With more than two decades of invaluable experience in screeding behind us, CSC is proud to launch the much needed Screed Testing Services for the industry. As screed failures remain a daunting issue, a reliable testing service is expected to go a long way in identifying the issues right at the root, facilitating intervention at the right time and helping in achieving high quality screeds compliant with British Standards.

Despite ensuring the best quality raw materials and high standards of workmanship, it often happens that the actual quality of the screed is affected by external factors such as the site conditions during and after the construction of flooring. In order to ensure that the actual quality standards meet the required quality parameters, it is essential to follow a meticulous procedure of inspection and testing during the various phases of construction, and take necessary rectification measures in case the standards don’t match.

CSC hopes to assist contractors, screeders and builders in achieving the expected screed quality standards through a range of specialised screed testing services. Our range of screed testing services include:

Level Survey by an Engineer, providing datum above sea level: The datum above sea level will be assessed accurately by a qualified engineer, using regular surveying methods.

Level Survey by laser level dip survey for departure from datum: Laser level dip survey will be used for higher precision in assessing the departure from datum of the installed screeds.

Surface Regularity Testing : The Surface Regularity of screeds will be measured using a 2m straightedge, in compliance with BS8204-1:2003 & A1:2009,

BRE Drop Hammer Test: The screed will be subjected to repeated impact blows by dropping a 4 / 2 kg annular weight vertically down a guide on to a hardened steel anvil placed on the screed surface. The depth of indentation on the screed after four consecutive blows will be measured to gauge the ability of the screed to carry traffic without crushing under the loaded weight.

Moisture Test by Calcium Carbide Method or Tramex Test: The moisture content of the installed screed will be assessed at the end of the stipulated drying time using the calcium carbide or Tramex meter method, to ensure the screed is optimally dry for taking on the final finish. Though often underestimated, the accurate assessment of the moisture content of screeds is one of the most important steps in ensuring the quality of the screed and the entire flooring.

We’ve got it covered – for you

In keeping with CSC’s tradition of meticulous attention to detail and quality, we hope our new screed testing services will help screeders, builders and contractors in bringing down the number of screed failures and achieve high quality screeds that meet the expected quality standards. All tests will be carried out by our expert team in accordance with the British and European Standards Code of Practice.

The development which is scheduled for completion by early 2012 will comprise of 339 student rooms, nine residential apartments, a reception area, complete with retail units on the ground floor. The site is located close to the Aldgate East tube station and is within easy commutable distance from the Queen Mary’s College, King’s College, the Imperial Colleges and the London school of Economics which admit nearly 60,000 full time students every year.

CSC Screeding worked with both main contractors Mace Group and JR Pickstock on the project, delivering high quality installation of 6000 sq.m of Gyvlon anhydrite screeds and 1200 sq.m of pumpable levelling / smoothing compounds for the development. Gyvlon self smoothing, self compacting anhydrite screed was installed as a ready mix and pumped with a remote controlled brinkmann pump, supplied by Tarmac.

The project was an opportunity for CSC to once again demonstrate our professional service and technical expertise, delivering quality despite adverse conditions on the site. Notwithstanding logistical hitches and onsite problems from late delivery of the ready mix trucks to carrying out the screeding before the installation of the roof for a screed that needs to be completed in a closed and water tight environment, CSC was able to handle the situation smoothly, delivering high quality against the odds.

CSC expects to secure further contracts from the Mace Group and JR Pickstock, with hope to continue providing quality and expertise gained from years of experience, working on extensive demanding and highly varied projects.

The £35m Stanley Park School, Sutton reaches completion on time despite a series of setbacks that were feared to prolong the opening of the new seven form entry school. The school which is scheduled to open for the new term in January will have nearly 560 seats every year, with reserved places and specialist tutoring for students with Autistic Spectrum Disorders.

CSC Screeding is proud to have played our part in the quick completion of the project, getting nearly 1000sq.m of screeded flooring ready for the final floor finish within just a week of the screed installation. Fast drying floor screed- FlexiDry F1, was used to expedite the drying while ensuring strength and durability. FlexiDry screed of the F3 formulation, which comes with a drying time of 21 days was further used for screeding another 2000sq.m of the school building, making sure that the floor finish contractors could begin the installation of the final floor finish without any delays.

The construction work for the school which is built on a former hospital site was earlier subjected to considerable delay owing to negotiations over access rights to neighboring land. A series of further delays followed when excavations unearthed prehistoric remains and Bronze Age pottery at the school site. Ancient Roman remains and bits of pottery were dug out by archaeologist after pre historic remains were spotted at the site during excavations for laying the school foundation. Nonetheless, Sutton Council members are delighted that the historic findings add new value to the school site and it would provide the students with a firsthand opportunity to get better acquainted with history.

