What is bonded and unbonded screed?

Bonded – screed laid onto a mechanically prepared substrate with the intention of maximising potential bond. Unbonded – screed intentionally separated from the substrate by the use of a membrane. Floating – screed laid on acoustic or thermal insulation. This is a type of unbonded screed.

What is difference between bonded and unbonded screed?

Bonded screeds would be from a thickness of 15mm to a thickness of 50mm. As the name suggests, unbonded screeds are not bonded directly to the base, but applied to polythene/ Damp Proof Membrane (DPM) laid on top of the concrete base. This is ideal for thickness greater than 50mm for standard screed.

What is a bonded floor screed?

A bonded screed floor is where a screed has been installed over the top of the concrete slab and bonded to the slab using an adhesive. This is distinguishable from an unbonded screed floor where no adhesive has been used and the screed is separated or isolated from the slab normally by using builders plastic.

What are the different types of screed?

What is non structural screed?

Niel. A structural screed is a layer of concrete that is placed as the top or outer layer of preformed concrete flooring. To be considered to be a structural screed instead of a non-structural screed this layer must included reinforcing fibers or components like a steel mesh.

Bonded or Unbonded Screed?

How do you bond a screed membrane?

Bonded topping screeds are generally applied with a bonding slurry coat consisting of a liquid polymer additive (e.g. acrylic or SBR Rubber latex) mixed with cement. The bonding slurry is broomed thoroughly over the dry membrane and the mixed wet topping mortar applied over the still wet bonding slurry.

What is the maximum thickness of screed?

What is the maximum screed thickness? Generally smoothing compounds, are designed to be used up to 10mm. Certain smoothing compounds maximum is up to 50mm. The range of those products would be something like 5-50mm.

What is partially bonded screed?

Screed Options

Partially bonded screed is more affordable but is also not as durable. It needs to be at least 50mm deep to ensure it does not break too easily, and it should be laid on a rough slab for best results. Unbonded floor screed will not be directly bonded and is separated by a membrane.

What is the minimum screed thickness?

The minimum thickness of an unbonded traditional screed will usually be around 50mm. An unbonded Cemfloor Screed would usually require a minimum of 30mm thickness. Floating screed: This is where the screed is overlaid on something that is compressible and not rigid.

What is the difference between concrete and screed?

Concrete is a mixture of cement, water, aggregates and sometimes admixtures. It is typically used for structural purposes such as foundations, floors, walls and beams. Screed, on the other hand, is a thinner mixture of cement and aggregates, without any water.

What is bonded concrete?

A bonded concrete overlay (BCO) consists of a new concrete overlay placed directly on top of an existing concrete pavement. The overlay bonds to the existing concrete to create a monolithic slab.

Why do floor screeds crack?

Cracks typically form in new screeds because the excess water evaporates from the surface at a faster pace than it is replaced by the residual water, trapped in the concrete slab. Or at stress points such as doorways and corners.

What is the best mix for floor screed?

Screed is usually a cementitious material made from a 1:3 to 1:4.5 ratio of cement to sand. A simple cement and sand mix will be fine for a simple application but more sophisticated mixes are suitable for a wider range of applications.

Do you need to prime concrete before screeding?

Primer is absolutely necessary if you have an anhydrite screed (aka calcium sulphate). This is a liquid screed pumped onto the sub-floor that self-levels. It's quite common in modern construction and has many benefits over sand and cement screeds, but you can't tile straight onto it with standard adhesives.

Can you screed over waterproofing?

Do we waterproof above or below the screed? AS 3740-2010 3.2 states: Where a tile bed or screed is used, the waterproof membrane shall be installed above or below the tile bed or screed. Both are correct, and have their various uses.

What is granolithic screed?

Granolithic screed, also known as granolithic paving and granolithic concrete, is a type of construction material composed of cement and fine aggregate such as granite or other hard-wearing rock. It is generally used as flooring, or as paving (such as for sidewalks).

What is the thinnest screed?

The screed thickness should not be less than 50mm; therefore, to allow for deviations in the finished levels, the specified design thickness should be a minimum of 70mm. However, BS 8204-1 emphasizes that there is a high risk of screed curling with unbonded and floating levelling screeds.

Can you screed 10mm?

10mm would general be the minimum of any sand and cement screed, and would require bonding. A bonding agent is used to bond the screed to the substrate. You need to take particular care when bonding to the substrate, make sure that it's clean, dust free, free from contaminants and that it is actually sound.

Can you screed over existing concrete?

Can I pour screed over concrete? Yes you can. The main reason to use concrete screed is to pour over a pre existing concrete floor / slab / sub base to level it out and leave a smooth finish.

What is reinforced screed?

Screed reinforcement is a recommendation for use in screed constructions. There are various options that can be adopted which consist of fibres or metal mesh. The general purpose is to restrain the drying stress generated from the cement in a screed system.

What is a floating screed?

Floating screeds are unbonded screeds but generally laid on a layer of insulation. They are mainly used in structures with underfloor heating or for situations where acoustic or thermal insulation is needed. It requires a thickness of 50 – 65mm, even up to 75mm for heavily-loaded floors.

What is pigmented screed?

Pigmented Screed floors is a 3mm cementitious screed which can be applied over existing floor or wall substrates and are mainly used for indoor purposes. Pigmented Screed Floors must be hand applied by a trained contractor.

What is the minimum thickness of sand and cement screed?

The optimum thickness of a sand and cement bonded screed is 25–40mm, an unbonded screed should have a minimum thickness of 50mm, whilst a floating screed should have a thickness greater than 65mm for lightly loaded floors and 75mm for more heavily loaded floors.

How deep can you go with screed?

Bonded Screed Maximum Depth

Modified sand and cement screeds can go up to whatever thickness you would like, however you would question doing so, if you are starting to get up to 150mm, 200mm. At those kind of depths, you would using void formers (insulation and then screed on top).

How do you prepare a floor for screeding?