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Tiling Basics

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Tiling Basics

by Pietro Scalise

Tiling is often one of the last undertakings during the construction process and is sometimes rushed due to delays. Not surprisingly, together with failure of the waterproofing in wet areas, defective tiling is possibly the most reported and most disputed component of a completed dwelling. The cost of rectifying poor or defective tiling work is often many times more than the cost of preventing it.

Before lodging a complaint about tiling work it is important to note that tiling is considered defective where:

  1. a builder supplied, laid and built the sub-strata for the tiles and any of the materials are defective and/or the application of the adhesives, tiles or backing sheets is not carried out according to manufacturer’s directions and/or there is unsatisfactory workmanship beneath the tiling.
  2. the client supplies the materials but the builder lays the tiles and carries out all the initial work and/or any of the materials the builder supplies are defective and/or the application of tile adhesive, tiles or backing sheets is not carried out to manufacturer’s directions and/or there is poor workmanship beneath the tiling.
  3. the client supplies and lays the tiles but the builder carries out preparatory work and there is unsatisfactory workmanship beneath the tiling e.g. concrete slab failure.

If the client installs the substrate then it is his responsibility to ensure that this is done according to manufacturer’s directions and that the framing or concrete slab is satisfactory.

According to the Office of Fair Trading’s “Guide to Standards and Tolerances”, cracked, loose or drummy tiles are only considered a defect if the cause can be attributed to the builder and then, only if more than 10% of the tiling area is affected.

Tiling and waterproofing need to be carried out in accordance to the manufacturer’s instructions. Substituting ingredients or products from another manufacturer is not acceptable as it may compromise performance and may also render any guarantees void.

Common problems

These are common problems often reported to building consultants and building inspectors:

  • Elementary yet still reported is the omission of waterproofing in wet areas
  • Poor detailing and installation of waterproofing in wet areas
  • Tiles that are cracked due to:
    1. shrinking of the substrate after tiles have been laid. A concrete slab and any cement-based substrates need to be given ample time to dry
    2. substrates that deflect
    3. tiles that are laid across joints in the substrate. Joints in the substrate need to be reflected to the tiling surface.
    4. the omission of control joints to allow for movement
    5. poor installation of the tiles onto the adhesive
    6. wrong selection of tiles for their allocated location such as using wall tiles on floors or tiles with a high moisture absorption rate in wet areas.
    7. wetting of tile adhesive between tiling and grouting
  • Prior to tiling, check that the maximum deflection of substrates does not exceed 1/360th of the span under dead and live loads. So if you have floor joists spaced at 400mm centres, the maximum allowable deflection between those joists is 1.1mm. A concrete slab that spans 2.4metres should not deflect more than 6.6mm midspan. If the span is more that 3 metres, or where you’re using very large tiles, the deflection should not be more than 1/480th of the span.

Waterproofing materials

  • For interior use:
    1. liquid-applied acrylics
    2. PVC sheets
    3. reinforced resin-based systems
    4. pre-formed metal or acrylic trays
    5. CPE, chlorinated polyethylene
    6. fleece-coated polyethylene mats
    7. gridded polyethylene sheets
  • For exterior use:
    1. synthetic rubbers
    2. liquid applied acrylics
    3. modified bitumens

Waterproofing membranes, according to the Building Code of Australia, need to be placed under mortar beds but there is valid reason to place these over them and immediately below the tile adhesive. Doing so will ensure that all substrate material stay dry and help in the long-term performance. Water saturation of a mortar bed may affect acrylics that haven’t cured properly and promote mould growth and grout deterioration.

There are minimum standards required for areas that need to be waterproofed. It is advisable that more than this minimum be applied e.g. behind all tiles in an enclosed shower area; to 1800mm above floor surface and 300mm above the shower rose in an open shower; to all surfaces within 1500mm from the shower rose and 1800mm on the wall from the base of the bath where a shower is combined with a bath. It is also good practice to waterproof the whole of a bathroom floor.

Flood testing should be carried out to test the waterproofing membranes before tiling commences.

Tiling over structural concrete

  • Allow a minimum drying period of four months or one month per every 25mm thickness for structural concrete to allow most of the shrinkage to take place before tiling.
  • Do provide a damp-proof membrane under the concrete slab on ground that will prevent moisture from rising
  • Finish concrete surfaces that will be tiled with a light wood float texture and incorporate required falls when placing the concrete
  • If the concrete surface is not suitable for direct application of tiles, consider scabbling or water/sand blasting to remove any impurities or powdery surface.
  • If the concrete surface is unsuitable for tiles to be directly laid over it, then a topping slab with a minimum thickness of 20mm may be laid over it. This layer still requires one month drying time per every 25mm thickness. In areas where the time is limited, rapid-setting mortars, which consist of a polymer-modified sand-cement mix can be used and whilst these can set in around two hours, it is advisable to allow 24 hours or longer before tiling or applications of waterproofing membranes.

Tiling over existing tiles

  • Although not recommended, tiling over an existing tiled surface can be done provided the existing tiles and substrate are in sound condition
  • In wet areas, the waterproofing needs to be undamaged else a new waterproofing membrane suitable for the application may have to be placed over existing tiles
  • The surface needs to be cleaned and degreased prior to tiling.
  • Loose or broken tiles need to be replaced
  • A sufficient key to the existing tiles needs to be achieved especially when tiling over glazed tiles.

Control joints

  • Allow control joints to be placed through the tiling surface where there are control joints through the underlying substrate; around the perimeter of the tiled area; at the right angles where a floor meets a wall or column; where substrate materials change; where types of tiles change.
  • On floors, allow control joints at no more than 4.5 metres intervals for externals floors and internal floors exposed to sunlight; no more than 6 metres for shaded internal floors
  • On walls, at centres of 3 to 4.5 metres along their length.

The Office of Fair Trading requires anyone who undertakes residential building work where the labour content is more than $200 to have a contractor licence. Demand also a written contract for any work that is worth over $1000.

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