The construction industry and property owners have problems with drip-shaped stains and streak marks that cannot be removed from glass surfaces in newly built and re-built/renovated buildings. Due to the difficulty in establishing the underlying causes, disputes sometimes arise between the property owner, building contractor and the glass provider.
Concrete run-off is a fairly common problem all over the country. Previous attempts to solve it through the treatment of both concrete and glass have been ineffective. In the majority of cases, the problem arises on glazed balconies or alternatively on glass railings in combination with concrete balcony slabs.
Concrete run-off occurs when water has been in contact with new concrete and thereafter affects the glass surfaces of facades/balconies/windows. The impact can be physical and sometimes even chemical. The process results in drip stains, streak marks and deposits that impair the translucency of the glass as well as the aesthetic impression.
Provided that the impact is only physical, this damage is relatively easy to remove, either through mechanical buffing or by wiping the glass with diluted acid. However, the process often progresses into a chemical reaction with the glass, which is permanent and cannot be completely removed using the above-mentioned methods.
Varying the pH level of the concrete and using a protective coating on the glass does not help
Within the Smart Housing pilot study “Corrosion of flat glass within the construction industry linked to concrete”, simulations of the concrete run-off reaction have now been carried out, in both a controlled environment in a laboratory and outdoors. Two different types of concrete were used (to assess whether the pH level in the concrete affected the reaction) and glass with and without a protective coating. However, these variations were unable to eliminate the problem.
After the indoor test, which lasted for four months, it was possible to wash the deposits off with a hydrochloric acid solution, and no deeper, permanent corrosion damage appeared on the glass.
After an eleven-month outdoor test, it was established that damage to the glass surfaces was sustained after the deposits had been washed off.
The right construction eliminates the problem
To avoid the problem, the correct construction should be used to prevent water from dripping down onto the glass.
In addition to the correct construction, regular cleaning of glass railings or glazed balconies is deemed to help and will probably become a maintenance requirement for customers.
There is now a need to educate the industry in appropriate construction solutions as well as formulate guidelines to avoid the problem of concrete run-off.
Similar reactions can occur in other contexts, such as shower screens made of glass. A broader project could examine how to treat and evaluate the corrosion of flat glass generally.
It would also be interesting to research whether this has been solved elsewhere in the world.
Project partners: RISE (Glass and CBI Cement and Concrete Research Institute), Glascentrum i Växjö AB, NCC, Saint-Gobain, PEAB and SKANSKA Sverige AB.
Project manager: Stefan Karlsson, RISE, firstname.lastname@example.org, +46 (0)10 516 63 57
Text for picture: Example of what concrete run-off can look like on glass.