The recognised benchmark for screed hard times are 1mm per day up to 40mm and 0. 5mm per day thereafter. This means that a 75mm thick traditional screed shall take 110 days to hard to an acceptable position for applying sensitive floor finishes. The drying time shall also be very reliant on a good airflow around the screeded region plus a controlled heat of 20 deg C and amp; 50% RH. Once the compulsory hard time has elapsed the screed should then be tested by the floor finishing contractor prior to applying sensitive finishes, for example vinyl, carpet, wood flooring, etc.
Testing methods for the moisture content of floor screed vary in most time taken to achieve conclusions and their reliability. A hair hygrometer is the testing method recommended by The British Standard to record the Relative Humidity RH in screed. When creating use of a hood to obtain conclusions from above the surface regarding the screed the hood has to be left in location for 72 hours to let the chamber below it to reach equilibrium with the humidity and the heat regarding the floor slab. This is a timely testing method requiring a return see to location and it is often impractical to make sure that the hood is not disturbed by traffic on a busy site. An RH Probe shall be used to test the relative humidity within the screed below the surface in situ and requires a many holes to be drilled within the screed.
A glass sleeve hole liner is placed into the drilled holes and these are then sealed left in location for 72 hours to let the humidity within the sleeve to reach equilibrium with the humidity within the screed prior to creating the humidity measurement with the RH Probe. The probe is inserted into the sleeve to record the RH and for each recording it wants to be left in location within the sleeve for approximately 40 periods to reach the heat and humidity equilibrium of that within the concrete floor slab. Readings should then be taken over a period of 20 periods to let for any drift within the meter readings. Once again, this is a timely method requiring a 2nd see to site. For an accurate speedy result, the Moisture Content MC test is recommended.
This is the testing method preferred by most product manufacturers particularly when testing modified screeds which are not currently covered by the final revision of The British Standard. The Moisture Content test shall be carried out neither by a destructive method, a calcium carbide test, or non-destructive method creating use of a Tramex Meter. When carrying out a destructive calcium carbide test a sample regarding the screed is removed to approximately 50% regarding the depth regarding the screed and the mass regarding the sample carefully measured with scales. The sample is the entered into a vacuum flask together with a reagent and the flask is rotated in an orbital fashion and, following a timed process, the result is displayed in a compression gauge like a CM%. This measurement is very accurate and is fairly quick to carry out each test c.
30 periods but being destructive some remedial repairs to the screed are necessary. Using a Tramex Meter to measure the moisture content regarding the screed is non destructive and gives instant conclusions for the moisture content regarding the screed. It uses the principle of electrical impedance measurement creating use of electrodes with special spring mounted probes on the base regarding the instrument with a little frequency signal being transmitted into the screed to obtain the measurement. Multiple MC readings shall be taken in a very brief time with the moisture content being instantly displayed and recorded. These are approximated equivalent reading to the carbide test method.
Prior to applying final floor finishes the final flooring contractor has a responsibility to test the substrate with the conclusions being presented to the client for agreement. If the screed is above the maximum compulsory moisture position specified by the floor covering manufacturer a decision has to be created on verification. There exists 3 options: wait longer; employ an independent third party to carry out distant testing or apply a surface DPM. The latter is expensive and ranges from 8 - 13 a sm that is sometimes more expensive than the screed itself. The lack of time usually forces a decision to proceed with surface DPM below duress.
The Solution Cutting edge designs has moved on to where screeding has grow to a science. There exists many businesses within the market location currently for example FlexiDry offering fast drying screed products; most additives and cement replacements. When creating use of a fast drying accelerant it is important to review the published data as most manufacturers rely on the benchmark of 20 deg C and 50% RH so it is greatest practice to let some extra time within the program to make sure that a positive result. FlexiDry is a proven product within the real environment where hard times have not been dependant on heat bench marked at 20 deg C. FlexiDry F0 was tested by DMC Rail Ltd and Balfour Beatty prior to installation at London's Blackfriars Station and FlexiDry F1 was tested with CSC Screeding Ltd at The Lancasters residential project overlooking Hyde Park.
These projects had a total screed region of over 22,000sm. A mini project was benchmarked recently with an Essex based primary contractor where temperatures were recorded 3 times daily and moisture tested subsequent to the 21 day expiration F3 and even though temperatures did not exceed 12C at any time, the test confirmed the screed was hard enough to receive final finishes. A recent example of howcome a floor finish fails - Uxbridge College Case Read March 2011 A screeding contractor was employed to install FlexiDry F2 14 day hard screed to the new hobbies hall and associated changing parts at Uxbridge College on behalf regarding the primary contractor. Within the primary hobbies hall the screed was tested by the screed contractor at the request regarding the primary contractor subsequent to 13 days. All parts had reached the compulsory moisture content with the exception regarding the final region which was effectively tested prematurely.
The floor finishing contractor argued that his test machinery should supersede the testing method recommended by the manufacturer. Increased compression had been applied to the primary contractor and it was decided to install a surface DPM to the 650sm at considerable unnecessary cost. Within the changing parts a moisture challenge seemed to have occurred as the vinyl floor finish had bubbled and lifted. The vinyl was removed to expose the substrate and located that the adhesive had turned milky and wet. A layer of latex had been removed to directly expose the screed for testing.
Within the presence regarding the primary contractor, floor screeding contractor and screed manufacturer a Tramex moisture test was carried out. The screed was a recorded as an average of 1. 6CM%, the latex recorded at 3. 0CM% with the adhesive being well and truly wet. The conclusions determined that the screed was hard but the floor finishing contractor had failed to test the screed to the manufacturer's instructions prior to applying a latex finish to receive the vinyl.
Like a result regarding the moisture test not being completed by the floor finishing contractor, it was not likely to determine the route cause regarding the challenge and whether it was due to applying the vinyl whilst the latex compound was still wet; the failure regarding the adhesive; h2o penetration regarding the vinyl or that h2o had been reintroduced to the screed during construction.
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