How To Avoid Screed Failures On Large Commercial Projects
Floor screed failures on large commercial projects are more common than they should be, and the consequences are rarely minor.
A failed screed can delay the entire programme, hold up subsequent trades, require costly remedial work and, in the worst cases, result in a floor that needs to be completely removed and re-laid. The good news is that the vast majority of screed failures are preventable.
They almost always result from errors in specification, preparation or installation rather than from any inherent weakness in the materials themselves. Here is what main contractors and developers need to know to avoid them.
Specify The Right Screed For The Application
Screed failures frequently begin at the specification stage, long before any material is poured. Selecting a screed product without properly considering the specific demands of the application is one of the most common routes to a poor outcome.
The key factors that should inform the specification include the size of the floor area, the required depth, whether underfloor heating is present, the intended floor covering, the programme timeline and the loading the floor will be subjected to in use.
A liquid anhydrite screed, for example, is an excellent choice for large areas with underfloor heating but is not suitable for use in wet areas or where it will be directly exposed to heavy industrial loading without an appropriate surface treatment.
A fast-drying screed may be essential on a project with a tight programme but will add cost compared to a standard product. Getting the specification right at the outset is the single most effective way to avoid problems downstream.
Prepare The Subfloor Thoroughly
Even the best-specified screed will fail if it is laid on a subfloor that has not been properly prepared. Contamination, inadequate concrete strength, high moisture levels and poor surface profile are all common causes of screed delamination and failure.
Concrete Strength & Surface Profile
The structural concrete slab must have achieved sufficient strength before screeding begins, and the surface must be clean, free from contamination and of adequate profile to allow the screed or bonding agent to adhere correctly.
On large commercial sites where multiple contractors are working in sequence, it is not uncommon for the concrete slab to be contaminated with oil, release agents, curing compounds or construction debris by the time the screeding contractor arrives on site.
Identifying and addressing these issues before screeding begins is a responsibility that must be clearly allocated and managed.
Moisture Testing
Carrying out calibrated moisture testing of the concrete slab before screeding is a non-negotiable step on any commercial project.
Excess moisture rising from the slab can prevent the screed from curing correctly, cause delamination and damage floor coverings applied above.
Where moisture levels exceed the acceptable threshold for the screed system being used, a surface damp proof membrane must be applied before the screed is laid.
Install Expansion Joints Correctly
On large commercial floor areas, the correct installation of expansion joints is critical to preventing cracking.
Screed expands and contracts in response to changes in temperature and moisture content during curing and in use, and without adequate provision for this movement, cracking is almost inevitable.
Perimeter expansion strips must be installed around all walls, columns and fixed structures before the screed is poured.
On larger areas, intermediate day joints or movement joints need to be incorporated at appropriate intervals in accordance with the screed manufacturer's guidance.
These joints must be correctly positioned, correctly detailed and, where the floor covering requires it, correctly treated before finishes are applied.
Control The Curing Environment
The conditions in which screed cures have a significant impact on the finished result.
Draughts, direct sunlight, underfloor heating running too soon and excessive heat or cold can all affect the rate at which moisture leaves the screed and cause surface defects, cracking or uneven drying.
On large commercial projects where the building envelope may not yet be fully closed, or where other trades are working in the same area, controlling the curing environment requires active management.
The screeding contractor should provide clear guidance on the conditions required during the curing period, and the main contractor should make sure these conditions are maintained.
Allow Sufficient Drying Time
One of the most common causes of floor covering failure on commercial projects is insufficient drying time before the covering is applied. Screed must reach the correct residual moisture content before tiles, resin coatings, carpet or other floor finishes are installed.
Applying a floor covering over screed that has not dried sufficiently traps moisture beneath the covering, which can cause adhesive failure, tile lifting, resin blistering and a range of other problems that are expensive and disruptive to put right.
The drying time required depends on the type and depth of screed, the ambient conditions and whether forced drying using heating and ventilation is being employed.
On commercial projects with tight programmes, using a fast-drying screed product and employing a managed forced drying regime from the appropriate point in the curing process can significantly reduce the time before floor coverings can be applied.
Work With An Experienced Screeding Contractor
The quality and experience of the screeding contractor is one of the most important factors in achieving a successful outcome on a large commercial project.
A contractor who understands the demands of commercial screeding, works to current industry standards and brings the right equipment, products and technical knowledge to the project is far less likely to produce a floor that fails than one whose experience is primarily domestic or whose approach is to pour and move on.
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