Mastics are soft plastic materials, often supplied in tubes, which can be injected into cracks and cavities, or used for sealing purposes.

Fibre Mastic are thinned down, plasticized Fibre Plaster. They are used for sealing cracks in brickwork, gaps between fibre modules and repairing furnace door seals.

Zirconia Mastic is a non-sintering compound for temporary seals at high temperature. The main application is in sliding gates for tapping of molten steel.

Kerasil Mastic is a strong adhesive used for sealing leaking flanges etc.

Fibre Mastic

Description: Alumina enriched ceramic fibre in extrudable plastic form, supplied wet, ready to use, in mastic tubes. Very easily applied to any surface or crack.

Applications: High temperature insulation plugging of furnace holes, heat shields, burner cores, thermal shock protection, Furnace hoods, preheater lids, ladle lids, seating surfaces high gas flow areas of fibre lined furnaces, repair of cracks and joints protection of equipment, repair of shrinkage in fibre linings. Upgrading of linings for thermal efficiency or faster cycle times. Repair of broken element holding lips. Sealing of kiln and furnace doors

Properties: Very low thermal conductivity, Electrically insulating, Very low density; 1.2g/cm³ wet, 0.6g/cm³ fired. Resistant to high gas velocities. Low shrinkage; normally 12% but all taken up in the thickness of the layer, therefore no cracks. Extreme thermal shock resistance. Very low thermal mass. High reflectivity. Low permeability compared to fibre blanket or modules. Rapid commissioning. Excellent adhesion to all surfaces. Minimal anchoring required. High strength.

Installation: Fibre Mastic is supplied wet in 300ml plastic mastic tubes. It can be taken out and remixed or thinned down with water, or it can be ordered softer for injection. Cut the nipple off the tube, screw on the nozzle place it in a mastic gun. (±35  in hardware store) Cut the nozzle to give the desired flow diameter.

Onto brick: Blow dust off and squeeze on.

Insulating firebrick or very porous surfaces:   Rub a thin layer on very firmly before building up the profile.

Ceramic fibre: Over fresh fibre, softening by water dilution may help. You can order mastic in 10kg buckets.

Door seals: Plaster a narrow strip onto one surface, cover with fibre paper and close the door to press the Fibre Mastic into the exact thickness required.

Chemical composition:

Al2 O3 24.0%
Fe2 O3 0.07%
SiO2 31.0%
TiO 0.12%
CaO 0.05%
Alkalis 0.27%
Volatiles 44.5%

Development no. 27019

Claimer: The above information had better be correct because Dave Onderstall stakes his reputation on it.

Kerasil Mastic

Kerasil mastic is supplied wet in mastic tubes, ready to use. It has a soft consistency and is almost fluid. It coats very well and easily to all surfaces, and sets very hard and strong. It sets rigid and permanent, and should therefore be used with discretion in moving structures. It can be injected deep into cracks and joints, without being sucked dry by the surrounding material.

As a brick mortar the soft consistency allows thin joints to be made. As a fibre module cement it gives a considerably larger contact area than normal mortars. Exposed surfaces normally become smooth and exhibit no cracking. A thin dry film develops rapidly on the exposed surface, so bonding should be performed quickly.

Kerasil mastic is 90% pure silica and can be used up to 1300°C. It is light brown when wet, and becomes almost white when fired.

Packaging is in mastic tubes, with a nozzle. The nozzle must be removed and the tip cut off. Then the tube is placed in a hardware store gun (as used for silicone sealants) and the nozzle replaced. Cut the nozzle for the appropriate size to insert in the crack or flange, and squirt it in.

Wash hands well after contact and apply a moisturising cream.

Setting is slow at ambient temperature and rapid at high temperature.