. If the joint is not sealed after pest treatment, the same warmth, moisture, and existing cavity that attracted the first colony will attract another — often within the same season, since the conditions have not changed.
Water continues moving through the damaged joint. Pest treatment does not close the holes. Water intrusion continues through every pinhole and channel the colony created, putting ongoing stress on the coping, deck substrate, and pool shell with no visible sign that it is happening.
Damage compounds quietly. Unlike a visible ant mound, slow water intrusion through a damaged joint does not announce itself. Coping can begin to shift, deck sections can settle, and the bond beam can start to absorb water long before the damage becomes visible.

The correct sequence is pest treatment first to eliminate the active colony, followed by proper joint repair to close moisture pathways and remove the conditions that attract ants in the first place. Skipping the second step means the job is only half done.

What Proper Repair Looks Like After Ant Damage

Repairing an expansion joint after ant activity requires a few additional steps compared to a standard mastic replacement, because the joint has typically been compromised in ways that go beyond normal surface-level sealant failure.

Complete removal of old sealant and debris. After ant activity, the joint often contains old sealant fragments, sand, soil, and organic material from the colony. All of this must come out before new sealant is applied. Packing new sealant into a joint full of contaminated material gives the new product nothing solid to bond to.
Thorough joint cleaning and drying. The joint cavity needs to be clean and fully dry before sealant is installed. Ant colonies keep soil moist by design, so additional cleaning and drying time may be required after removing debris.
Backer rod installation where needed. If ant activity has effectively widened or deepened the joint, backer rod may be required to fill the lower portion of the gap before sealant is applied. This gives the sealant the correct geometry to flex and bond correctly over time.
Full-perimeter inspection. Ant colonies rarely confine themselves to one section of the joint. The full coping perimeter should be inspected for pinholes, soft sections, and gaps that may have been created by tunneling activity further along the joint line from the visible entry points.
Commercial-grade, flexible sealant. The replacement sealant should be UV-resistant and specifically formulated for pool joint applications. A product that handles Texas heat, chemical exposure, and clay soil movement is the right choice for a repair that is meant to last.

Prevention Tips After Repair

Once the joint is repaired and the ant problem is addressed, these habits protect the joint long-term and reduce the chance of the problem returning:

&checkmark;Inspect the joint annually. Look for early signs of cracking, shrinking, or separation before they open up enough to attract insects or allow sustained water movement. A small crack caught early costs far less to address than a joint compromised by a full ant colony.
&checkmark;Manage irrigation and drainage near the pool edge. Consistent moisture near the coping edge — from sprinklers, rain runoff, or deck drainage — creates conditions ants look for. Directing water away from the pool perimeter reduces the environmental attractiveness of the joint area for colony establishment.
&checkmark;Keep vegetation back from the pool edge. Mulch, ground cover, and landscape plants adjacent to the pool coping create protected zones where ant colonies can establish near the joint. A clear zone around the pool perimeter makes the area less hospitable for new colonies.
&checkmark;Schedule a spring inspection. In Dallas, the period after winter is when ant activity ramps up significantly and when mastic damage from cold-weather thermal cycling becomes visible. A brief spring inspection of the full joint line catches emerging problems before the summer season drives them further.

Already Have Ant Damage in Your Joints? We Can Fix It

Jonathan at Dallas Mastic handles joint repair after ant activity — complete debris removal, thorough cleaning, and professional-grade re-sealing that closes moisture paths and removes the conditions that bring ants back. Text a photo of your pool coping to 214-924-8483 for a straight answer on what your joint needs.

Call 214-924-8483 See Pool Mastic Repair