The procurement phase of an upcoming project is about to commence, and you are need of concrete flooring contractors.
This C-Link article aims to offer procurement information on concrete flooring, offering valuable advice on how to ensure that you compare like for like quotations. We’ve also included a handful of useful value engineering options and some pitfalls to avoid with programme.
Comparing Apples vs Apples
When reviewing supplier quotations there will be several comparative factors on which to determine the best value proposition, especially when an element of design responsibility is apportioned to the specialist. These include the following:
- Concrete Strength
- Concrete Thickness
- Concrete Finish
Prelim allowances can typically account for up to 15% of a contractor’s quotation. It’s a useful exercise to request a breakdown of inclusions, allowing a better understanding of whether a reasonable estimation has been made.
For example, Specialist A has allowed for 100Hrs Management, Hours at £100p/hr, versus Specialist B who has allowed for 200Hrs at £95p/hr. Whilst both specialists have similar rates, the quantity of hours of Specialist B is double that of Specialist A. Resulting in a £9,000 higher cost. This prompts the question, why? Are there previously unknown issues, an over allowance or simply an error?
2. Concrete Strength
Type of Concrete will play a major factor in the analysis of any quote. Whilst the basic formula of concrete is cement, water and hard aggregate, the composition of these aggregates governs the strength and type of concrete produced.
Different compositions are categorised into ‘grades’ based on their strength (MPa) after 28 days of curing. Compositions of higher strength will typically have a larger volume of aggregate and therefore be more expensive than lower grades.
Concrete grades are defined by ascending numbers of 5, starting at C10. For example, C10 concrete will have the strength of 10 newtons versus C15 that will have a strength of 15 newtons. As a guide, C25 concrete can be sourced for circa £77 per cubic metre, compared with C30 at £80 per cubic metre.
The choice of concrete grade will be important dependant on the anticipated dynamic and static loads to be imposed onto the flooring. Some examples and their suited uses include:
- C10 / Patio slabs, pathways and non-structural work / Domestic & Commercial;
- C20 / Domestic floors and foundations (where the weight of structure will be lighter). Also good for workshop bases, garages, driveways and internal floor slabs. / Domestic
- C30 / Pathways and roadways (this is the lowest grade concrete mix that can be used for this purpose). More durable than the grades that have come before, and thus is much more weather-resistant and can take heavy road traffic. / Commercial
- C40 / Commercial construction sites, creating foundations and beams for structural support and roads. The most durable in this list, C40 can withstand chemical corrosion also, so is frequently used on farms where slurry could corrode structures, or in septic tanks / Commercial
3. Concrete Thickness
With concrete measured by the volume poured (i.e. cubic metres), the thickness of concrete has a direct impact on the overall cost. Pertinent if no thickness has been specified and it is for the specialist to quote a thickness of their design.
If we consider a floor area of 10,000mm (length) x 10,000mm (width) x 50mm (thick) it will mean a concrete pour of 5 cubic metres. Increase the thickness by 10mm and it will result in a pour of 6 cubic metres. At £65 per cubic metre for C10 concrete, your total cost has increased from £320 to £390. Extended over a larger area the potential implication is clear.
4. Concrete Finish
Concrete Finish. Concrete is no longer simply the hidden skeleton of a building, over-clad and covered by more ‘aesthetically pleasing’ materials – take the Southbank Centre (London) as prime example. With this often-obtrusive material becoming ever more exposed in domestic designs, such as for kitchen islands or flooring. The finish is therefore a canny comparative as each will involve a different methods and resources to achieve the desired look. From an automated concrete smoothing machine all the way to polished concrete, involving a more labour-intensive process of grinding, polishing and chemical treatments. Be inquisitive with the supplier and get to understand the methods used to achieve the quoted aesthetic.
Formwork covers a large quantity of the entire cost of concrete construction. When assessing quotations, consider if the form is owned or rental and its complexity. Is lifting equipment needed? What plant is required to transport materials? The formwork will typically be included within the measured work rates and it may be prudent for it to be shown as a separate cost alongside the intended design.
