Screed Care

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.

Caring For Your Screed

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.

Prevention Is Always Better Than Cure

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.

Screed Problems: Common Signs And Their Remedies

Screed problemSigns to look out forCommon ReasonsRemedyPrevention
1. Inadequate soundness of screed / Hardness of the screed does not meet required specifications1. Crumbling of the screed/ friability 2. Poor screed colour and extensive patches of broken down screed below the vinyl1. Semi-dry consistency cement/sand or fine concrete sands are most prone to unsoundness 2. Screed mix containing less than the required amount of cement 3. Very dry screed mix or poor compaction (however over-wet screed mixes can lead to shrinkage problems and affect the flatness of the finished screed). 4. Screed has been directly trafficked and damaged during the construction phase of a project.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 overlayCheck 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.
2. Unacceptable deviations in the flatness of the finished screed1. Humps on the floor 2. Problems in laying the final floor finish 3. Difficulty lining up with existing floor finishes1. Inaccurate assessment of level/surface regularity 2. Inadequate surface preparationRemedial options depend on individual circumstances Apply underlayment such as smoothing compounds Localised grinding to flatten the surfaceCheck 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.
3. High moisture content in the screed1. Rippling and bubbling up of vinyl 2. Damp smell 3. Lifting up the final floor finish for inspection will show moisture residue on the surface. For vinyl, the residue would usually appear to be milky.1. External ingress of water 2. Condensation 3. Water spillages and leaks 4. Final floor finish laid before allowing the screed to dry completely 5. Inadequate protection of the screed after installationRemedial 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 availableEnsure 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
4, Cracking of screedExtensive cracking of screed1. Poor design 2. No expansion joints/cuts on the screed 3. Early and excessive loading 4. Cement shrinkage 5. Impact 6. Insulation giving way underneath the screed 7. Surface abrasion 8. Inadequate screed protection 9. Excessive water content in the screed mixCutting 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 repairCracking 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
5. Wrong level of screedAlignment 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 suppliedInaccurate assessment of level-Carry out a reliable level survey
6. Collapsing of screedCollapsing 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 traffic1. Poorly mixed screed 2. Inadequate compaction 3. Screed consistency having been too dry 4. Inadequate soundness of the screed 5. Inadequate screed protection after installation 6. Early loading of weight, before the screed is sufficiently dry 7. Insulation is not suitable for heavy loading such as mobile electrical working platformsInvestigate 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 usageUsing 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
7. Curling and lippingDifference in screed level at joints. One side higher than the other Bouncing of the surface at the joint locationsCommon in unbonded and floating types of screed constructionFor severe curling, applying an impervious sheet flooring and leave in situ 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
8. Compaction of screed around pipesCompaction of screed around and beneath the pipes in underfloor heating systems, causing inadequate soundnessTraditional semi-dry cement/sand screeds that are mixed too dry can present problems of compaction around pipesMix 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 regularityReinforce 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:

  • Screeds, flooring and finishes – selection, construction and maintenance, CIRIA Report 184
  • BRE Building Elements, Floors and Flooring – performance, diagnosis, maintenance, repair and the avoidance of defects