How to Repair Roughcast Render: Step-by-Step Restoration Guide

Why Roughcast Repair Terrifies Most Builders (And How to Master It)

*"I've rescued 47 botched DIY roughcast jobs this year alone. Why do they fail? Pebbledash isn't just thrown on - it's a system. Miss one element and you get..."*

• Patchwork effect (repairs scream "look at me!")

• Differential weathering (new sections erode faster)

• Hollow spots (trapped moisture = frost damage)

George's Golden Rule:
"Repair with the original mix - or better. Modern substitutes destroy historic walls."

George's Roughcast Repair Kit (Pro-Grade)

Essential Tools:

• Harling trowel (£45-£75)

• Mixing hawk with rubber edges

• Grading sieves (3mm, 6mm, 10mm)

• Aggregate slinger (for large repairs)

• Moisture meter with deep probes

Materials:

• Aggregate match: *"Take 1kg sample to Buildbase - their spectrometer nails the blend"*

• Binder: Lime NHL 3.5 (heritage) | CEM II + polymer (modern)

• Primer: Tyrolean HP200 (key coat)

Step-by-Step Repair: George's Invisible Fix Method

Stage 1: Forensic Preparation

1. Stabilise Surroundings

   • Apply masking tape 5cm beyond damage

   • George's Tip: "Cut tape with Stanley knife for fractal edges - blends better"

2. Depth Assessment

   • Probe with bradawl: "If it sinks >15mm, substrate is compromised"

3. Remove Loose Material

   • Use chisel at 30° angle - "Never grind! You'll scar adjacent stones"

4. Profile Creation

   • Undercut edges to 45° (creates mechanical key)

Stage 2: Mix Matching (Art + Science)

George's Ratio Book (per 10kg mix):

Consistency Test: "Scoop mix - it should slump slowly like porridge"

Stage 3: Application - The "Chuck Don't Spread" Method

1. Key Coat

   • Flick Tyrolean primer forcefully (creates peaks)

   • *"Coverage: 1kg/m² - no more!"*

2. First Throw

   • Stand 60cm back, sling mix UNDERARM

   • *"Overlap repair zone by 10cm - critical for blending"*

3. Curing

   • Cover with damp hessian for 72hrs

   • "Remove in dawn/dusk - avoids thermal shock"

Pro Tip:"Rotate your wrist during throws - creates random orientation like original work"

Cost Breakdown: UK Repair Pricing 2024

Real Case:"Bath stone cottage: 8m² repair quoted £1,800 elsewhere. We did it for £1,100 by salvaging original pebbles."

George's Horror Story: The £28,000 Lesson

"A Cheltenham homeowner used pressure washer on lime roughcast. It blasted out £14,000 of historic aggregate. Our restoration took 6 weeks of hand-sieving original pebbles from their garden soil!"

Final Advice from the Trenches

*"Repairing roughcast isn't plastering - it's masonry surgery. I carry aggregate samples from 120 UK quarries because a 1947 Aberdeenshire dash needs different stone than a 1990s Brighton job. When we repair, we preserve the wall's story - botched patches erase history. That's why at HouseRenderPro, we document every mix ratio and stone source for future generations."*

Got failing pebbledash?Send George photos - *Free aggregate matching + 20% discount on diagnostic surveys (code ROUGH24)*

Roughcast Render Decoder: Know Your Mix

Field Test: "Drop vinegar on surface - if it fizzes, it's lime-based. If no reaction, it's cement."