No construction work estimate is 100% accurate and there is no guarantee of continuity in concrete pour, for example natural events like rain impact the continuity. The contractor will therefore allocate a certain percentage to the total cost to cover such eventualities.
Whilst being fair and reasonable in assessing a sub-contractor’s quotation is important, any Project Manager or Quantity Surveyor loves a saving! Here are some strategies to help.
The specialist will know what resources they require to complete job on time and to the required quality. That said, it is reasonable to compare with other specialists to see if there are any excessive or under estimations. VE considerations may include:
- Rationalising the number of site managers
- Consider the subcontractor as a whole company, is it a company with fewer projects to re-coup its overheads?
- Are there services you could provide as the developer, procuring at cost as opposed to incurring the specialists margin?
A contractor may include for up to 10% contingency/risk so a useful trick may be to specify such contingencies as separate item to the main quote after first stage tender submissions. At which point, you can look to negotiate down by creating a risk profile and collaborative assessment of where risks could be eliminated or mitigated to reduce contingency costs. You could even put the value as a provisional sum item, attached to specific caveats.
This is often the most single influential factor to realise value engineering opportunities. By optimising an existing floor slab pile design you could reduce material quantities, construction method costs and time. While maintaining or improving the functioning and quality of the piling works.
4. Pour Method
Concrete pour options include ‘Ready Mix’ concrete options, ‘Volumetric’ wagons or on-site Silos. Make an assessment on the complexity of design, scale and logistical nature of the development to determine the optimum pour method. For example, on a 100 cubic metre pour you will find the average 10 cubic metres held by a volumetric mixer would mean 10 visits. Alternatively, an 8 cubic metre ready-mix wagon would need 13 visits, not to mention the added time and accuracy benefits a volumetric mixer provides. Conversely, on a 1,000 cubic metre concrete pour the use of an on-site silo may be preferential, allowing concrete to be mixed on site and reducing the need for transport logistics.
Labour will be factored into the measured work rates with the level required linked to the scheme’s design and finish.
Labour histograms will assist in understanding the reliance on manual labour as opposed to plant, giving you the ability to conduct a ‘breakeven analysis’ i.e. a comparison of the volume that could be poured by manual labour and its associated cost versus plant. Labour time becomes more prevalent when considering the concrete finish as these methods are often are done by hand.
6. Ancillary Services
Look for services within the quotation that are not in strict relation to the concrete pour, services that you as developer may be able to provide. For example, the provision of Banksman and Lift Supervisors, which would be used by other trades.
Programme is one of the fundamental performance indicators of a successful project. In this section we offer guidance on how this could be achieved.
Review each element of the build and plan the pour phases. Consider engineering implications, logistics, follow on trades, and access. Continually refresh your project knowledge by reviewing information like layouts quantities and depths. Devise a contingency plan to plan for unexpected changes and events, for example switching elevations or alternative suppliers.
The use of software is increasing within the industry. BIM (Building Information Modelling) is now mandatory on government contracts and ever popular in the private sector. By becoming an early adopter of this trend, you will not only stay ahead of the game but it also assists in creating a visual representation of the scheme and the ability to foresee any build clashes.
By investing in your staff, you are demonstrating trust and commitment to both their personal and professional development. It will lead to happier and more productive staff, in turn generating efficiencies.
Miscommunication is the bane of any project team. Create clear defined roles and tasks so repetition and overlaps are avoided. With the given person becoming an expert in their ‘field’ i.e. procurement. Whilst at the same time understanding wider project awareness is vital so consider using tools such as Microsoft Team Planner or Favro, so everyone is in the loop.
Staff in whatever capacity are the eyes and ears of your organisation and those experienced workers will always be better placed to spot potential problems. Incentivise participation in company improvements, in weekly project meetings or in private if necessary.