Grout is strictly a cosmetic filler between tiles and coping stones. Grout does not serve any structural purpose, other than to fill the voids between materials.
Hairline cracks in the grout between swimming pool copings is totally acceptable. As the grout cures and loses moisture, it shrinks slightly, possibly even pulling away slightly. Combined with the natural expansion and contraction of the coping material, these cracks will develop - GUARANTEED.
A hairline crack along one side of a joint or through it's length is to be expected. As long as the grout does not begin to crumble, dislodge or decay, hairline cracks are totally acceptable.
Many new pool owners are alarmed when they observe small hairline cracks in the grout of the copings or tiles. The assertion that grout does not crack inside their residence, does not apply to outdoor materials. Outdoor materials are subject to daily 30-50ºF temperature swings, while indoor materials are in a shaded and climate controlled environment.
Of course, grout that is crumbling or dissolving is defective and should be removed and replaced.
Exposure to extreme temperature differentials may cause grout to spall - that is, a surface flaking. This is usually an indication of some compressive forces at play. It may be due to thermal expansion or from differential movement. After an initial replacement, the defect reoccurs, then that joint should be replaced with a flexible construction sealant.
Not every crack is a defect.
Paolo Benedetti, SWD, Principal
Aquatic Technology Pool and Spa
International Swimming Pool Consulting and Design, Aquatic Consulting, Watershape Consultants, Expert Witness, Hydraulic Design, Landscape Architecture, Construction Management
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