Pool Mastic and Expansion Joint Repair in Flower Mound, TX

What pool mastic does

An isolation joint

The trade calls it an expansion joint, but it is more properly an isolation joint, one that lets the deck and the pool move separately. The National Ready Mixed Concrete Association describes isolation joints the same way for any slab, separating it from walls, footings, stairs and other fixed points, and says concrete cracks where design and construction don't allow for its movement with moisture and temperature. Sections 306.7 and 306.7.1 of the 2021 International Swimming Pool and Spa Code set two tests for this joint: it must keep water out, and it must be built to protect the coping and its mortar bed from the deck's expected movement.

When the joint stops working, pressure from the deck can loosen or crack the coping and tile and, in extreme cases, the bond beam beneath them, and the damage often shows as horizontal cracks in the waterline tile. The same engineering firm adds that no steel should run from the bond beam into the deck.

Coping, pavers and poured decks

Marion Ceramics, as quoted by Acme Brick, leaves an open joint between the tail of the coping and the deck and seals it to keep moisture out, noting that mortar can work its way out of coping joints over time. Where pavers meet the coping, Belgard calls for foam expansion material to protect the bond seam and Unilock for grout or flexible sealant. The code also wants a joint wherever a deck meets existing concrete work, so relative movement can't damage the pool. For public pools, the CDC's Model Aquatic Health Code, a model rather than Texas law, asks for a continuous watertight joint between the deck and the coping.

Where the coping itself has cracked or lifted, pool coping repair comes before new sealant. Flower Mound Pool Resurfacing will look at the joint, the coping and the deck together.

Why mastic joints fail around Flower Mound pools

Much of the ground here moves with moisture. The 1980 soil survey of Denton County warns that clays high in montmorillonite swell when wet and shrink and crack when dry, with enough pressure to crack walls and foundations unless, and sometimes even if, they are specially reinforced. NRCS rates 33.9 percent of the town's non-water land Very limited for homes with shrink-swell among the reasons, and rates its heaviest clays, Heiden and Branyon, Very limited for concrete driveways and sidewalks for the same reason. No official source covers what that movement does to pool decks in particular, though a 2007 engineering guideline for pools in Houston's expansive soils places isolation joints between the coping and the surrounding flatwork.

Weather sets the working window. W. R. Meadows applies DECK-O-SEAL between 40°F and 122°F; the two-part sealant is tack-free in four hours, sets firm within 24 hours at 77°F, longer in cool weather, and needs 24 hours before rain, while the one-part ONE STEP takes 5 to 10 days to cure. Grapevine Dam's 1991–2020 normals make May and October the wettest months and count 44.3 nights a year at or below freezing. Pool chemistry shows on the joint too: heavy shock treatments can leave a temporary white chalking on DECK-O-SEAL that fades as chlorine returns to normal, and the maker cleans it with a mild detergent and a soft bristle brush, never abrasives.

In Lakewood Village, where about 88.8 percent of the mapped land sits in soils NRCS rates Very limited for homes with shrink-swell among the reasons, the same work is covered under pool mastic repair in Lakewood Village. Cracked, sunken or rocking slabs are a job for pool deck repair, and Mortex, which makes Kool Deck, also makes a PVC control joint for pool decks with a replacement top that fits over existing joints, part of cool deck repair.

Pool mastic questions and answers