CPC31320 Wall & Floor Tiling common mistakes
CPC31320 Wall & Floor Tiling · Understand the traps and how to avoid them.
Reading a plan or drawing and starting to set out tiles without first checking the stated dimensions against a scale rule and the written dimension string, then discovering the setting-out is out by the amount of a drawing revision.
Candidates treat the drawing as a picture rather than a controlled document, and skip the habit of scale-checking one known dimension before trusting the rest. On site this habit is drilled in; in an exam it feels like wasted time.
What to do instead
Before any setting-out answer, state the step of identifying the drawing number, revision, and scale, then verify one written dimension against the scale. Practise this on two or three sample plans until it becomes automatic, and write the verification step into any method statement answer.
Confusing the roles of the National Construction Code, Australian Standards, and manufacturer instructions when asked which document governs a particular tiling decision, for example quoting a standard where the manufacturer's written system specification controls.
Candidates memorise document names as a list rather than understanding the hierarchy: regulation sets performance, standards give deemed-to-satisfy detail, and manufacturer instructions control proprietary systems. The overlap is genuinely confusing and rarely taught as a hierarchy.
What to do instead
Build a one-page hierarchy map for each common decision (waterproofing, substrate preparation, adhesive selection) showing which document speaks first and which fills gaps. In answers, name the governing document and say why it takes precedence.
Describing a wall or floor set-out that starts from a full tile at one end of the room, leaving a sliver cut at the opposite wall or at a doorway threshold.
Candidates set out from a convenient datum (a corner or a door) rather than from the finished sight line, because the corner is easier to measure from and the consequence at the far end is invisible in a written answer.
What to do instead
Always centre the set-out on the main sight line or doorway and state that cuts at opposing edges are balanced and no cut is smaller than half a tile unless unavoidable. Write the datum, the centring calculation, and the resulting edge cuts as three explicit lines.
Calculating tile quantities by dividing floor area by tile area and rounding up, without adding a wastage allowance, an allowance for cuts, or a separate allowance for spares and future repair.
The area division is the only calculation candidates have practised, and wastage percentages feel arbitrary. The distinction between cutting waste and retained spares is rarely made explicit in training.
What to do instead
Show the calculation in three parts: net area, cutting and breakage wastage (commonly of the order of ten per cent, higher for diagonal or complex layouts), and a small retained spare quantity. State each percentage and justify it by layout complexity.
Specifying a waterproofing membrane application without naming the required substrate preparation, priming, coat thickness or number of coats, curing time, and upstand and penetration detailing.
Candidates remember that wet areas need waterproofing but reduce it to a single word in the answer. The system nature of membranes, where one omitted step voids the whole installation, is under-rehearsed.
What to do instead
Answer waterproofing questions as a sequence: substrate sound, clean, and within moisture limits; primer applied as specified; first coat, reinforcing tape to internal corners and junctions, second coat at right angles; thickness checked; cure before tiling. Name each step in order.
Treating substrate tolerance as a single flatness number and applying it to walls, floors, and large-format tiles alike, or accepting a substrate as ready without checking moisture content and contamination.
Candidates learn one tolerance figure and generalise it. They also focus on flatness because it is measurable with a straightedge, and neglect moisture and bond-inhibiting contamination, which are less visible.
What to do instead
Learn tolerances as a table keyed to substrate type and tile format, and always add a pre-tiling check list: flatness under a straightedge, moisture reading against the adhesive or membrane limit, and freedom from dust, oil, and loose material. State the check before stating the tolerance.
Selecting an adhesive by habit or by the word 'tile adhesive' on the bag, rather than matching the classification to the tile type, substrate, and service conditions such as wet areas or external exposure.
Candidates recall brand familiarity rather than classification codes, and do not connect the classification system to the actual selection decision. The letters and numbers are memorised without meaning.
What to do instead
Practise decoding classification codes into plain requirements and matching them to a scenario: tile porosity and size, substrate type, and exposure. In answers, state the required class, then the reason, then the trowel notch and coverage expectation.
Describing tiling over a substrate joint, movement joint, or construction joint as if it were a normal field area, and omitting movement joints from the layout entirely.
Movement joints are invisible in a finished job and easy to forget in a written layout. Candidates also confuse a substrate joint with a tile joint and assume tiling bridges them.
What to do instead
Mark movement joints on every layout answer: at perimeters, at substrate joints, at changes of substrate, and at intervals in large fields. State that the joint runs through the tile and bedding and is sealed with a compressible sealant, not grout.
Answering a supervision or quality question by describing what the tiler does, without addressing consultation, instruction, monitoring, or recording, which are the actual duties being tested.
Candidates default to trade tasks because that is their comfort zone, and read a supervision question as a technical one. The performance criteria for supervising work are less familiar than the tiling content.
What to do instead
For any supervision question, structure the answer around four verbs: consult, instruct, monitor, and record. Give one concrete example for each, such as a pre-start briefing, a written instruction, an inspection point, and a signed check sheet.
Writing a safe work method statement or hazard answer that lists hazards but omits the control measure, the responsible person, and the review or monitoring step, or that relies on personal protective equipment alone as the control.
Candidates list what can go wrong because that is the easy part, and stop before the hierarchy of control. Personal protective equipment is the most memorable control and gets over-used.
What to do instead
Use the hierarchy of control explicitly: eliminate, substitute, engineer, administer, then personal protective equipment as the last line. For each hazard named, write the control, who implements it, and how it is checked. Two hazards answered fully beat six listed.