After repairing hundreds of chimneys across Dublin, we see the same problems repeatedly. Here's what causes them and how we fix them permanently.
Failed Chimney Flashing (Most Common Leak Source)
The Problem: Lead flashings around chimney bases fail after 30-50 years. Mortar joints crack, lead splits, or flashings pull away from brickwork. Every heavy rain sends water down interior chimney breasts, damaging plaster and causing damp.
Why It Happens: Original installations often used thin Code 3/4 lead which splits. Mortar joints weren't raked deep enough for proper lead dressing. Dublin's freeze-thaw cycles crack the mortar. Wind lifts poorly secured flashings.
Our Solution: Complete flashing replacement with Code 5/6 lead (50+ year lifespan). We rake out mortar joints 25mm deep, dress lead properly into joints, seal with appropriate compound, and ensure 150mm+ overlap onto roof covering. Replace any damaged slates/tiles around chimney base. Guaranteed watertight.
Deteriorated Mortar Joints (Repointing Needed)
The Problem: Mortar between chimney bricks becomes soft, crumbly, and falls out. Bricks loosen, water penetrates deep into the stack, and in severe cases, chimneys lean dangerously. Interior damp on chimney breasts is common.
Why It Happens: Mortar lasts 40-60 years before Dublin weather breaks it down. Freeze-thaw cycles are the main culprit - water in cracks freezes, expands, and widens the gaps. Original lime mortar on period properties is softer and more vulnerable. Lack of chimney caps allows direct water ingress.
Our Solution: Rake out all failed mortar to 20-25mm depth. Brush joints clean and dampen. Repoint with mortar matched to brick strength - lime-based (NHL 3.5/5) for pre-1940s properties, appropriate cement mix for modern. Install lead caps on pots if missing. Weather-struck pointing sheds water effectively.
Leaning or Unstable Chimney Stacks
The Problem: Chimney stacks lean visibly out of vertical - a serious safety hazard. In severe cases, bricks can fall onto neighbouring properties. Often discovered during home insurance surveys which then require immediate remediation.
Why It Happens: Years of deteriorated mortar allow movement. Storm winds push against tall exposed stacks. Original construction used inadequate foundations or bonding. Previous poor-quality repointing with cement mortar that's too hard for soft old bricks causes spalling and structural failure.
Our Solution: Emergency scaffolding for safety. Carefully dismantle the dangerous section. Assess the remaining stack structure and foundation. Rebuild with matching bricks and correct bond pattern. Install proper DPC and lead capping. Reinforce internally if needed. Provide structural certification for insurance.
Spalling Bricks (Surface Flaking Off)
The Problem: Brick faces flake and crumble, especially on south-facing and west-facing chimney sides (prevailing wind/rain). Severely spalled bricks lose structural integrity and need replacement.
Why It Happens: Water-saturated bricks freeze in winter - the ice expansion blows the brick face off. Original soft Victorian bricks are particularly vulnerable. Using cement mortar that's harder than the bricks forces moisture into brick bodies rather than allowing it to escape through softer mortar.
Our Solution: Replace severely spalled bricks with matching reclaimed or new bricks. Repoint with lime mortar (softer than bricks) so future moisture escapes through joints, not bricks. Install chimney caps and waterproofing to prevent water ingress. On period properties, source authentic matching bricks.
