How to prep your walls for paint or wallpaper

Applying paint to a wall that hasn't been dusted, repainting over a dirty wall, hanging wallpaper over old wallpaper that's hanging by a thread or attempting to paint over an uneven surface... there are plenty of mistakes to avoid when redecorating a room! Preparing your wall correctly will help to ensure that your paint or wallpaper goes on smoothly and lasts for a long time.

Steps 

1. Start preparing your walls

2. Fill in cracks and holes

3. Tackle uneven walls

4. Sand the walls

5. Clean the walls and room

If you are working with a surface that has been painted using lead paint, the following instructions do not apply. Extremely toxic by nature, lead paint is trickier to cover up than any other wall covering and requires specialist care.

Wallpapered walls should be stripped before you proceed. Using a wallpaper scraper or chemical stripper will make the wallpaper easier to remove.

If your walls have water or salt marks, it's important to treat the underlying issue. Before you attempt to cover up the marks, you'll need to find out what's causing the dampness. Flaking paint or air bubbles are also usually caused by a recurrent damp issue.

This preparatory stage might seem drawn out but preparing your surface properly is the only way to guarantee a good finish. Do not skip this step before moving on to painting or hanging wallpaper.   

It is a good idea to apply an undercoat to finish off this stage but be sure to pick the right type of undercoat. Undercoats and primers come in various formulas to match each surface.

Filling a small crack

• If the crack is thin, you can lightly scrape the area using a shavehook or the pointed edge of a flat scraper to enlarge it slightly.

• Dust everything down before applying an acrylic or fibre-based sealant and smoothing with a spreader tool.

• Once dry, you can lightly sand down the area or apply a skim coat for the cleanest possible finish.

Filling in a large crack

• If you have a larger crack to fill, scrape the length of the crack with a shavehook and lay some jointing tape before fixing it in place with a jointing compound.

• Smooth down, then sand with a fine grit sandpaper.

Filling a hole in plasterboard 

• If you've installed fixing plugs in the wall, insert a screw halfway into the plug to make it easier to pull it out using pliers.

• If you're having trouble removing the plug or you're worried about leaving a big hole, leave the wall plug in place making sure that the plug collar doesn't jut out from the wall (you can hammer it in, if necessary).

• Dust everything down and fill the hole with a filler putty.

• Sand down using a fine grit sandpaper once the putty is dry.

There are a few different techniques to make your walls look brand new.

• If your walls are very uneven, a good skim coat all over your surfaces might do the trick. However, you do need to have the right technique – a plasterer's skills don't just appear overnight! There are a few alternative solutions such as hanging a glass fibre wall covering or another type of textured wallpaper that will offer a neat finish.

• If your walls are new and have few faults, a basic filler in the problem areas followed by a quick sand will do the job.

Wait until the skim coat or filler is completely dry.

If you aren't very handy with the trowel and your walls still aren't as smooth as you'd like, you can tackle your walls with an 80-grit sandpaper. Please note that if your sandpaper is any coarser, you may mark the walls. Finish off with a 120 or even 240 grit sandpaper using a sander or sanding block.

Use your hand to brush over your walls to check they are nice and even.

• Dust your walls throughly.

• Make sure that there is no powdery residue left on the walls that could interfere with your undercoat. Vacuum your room so that dust does not lift up and settle on the walls.

• At this stage you simply have to clean your walls to get rid of any greasy marks and proceed to applying an acrylic paint. Be sure to wipe away any cleaning products and leave your walls to dry before applying your paint.

• Finally, get rid of any rubbish.

Required skills

Any DIYer should be able to prep a wall. The skills required – including using a sander or sanding block, pliers and filling tool and putty – aren't particularly technical. That said, working on a stepladder can be tricky for the less agile among us and working with dust can pose problems for people with respiratory issues.

Time required

On average, you'll only need about a day to prep the walls for an undercoat in a room measuring 10 m² with some damage to repair; this includes drying time before sanding.

Number of people required

1 or 2 people

Tools and equipment

• Scraper tool, spreader tool and shavehook

• Pliers

• Sander or sanding block with 120 to 240 grit sandpaper

• Bucket

• Sealant gun and acrylic or fibre-based sealant

• Filler putty or coat

• Blade knife

• Overalls, mask, safety goggles and gloves