Refractory Mortars

Mortars are the cement or “dagha” used to lay bricks. In civil construction these joints are around 10 to 15mm thick. In refractory brick structures these joints are made as thin as possible, and average about 2mm thick. Refractory bricks are manufactured to every tight dimensional and geometric tolerance to enable thin joints to be used.

Refractory bricks are made in a wide variety of chemical compositions for different services environments. Each one requires a mortar of the same chemical composition.

Refractory mortars have a “grab time”. As the pores of the brick suck liquid out of the mortar, it stiffens and suddenly the bricks stick together. The grab time should be long enough to allow you to wiggle the bricks down to a joint no wider than 2mm. If this is not achieved, throw it away and buy a Keramicalia mortar. Mortars may be “air setting”, “heat setting” or chemically setting. Some are supplied wet, ready to use. All Keramicalia wet supplied mortars are literally ready to use, whereas most others require re-mixing, as they stiffen and settle out. Many products have a 3 month shelf life; ours have a 2 year shelf life.

Kerasil Mortar is our silica mortar with a long grab time. It is the only one which is practical for our pizza oven mouth arches. Our Chamotte Mortar also makes particularly tight joints compared to other chamotte mortars. Our Black Mortar was developed to replace Blakite. All three of these have long shelf lives, no settling out and remain READY TO USE with no re-mixing.

For wet ash sumps in power stations we supply Hydraulic Mortar which works submerged under water.

We do not manufacture a dry supplied aluminosilicate mortar, because these products need to soak in water overnight before use and still do not stick as well as Kerasil, Chamotte and Black mortar. If you want a mortar which seals but does not stick, use our fireclay, if you may want to dismantle the structure.

Graphite glue is used for carbon and graphite bricks. It can be used to repair clay-graphite crucibles used for melting zinc and aluminium.

We make a Chromag Mortar for chrome magnesia bricks. Very fine for tight joints.

Our High Temperature Fibre Glue is an 80% alumina heat setting mortar.

Our Spinel Mortar is a highly abrasion resistant mortar, supplied dry, which requires extremely intensive mixing in bakery mixer to a putty consistency.

Hardcast Fine Acid Resistant Mortar is used for acid resistant bricks. It is chemically setting. We have made some chemically setting mortars using Versimould technology.

Brickstick is unique as far as we know. It is used for lining rotary kilns. Traditionally rotary kilns are lined with a hydraulic jig which holds all the bricks in place until the ring is completed. With Brickstick, the bricks are forced into place and stay in place without support for more than a week.

We have made chrome alumina mortars such as Keramor 9, but these are getting to be unfashionable.

Our Core Glue and Shorten Glue can be used as ultrafine mortars.

We make some water free mortars for magnesite bricks.

Our silicon carbide mortar is called Kerasic mortar.

For alumina tiles we supply Water Based High Temperature Tile Grout

Out of this very wide range of technologies we can custom make a mortar for any particular requirements. List your requirements regarding particle size, shrinkage, strength, stickiness, chemistry, solubility, chemical resistance, temperature, colour grab, time, permeability etc. 


Description: A refractory material for resistance to chlorides.
It has low permeability and actively scavenges chlorine to form sodium chloride.

Applications: Incinerators burning PVC. Vessels in which metal chlorides are reacted. Protection from chlorine or HCl vapours.

Add +17% Hardcast Binder to Chloresist powder and vibration cast, or
Add +30% Hardcast Binder to Chloresist powder and pour it.
Use gloves, the material is highly alkaline.

Wet vibrated density: 2.3g/cm³
Wet poured density: 2.1g/cm³

Packaging: 22kg polythene bags of powder plus 6.5kg polythene bottles of Hardcast binder.

Hardcast Fine Acid Resistant Mortar

Hardcast is a product range based on a complex silicate bonding system. It is totally inorganic, quick setting, strong, acid resistant and refractory. Hardcast is also made in plaster and casting grades. Hardcast is also available as a lightweight insulation material. The lightest is the injectable insulation, with a density of 0,3g/cm³. Normally the density is around 2.2 to 2.4g/cm³.

