How to Fill Chasing
After cables and pipes have been routed through walls, the chased channels left behind need filling. They are deep, narrow, and often have services sitting inside them. Because of the depth and width, a standard ready-to-use filler will not be the best option, and a poor fill will crack or show through paint. Here is how to fill a chase properly so the repair lasts and stays invisible.
What makes chasing different from a standard fill?
Chased channels are typically deeper than most surface repairs, often 20mm or more, and they usually have cables or conduit running through them. The filler has to be pressed firmly around the services so no voids are left behind. Air pockets behind the fill lead to cracking and hollow spots once the filler dries.
Step 1: Prep – Clean Out and Stabilise
Brush out all dust, debris, and loose material from the channel. There will be plenty of it after the chasing. Make sure the channel is clean and free of anything that will stop the filler bonding to the substrate.
If the exposed masonry inside the channel is porous, powdery, or crumbling, apply Wall Hardener to stabilize the surface. Work it in with a brush, getting into the back and sides of the channel. Let it dry for a minimum of 24 hours before filling.
Step 2: Fill - Pack Out the Channel
A chase is a deep gap, so always use a powder filler: Interior Filler or Quick Dry Filler . Mix with water to the ratio on the pack. At that consistency the filler holds its shape and will not slump, even on vertical runs.
Using a filling knife, apply the filler firmly into the channel. Press it in hard - you need to get filler right around any cables or conduit and into the back corners of the channel. Work in from both edges and push toward the center to make sure there are no voids behind the fill. Take your time with this. Trapped air is the main reason chasing repairs crack later.
Build the filler up flush with the surrounding wall. Use your filling knife at a shallow angle to scrape off any excess.
For ceiling chases, work in smaller amounts and apply firm upward pressure. Let the filler grip before loading more on.
Once the filler has set, sand it back with medium-grit sandpaper (120 grit) to bring the surface level with the surrounding wall.
The repair is now complete and ready for decoration.
Step 3: Finish - Smooth for Decoration
For a premium finish, apply your chosen finish product over the repair and feather it out across the surrounding area. Chased channels run in straight lines, so the repair can be visible under paint if you do not blend it properly. Feathering the finish coat out well beyond the edges of the channel is what makes it disappear. Let the finish coat dry, then lightly sand. The repair is ready for decoration.