So what kind of blowholes are affecting our visual concrete? Big ones, medium ones and small ones? Yes those ones but there’s something else…
In our quest for an ever growing understanding of potential issues with visual concrete, like learning a language, the more you know the more there is to know.
We’ve come across another type of blowhole that we call ‘Milky Way Blowholes’… trillions of tiny minute pinpricks of air that make the concrete appear slight ‘browner’ in tone. In essence swathes of Milky Way Blowholes look fine, especially at 3m or so. There’s no point in touching them at all.
But what if within the galaxy of visual concrete these Milky Way Blowholes are punctuated by numerous ‘normal’ blowholes? A wormhole is opened and swallows you up for the following reasons:
Milky Way blowholes make the surface less dense with increased porosity. Whilst filling punctuated blowholes surrounded by dense concrete is not necessarily an issue, filling large blowholes surrounded by the Milk...
GreyMatter concrete is now 6 months old….To pat ourselves on the back and reflect upon this mini journey of Architectural Visual Concrete remedial work and consultation, here’s a list of projects we have undertaken and continue to undertake.
• Greenwich University School of Architecture
Architect: Heneghan Peng
Main Contractor: Osbourne
GreyMatter employed by Foundation Developments Ltd.
Fair faced concrete repair to insitu walls and columns.
• Watergate Farm
Architect: James Gorst
Main Contractor: Kingerlee
GreyMatter employed by Kingerlee.
Fair faced concrete repair to external wall and cantilevered soffit.
• Lancaster University Engineering building
Architect: John McAslan + Partners
Main Contractor: Eric Wright Construction Ltd.
GreyMatter employed by Eric Wright Construction Ltd.
In situ Architectural Concrete production is a specialist activity where quality is subject to many varying factors both within and outside the direct control of the contractor. Evaluation of the aesthetic quality is widely open to subjectivity making the whole activity rather prone to issues further down the line.
The current status quo (in my opinion) allows for little instruction, scope or understanding of post finishing works, processes and techniques which all in situ Architectural Concrete will be subject to at some point or other. I don’t think I’ve ever seen a specification that goes any further than glossing over the subject putting all the emphasis on expecting such works to be struck and be good enough to be left ‘as struck’.
There is also no attention or understanding as to how integrating post finishing techniques within formwork production, concrete placement and striking can and will save time, money, boost moral and quality. Visual concrete repair should not be relied o...
Segregation in concrete is generally due to excessive water in the matrix but can also be caused by over compaction (vibration), dropping the concrete from a height or simply through inappropriate mix design.
If the mix looses its cohesion, excess water will naturally attempt to escape at the path of least resistance, upwards at the form face. Once a path of escape is achieved more excess water will find this path and a sand run will be created. Sand runs are also exacerbated by minimal form face absorption. If the formwork face has the capacity to absorb some moisture then this will reduce the strength or path of a sand run.
Sand runs are difficult repairs to deal with. Primarily because they flow in a vertical direction and tend to be very well defined. Fair-faced concrete when compacted tends to have natural variations in tone that run horizontally as the concrete is placed and compacted. We generally accept these horizontal variations more easily so a sharply defined vertical repai...
Honeycombing occurs due to lack of compaction. I've often seen, heard and read that honeycombing is attributed to poor workmanship as lack of compaction seems to be equated with not bothering to compact, consolidate or vibrate the mix adequately. I won't go off on one but this is one dimensional thinking as equally the case could be that there is congested reinforcement that does not easily allow for full compaction for example. Anyway that's up for further discussion which hopefully will happen. Back to the repair category...
Honeycombing sits closely with construction damage as a category of repair.
By definition, if it is hard to compact concrete it is usually in a hard to reach place (with a poker vibrator or similar). Hence, honeycombing will naturally tend to occur at the extremity of a pour... at the base, corner, edge or some form of junction point (knockout for example). Honeycombing may look like a disaster but is forgiving as a repair mostly because of it's positioning. Plea...