Insulating Concrete Roof and Floor Screeds using Vermiculite

Lightweight concretes and screed made with exfoliated vermiculite ultra-lightweight aggregate can be used to reduce loss of heat through floors. Typically ground floors are constructed with dense concrete covered with dense screed; second storey floors over garages and car parks are also usually built with dense concrete and screed giving little thermal insulation. A screed containing vermiculite can reduce thermal conductivity from 1.04 to 0.9 w/m ^oC.

Benefits

Standard concretes and screed have densities between 2000 and 2200 kg/m³. The density of vermiculite concretes and screed is from 400 to 900 kg/m³ which improves the thermal efficiency and also reduces the weight of the final structure. It should be noted, however, that lightweight concretes and screeds are susceptible to wear and should therefore be protected with an adequate toppping to prevent indentation and dusting.

Applications

Vermiculite concrete and screeds are ideal for:

Roofs decks over metal profile decking.
Over dense concrete roof and floor slabs.
Sandwich construction.
Swimming pool bases.
Pig pens and farrowing pens.
Any other installation that required lightweight concrete with a compressive strength not exceeding 8 n/mm² for concrete and 13 n/mm² for screed.

Performance

Typical properties of lightweight concretes and screeds:

Mix volume proportions (cement:vermiculite)

1:4

1:6

1:8

Bulk density as placed (kg/m³)

900

750

650

Air-dried density of set screed/concrete

570

480

400

Thermal conductivity (air-dried)

w/m ^oC or w/mk 10^oC mean

0.16

0.12

0.09

28 day compression strength (n/mm²)

1.23

0.95

0.70

Note: if mixing dry, do not mix longer than 1 minute dry and 1 minute wet.

Fire Protection

All concretes and screeds are non-combustible as defined in BS 475 Part 4 1970 and designed in Class 0 in accordance with the requirements of the Building Regulations.

Materials Required

Exfoliated vermiculite grades V2, V3 and V4 are suitable for screeds and concrete mixes. All grades are supplied in heavy duty economy plastic sacks holding nominally 100L (3.5 ft³) and weighing 7 to 9 kg depending on the grade or 1.25 m³ bulk bags weighing 88 – 113 kg.

Cement should be ordinary Portland and conform with BS EN 197 part 1. In cold weather, or when a quicker than normal set is required rapid hardening Portland cement may be used.

An air-entraining admixture, conforming with the requirement of BS EN 934 part 2 is advisable.

Site Mixing

It is essential that the exfoliated vermiculite, cement and air-entraining admixture are accurately proportioned and the mixing time carefully controlled. The strength figures given in this data sheet are those obtained when the screed is tested by the methods of BS EN 1015 PART 11. In practice dry strengths are likely to be higher.

A free-fall drum-type concrete mixer is satisfactory for mixing. First add most of the required water to the mixer, then the air-entraining admixture followed by the cement. Mix until a slurry is formed, then add the vermiculite. The mixing time after the addition of the vermiculite should be as short as possible. Additional water can be added to obtain the required consistency.

Site Placing

The concrete or screed should be laid, levelled and then covered with a polythene membrane and allowed to cure for at least 18 hours. Power compaction should not be used. The surface will require topping with either a traditional cement and sand screed or mastic asphalt or proprietary brands of resinous screed. On external flat roof decks, it is advisable to make provision for breather vents especially where the topping is built up felt or mastic asphalt.

Specification

It is recommended that the placing of the concrete mix and topping or screed should be the responsibility of one trade only and the specification should read:

"For concrete (or screed) Grade.....to be mixed by volume with Ordinary Portland Cement plus air-entraining Admixture to a.....consistency and placed to a thickness of.....mm depth. After setting and curing for.....days it shall be topped with.....to a thickness of.....mm."

Prices and Conditions of Sale

Prices will be quoted on request of a volumetric basis, ex works plus haulage. All quotations given, orders placed and materials supplied are suject to our Standard Conditions of Trading, a copy of which is available on request.

Supply

Exfoliated vermiculite can be collected from our Gainsborough works or delivered direct to site anywhere within the United Kingdom.

Rev: Jan 2008