RonaScreed SBR is an admixture for site batched screeding mortars and fine concretes. The mix design for each is RonaScreed SBR admixture, cement, medium grade sharp sand, aggregate as determined by the mix design, plus water. The components are measured by weight (or by volume using batch boxes) and mixed using a forced action mixer.

Bonded screeds are primed with a mixture of RonaScreed SBR and cement, which achieves monolithic adhesion to correctly prepared concrete or screeds.

Quick Links - Click To Jump To Section:

   
• Features & Benefits
• Mix Designs
• Physical Properties
• Preparation
• Damping
• Priming
• Mixing
• Placing
• Curing
• Initial Traffic
• Overlaying with Floorings
• Working Temperatures

Features & Benefits

• Outperforms similar products
• Improved physical properties
• Will accept foot traffic after 24 hours
• User friendly mix designs
• Rapid drying—can receive floor coverings such as vinyl, tiles and carpet after 10 days @ 50mm thick
• Compatible with underfloor heating systems
• Excellent wear resistance
• Bonded screeds from 10mm
• Excellent resistance to passage of water and water vapour

Mix Designs

Physical Properties

Preparation

The substrate on which the screed is being placed must be structurally sound and stable and suitable to receive a high strength screed or topping.

Surfaces should ideally be vacuum shot blasted or similar to expose the aggregate and provide a mechanical key.

All grease and oil must be removed.

Dust, debris and loose material must be removed by vacuuming.

Weakness in the substrate may result in debonding and failure of the screed or topping applied to it.

The recommendations regarding assessment of the substrate given in BS8204-3: 2004 should be followed. Note the minimum and maximum application depths for each mix design.

For patch repairs, the existing substrate must be square cut to the minimum screed depth, to allow the minimum depth of mortar to be placed.

Damping

The prepared surfaces must be thoroughly damped with clean water.

Very porous surfaces may require soaking for up to 24 hours.

All free water must be removed before the primer is applied.

Priming

Brush apply a coat of RonaScreed SBR/cement primer mixed 1:1 by volume to the damp surface immediately before applying the screed, at the rate of 3-4m² approximately per litre of RonaScreed SBR.

Mix the primer thoroughly and apply evenly over the surfaces ensuring total and uniform coverage, taking care to avoid ponding. Only prime an area of floor which can be covered by the mortar within the working time of the primer.

Note that the primer must not be allowed to dry. If it dries it must be thoroughly scratched and reapplied.

Mixing

RonaScreed SBR screeds should be mixed by forced action mixer, to ensure adequate dispersal of mix components. The use of a forced action mixer (e.g.. CreteAngle or Baron M200/ 300) will provide optimum performance; free fall mixers must not be used, dispersal of components is poor.

When using an efficient mixer, a mixing time of 3/4 minutes is normally sufficient.

It is essential to the performance of the screed that there is sufficient gauging liquid in the mix and that the correct amount of RonaScreed SBR is used. The consistency of the screed must not be semi-dry, adequate hydration of the cement is essential to achievement of strength.

To test for correct consistency, make a ball of the mixed material. If the ball can be pulled apart without crumbling, the mortar will contain sufficient gauging liquid to fully hydrate the cement and allow proper compaction.

Once mixed the mortar should be used as quickly as possible.

Placing

Screeds and toppings with an overall thickness greater than the maximum depth per layer, 50mm approximately, must be placed monolithically (wet on wet) in more than one layer to ensure compaction. Each layer should be of approximately equal thickness and using the same mix design.

To ensure satisfactory adhesion the lower layer(s) should be combed or raked to provide a key for the next layer. Should intermediate layers be allowed to dry, a priming coat must be applied before application of the next layer.

Stress relief joints should be formed in bonded screed/ topping over day joints in the concrete and expansion, contraction and movement joints must be expressed in the screed and on suspended slabs, over beams to accommodate deflection.

Floating and unbonded screeds should be separated from other building elements with isolation joints at screed perimeters, in doorways and around columns, manholes and fixed bases.

Joints should also be formed between any hot and cold areas of the floor.

For further information refer to BS8204-1 or contact Rawlins Technical on 0113 2455450 (option 2) or send a message to [email protected].

Curing

As soon as possible after finishing the surface, cure with tight fitting polythene or Ronacrete Curing Membrane.

Leave polythene in place for at least 24 hours to prevent rapid moisture loss and surface cracking and crazing.

Take care not to damage the surface.

The use of Ronacrete Curing Membrane is preferred for screeds which will not receive bonded floorings or sealers, curing may commence immediately after trowelling is complete.

Initial Traffic

RonaScreed SBR screeds, toppings and repairs can receive foot traffic after 24- 48 hours (typically at 20°C) and after 3-5 days (typically at 20°C) heavy traffic may be allowed.

This time will vary according to temperature, amount of liquid added during mixing, air circulation and other site conditions.

Overlaying with Floorings

The time at which floor coverings can be laid over a RonaScreed SBR screed is dependent on residual moisture content.

Testing for relative humidity (RH) at the surface is an accepted non-destructive means of determining residual moisture content.

Typically, a RonaScreed SBR screed will achieve 75% RH after 10 days air curing at 50mm thickness (at 20°C & 65% air humidity).

Measure RH with a correctly calibrated hygrometer attached to a humidity box, see BS8203.

Working Temperatures

RonaScreed SBR screeds can be used in most weather conditions and in a wide temperature range, typically from +3°C, on a rising thermometer, to 25°C and above.

Note that at high ambient temperatures the working time of the mix will be reduced and increased at lower temperatures.

Materials should ideally be stored in dry frost free conditions between 10°C and 20°C before use.