This blog is dedicated to my good friend and concrete colleague Elaine Toogood. She recently inspired me to ‘get off my horse and write my blog.’ This came about through a discussion on sandpaper of all things.
"80 grit? 120 grit or indeed True Grit?" That was the question.
Of course we weren’t discussing the thespian talents of John Wayne or even listening to Glen Campbell... because the usual focus was on Visual Concrete of course. The subject in Elaine's holster was if sandpaper was a good idea to use for cleaning concrete surfaces…
We never got round to having that shoot out before, during or even after Eco Build. So in the spirit of sharing and, as John Wayne once said, “Tomorrow hopes we have learned something from yesterday.” here's what I think:
Ok, so if you want to find your True Grit for dry or wet cleaning concrete then Diamonds are a concrete’s best friend. Flexible Nickel encrusted Diamond hand...
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...
Grout loss occurs when the formwork is not completely sealed. Grout will find its way through the tiniest of gaps especially when the concrete is compacted. The issue of grout runs causing striations on a concrete surface is a common occurrence and a very frustrating one.
Grout will run down the face of a previously poured wall or column when the section or slab above is poured and the new formwork is not sealed properly. A grout check is normally detailed in this intersection to prevent this. However, if there is any deflection in the wall below (which is likely) a straight cut of new formwork board will not snugly fit. Sometimes a decent grout check is not enough. Proper protection should be in place for the concrete below the pour and it is wise to consider using silicone, tape and plastic sheeting sealing the older face from the new first then adding the grout check. The protection will serve the older pour and the grout check will prevent issues with the new pour. Even if the tape...
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...