Method Statement - DUBAI

Interiors Sources Decor LLC

Method Statement Sand Cement Concrete Screed Civil Works 6/26/2016

The purpose of this Work Method Statement for Mortar Screed Works of Building is to outline and describe in detail the procedure such as design mix, mixing, pouring and curing. Inform all concerned supervisor including workers the value and importance of this activity prior to implementation. This activity should be performed with strict compliance and implementation of Safety Requirements & Procedure and project specifications to complete the work for concrete screed..

ISD Format 033.8 – Rev 00

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Screeds and toppings are commonly used as a means of providing smooth flat floors in residential, commercial and industrial buildings. Toppings may also be used to increase the structural depth and strength of the base slab.

TABLE OF CONTENTS 1. SCOPE 2. TRADITIONAL SCREED 3. LAYING 4. SYSTEMS FOR TRADITIONAL SCREEDS 5. THE RIGHT FLOOR SCREED 6. THE RIGHT SCREED MIX 7. PRILIMINARY PREPARATION 8. THE RIGHT SCREED PROTECTION MEASURES 9. FINISHING 10. ORDINARY NON SLIP 11. STEEL TROWELLED 12. REMEMBER 13. TOOL BOX TALK ONs 14. ATTACHMENT

ISD Format 033.8-Rev 00

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SCOPE


The scope of this Method Statement covers the works in any Project for Sand Cement Concrete on floor slab or unbounded screed. A screed is a construction element laid in a range of thickness, and its purpose is to bring the installation surface for the flooring to the design height and to provide a surface suitable for installing the specified flooring. Screeds are usually made from pre-blended mortar mixed with cementitious blinders or anhydrite-based blinders. Depending on whether it is laid directly on a supporting structure (for example a reinforced concrete floor slab), on a isolating layer (for example a vapour barrier) or on a layer of thermal insulation and/or soundproofing materials, it is known as a ‘bonded’’, ‘unbonded’’ or ‘floating’’ screed. When choosing which product to use to make the screed, be it a special binder, a pre-blended mortar or traditional site prepared mortar, you must take into consideration the final use of the screed, site conditions (internal or external, the thickness to be laid etc.,) the type of the flooring to be installed, the time to wait before installing the flooring and the time required before putting the flooring into service.

TRADITIONAL SCREED Traditional floor screed basically consists of sand & cement mixed at a ratio of between 3 to 5 parts sand & 1 part cement. In the majority of cases 4 to 1 is quite sufficient. In the past reinforcement was achieved by using Hex wire (chicken wire) or D49 mesh. In the early 90’s Polypropylene Fibres (PPF) started to become very popular, and today PPF is the most common used reinforcement for traditional floor screed. For marble laying works the screed can be filled without any reinforcement Traditional screed drying times vary according to the weather conditions, depth and manufacturers admixtures used.


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LAYING


Traditional floor screed is applied with a straight-edge, wooden / plastic float and finished with a trowel or power float. The basics are to find four level points, level between two with the straightedge, level between the opposite two, and pull off between the ‘screeds’ with the straight-edge, to find a flat area. Top quality floor layers can easily achieve a surface regularity of SR1. A traditional floor screed system is the only reasonable method to achieve a floor in a wet room to falls.

SYSTEMS FOR TRADITIONAL SCREEDS There are three main systems for traditional floor screed. 

Fully bonded

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Partially bonded

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Floating.

FULLY BONDED SCREEDS need to be laid on a shot-blasted / scrabbled concrete base, and be bonded using an adhesive such as PVA, SBR, epoxy resin or good old fashioned cement. PVA glue is a good screed adhesive especially if it is mixed with water & cement, to make slurry. If the concrete base is primed the day before with PVA & water mixed, then a slurry applied prior to screed, then it is quite reasonable to expect screed to fully bond at just 25mm thick. SBR has approximately the same characteristics as PVA, but it is not water soluble after drying, and so is recommended around wet areas, such as swimming pools. Epoxy resin, such as Isocretes’ M-bond’ allow screeds to fully bond at depths as little as 15mm. It is quite an expensive system, but has many advantages over other bonding agents. One such advantage is that if two-coats of epoxy resin are applied (one 12-24hrs before the second coat & screed), then the epoxy resin acts as a top end DPM. Cement makes a reasonable bonding agent if there is reasonable depth of at least 50mm. a good slurry must be formed using water, and must be brushed in thoroughly and any drying spots must be kept damp as screed is applied. Always a good idea to damp the concrete slab a day before.

