Cracks due to Defective Concrete Blockwork (Mica / Pyrite)

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Cracks due to Defective Concrete Blockwork (Mica / Pyrite)

Over the past few years, we have encountered a significant number of houses in Limerick & Clare which have cracking due to defective concrete blockwork. This type of cracking and defect has only become prevalent in the Limerick & Clare areas in the past few years. This latent defect has primarily affected houses which were constructed in the 1990’s and 2000’s although there are exceptions. We have prepared some information on frequently asked questions on the topic below for any homeowners that may be concerned about cracks in their house.

What is Defective Blockwork?

Defective blockwork is a term used to describe concrete blocks in buildings which have failed to maintain their structural integrity. The concrete blocks loose compressive strength and also appear to ‘crumble’. Expansion of the concrete blocks result in de-bonding of external renders and also sporadic cracking in the house or building.

What causes Defective Blockwork – Pyrite / Mica?

Concrete blocks are made of a number of materials including stone aggregate, sand, water & cement. Laboratory testing on similar defects in Counties Mayo & Donegal revealed the presence of muscovite mica and / or pyrite within the constituents of the concrete blockwork. These naturally occurring minerals when exposed to moisture & oxygen, expand via a chemical reaction resulting in deterioration of the block. These materials are deleterious materials and have a detrimental impact on the concrete blocks.

What are the symptoms of Defective Blockwork?

The cracking that occurs with defective blockwork primarily affects the outer leaf of the external walls. In very progressed cases, the inner leaf blockwork is affected also due to the expansion of outer leaf which in turn, exerts forces on roofs which are connected to the inner walls. The pattern cracking that occurs is not consistent with typical shrinkage or settlement cracks. Symptoms of cracking due to defective blockwork include:

  • Horizontal, vertical & diagonal cracks on external leaf of gable walls.
  • Vertical cracks at corners of the building.
  • Cracks primarily affect the outer leaf.
  • De-bonding of external render.
  • Extensive cracking in exposed parts of chimneys.
  • Horizontal displacement at window & door opening reveals.
  • Cracking typically more prevalent on more exposed elevations

Some images of defective concrete blockwork that we have encountered are included in the photo gallery at the end of this article.

What areas are affected?

We have encountered defective blockwork in the Limerick & Clare areas. Defective blockwork has also been encountered in Counties Mayo & Donegal. The Department of Housing, Planning & Local Government commissioned a report on the defective blockwork reported in Counties Mayo & Donegal. The expert panel report can be read here –> Expert Panel Report on Concrete Blocks

Pyrite problems have also been experienced in the greater Dublin area however, this primarily relates to the presence of pyrite in graded stone fill material which is placed underneath the ground floors of houses & buildings.

What to do if you’re concerned about your house / building?

Cracking in houses occurs for a number of reasons, most of which do not relate to defective blockwork. Causes of cracks in houses include;

  • Shrinkage of the blockwork / masonry.
  • Settlement of foundations
  • Subsidence due to an escape of water or other external factor.
  • Roof spread
  • Crazing of external render
  • Damage
  • Defective Blockwork

It is important that the cause of the cracking be ascertained prior to prescribing or undertaking remedial works. A visual assessment of the cracking by a chartered structural engineer should be carried out.

Building Assessment – I.S. 465:2018

Following on from the Expert Panel Report, a Irish Standard Code has been developed for the Assessment, testing and categorisation of damaged buildings incorporating concrete blocks containing certain deleterious materials’.  This code is known as IS 465:2018.

Engineers Ireland have formed a Register of chartered engineers who have the necessary direct professional experience, competence and specialist training  in accordance with the requirements set out on  I.S. 465:2018 – Assessment, testing and categorisation of damaged buildings incorporating concrete blocks containing certain deleterious materials’.  Our John Reidy, chartered engineer is on the Engineers Ireland, I.S. 465:2018 Register.

2019-10-11T17:44:42+01:00September 2nd, 2019|Uncategorised|

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