Materials used for Thermal insulation

List and explain in brief the materials used for Thermal insulation

1. Hollow bricks -

Walls made in hollow bricks are very good heat insulators. Hollow bricks could be of Burnt-Brick type or Concrete blocks. Air is a bad conductor of heat and these cavities retard the heat transfer through the wall. Porous bricks also have same properties.

2. Light weight concrete -

Concretes having density less than 1920 Kg / m³ are called Lightweight concretes. Normal concrete where crushed stone or Gravels are used have a density 2400 Kg / m^3. In lightweight concrete, instead of crushed Stones/Gravels, expanded blast furnace slag is used. This blast furnace slag has a very good compressive strength and the concrete works out to be adequately strong. Thus, the walls with this concrete are good thermal insulators.

3. Air entraining Concrete/ Mortar / Plaster

Air entraining Cement, if used in concrete, creates minute air bubble in the mixture and, these air cavities assist the insulation. The air entraining cement is made by adding organic agents like Vinsol resin or Darax to the Portland cement. Air entrained Mortars and Plasters are also used for mortaring and plastering the walls. The use of air entrained concrete in cold countries is a normal practice for thermal insulation.

4. Combination of light weight concrete & Air entrained Concrete –

For better results of heat insulation, a combination of these two concretes is also possible. However, the multiple loss of strength by using the two relatively weaker concretes has to be considered while designing RCC structure.

5. Cork –

Cork is made from the bark of cork-oak tree. The bark of tree is cleaned, sized, ground and then baked. While it is being baked, it oozes natural resin. This resin binds the powdered cork to form a slab/sheet when pressed or rolled. Cork is a very light material having Sp. gr. 0.25. It is porous and not affected by moisture. It is a good Sound insulator both for sound transfer and acoustic effects. It is an electric insulator and heat insulator for temperatures below 70^o C.

Cork sheets are available in market and can be used for panelling. These can be coated with melamine polish to reduce abrasion damages, but the acoustic control is marginally affected.

6. Eel grass tiles:

Eel grass is used for making ceiling or panelling tiles. These tiles are used for both Thermal and sound insulation. Eel grass is a marine plant containing silica and iodine. Silica imparts the property of non-inflammability & iodine makes it termite proof. The grass obviously is a fibrous structure.

These tiles are very light in weight. These are specially recommended for acoustic control and thermal insulation. These have poor abrasion resistance. Hence the use may be restricted to ceiling and panelling above 2.4 meter heights.

7. Quilt -

Quilt is normally referred to some padded material like cotton pad stitched in linen cloth for bed covering or body covering. This cotton quilt can be a good heat & sound insulators. However, it is not moisture & termite proof.

For heat and sound insulation, a material called ‘Cobalt Quilt’ is used. This is created by stitching treated ‘Eel’ grass between very tough craft papers or canvas sheets. Eel grass is a marine plant containing silica and iodine. Silica imparts the property of non-inflammability & iodine makes it termite proof. The grass obviously is a fibrous structure.

8. Rock wool -

Rock wool or mineral wool is produced from flint stone, a calcareous stone. The stone is melted in a furnace at 1700^o C. This molten stone while it is leaving the furnace is acted upon by a blast of steam. This blast of steam converts molten mass into beads while getting solidified. These beads, still in hot condition are pressed to convert these into boards or blankets.

Rock wool is soft, light & flexible but has some resilient properties. It is available in markets as boards, blankets or quilts. This is used for thermal insulation.

9. Glass wool or Fibre glass

It is made from molten silica glass by forcing the same through apertures under steam or air pressure. A thread like mass is obtained and is known as Fibreglass or Glass wool.

It is fibrous in structure and has a good tensile strength. It is durable. It is a good thermal insulator and is abundantly used for thermally insulated partitions and panelling. It is also a good sound insulator from sound transfer point of view.

These are available in market in blankets form, but the blankets are not firmly built. And the blankets get de-shaped to bulk if not handled properly. Also, if these blankets or the bulk is handled with bare hands, the skin will irritate. Hence, use of hand-gloves is a must while handling these.