PARTIALLY BONDED SCREEDS are a cheap alternative to doing the job properly, and have the added risk of the floor screed failing, because at depths less that 50mm, the screed can start to


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Interiors Sources Decor LLC break up if the bond to the concrete is lost. This system is only used when people are tryin to save money, and sometimes bonding agents like PVA & SBR are still used, but they are still at high risk from failing due to the slab not being shot-blasted or scabbled.

UNBONDED SCREEDS as the name suggest are not bonded directly to the concrete base, but are intentionally debonded with the use of a DPM (damp-proof membrane). The advantage is that any cracking from the sub-base is not carried through to the screed; drying times can be reduced by omitting the concrete drying time. All walls and pillars must be lined with edging foam or 20mm insulation, such as kingspan, to protect against shrinkage cracking. Floating Screeds are laid on insulation to provide an insulated floor area. All walls and pillars must be lined with edging foam or 20mm insulation, such as kingspan, to protect against shrinkage cracking. This system is the most commonly used in house building, especially with under floor heating systems. There is very little difference between unbounded and floating screeds. High-impact insulation such as extruded polystyrene can give the same levels of rigidness on floating screeds as you would expect from unbonded screeds

THE RIGHT FLOOR SCREED With the different kind of screed types, screed constructions and screed brands available, it could be a laborious task to arrive at a decision quickly. It is important to consider what each type has to offer and how well it fits in with your requirement and make an informed choice. 

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TRADITIONAL SCREED: The standard screed mix of cement and sand mixed in the ratio of 1:3-5 is used for creating a defined layer for installing the final floor finish such as tiles, wood, linoleum, vinyl etc. Traditional screeds are generally suitable for use in hospitals, schools, hospitals, retail, homes etc. FREE FLOWING SCREEDS: The anhydrite free flowing, self-leveling and self-compacting screeds present the major advantage of easy placement and provide reliable results. However, the anhydrite screeds are not suitable for areas that are prone to getting wet. They cannot be used as a final wearing surface and are not compatible with cementitious products. FLOOR LEVELLING COMPOUNDS: These compounds vary from the general screedsin that they are used for levelling or as the final layer of screed to increase the tolerance while laying the floor finishes such as tiles, vinyl etc. They are generally expensive and are used for screed in warehouses and areas which require a very high level of surface regularity or flatness. STRUCTURAL SCREEDS: This type of screed suitable for installing on precast floor surfaces. It is important to seek accurate specifications and calculations from a structural engineer before the installation of structural screeds as the information is vital to decide on the load requirements, flexural strength, bending moment, point loadings, etc. FAST DRYING FLOOR SCREEDS/ACCELERATED SCREEDS: If your project is on a strict time line and you do not have the time to wait for the industry benchmark of 1mm per day and 0.5mm


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Interiors Sources Decor LLC thereafter (110 days for 75mm) for the screed to dry, it would be best to go for fast drying floor screeds like FlexiDry which allows you to go for the installation of the final floor finish as early as 3 days after screeding.

THE RIGHT SCREED MIX The right screed mix is one that is homogenously blended in the right proportion, following the agreed mix design. When there is the option to choose between ready mix and site mixing of screeds, it is important to consider the viability of each option depending on the location and available space at the work site. SITE MIXING OF SCREED is a very efficient and economical way of screed mixing and is suitable for most projects, provided the screed is force action mixed and the work is handled by a skilled work force. The three methods that are generally followed by screeders for site mixing of screeds are: 

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HAND MIXING: This is suitable only for very small areas and is not recommended for bigger projects, as the work is strenuous and the estimated quantities and manual errors while mixing can seriously affect the quality of the screed. FREE FALL MIXERS: Free fall mixers are sometimes used by screeders for mixing larger quantities of screed at the work site. When these are sufficient for mixing general concrete mixes and mortar which are of a fluid consistency, screeds mixed using free fall mixers are often found to be of poor quality, weak and crush easily under impact. FORCED ACTION MIXERS: Forced action mixing is the most efficient and economic method for producing high quality screed mixes on site. Forced action mixing blends the cement and mix homogeneously and is ideal when additives or admixtures are to be added. Forced action mixers are usually of two types:

i) Screed Pumps: These are generally used for forced action mixing of large quantities of screed at the work site. ii) Pan mixers: These are portable forced action mixers which are ideal for producing high quality screed mix at work sites where the use of bigger equipment is difficult.