The school building follows high standards of sustainability, and has received very high ratings from BREAM. The school also features several community facilities including a three badminton court sports hall, a school hall with electronic retractable seating system and a series of class rooms which can be hired for community activities and meetings.

Among the most common issues that screeders are faced with during the drying of screeds are- shrinkage, curling and cracking. It is the inherent property of all concrete slabs and screeds made with Portland cement and aggregates to shrink during the process of drying. But, since the drying process takes place from the top surface down for standards screeds, the upper surfaces usually shrink first, resulting in a tendency for the screeds to curl upwards at the edges.

The extent of shrinkage cracking and curling of screeds are generally influenced by:

• Mix Proportions
• Bond Strength
• Thickness of screed
• Curing
• Drying times

Mix Proportions: Excessive amount of cement or water in a screed mix can be as harmful to the screed as insufficient cement and water. When screed mixes which contain less than the specified amount of cement or water a screed may not develop the required​ strength, screed mixes with excessive cement or water can be more prone to curling and cracking. It is therefore advisable to conduct a BRE drop hammer test in case of any doubts regarding the mix proportions, mixing or compaction.

Bond Strength: The tendency of screeds to curl upwards at the edges during drying is generally resisted by the bonding to the subsurface and the thickness of the screed. Bonded screeds are therefore found to have the least risk of curling and cracking compared to unbonded screeds, and this is one of the major reasons why fully bonded screeds are preferred where heavy duty usage or rigid flooring is required.

Unbonded screeds and floating on the other hand are found to have a higher risk of curling and cracking at joints and perimeters. This can however be minimized by reinforcing the screed joint with a steel mesh or ties, at mid-depth of the screed.  Polypropylene fibres are generally used for diffusing stress created during curing and reducing the impact of crack formation.

Thickness of screed: The thickness of the screed also plays a major role in controlling curling and shrinkage cracking. The tendency to curl is generally found to be lower in thick unbonded screeds than thinner ones as thicker screeds have more strength to resist the curling forces.

Curing: Curing is required on standard screeds to prevent excess evaporation of moisture from the surface. As these screeds generally dry from the top down, a polythene layer is laid on top to reduce the moisture evaporation during this period and allow the screed to gain strength. This helps to reduce curling by preventing the top layer from drying too quickly before the bottom layers.

However, the practice of curing isn’t widely adopted nowadays owing to environmental and health and safety issues posed by the use of polythene sheets.

Drying times: Nearly one third of the mixing water used in a screed is used for hydrating the cement. Most of the remaining water must be allowed to escape before the installation of moisture sensitive floor finishes. Though this could take quite long (110 days at 75mm thick, based on a controlled environment of 20C and 55% RH) for standard screeds, it is important not to resort to forced drying as it is another major cause that leads to excessive drying shrinkage, causing cracking and curling.

The best alternative under such circumstances, for time sensitive projects would be to go for a modified screed like FlexiDry. FlexiDry fast drying floor screed yield very quick drying times through a controlled drying process along the full depth of the screed, preventing curling or cracking of the screed. These screeds require a low water / cement ratio to achieve plastic consistency, allowing quick drying and also present the advantage of doing away with the process of polythene curing completely.

The Lancaster is yet another addition to CSC’s portfolio of exceptional quality and superior workmanship. We are proud to have delivered to perfection, 16,000 sq. m of high quality screed for the iconic residential development- ‘The Lancasters’. The stunning prime-value apartment complex overlooking the Kensington gardens, Hyde Park was originally an array of 15 Grade-II listed mid-nineteenth century houses, which has been restored by a team of London’s leading developers, architects and interior designers.

The gleaming white development with the Victorian stucco façade, houses 77 super luxury apartments. The Lancasters demonstrate the perfect blend of traditional architecture and contemporary design and construction. When every individual apartment features the most modern amenities and contemporary finishes, special care has been taken to retain the ornate cornicing, fireplaces and high ceilings reminiscent of the grandeur of the original architecture.

The floor finishes for the development range from walnut timber finishes for the reception areas and master bedrooms to grey stone porcelain tiles for the kitchens/utility areas and marble tiles with contrasting inserts for the entrance halls and carpets for the other bedrooms. CSC provided the supreme quality floor screed suited for the varied array of floor finishes for the heated floors.

The F1 formulation of FlexiDry, which comes with a drying time of 7 days was used for screeding 16,000 sq.m of the luxury development. FlexiDry was specifically chosen for the  high quality and quick drying time that the floor screed provides and also because it acts as one of the best complementary sub floors for underfloor heating.

The Lancasters was originally built as ambassadorial residences in early 1850s, and was later converted to a hotel before being refurbished to form the luxury residential development.

