How to undercoat a wall

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How to undercoat a wall

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Project Overview

When it comes to painting, preparation is the key. That’s why it’s important to apply an undercoat, especially on a new wall. An undercoat provides a layer for paint to adhere to, makes a surface flatter, fills in the grain and can even be used to seal in stains. Continue to step-by-step instructions
paint keep clean
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How to keep a paint can clean and avoid sticking

Trying to pry open a paint can lid that’s stuck can be frustrating. To solve this problem, you have to stop any paint from getting into the lip of the can. A quick and easy way to do this is with a coathanger. Simply measure the width of the can and cut the bottom of the hanger a bit longer with some pliers. Then, bend the ends of the wire over the edge of the can. Now, when you dip your brush, you can wipe the excess paint onto the wire and keep the lip grooves free of paint. And if there’s no dried paint in the grooves then the lid will be easier to get on and off.

Step by Step Instructions

1 Protect the floor
2 Prepare the walls
3 Clean the wall with a damp cloth
4 Cut in the undercoat
5 Paint with the roller
6 Remove the masking tape
7 Job done
  • Step 1. Protect the floor

    To protect the floor from getting undercoat onnit, stick masking or painters tape where the wall meets the floor. Then lay drop sheets on the ground.
  • Step 2. Prepare the walls

    Before you paint it’s important to make sure that your walls have been prepared. Older walls need sanding or old bits of flaking paint to be scraped off. Fill any cracks and gaps with filler. Let it dry and then sand it back again. When you’re sanding, use a fine grade sandpaper, such as 120 grit. With your dust mask and safety glasses on, hand sand for small areas or, for larger areas, use an orbital sander.
  • Step 3. Clean the wall with a damp cloth

    After sanding, wash the wall thoroughly. The undercoat won’t stick to the wall if it is dirty. We used water and sugar soap to clean our walls, then let the wall dry.
  • Step 4. Cut in the undercoat

    Use a paint brush to cut in areas that are too tight for rollers to paint such as corners of the walls and where the walls meet the floor. It’s a good idea to do this before putting on the skirting boards.
  • Step 5. Paint with the roller

    After you’ve finished cutting in, use a roller to paint the rest of the wall. Use an extension pole with your roller to make the job easier to reach high places. Work in small zones, about one square metre at a time for a great finish.
  • Step 6. Remove the masking tape

    An hour after painting, peel the masking tape off slowly, holding the end at a 45-degree angle away from the wall. Don’t wait until the undercoat is dry because the undercoat may crack and lift when you peel the tape off.
  • Step 7. Job done

    Now that your undercoat is complete, you’re ready to apply the top coat.

Tools and Materials


  • Drop sheet
  • Dust mask
  • Extension pole
  • Filling knives
  • Ladder
  • Masking tape
  • Orbital sander
  • Paint brushes
  • Paint rollers
  • Paint scraper
  • Paint stirrer
  • Paint tray and disposable liner
  • Sanding block and float


  • Disposable gloves
  • Filler
  • 80 grit and 120–180 grit sandpaper
  • Sugar soap
  • Undercoat

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 or visit our Health & Safety page. You can also use a simple test kit from Bunnings to indicate the presence of lead-based paint.
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