READY MIX SCREEDS are a good option for work sites where the storage of materials is difficult. But there is always the drawback of heavy traffic posing as a hurdle in getting the screed at the site on time, and might result in a considerable amount of wastage and economic loss.


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PRILIMINARY PREPARATION Make sure old concrete has to be in sound surfaced except for roof slab wherein the surface has to be smoothed and cleaned prior to install vapour barrier. 

Put markings for survey lay-out and slope to final and correct elevation.

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Install all embedded items prior to mortar screed.

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Install wire mesh

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Avoid any damage for installed wire mesh during mortar screed placing.

It is important to carry out the process of screed installation in a systematic manner to achieve the best results. There are several steps to be followed while preparing to install the screed:    

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Make sure the substrate is ready to receive the screed. Check the access and egress is suitable for screed installation, plant and materials. Check the building is watertight. Check the datum levels, record the measurement down to finished screed level to ensure minimum and maximum depths are achievable and compliant with tendered nominal allowance. Check that running potable water is available at an adjacent point of the material location. Check that a waste facility is adjacent to the working areas. Check the mixing plant is safe and suitable to use. Make sure the screed mix in the correct proportion. Apply the screed in a sequential manner, avoiding dry joints. Apply trowel cuts where necessary for crack control. Keep the working area tidy.

THE RIGHT SCREED PROTECTION MEASURES The last step in screed – but this is definitely not the least important of the lot. Appropriate screed protection measures right after screed installation until the laying of the final floor finish is an


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Interiors Sources Decor LLC extremely important step in preventing screed failures, and is of utmost importance in achieving a screed of high quality, finish and durability. From the regulation of site traffic to covering the screed surface with screed protectors, there are several measures to be considered for protecting the screed. At a basic level, it is imperative to ensure that:   

No site traffic is allowed at least for 24-48 hours after the installation of the screed Heavy site traffic is regulated until the installation of the final finish Heavy weights are not loaded unless after the consultation with a structural engineer

FINISHING 

Finish the surface as required by the approved drawing or as needed for the type of flooring to be supplied.

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Finish to a flat surface with a hand or powered steel trowel.

Types of surface finish are described below, the choice being made according to circumstances

ORDINARY NON-SLIP ISD Format 033.8-Rev 00

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Interiors Sources Decor LLC The surface is left as finished with wooden floats, except that if it is too open or too coarse it may be given a few passes with either Perspex or aluminium floats to close the surface without smoothing it. Over-working should be avoided.

STEEL-TROWELLED If a hard, smooth finish is required, the surface will have to be steel-trowelled, using the delayed trowelling method. After the screed or topping has been spread, compacted and screeded to level, it should be bull floated. Bull floating should immediately follow screeding and should be completed before any excess moisture or bleed water is present on the surface. The purpose of bull floating is to eliminate ridges and fill voids resulting from straight edging.

REMEMBER! Access clearance shall be obtained from the General Contractor/electrical and plumbing contractor before laying screed.

Prior to start the screed works all necessary Materials, tools and PPE should keep at work area for ready to use, those are: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

8-10 feet aluminium section Spirit level Trowels, Shovel and wheel barrow Bucket & Brush Spreader Hand gloves & Goggles Gumboot/safety shoe & Helmet Task light Wire brush 1000g plastic sheet & Polyurethane bed 3mm ply Sand & Cement


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Interiors Sources Decor LLC 13. Admixtures and additives

TOOL BOX TALK ON: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Importance of PPE Use and service of hand tools and electrical tools Safe handling of power supply Use of mechanical equipment and service Housekeeping safety Risk Assessment MSDS (Material Safety Data Sheet) Access clearance Lifting, Shifting and Storing Rest Area Restriction of Mobile and Radio Noise restriction Cutting of materials that makes noise and dust Approved shop drawing


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Method Statement - DUBAI

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