A Practical Guide to Screed Testing: What Do the Experts Say?
A Practical Guide to Screed Testing: What Do the Experts Say?
Hello Folks,
Welcome to our screed care section. I am your screed doctor, and I am here to make sure that all screeds stay healthy and strong.
In the course of my long career as the official screed doctor, I have tended to many a screed with afflictions ranging from cracking and curling to serious issues arising from inappropriate judgement of floor level, surface regularity, bay sizes, screed drying times and screed compatibility, and the list just goes on.
I must say, I have been really shocked to see how many screeds succumb to an early demise, just because the real cause of affliction is not diagnosed correctly or because appropriate intervention isn’t initiated on time
And, contrary to common perception, it is not just those weak, inexpensive screeds that are prone to such serious screed issues. I have seen expensive screeds laid by expert screeders crumbling miserably because of the lack of appropriate screed care during the crucial post-installation stages.
That was when I thought, I seriously have to do something to help protect the screeds before it is too late to intervene. I called up my old friend, the charming old Screed Scientist. We put our bald heads together. And we finally came up with this idea of an educational campaign to create awareness about the important screed care steps, complemented by a professional and reliable screed testing service to detect any signs of flaws right at the root.
We sincerely hope, our initiative will help each new screed to turn out to be sturdy, strong and flawless, and help you keep your budget in check.
As I mentioned earlier, there are a lot of internal and external factors that affect the quality of a screed. Right from the level of the substrate and the consistency of the screed to the surface regularity, soundness and moisture content of the installed screed, the regulation of the traffic on the site, the weather conditions and the adoption of appropriate screed care measures – there are a lot of factors that affect the final quality of the screed. A flaw in any of these can seriously affect the quality at a later stage, making repair works at the latter stages quite expensive and tedious.
Keeping your eyes open for the little signs and symptoms is the first step to keep your screed healthy. The tell-tale signs of cracks at the joints, the curling of screed at the edges, minor variations in surface regularity – these are all simple signs which if left unaddressed for long, can lead to serious issues which will be hard to resolve later.
So, the best thing to do is follow a simple and systematic approach of monitoring and inspection at each level of screeding, ensuring all the way that the standards at that stage conforms to the expected standard. If in serious doubt at any stage, the best thing to do is go for a professional screed test and initiate remedial action immediately.
Inadequate soundness of screed / Hardness of the screed does not meet required specifications
If the soundness test reveals inadequate soundness, the normal course would be to cut out and replace the unsatisfactory areas.
Another alternative is to upgrade the unsound screed by impregnating with an ultra-low-viscosity resin or a fibre-reinforced flow-applied cementitious overlay
Check the workability of the screed before installation using the 'snowball test'.
Consider carrying out a level survey before commencing screeding and make an accurate assessment of the correct amount of materials required
Use a hand-rammer or roller to ensure adequate compaction
Adding a water-reducing / plasticising admixture can help in bringing down the water-content of the screed mixture and can improve the strength and soundness of the screed. FlexiDry fast drying floor screed is a product that yields very good results.
Make sure the soundness of screed is verified by in-situ testing ( BRE drop hammer test ). Carrying out the test after 14 days of screed installation which can show whether the set and hardened screed will have the intended strength. Screed will reach final strength after 28 days of install.
Unacceptable deviations in the flatness of the finished screed
Remedial options depend on individual circumstances
Apply underlayment such as smoothing compounds
Localised grinding to flatten the surface
Check that adequate surface preparation is carried out before the installation of the screed.
Ensure the screed is of 'semi-dry' or 'earth-moist' consistency, as it enables the screed to be finished to the required level of surface accuracy.
Carry out a reliable surface regularity test shortly after the installation of the screed. It is recommended not to leave the testing until the flooring is complete.
