How to Fill Holes in Walls: Professional Guide

DIY Guide Overview:

How to fill holes and cracks in interior and exterior walls. We’ll be looking at some simple-to-follow methods as well as guiding you on the tools and type of filler you’ll need to complete the job.

Types of Filler You Might Need

Fillers are not all created in the same and different fillers have different purposes. For example, interior fillers are not going to be able to withstand the elements if you’ve used them to fill holes in an exterior wall. With that in mind, let’s take a quick look at the different types of fillers to help you identify which one you’ll need for your project.

Powder

Powder filler is exactly as it sounds. It comes in powder form and when mixed with clean water, takes on a putty consistency that you can apply to interior or exterior surfaces. Powder filler takes a little bit longer to prepare than ready-mixed filler but is typically much easier to sand and rarely flashes when painted.

Ready-mixed

Ready-mixed filler typically comes in a tub or tube and can be applied directly to surfaces. As suggested by the name, this filler doesn’t need to be mixed which is a benefit for those not confident enough to mix powder filler. However, this type of filler will need to be spot-primed in order to stop it from flashing once painted.

Cement-based

Cement-based exterior filler is purposely made for masonry surfaces and has special qualities that allow it to adhere to masonry surfaces even in damp conditions. It also has weather-resistant properties to stop it from cracking or falling off after exposure to the elements and does a good job of reinforcing concrete.

Flexible

Flexible filler is a great choice for those who have issues with cracks resulting from substrate movements. This filler is more suited to shallow holes in walls and ceilings and is designed to expand and contract with the substrate. You can also consider using a flexible paint filler that doubles up as a 2-in-1 paint/filler.

Filling Deep Holes in Walls

Formally known as patching up, filling deep holes in walls is a relatively simple procedure, all you need is the right filler and a dose of patience! For filling deep holes in walls, follow our guide below:

1. Using the edge of a scraper, remove all defective substrate from the deep hole. Ensure you scrape until all loose or flaking material is removed.
2. Once all loose material has been removed, prepare your filler. I recommend using a powder filler but you can use a ready-mixed filler if you’re more comfortable with that.
3. In order to ensure the filler adheres well to the surface, you should follow a process called wetting in. All you need to do is apply some clean water or a diluted PVA solution to the hole.
4. Now use a process called proud filling to fill the deep hole. Proud filling is applying filler so that the filler is ever so slightly raised above the surface of the hole. You can simply use a filling knife to apply the filler.
5. Allow the filler to fully dry.
6. Rub down the filler with fine aluminium oxide paper so that it is level with the surface.
7. Dust down/spot prime before painting.

IMPORTANT: Some decorators recommend over-filling holes with the hope that the filler will shrink down and fit the hole perfectly. I’d recommend ignoring this advice. The filler will rarely shrink down enough to fit the hole and what you’re left with is surplus filler that will take a lot of effort to sand down.

It’s often quicker to fill holes twice as opposed to using the over-filling method so save yourself some time in advance.

How to Fill Small Holes

For fine surface cracks and small holes, you’ll want to use a technique called flush filling. This is basically filling the hole so that it is level with the surface. Here’s how to fill small holes and cracks:

1. Rake out all of the loose plaster around the hole or crack with the edge of a filling knife or screwdriver. This will give the new filling something to adhere to.
2. Wet in the area where the defect has occurred. You can either use clean water or diluted PVA. This will provide even more adhesion for the new filling.
3. Apply your plaster-based filler so that it is level with the surface. Gyproc Easi-fill or any plaster filler made by Toupret is the go-to for most decorators. Simply follow the instructions on the packet.
4. Once the filler has dried (usually around an hour or so), use a fine abrasive to sand down the area to a smooth finish.
5. Dust off the surface so that it’s ready for a new coating.

How to Fill Drill and Screw Holes

Filling drill and screw holes is much the same process as filling deep holes. Here’s my preferred technique:

1. Using a good quality scraper, scrape off any plaster that has bulged up around the screw holes.
2. Apply your filler mix to the hole, and using the back of the filling knife, twist the filler into the hole before leveling it out so that it is level with the surface.
3. Wait for the filler to dry. If it has shrunk, add some more filler.
4. Sand down the surface to a smooth finish with a fine abrasive.
5. Dust off the surface and apply your paint.

Filling Holes in Exterior Walls

As mentioned above, filling holes in exterior walls will need a filler that’s been formulated for use on exteriors. My recommendation would be Toupret External Filler.

As for technique, feel free to follow this guide:

1. Scrape out any loose or defective material from the hole.
2. Mix the filler to a stiff paste.
3. Apply the filler to the hole using a filling knife and hawk. The hawk will ensure the filler is flat against the surface.
4. Allow the filler to dry.
5. Once the filler is entirely dry, it’s worth using giving it a coating of alkali-resistant primer. This will ensure the exterior material doesn’t become loose again.

Final Thoughts

Hopefully this guide to filling holes in walls has given you all the information you need to repair your defective surfaces. Remember to follow the specific guides above depending on what type of hole or crack you have and you’ll be flying!

If you’re filling a crack and it returns multiple times then unfortunately no amount of filling will be able to cure the problem. In this instance, movement of your property will continue to cause cracks and you’ll need to get a plasterer out to line the crack with lining paper.