Artex - Repair holes in plaster

3 ways to fill deep holes in plaster walls

Removing fixings or cables can leave unsightly holes in plaster walls. To repair them, you need both a deep fill and a smooth finish, and you can achieve this using two coat plaster, one coat plaster, or ready mix filler.

Here we show you how to use each method to fill deep holes in plaster walls.

1. Filling holes with two coat plaster

The two coat plaster method involves using an undercoat and a finishing plaster. It’s most often used by professional plasterers, and can provide a long-lasting, seamless repair. Applying plaster in two layers gives you a finish that doesn’t slump or create air pockets, and it also speeds up drying time.

Applying undercoat

Undercoat plaster is a base coat used to build up to the right thickness before applying finishing plaster. As well as plaster walls, Thistle Undercoat Plaster is suitable for indoor backgrounds including brick, blockwork, and most smooth or low-suction surfaces.

To apply the plaster, first make sure your surface is clean and free from dust. Use your filling knife (or a scraper if you have one) to remove any loose pieces of plaster and paint from around the area being filled, then brush or wipe down the area.

Next, sprinkle the power into clean, cold water according to the instructions on the bag. Use a clean bucket, as contamination from previous mixes can shorten the setting time and reduce the strength of the plaster. Also make sure your tools and water are clean.

Using a paddle mixer, mix the plaster until it’s thick and creamy. If you’re using a mechanical mixer, take care not to overwork it.

Before filling the hole, dampen the area around and inside it with a paint brush to help the plaster stick. Use your filling knife to apply the plaster in a series of layers up to 13mm thick, letting it set in between applications. Do this until you’ve built up to just under the level of the surrounding surface.

Applying finishing coat

While it’s still wet, lightly scratch the undercoat to form a key that will help the next coat stick. Apply the finishing plaster after two to three hours, when the undercoat is set but not dry. If you leave the undercoat to dry completely, it could suck the moisture out of your finishing coat, meaning it will dry before you can achieve a smooth finish. If it has dried, you should wet the area before applying the finishing plaster.

As with the undercoat, you should mix the finishing plaster with clean, cold water, using a clean bucket and mixer. To make this easier, wash everything as soon as you’ve finished mixing the undercoat plaster.

Mix until it’s thick and creamy. Mechanical mixing should be carried out with a high torque and a slow or variable speed.

Apply the first coat in a 1mm layer and wait for it to firm up (but not set) before applying a second coat to reach a total thickness of around 2mm. Use your knife or trowel to create a smooth finish, then allow the plaster to fully dry before priming and painting. Thistle Finishing Plaster takes between 90 minutes and 2 hours to set, although atmospheric conditions can affect this.

After it has dried, you can decorate the surface with almost any paint or wallpaper that’s designed for this type of surface. Always follow the paint manufacturer’s instructions for porous surfaces before you decorate, and don’t apply impermeable finishes such as tiles until the background is thoroughly dry.

2. Filling holes with one coat plaster

If you want a professional finish that’s faster than two coat plaster, Thistle One Coat Plaster is your best bet. It provides a deep fill and a finish all in one.

Using one coat plaster is very similar to the two coat method above. Start with a clean, dust-free surface by removing loose bits with your filling knife, then wiping or brushing down the surface. Before filling the hole, dampen the area around and inside it with a paint brush to help the plaster stick.

Add the powder to clean, cold water, using a clean bucket and paddle mixer until it reaches a thick consistency.

Using your filling knife or trowel, apply layers of the plaster until the hole has been filled. Allow it to stiffen a little, then create a smooth, flat surface with your knife.

Thistle One Coat takes between 90 minutes and two hours to set. Once it’s dry, you can decorate over your newly repaired surface with any paint or wallcovering designed for plastered walls. Always follow the paint manufacturer’s instructions for porous surfaces before you decorate.

3. Filling holes with ready mix filler

For a quicker, cleaner option, use our ready mix EasiFiller range. EasiFiller Light is designed especially for small but deep holes. It sticks to painted surfaces, making it easy to use for indoor repairs.

Apply the filler straight from the tub, using your filling knife to smooth it into the hole. You can apply it up to 20mm thick in one application.

Create a smooth, flat surface with your knife, then leave it to dry. EasiFiller Light doesn’t need to be sanded, meaning you can paint over it almost straight away.

When choosing between plaster and a ready mix filler, consider that powder plasters are ideal for larger areas, or where you need a professional finish. On the other hand, ready mix can reduce mess, waste and preparation time.

Staying safe while filling holes in plaster

It’s important to limit the risk of injury while carrying out DIY, especially if you’re working on a large area.

Firstly, always wear the appropriate protective equipment. Mixing plaster produces a lot of dust, so you’ll need to wear a dust mask, gloves and protective goggles. Ventilate the area as much as possible, or better still, mix outside if you can.

If you’re carrying out minor repairs, take a look at our convenience plaster bags. Available in 7.5kg and 12.5kg bags, they’re easier to handle and ideal for small jobs. Want more advice on making repairs? Check out our Repair Hub.