installation and maintenance of external faÃ§ade tiles on tall buildings

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Intermediate substrate - S<strong>and</strong> <strong>and</strong> cement material either with or without additives appliedto the substrate as an intermediate layer to level irregularities <strong>and</strong> provide desired pr<strong>of</strong>ile.Often referred to as ‘render’ for <strong>external</strong> application, the terms plaster <strong>and</strong> render have thesame meaning.Mortar – Cement <strong>and</strong> fine aggregates either with or without an additive, refers primarily tomortar bedding for <strong>tiles</strong> although renders <strong>and</strong> tile grouts may also be mortars.Plaster – See intermediate substrate above.Render –See intermediate substrate above.Slurry – Cement <strong>and</strong> water either with or without additives that is sometimes used as a tilebedding material.Spatterdash – Mixture in varying proportions <strong>of</strong> s<strong>and</strong>, cement, water <strong>and</strong> possibly additivesplattered onto the substrate prior to the application <strong>of</strong> the render intermediate substrate.Substrate – The building structure to which finishes are applied, normally either concrete orbrick / block-work.Tile – Used as a decorative <strong>and</strong> protective finish to the exterior <strong>of</strong> buildings, normally eitherceramic, porcelain, glass, homogenous or natural stone <strong>and</strong> either glazed or unglazed.Tile Bedding – A thick or thin bed tile adhesive (<strong>of</strong>ten proprietary product) or mortar systemused to adhere <strong>tiles</strong> to the substrate or intermediate substrate.Commonly Used Tiling SystemsThe majority <strong>of</strong> tall buildings in Hong Kong with <strong>external</strong> façade tiling systems areconstructed using reinforced concrete, where the reinforced concrete or sometimes blockworkacts as the substrate onto which the <strong>tiles</strong> are applied normally with the use <strong>of</strong> a renderintermediate substrate.Tile system defects causing problems can be conveniently broken down into two categories;design <strong>and</strong> workmanship. For the purposes <strong>of</strong> this paper design is taken to include allaspects <strong>of</strong> material selection, specification, design, detailing <strong>and</strong> provision <strong>of</strong> resources.Workmanship covers all aspects <strong>of</strong> construction under the control <strong>of</strong> the site tradesmen suchas surface preparation, mixing, application timing, correct use <strong>of</strong> materials, etc.DesignDesign guidelines for <strong>external</strong> wall <strong>tiles</strong> are given in British St<strong>and</strong>ards (BS). The followingBS are currently available to provide the necessary design guidance <strong>and</strong> for historical reasonsare the st<strong>and</strong>ards must commonly referred to in Hong Kong:• BS 5385 Part 2: 1991 Wall <strong>and</strong> Floor Tiling. Code <strong>of</strong> practice for the design <strong>and</strong><strong>installation</strong> <strong>of</strong> <strong>external</strong> ceramic wall tiling <strong>and</strong> mosaics.• BS EN 12004: 2001 Adhesives for <strong>tiles</strong>. Definitions <strong>and</strong> specifications. (replacementfor the old BS 5980:1980 Specification for adhesives for use with ceramic <strong>tiles</strong> <strong>and</strong>mosaics)• BS 5262: 1991 Code <strong>of</strong> practice for <strong>external</strong> renderings
The majority <strong>of</strong> Hong Kong specifications are based on these BS or the older versions thathave been withdrawn <strong>and</strong> superseded.Reinforced concrete (including the majority <strong>of</strong> <strong>tiles</strong> substrate) is normally designed inaccordance with BS 8110 Part 1: 1997 Structural use <strong>of</strong> concrete. Code <strong>of</strong> practice for design<strong>and</strong> construction.Specifications <strong>and</strong> st<strong>and</strong>ards relevant to <strong>external</strong> wall <strong>tiles</strong> have been reviewed. The keyclauses reviewed vary somewhat in detail but essentially synthesise to a two-fold structure:• direct application <strong>of</strong> tile/tile bedding to a parent concrete substrate or the use <strong>of</strong> anintermediate render stratum to smooth irregularities in the parent substrate.• the application <strong>of</strong> alternative tile/tile bedding systems directly or indirectly (via therender intermediate) to the parent concrete substrate.Overview <strong>of</strong> St<strong>and</strong>ards for External Wall TilesThe following discussion reviews the tiling system substrata in turn with reference to somest<strong>and</strong>ard specifications. All mix ratios presented refer to batching by volume.The Parent SubstrateNormally concrete or block-work, must satisfy certain requirements for cleanliness,soundness/integrity <strong>and</strong> dimensional flatness. Such requirements are stated in mostspecifications <strong>and</strong> st<strong>and</strong>ards in broad terms with particular flatness/smoothness criteria.Failure to achieve the latter necessitates the use <strong>of</strong> an intermediate render substrate.BS 5385 Pt 2 :1991 recommends the concrete substrate is allowed to dry for 6 weeks beforerender or tile bedding application. The intention is to reduce shrinkage <strong>and</strong> the risk <strong>of</strong>debonding.SpatterdashSpatterdash is used at the concrete/render interface to improve mechanical bond, <strong>and</strong> isapplied to partially cover the concrete surface. It is common in local specifications but tendsto be optional in international specifications <strong>and</strong> could be replaced by or used in conjunctionwith a bond coat. Typically a 1:2 cement:granite fines mix is used in Hong Kong.Bond CoatThe bond coat is normally applied to the cleaned concrete/spatterdash (if used) surface justprior to render application. Typically specifications insist “apply the render whilst the bondcoat is still tacky”. The bond coat is normally a mix <strong>of</strong> cement <strong>and</strong> water. An additive mayalso be used (particularly if used in the render); compatible additives are supplied by thematerials manufacturer.The “bond coat application” is one <strong>of</strong> the most critical in achieving acceptable adhesion bondstrength for the tiling system, because the common failure position is at the concrete substrateto render interface.RenderRender forms the intermediate substrate <strong>and</strong> is normally a 1:3 cement:s<strong>and</strong> mix applied to amaximum thickness not exceeding 20mm, but more commonly to 15mm or less.
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installation and maintenance of external faÃ§ade tiles on tall buildings

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