10. Coir

Coir is a hairy substance grown on Palm trees either on the fruit or on the trunk or under the leaves. This fibrous part is cleaned and used. Coir does not perish or degenerate under normal circumstance or in moist conditions and lasts long. Coir is a good thermal and sound insulator. Coir curtains and coir mats are insulating materials used by people under low income group. Coir quilts were also used earlier for padding and cushioning sofa.

11. Woollen carpets

Woollen carpets are a very good alternative for treating floor for thermal and sound insulation. For acoustic effects, it is the best. Natural wool is best but synthetic wool also give satisfactory results. It is normally backed by the jute cloth and is laid with an under-layer of PU foam or coir foam or some other synthetic foam. The jute backing cloth and the under-layer, both increase the insulation effect. Cleaning of these carpets is a bit tedious and vacuum cleaner is a must. Removal of stains is more difficult and Petrol-dry-washing agencies need to be called.

Woollen carpets are available in the market with varying thicknesses ranging from 8mm to 25 mm. The under-layers are of thickness from 12 mm to 25mm. These carpets are available in roll form of about 1.5m or 1.8m. Both the under-layer and the carpet are laid on the floor with intermittent use of rubber adhesive. The edges of the roll need to be hand-stitched for necessary width adjustments.

12. PVC carpets.

PVC carpets are good thermal insulators. These are fairly good sound insulators from sound transfer point of view but, for acoustic effects do not play a significant role. These are good electrical insulators.

The thickness available is from 0.6mm to 3mm. 1.5 mm or 2mm thick PVC, is normally used for flooring. These are available either in tile form or in roll form. The tile sizes vary from 250mm x 250mm till 450mm x 450mm. The roles have widths varying from 1.2m to 1.8m. These are pasted to floor with rubber adhesive. These can be pasted on smooth surfaces and not on rough surfaces like that of ‘rough Shahabad’. These can be easily cleaned by wiping with wet cloth.

13. Wooden flooring.

Wooden flooring done in natural timber is a good thermal insulator and fairly good sound insulator. Wooden flooring done in artificial timber like laminated particle/fibre board; does have thermal insulation properties but their sound insulation properties have some limitations. Wooden flooring are normally used for thermal insulation purpose or for places like dance floor, badminton hall etc.

Wooden flooring has a longer life than PVC flooring but can catch fire. The artificial timber floor is easy to clean with a damp cloth. The natural timber floor, if polished, cannot be cleaned with a damp cloth.

14. Thermocole, Polyurethane foam, Polyurethane beads etc.

Thermocole is a type of plastic and has good thermal insulation properties. It is available in sheet form up to 50mm thickness. It can also be molded to any desired shape in Plastic molding machine. Thermocole is used for sealing gaps in refrigeration chambers or for storing chilled articles. Thermocole tiles are used in false ceiling either as face tiles or as backing tiles. Thermocole is very light and is not adequately strong. It gets abraded with slight friction. Hence for thermally insulated partitions, it is only a filling material and not a surface material. Thermocole has moderate sound insulation properties.

Like Thermocole, PU foam or PU beads are also very good thermal and sound insulators. But these are expensive and are used in expensive refrigeration machinery. In interior jobs, where large quantity is required, Thermocole finds a better alternative.

15. Asbestos Cement sheet [A. C. sheet]

Asbestos is a natural mineral available in fibrous form. It is composed of silicates of calcium and magnesium [CaSiO3. 3MgSiO3]. This is mixed in cement and AC products are made. These products include pipes, plain AC sheets, corrugated AC sheets etc. AC sheets are good thermal insulators, but these are brittle. However, these find use in ovens etc. Also corrugated AC sheet roofing in factories, godowns and terraces/balconies is a better alternative from preventing radiated heat.

More information about this is given in chapter on Plastics.

16. Porcelain.

This is a clay product. It is a very good Electrical and Thermal insulator. It can withstand high temperatures. It is used for making Fuse boxes, High tension line holders.

17. Jute.

This is a vegetable fibre and is produced from ‘Jute plant’. The colour of the fibre varies from white to dark brown. It is bio-degradable. It is extracted from the stem of the plant after soaking it in the running water. The running water loosens the fibre and drives away the non-fibrous vegetable matter. Jute has very low thermal conductivity, it is electric insulator and is a very good sound insulator. Jute carpets, Jute curtains, Jute packaging and covering hot water pipes with Jute threads are Insulation applications.