TN 20.23 Swimming Pool Water Conditions and the Selection of Tile Grouts TN 20.23 Swimming Pool Water Conditions and the Selection of Tile Grouts

TN 20.23 Swimming Pool Water Conditions and the Selection of Tile Grouts


Tile grouts conforming to BS EN 13888 should be specified and selected for their suitability to meet the demands of the pool water supply and those chemicals selected for the treatment of the pool water. This is to ensure durability and long-term performance in service.

The main factors which influence tile adhesive and grout selection in swimming pools include:
- Tile type.
- Mains water supply (Hard or soft).
- Pool chemicals & water balance.
- Chemicals used for cleaning & maintenance.
- Pool design e.g. wave making equipment.


The chemistry of pool water is quite complex and is largely dependent upon whether the water supplied into the swimming pool is hard or soft water or is variable, dependant upon where the water is supplied from.

Hard water contains a high mineral content as it filters through limestone or chalk deposits.

In the UK, soft water has a total hardness (calcium and magnesium hardness) of
<100 mg/l

Soft water is deficient in calcium or magnesium ions. It is, therefore, naturally aggressive towards cementitious based materials and can leach calcium ions from cement. In cementitious grouts, this weaken the structure of the cement resulting in a softening or erosion of the grout from between the tile joints.


In order to facilitate long term performance of the tiling installation, the pool water should be maintained in a balanced condition.

As a general guide, a calcium hardness of at least 250 mg/l expressed as CaCO3 or a total alkalinity of at least 80 mg/l expressed as CaCO3, is required where pool water is in contact with cementitious based grouts.

The use of sulfate based chemicals such as alum, sodium hydrogen sulfate or sodium bisulfate (dry acid) should be avoided if possible. This is to reduce the risk of sulfate attack on cementitious based grouts, tile adhesives, screeds, rendering and concrete.
BS 5385: Part 4 2015 advises in clause Pool water conditions;

“NOTE The durability of the grouting depends on the nature of the pool water supply and the chemicals used in the treatment of the water and the cleaning of the tiling.                                                        Cementitious grouts should only be used where the pool water has adequate calcium hardness and alkalinity so that balanced water conditions can be consistently maintained at the recommended pH level”.


The Langelier Saturation Index (LSI) is a calculation to designed to assess the water balance. It indicative only but will provide an overview of the water conditions at the time of testing and includes pH, calcium hardness, total alkalinity, temperature and total dissolved solids (TDS).

The calculation requires the following values determined from testing of the pool water;

LSI = pH+ CF + AF + TF – TDS (Typically -12.1)

• pH is the actual value
• CF is the Calcium Hardness factor (Range = 0.3 – 2.5)
• AF is the Total Alkalinity Factor (Range = 0.7 – 2.9
• TF is the Temperature in °C e.g. 28°C = 0.7
• TDS -12.1 to -12.3 (1000mg/I to 3000mg/l)



e.g. Pool A has a pH of 6.9, a calcium hardness of 300mg/l, Total Alkalinity of 100 mg/l, a water temperature of 24°C and a TDS of 1000mg/l. 

Example calculation: LSI = 6.9 + 2.1 + 2.0 +0.6 -12.1. LSI = -0.5 e.g. the pool water is currently in a corrosive condition

LSI = 0.0 to + 0.5 Ideal (slightly scale forming)

A negative value indicates corrosive water conditions which, if not addressed, could have a cumulative effect on metal components within the pool, cause cementitious based grout loss etc. A positive value indicates the water tends to form scale. Consistently high values can result in precipitation of salts which can block pipework and equipment with calcium deposits.



As defined in BS EN 13888, there are three basic types of tile grouts;

CG1 = Normal cementitious based grout

CG2 = Improved cementitious based grout

RG = Reaction grout

Additional Characteristics W= Reduced water absorption A = Higher abrasion resistance
BAL recommends the following grouts;


Type of Water/Pool Type BAL Grout Comments
Hard water area

BAL Grout Flex Wide Joint – (CG2 WA) for 3-20mm joints

BAL Grout Flex – (CG2 WA)

For joints up to 5mm


BAL Absolute Grout

Pool water should be maintained in a balanced condition, and;

>250mg/l Calcium hardness

>80mg/l Total alkalinity

Soft Water Area

BAL Absolute Grout – (RG)

2-12mm joints

Soft water more difficult to maintain in a balanced condition long-term.
Transient aggressive water conditions

BAL Absolute Grout – (RG)

2-12mm joints

Mosaics should be fixed and grouted with BAL Absolute Grout.
Pool with wave machines/ Rapids/Beaches etc

BAL Absolute Grout – (RG)

2-12mm joints

High abrasion resistance required for grout when in contact with fast moving/circulating water.


For cleaning and maintenance of pools, acidic-based cleaners should be avoided with cementitious based grouts. If frequent use of a diluted proprietary acidic based cleaners is deemed to be necessary, the grout between the tiles should be an epoxy grout e.g. BAL Absolute Grout.

For free expert guidance on the use of BAL products, or any aspect of ceramic tiling with BAL products, contact the BAL TECHNICAL ADVISORY SERVICE on 01782 591120.

BAL products are supplied with a 25-year product guarantee. For further details and/or copies please contact the Company’s marketing department.


The customer must verify the suitability of any information, opinion, recommendation or advice (“information”) provided by the Company for the particular application for which any goods are intended to be used and the Company accepts no liability (whether in contract, tort or otherwise) whatsoever for any loss, damage or expense arising from the misuse of any information it supplies, nor for the use of any information in or for applications which are unsuitable or inappropriate. Building Adhesives Ltd operates a continuous research and development programme and reserves the right to alter or to update information from time to time.


“Note: Any advice, opinion or information is given to assist the use of the Company’s products on the basis that the user will ensure its suitability for the application intended. In particular the Company cannot accept liability for loss or damage which may arise from incorrect use of its products or from poor workmanship. The Company operates a continuous research and development programme and reserves the right to update information without notice.”