High moisture content in the screed
Remedial options depend on individual circumstances
If the high moisture levels are detected early ( before the installation of the final floor finish) carry out a reliable Moisture Test, and allow continued drying of the screed with a balanced combination of warm conditions and ventilation -depending on the time available
Ensure that the screed is allowed to dry naturally for the time specified by the manufacturer. As per BS8203 for traditional screeds up to a thickness of 40mm should be given a drying rate of 1mm/day, followed by an increasing time of 0.5mm per day for the remaining thickness. Eg. 75mm screed will take 110 days to dry in good conditions with the temperature maintained at 20C and a relative humidity of 55%. Proprietary screeds can be dry considerably faster. FlexiDry can dry at rates of 3, 7, 14 & 21 days.
Take all necessary screed protection measures to keep the screeded area water tight and protected from dampness and moisture
Where required, use a surface applied Damp Proof Membrane to isolate the flooring from the base substrate
If the flooring is to be an in-situ applied resin, consult with the manufacturer on the use of a moisture tolerant primer systems
Moisture resistant adhesives can be helpful for flexible applied floorings
Use dehumidification equipment
Cracking of screed
Extensive cracking of screed
Cutting out and replacement is generally not recommended as it may extend the area affected.
For screeds that is well compacted and otherwise sound, specialist repair techniques such as resin injection can be used economically. But, make sure specialist advice is sought before initiating repair
Cracking of the screed within reasonable limits is usually a result of drying shrinkage and is not of serious consequence. However, it is important to carry out regular monthly inspections ( commencing from 1-2 months after installation) to make sure there is no further extension or severity in the cracks.
Carry out repairs before installing floor finishes
Incorporating crack inducement joints or day joints
Reinforcing the screed with metal mesh
Using modified screeds like FlexiDry which follows a controlled drying process, reducing the formation of cracks
Wrong level of screed
Alignment of fixed positions such as stair treads, lift lobbies, window and door thresholds, joining up to existing floors
Difficulty in fitting insulation and maintaining adequate screed coverage
Inability to cover the given area with the materials supplied
Inaccurate assessment of level
Carry out a reliable level survey
Collapsing of the screed in positions where heavy loads are regularly placed eg) beneath chairs, tables etc , or in areas with frequent traffic –corridors, hallways etc
Excessive loads both pre and post construction phase
Insulation loading capacity
After the initial collapse, it may extend to surrounding areas with continued traffic
Investigate the cause of collapse, verify the quality of adjacent screeds and assess the extent of inadequate soundness by using the BRE drop hammer test
Repair methods would depend on the cause of the failure, the extent of collapse, the type of flooring and the time available before normal usage
Using forced action mixers instead of manual mixing of screed
Conducting BRE drop hammer test can give assurance of the quality and soundness of the screed, and can help in initiating adequate remedial measures before proceeding with the final floor finish
Curling and lipping
Differnce in screed level at joints. One side higher than the other Bouncing of the surface at the joint locations
Common in unbonded and floating types of screed construction
For severe curling, applying an impervious sheet flooring and leave insitu seven days before applying finishes. This can help in redistributing the moisture and reverse curl the screed.
Differential curling at cracks or joints can be minimised by reinforcing the screed with steel fabric at mid-depth. This restrains lateral movement
Compaction of screed around pipes
Compaction of screed around and beneath the pipes in underfloor heating systems, causing inadequate soundness
Traditional semi-dry cement/sand screeds that are mixed too dry can present problems of compaction around pipes
Mix the screed slightly wetter and apply a base layer ensuring adequate compaction. A slightly dryer mix to top off the screed and achieve the surface regularity
Reinforce the screed with PP Fibres or steel mesh such D49 or D98, over the pipes
Use a high-workability fine concrete screed with a super-plasticiser to increase compaction properties
I have listed above some of the general problems with screeds, their signs and ways to prevent/ rectify them.
I hope this will be a useful guide to spot the little problems with your screed before they become too late or expensive to rectify.
But, as individual problems may vary due to internal and external factors specific to the particular case, it is always ideal to seek the advice of an expert
before initiating remedial action. In case you would like any advice or information on your particular screed issue, please feel free to post your message here,
and I will answer your question personally.
Yours Sincerely,
The Screed Doctor
Reference and further reading: