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A room given an undercoat of paint

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.

Steps

1Protect the floor

To protect the floor from getting undercoat on it, stick masking or painters tape where the wall meets the floor. Then lay drop sheets on the ground.
The edge of a floor being sealed ahead of an undercoat being applied to the wall above

2Prepare the walls

Before you paint, it's important to make sure that your walls have been prepared. Fill any cracks and gaps with filler. Let it dry and then sand it back. 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 use an orbital sander for larger areas.
plaster being sanded down with a folded sheet of sandpaper

3Clean the wall with a damp cloth

After sanding, wipe the wall down with a damp cloth to remove any dust and grime, then let the wall dry. The undercoat won't stick to the wall if it's dirty. 
A wall being wiped clean before being given an undercoat

4Cut in the undercoat

Use a paint brush to cut in around the edges and corners where the roller can't reach. If it's a new wall, it's a good idea to paint before putting on the skirting boards.
The bottom of a wall being painted with a brush

5Apply the undercoat with a 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 it easier to reach high places. Work in small zones, about 1 square metre at a time for a great finish.
A paint roller being used to apply an undercoat

6Remove 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.
Painter's tape being pulled up from the carpet

7Job done

Now that your undercoat is complete, you just need to clean up your roller and brushes.

To finish the wall, just repeat the process – masking, cutting in, rolling – with your chosen top coat colour. 

A room given an undercoat of paint

Suggested products

More D.I.Y. Advice

Health & Safety

Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. 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.

When following our advice in our D.I.Y. videos, make sure you use all equipment, including PPE, safely by following the manufacturer’s instructions. Check that the equipment is suitable for the task and that PPE fits properly. If you are unsure, hire an expert to do the job or talk to a Bunnings Team Member.