Crumbling Homes: is render the problem? | Seamus McDaid

14 March 2017

The article  “Our home is crumbling into the ground’: Family in Mayo forced to abandon house”  in highlighted the problems faced by owners of 12,000 homes affected by pyrite and mica.  At an average cost of €64,000 per home to remediate, the state will be paying a high price for not adequately staffing Local Authorities responsible for policing the materials sector.  The BRegs Blog received the following comment from Seamus McDaid:

I spoke on the issue of the crumbling blocks in Donegal last year and I would like to add some further comments on this issue.

I mentioned render and its practices, a lot of people mention building control or the lack of it in Ireland, but in this case it will have no relevance. The point is, architects are specifying a render type that is not suitable for the environment. The purpose of a render is to protect the block work, specifications in the past for render was meant to be taken from standards like B.S 5262:1991. Donegal is designated to be an area of severe exposure and with this a Roughcast, Butter coat with dry dash or a Tyrolean is only recommended. However the majority of problematic crumbling block cases occur with houses having a wood float finish which is recommended for moderate exposure.

As a engineer one has to ask why or what has changed for this type of render to be accepted. When this type of render was used in the past the addition of lime was added and this helped with autogeneous healing, but as admixtures have shelved the use of lime, this movement accommodation contribution is gone. Back to the question what has changed that this render type is now acceptable and the answer is nothing, sand and cement or smooth render doesn’t work in costal areas, it will break down especially now as the historic know how on render practice is lost. Speed is a problem and the lack of knowledge on render practice all contribute to cracking due to various reasons but mainly drying shrinkage and rich brittle cement mixes “for speed”.

Just a simply question should be asked “would you recommend a smooth render house in a place like Malin Head” its madness but at least 85 per cent of the houses constructed there in the last 20 years have smooth render.

The need for movement joints, the NHBC Technical Guidance 6.1/28 January 2016 clearly shows this and Home Bond are advising on this now see technical seminar 5/9/2016. The question is why give advise on them now and what has changed.

Again its not a building control issue but a design and specification issue.

Now at this stage we have water ingress due to the poor render which resulted in capillary cracking which sucks in water at every opportunity which is daily in Donegal. We are now creating the perfect environment for excessive carbonation to occur. We hear on the media of a low cement content or a high aggregate to cement ratio, however this is not present on the inside block which points the finger too extensive leaching of the cement of the outside block ” the cement has been dissolved away by repeated water saturation”.

Atmosphere carbonation can lead to reduced porosity and possible disruption, leaching of soluble components can also lead to increased porosity and degradation of the cement matrix. Finally acceleration of this problem can be aided freeze thaw expansion /contraction when the product is saturated. A useful point to make is this problem came to light after the 2010 winter.

On a final note, there is more to Ireland than a 30 mile radius around Dublin and what might work in the Capital might not work else were. We took our eye of the ball on this one, slowly but surely the higher strength blocks are creeping in and the use of the appropriate render is being specified but its too little too late. The block may be the victim in this case but its handier to blame it and save a lot of red faces and this can be made easier if you have the state media at your disposal.

BRegs Blog note: For anyone affected by the above and looking for more information, please contact the Donegal Mica Action group at; see Facebook page Here

Other posts of interest:

Donegal Mica + Render | Seamus McDaid

Property firm to contribute €1m to pyrite board | Irish Examiner

ALERT | Pyrite & Ground Floor Construction?

Pyrite + Mica | Continuing Problems

Donegal Pyrite update | BRegsForum

Department of Environment regulatory failure | PYRITE 10 years on

Defective “Mica” blocks problem – fresh hope as Junior Minister visits Donegal | Donegal Now

The €64,000 question: How big is the pyrite problem? | BRegsForum

FACTCHECK: “If my house is defective, Do I have any rights?”

Defective schools | Are our children safe?

The State still has no function in testing compliance of building regulations

ALERT : Asbestos Contamination in Wicklow

7 thoughts on “Crumbling Homes: is render the problem? | Seamus McDaid

  1. Nial Murphy Chartered Engineer

    The author is obviously very knowledgeable on this subject, and what he is saying makes a lot of sense – but why does he consider use of an unsuitable render is not a building control issue?

  2. Michael O'Neill

    We appear to have gone
    Pyrite as a defined problem
    Mica as an alleged problem
    Render as an alleged problem

    I’m all for a good brainstorm session, but is there any evidence of Mica or Render as causing defined problems?

    1. Seamus Mc Daid


      To date there is no such evidence of either render or mica, but however excessive carbonation will be the underlying issue and this can only happen if a render fails. Simple water absorption and magnesium soundness tests on aggregates will rule out mica. There is clear evidence of carbonation in this issue. Sit back and wait until this unravels, as this problem is popping up in many locations all over Ireland both southern and northern with different type of aggregates.

  3. Michael Tweed

    This is a clear case where having mandatory Building Control (BC) APPROVAL before construction, and mandatory BC Inspections during the construction stage would have resulted in appropriate use of materials. The local Donegal BC officers would know from local knowledge precisely what would be deemed to comply locally with the Building Regulations. The mandatory BC Approval mechanism would ensure that all architects, engineers, and designers specified correctly, if only to avoid the embarrassment of having to tell their clients that they received a BC refusal! The BC site inspections would ensure the builders knew what the correct materials and applications were, again locally applicable from having BC Officers with local knowledge. If you don’t critique architects, engineers, designers and builders through an independent outside agency you can only trust that they are self-critiquing their work. Seamus’s comments clearly prove that self critiquing isn’t working when it comes to the specification of render in Donegal! I for one would happily go through BC Approval and would see outside the outside critique as valuable, educational, and helpful in achieving high quality of construction. It’s the true gold standard and it’s what we should put in place.

  4. Damien McKay

    Its interesting that not “all” houses with smooth plaster render are affected; only those houses which are built with precast concrete blocks from particular suppliers. Furthermore there is evidence of similar defects on house with dry and wet dash renders.

  5. Michael O'Neill

    Where there are indications of inadequate cement in the mix you have found a prime cause of degradation of blocks.

    Yes this may be exacerbated by extreme exposure in terms of location and orientation

    Yes it is possible that an inadequately designed render mix will contribute to the problem

    Yes it is possible that sea spray will significantly affect renders and concrete in coastal areas

    Yes it is also possible that mica could play a part in reducing the strength of the concrete mix

    But everything flows from inadequate cement in the mix – whether its the effects of cracking of the wall as a whole or spalling of individual blocks due to frost action following saturation allowed by poor render.

    Profiling the age and location of affected properties against properties not affected as well as listing concrete block types and suppliers will expose any significant trends.

    I am reviewing online papers for mentions of Mica because at first this seemed like SUCH a red herring
    But then suggesting a bacteriological cause for stomach ulcers was seen as a red herring until the discovery of the H. Pylori bacterium and its effect on some people’s stomach linings/

  6. Lester Naughton

    So we are we saying a concrete block shoud not be exposed to water. Or is it an amount of water and the particular block type and therefore block and render in conjunction defined by local exposure and weather? Assuming a cavity wall is on use we assume the outer leaf us wet in any case. All rather complicated for an individual designer to fully grasp it would seem.


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