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How to install tile underlay

Underlay sheets are installed and evenly nailed to the floor Image Description: The image shows a room with underlay sheets securely fastened to the floor using evenly spaced nails.

Overview

Installing tile underlay is a crucial step in preparing your floor for tiling. It provides a stable, even surface, reducing the risk of movement that could lead to cracked tiles or grout. Follow this step-by-step guide for tile underlay installation to ensure a professional and long-lasting result. 

Safety tip: Always wear the appropriate safety equipment (safety glasses, gloves, ear muffs and a mask, for example) and always follow the instructions for the product or equipment.

Steps

  1. 1

    Calculate how many sheets you need

    Before starting, measure the area you’ll be covering. Use a measuring tape to find the length and width of the space, then multiply these numbers to determine the total square metres. From this, calculate how many tile underlay sheets you’ll need. Always allow around 10% extra for wastage to ensure you have enough material for cuts and adjustments. 
    A Bunnings Team Member is measuring the length and width using a measuring tape to measure the area.
  2. 2

    Prepare the floor

    Before laying any sheets, check that the substrate is as flat as possible. While achieving a perfectly level surface may not always be possible, it’s important that there are no significant dips or high spots. If the chipboard has cupped or warped, use a belt sander to sand down any raised areas. Once the floor is flat, sweep or vacuum thoroughly to remove dust, dirt, and debris. A clean surface is essential for proper adhesion and stability. 
    A Bunnings Team Member is using a level surface to check the substrate is as flat as possible before laying sheets.
  3. 3

    Plan your sheet layout

    Before cutting and laying the sheets, check that you won’t end up with very small offcuts. To do this, divide the length and width of the floor by the size of the underlay sheets. If any of the remaining pieces will be smaller than 100mm, trim the first sheet slightly to avoid having small, difficult-to-secure sections. Mark the sheets with a pencil and a straight edge to ensure accurate cuts. 

    A Bunnings Team Member is measuring the size of an underlay sheet using a tape measure for accurate cutting.
  4. 4

    Cut the underlay sheets

    Cut the sheets to size using the score-and-snap method or a hand guillotine. To score and snap, run a utility knife along the pencil line using a straight edge as a guide, then snap the sheet along the cut for a clean edge. This method ensures precise cuts and a good fit. 

    A person wearing gloves is using an orange cement sheet cutter to cut an underlay sheet to size.
  5. 5

    Dry-lay the underlay sheets

    Position the sheets in a brick pattern, running them opposite to the existing floorboards or substrate. Stagger the joints by at least 100mm from the substrate joints to improve stability. Leave a 3mm expansion gap between the sheets and the walls to allow for natural movement. Dry-lay all sheets first to ensure a good fit before securing them in place. 

    A Bunnings Team Member wearing safety gear is installing an underlay sheet in a brick pattern, running them opposite to the existing floorboards.
  6. 6

    Fix the underlay in place

    After dry-laying, keep one corner sheet in place and remove the rest. If laying onto chipboard or concrete, use a 3mm notched trowel to spread stud adhesive on the back of each sheet before placing it down. If installing onto hardwood floors, stud adhesive is not required. Secure the sheets using tile underlay nails, starting from the centre and working outward. Press down firmly to ensure strong adhesion. Follow the black dots on the sheets as a guide for nail placement, making sure all tile underlay nails are flush with the surface. 

    A person wearing orange gloves is spreading blue Gyprock acrylic stud adhesive on the back of sheet using a notched trowel.
  7. 7

    Perform final checks

    Once all underlay sheets are laid and secured, check that all nails are properly installed and that the expansion gaps around the edges are maintained. Sweep or vacuum the underlay to remove any dust or debris before tiling. With the underlay properly installed, your floor is now ready for tiling. 

    By following these steps, you’ll create a solid foundation for your tiles, ensuring a professional and long-lasting finish. 

    A person is using a hammer to secure a nail into an underlay sheet near the corner of a room.
  8. 8

    Now that you've installed tile underlay...

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Health & Safety

Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions that came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings Team Member.

Grave health hazards are linked to asbestos, which may be in homes built up to 1990. Health hazards may result from exposure to lead-based paints in older materials and copper chromium arsenic (CCA) treated timber. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer.