Vermiculite Floor and Roof Screeds

Floor Screeds Vermiculite concrete can be laid over a wide range of sub-bases to provide an insulated and resilient floor. Its lightweight properties are of particular importance when used over suspended floors or for infill to accommodate different levels. It may be used to advantage where fire resistance is important. Recommended Thickness For general applications a thickness of 80 - 150mm provides a satisfactory base, this may be reduced to 30mm for levelling purposes. Where the only requirement is to achieve minimum thermal insulation standards, thickness will vary with the shape, size and type of building. Based on a thermal conductivity of 0.12 W/mk, the table below shows the minimum thickness of screed necessary to achieve a U value of 0.45 W/m2k. Protective Topping As with some other lightweight concrete screeds, it is necessary to provide protection for the Vermiculite screed with a dense cement/sand topping. This distributes the floor loadings and prevents abrasion and other damage. There are two separate methods of applying this topping:

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1. Monolithically bonded topping
Immediately after the concrete is laid, a cement grout is brushed into the surface followed by a 15mm (max. 20mm) sand/cement topping. This system relies on the screed and topping bonding and drying together to provide mutual support. Great care must therefore be taken to ensure this bonding is achieved.

2. Unbonded topping
The vermiculite screed is allowed to harden. A 65mm sand/cement topping is applied over the dried vermiculite screed making no attempt to bond the layers.

Please note: Protective toppings with thicknesses of between approximately 25 and 55mm are likely to be unsatisfactory due to the difference in shrinkage of the materials.

Roof Screeds

Vermiculite concrete can be laid over a wide range of sub-bases to provide an insulated and resilient roof screed. It may be beneficial where fire resistance is important.

Suitable for concrete flat slab and low pitched roofs, and those constructed of hollow tile or pre-cast concrete beams. Vermiculite concrete is of particular value in the renovation of old roofs and to prevent ponding. The screeds should be protected by a suitable topping and for built-up felt or asphalt roofing.

Ventilation
Moisture entrapped in a roof is always a potential source of troubles, such as blistering, ceiling stains or mould. Appropriate ventilation should therefore always be provided to allow free water or moisture vapour to escape.

Recommended Thickness
Since the thermal insulation requirement of roof screeds varies considerably with its form of construction, it is only possible to give a general recommendation of minimum thickness of 100mm for new roofs, however each design should be calculated by using the Thermal conductivity for your chosen concrete. For renovation to existing roofs a minimum thickness of 20mm Vermiculite concrete should be used wherever possible, together with a suitable bonding material.

Topping
A sand/cement topping of 10 - 20mm should be provided to protect the Vermiculite concrete. This should be laid monolithically.

*Based on a standard 25kg bag of cement.

The above product information is given in good faith as accurate and reliable but is not to be taken as a guarantee. The figures provided are intended to be a guide to expected average values and should not be interpreted as a specification. Any potential applications referred to are not to be construed as recommendations. It is the responsibility of the user to determine suitability for any specific purpose.