Overview: Over the past 24 months we have investigated the formation of calcium on some limestones. Calcium is not to be confused with salt (efflorescence). Cases of calcium are not detrimental to the structural integrity, the substance is naturally occurring within the stone, but can be unsightly. Reports of calcium build up have occurred on less than 0.8% of our projects. Calcium appears as in image1. This bulletin will outlie possible causes, prevention and remediation. The characteristics of the stone are a major contributing factor as is the type of sealer applied. 7 out of the 14 customer concerns addressed by NTS&M over a 28 month period were due to calcium build up. This is in no way a large enough sample base to make definitive conclusions but the information and suggestions to follow will help mitigate this issue in the future. Note: NewTech has seemed the sale of all our Egyptian limestones prior to these findings.

Stones effected appear to be fine grain high density limestone with a low available porosity (relative) in our experience, and without prejudice, predominately Egyptian limestones with the common names:

• Sani Pearl (Egyptian)
• Royal Grey (Egyptian)
• Galala (Egyptian)
• Royal Crema (Egyptian)
• Sunny Yellow (Egyptian)
• Wallnut (Turkish)

Stones like Mist, Trumana and Smokey (since product change over 12 months ago), Celestial, and Lara Cream have not been noted with a calcium issue. Celestial and Lara Cream can only have this issue with foreign contamination. Mist and Smokey are not expected to have this issue however we caution against the use of non-consolidating sealer on these products.

Causes of Calcium:
All cases of calcium build up around pool coping have had a similar pattern. It is believed subsurface moisture is present in large quantities without a clear drainage or evaporation path. This can be due to the concrete being green when installation occurs, glues being over hydrated, or moisture being able to enter voids between substrate and stone.

Green Concrete (same principal although much less likely for glue):

Moisture Pooling between stone and substrate:

Calcium Occurrence on Concrete Pool Coping:

Notes:

  • This is a current working theory on Calcium formation around pools. We will work to understand these issues further to help create a deeper level of understanding throughout the industry.
  • We have noted the presence of Calcium is more prominent on the above-mentioned limestone that has been sealed with non-consolidating sealers or not sealed at all.

Possible Prevention:

Check with the supplier of the stone to obtain there recommendations regarding possible calcium build up on the above mentioned stone. Or avoid the stones.

Fibreglass Pools:

  • Never lay on green or moist concrete.
  • Always mix glues to manufacturers specification.
  • Ensure Sealant bead between coping and fiberglass is waterproof and free of voids.
  • Seal with a consolidator the front 150mm of the coping limestone on all sides.
  • Ensure project is sealed with a consolidating sealer.

Note: This recommendation does not extend to NTS&M’s current limestones.

Concrete Pools:

  • Never lay on green concrete.
  • Use waterproof grouts or adequately waterproof the shell.