CSC is proud to have successfully completed the screeding contract for Middle East construction giants Mivan-Depa’s maiden venture for the UK. FlexiDry fast drying floor screed was installed over underfloor heating for the luxury apartments in Bayswater, facing Hyde Park.

The location did bring with it logistical difficulties and problems with access and storage of materials. However, our expert team was successful in overcoming the issues and materials were delivered according to requirement and transported on site using pallets, with the pump placed in an alley.

CSC has completed several other prestigious projects in the Hyde Park area, including the Rolex Store for One Hyde Park, the Lancasters and three consecutive projects for the Bulgari Knightsbridge Palace Hotel. Porchester Gate is the first construction project of Mivan Depa in the UK, some of their famous works being projects for the world renowned Burj Khalifa, Dubai; Ferrari World, Abudhabi; Museum of Islamic Art Doha, and projects for Atlantis hotel, Dubai.

To see the actual magazine, follow this link and click on the orange screeding section.
http://content.yudu.com/A1uiy3/TFNov11/resources/index.htm?referrerUrl=

At CSC, we take quality management very seriously and make sure every possible step is taken to ensure high standards of quality. Right from regular management reviews for assessing the company’s risks, objectives and performance to the implementation of an effective system for addressing customer complaints- we are proud to boast of a highly competent system for ensuring quality at every level.

Internal audits are carried out annually and in-depth records and documentation are maintained in abidance with BSI standards. We see to it that all corrective actions are entered in a PSW, and subsequent follow up measures and corrective actions are carried out effectively and without fail.

Our resource training system is at par with the best in the industry, and has been instrumental in helping us mould our highly skilled and efficient work force.

Along with our various quality management assessments, we consider the annual BSI evaluation a highly constructive exercise in ensuring quality maintenance within our organization. All constructive feedback will be promptly implemented, and we hope to continue providing the high standards of quality that has come to be associated as the trademark of CSC Screeding.

CSC has successfully completed the screeding project for the new £3m sports hall for Trinity School, Newbury. FlexiDry F3 with a drying time of 21 days was used for the project, which is scheduled for completion by autumn 2011.

The much awaited sports hall will feature a range of facilities from an all-weather outdoor sports pitch, viewer’s gallery and main sports hall to all associated facilities including PE classrooms changing areas, shower rooms and even a café. In addition to improving the sports facilities available to the students of Trinity, the sports hall is expected to open up better facilities for community use and gatherings as well.

CSC has also been awarded the contract for the installation of leveling compound, Instarmac Level It One for the roof of the sports hall. The leveling compound is to be installed over pre-cast concrete blocks to provide a flatter surface which will further receive an insulation layer and water proof coating.

The pre-cast planks are manufactured off-site and designed to provide a quick structural flooring process, allowing projects to progress rapidly. They are manufactured at concrete plants based on a set of design drawings which span the void layouts of brick, block and steel supports.

The off -site methodology removes the need for structural decking, shoring and time elapse waiting for the curing of the concrete, giving logistical advantages at the construction site. The pre-cast planks are generally delivered to site by artic lorry and the flooring is lifted into place by on-site towers or mobile cranes.

However, the advantage presented by concrete planks comes with another set of problems that require consideration. Pre-cast planks are pre-stressed with cambers that do not always follow the same curvature. The effect is a stepping in the floor surface which is not suitable for the installation of insulations and acoustic layers.

Under such circumstances, a sacrificial levelling layer may be required to rectify this difference. It is recommended that a full level survey is carried out to ensure there is an adequate zone to encapsulate the entire flooring. It is important to evaluate the flooring surface to estimate the amount of pre-levelling required. This helps to ensure that insulations and/or acoustic layers can sit flat on the base. Voids in the layer can result in failure problems in the future as the screed and insulation could give way under load.

The detailed information regarding this is critical to the floor screeding contractor so the correct price can be submitted to allow for minimum, maximum and nominal (average) screed depths. This also gives them an insight into the amount of pre-levelling, if required. A design drawing that has a section showing 100mm maximum and 55mm minimum can be very different in reality. This is often the case when the nominal depth is not included in the M10 specification.

We have found that pre-cast concrete planks can have a huge variance in levels. There have been instances where the camber has been seen to be the other way round and is sometimes lower in the centre of the length.

A recent experience demonstrated that approximately 30% extra screed was required on a project to achieve datum levels and the client had not allowed for such variance in the construction budget. We were under pressure by the on site project manager to get the job done without any extension of time and to discuss the depth at the end of the project. The programme did not allow for any time to reconsider the options and progress had to be made. CSC Screeding Ltd provided the support to our client and completed the work on time. We had three teams of screeders and pumps on site, installing approximately sixty tonnes of screed every day for nine weeks.

Please see the photographs below of some projects recently found to have considerable variance.

A view from the underside

Steps in the floor surface require a sacrificial levelling process

Seriously out of level!