ASK THE EXPERT
“Where can I get advice about using stainless steel in swimming pool projects?”
The British Stainless Steel Association has been working with SPATA to provide guidance on some key points regarding the use of stainless steel in swimming pools and halls.
Stainless steel is used in both indoor and outdoor pools for structural and / or aesthetic reasons. However, to avoid problems associated with the use of it in the fabrication of pool halls, the correct grade of material must be used and maintained correctly. Examples of potential issues can be found in the stays for flumes, supports for suspended ductwork and ceilings, and in general any stainless steel in a load bearing situation.
Cases have occurred where the standard grades of stainless steel have been attacked by chloramines which originate from the pool and condense on stainless steel surfaces. In some circumstances, this has led to Stress Corrosion Cracking (SCC). With the increased use of pools and the greater temperatures to be found in them, it has been found that the grades of stainless steel generally used in pool halls do not have the resistance to SCC found in some more highly alloyed grades. Consequently, designers (in particular) are advised to follow the guidance given in the European Standard EN 13451-1:2011. The recommendations for selecting stainless steels for load bearing applications in swimming pools have been agreed following nearly 30 years of research and experience. It also goes without saying that the maintenance of good water balance, minimising the build-up of chloramines, and correct pool hall conditions will greatly reduce these risks.
The BSSA has a variety of information on its website about the use of stainless steel in swimming pools, including a paper (in PDF format) about indoor pools. This paper was originally published in The Structural Engineer (Volume 82 Issue 9, 4 May 2004) and reviews structural failures in swimming pool buildings, attributed to SCC of stainless steel and the progress made since it was identified where the risks of failure can occur. Pool building environments are reviewed in terms of water temperature, disinfection systems (chlorine), humidity and condensation. Prevention of SCC failure is the joint responsibility of the designer, structural engineer and pool operator. Grade selection to avoid SCC involves considering grades such as 1.4547, 1.4529 and 1.4565 rather than the 1.4301 (304) and 1.4401/1.4404 (316) types, which are more suited to non stressed, non safety critical or load bearing applications.
Stainless steel is also used for equipment, such as steps and handrails, etc for both indoor and outdoor pools. Where the pool is to have a salt chlorine generator fitted, designers are also to check with their supplier as to the adequacy of the stainless steel’s resistance to that environment. Additionally, the cleaning regime is important and the BSSA has some useful information about this topic as well. Finally, stainless steel is used for pool tanks and the benefits of using the material is that it is lightweight, can be used for renovations, can minimise water losses and can have a real ‘wow’ factor!
ALAN HARRISON
Alan is from the Stainless Steel Advisory Service (SSAS), a service provided by the British Stainless Steel Association (BSSA). Alan can be acted on 0114 267 1265 or email him ssas@
bssa.org.uk
www.swimmingpoolnews.co.uk
“Why do we need construction joints and movement joints in domestic pools?”
It is generally accepted that construction joints and movement joints are required in commercial pools with a tile and / or mosaic finish, but there is also a need for these joints in similar domestic pools as well.
Construction joints are normally formed in traditionally constructed shuttered and poured swimming pool tanks, as it is not normally possible to complete the tank as a monolithic structure in one day without some kind of construction / day joint. Where construction joints have been formed in the swimming pool tank, these should be followed through the render, screed and tile. Movement joints are needed as a result of factors such as drying, shrinking and moisture changes in the tiling. If not properly controlled, these stresses can sometimes be sufficient to promote loss of adhesion and bridging / arching, or cracking of the tiling and subsequent damage to the render and screed. Construction joints in sprayed concrete pool tanks are not usually formed, as long as the end of day joint and the continuing work the following day, are formed in accordance with the recommendations of the sprayed concrete society. Movement joints should be sited at junctions of the base and wall of the pool tank, at the junction of all corners of the pool and at any change in the profile of the base of the pool tank and should be carried through the render, screed and tile. Movement joints should not come to a ‘dead end’ and the width of the joint should not be increased or decreased from the original construction joint for aesthetic or other reasons. Movement joints should be placed at distances of no greater than 6.5 metres.
There are also sources of movement outside the tiling system that may affect the tiles themselves, e.g. settlement and subsidence of buildings. Settlement, subsidence and vibration are uncommon sources of trouble, but where the stresses they promote are considerable, wall and floor tiling are likely to be affected.
A movement joint will also be required where the surround pool structural slab is constructed against the external face of the pool tank, which should also be carried through the floor slab, screed and the tile.
It is worth pointing out that the tiles must be fixed and the adhesive and / or bedding are allowed to cure thoroughly before the joints are sealed. Joints must be cut or formed with parallel edges (free from contamination from grout, bedding or other materials). Any loose grout adjacent to the joint should be removed and made good with the sealant in the course of sealing the joint.
The above information is available from The Tile Association’s ‘Design and Construction Process for Swimming Pools’ publication. It can be purchased from TTA by visiting www.tiles.
org.uk/help/publications.shtml. Further invaluable information can be obtained from the relevant British Standards (BS 5385).
JIM GORDON
Jim is an independent consultant, a SPATA Inspector and a Member of SPATA’s Technical Committee.
SPN October 2013 35
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