Table of Contents
- What Is a Roof Verge?
- The Big Question: What Mortar Mix Should You Use?
- Dealing with Large Gaps
- Tips to Avoid Cracking in Verge Mortar
- Building Sand vs Sharp Sand for Roof Work
- Should You Use Washing-Up Liquid Instead of Plasticiser?
- Key Takeaways
Repointing or repairing a roof verge is a common DIY task, especially on older properties where weather and time can take their toll on the mortar bedding. But when it comes to the best mortar mix for a roof verge, opinions – and results – vary.
What Is a Roof Verge?
The verge is the edge of your roof where the tiles meet the gable end. It’s traditionally pointed with mortar to hold the tiles in place and protect against wind uplift and water ingress. This pointing can crack or fall out with time, allowing in moisture and potentially dislodging tiles
The Big Question: What Mortar Mix Should You Use?
There’s no single “correct” mortar mix for every roof verge job – but there are strong preferences based on practical experience.
Option 1: 4:1 Sharp Sand to Cement
This mix is common and provides a strong, durable result – especially when working on exposed verges. Sharp sand gives the mix strength and resilience. However, because of its coarse texture, some find it less workable (harder to spread and shape).
Option 2: Mixed Sands – Building Sand & Sharp Sand
Many professionals recommend blending sands: using mostly building sand for workability, and adding around one-third sharp sand for strength and to reduce shrinkage. A common ratio is 3 parts building sand, 1 part sharp sand, and 1 part cement (3:1:1 overall).
Option 3: 4:1 Building Sand and Cement + Plasticiser
This is an easier-to-use mix with decent strength, especially when paired with a splash of mortar plasticiser. It spreads and shapes well and sets firmly. Using building sand alone is not recommended as it may not be as resilient over time compared to a mix with added sharp sand – especially on very exposed rooftops.
Dealing with Large Gaps
If the gap between the tile and the wall is large it can lead to shrinkage and cracking once the mortar dries. In such cases:
- Insert slivers of tile or slate into the gap before pointing.
- Use a wider bed of mortar to ensure strength.
- Reduce water in your mix to avoid shrinkage.
Tips to Avoid Cracking in Verge Mortar
- Use less water: A stiffer mix reduces shrinkage.
- Don’t overdo the cement: Too much makes the mix brittle.
- Add sharp sand: Helps resist drying cracks.
- Work in cooler, overcast conditions if possible: Sun can dry the mix too fast and lead to cracks.
Building Sand vs Sharp Sand for Roof Work
Sharp sand has larger particles and gives strength but is harder to work with. Building sand is smoother and easier to shape but less strong. For roof work – especially on verges and ridges – it’s a good idea to include at least a third sharp sand. Never use building sand alone for exterior roof mortar. It’s simply too soft and won’t last.
Should You Use Washing-Up Liquid Instead of Plasticiser?
No. It’s a myth that a bit of washing-up liquid does the same job. Modern plasticisers are formulated to improve mortar workability without weakening the structure. Washing-up is for your dishes, not your roof!
Key Takeaways
- Recommended best general mix: 3 parts building sand, 1 part sharp sand, 1 part cement with plasticiser.
- For stronger finishes: 4:1 sharp sand to cement – more durable, less workable.
- Avoid: pure building sand mixes or too much cement.
Roof verge pointing isn’t overly technical, but getting your mortar mix right is key to avoiding cracks, gaps, and extending the life of the verge.