Hardcast sets within 2 hours, and is fully serviceable within 24 hours. It can be applied to any structurally sound surfaces. Damp floors or dirty floors should first be painted with Hardcast binder. Hardcast is fully resistant to Sulphuric acid, Hydrochloric acid, Nitric acid, Phosphoric acid and organic acids. It is not resistant to Hydrofluoric acid or alkalis.

Hardcast fine is supplied in two parts; 20Kg bags of bright white powder and 33.3Kg drums of the liquid Hardcast Binder. Add +50% binder to the powder. (Two parts powder to one part binder by weight) Shelf life is virtually indefinite in unpunctured bags.

Hardcast fine has a thick viscous consistency, and is very easy to work with. It should preferably be placed within 20 minutes of mixing, and should not be left exposed for more than 10 minutes, as it forms a thin air-set skin which will not bond. The surface texture is very smooth. It is not suitable as a traffic surface. It can be made non-slip by sprinkling clean sand onto the fresh surface immediately after trowelling.

Hardcast fine can easily be coloured. The natural colour is light beige. Other colours which have been made are; concrete colour, red, blue, white, green, black. Most other colours can be made at a slightly increased cost. Grindings from cutting of acid brick may be added to Hardcast fine and smeared over the joints to make the joints less visible when used with red acid brick.

Hardcast fine costs R77/kg. Installed cost is therefore around R120 per square metre at a thickness of 5mm. Ordering; If one ton is ordered, you will receive 10 x 33.3Kg drums of liquid binder and 33 x 20Kg bags of powder.

Applications: Mostly used as a mortar for acid resistant brick and tiles. It has very good adhesion, and less chance of failing at the contact surface. However, a continuous backing layer must always be trowelled on first as a backup seal.

Moulding: Hardcast fine takes up very fine detail. After about an hour, it can be stripped from a mould, at which point it has formed a thin liquid layer which acts as a mould release against impervious surfaces. Hardcast will not bond to plastic at all. It bonds well to glass.

When used as a surface finish, The air set skin may shrink and tear, especially in dry weather. To prevent this, cover with plastic immediately after the skin has formed. Otherwise paint the skin with oil. This skin is not chemically set, and is water soluble. It is however only a fraction of a millimetre thick.

All Hardcast products set very rapidly on a hot surface.

Hardcast is not porous, and will not absorb liquids.

Hydraulic Mortar

Description: A hydraulic setting mortar, ideal for use under water, such as in ash hoppers.
Also used as a pumping material.

Maximum service temperature:

Physical properties:

At +30% water At +40% water
Air dried 10.3MPa 1.44gcm³
400°C 4.8MPa 1.35g/cm³ 1.5MPa 1.35g/cm³
1000°C 4.6MPa 1.45g/cm³ 1.4MPa 1.43g/cm³
1200°C 3.6MPa 1.36g/cm³


Chemical analysis:

Al O 47% 40%
Fe O 1.5% 4.4%
SiO 30% 43%
TiO 0.8% 2%
CaO 15% 9.2%
MgO 1.7% 0.7%
Na O 0.6% 0.2%
K O 0.5% 0.3%
P O 1%
L.O.I 1.5%


Mortar: Mix with +30% water and trowel on.
Pumping: Mix with +40% water and pump it.

Keramor 9

Keramor 9 is a chrome-alumina mortar with particularly high strength and adhesion, and virtually no shrinkage. Keramor 9 is a relatively coarse mortar, with a maximum particle size of 0,4mm. The water content is only 10%. The shrinkage is very close to zero, and it actually expands at 1500ºC. Consequently it allows no slag penetration. Keramor 9 is heat-setting and develops very high strength.

Particle size distribution:

+425µm 0%
-425æm +210µm 35%
-210æm +106µm 25%
-106æm +45µm 11%
-0.045µm 29%


Chemical analysis:

Al2O3 80.0%
SiO2 4%
Fe2 O3 0.5%
Cr2O3 10.0%
TiO2 0.2%
MgO 0.5%
CaO 1.0%
K2O 1.0%
Na2O 0.2%

Applications: Areas of high erosion Areas of aggressive slag attack Areas where high strength and adhesion are required.

Kerasic Mortar

Description: Kerasic mortar is alumina bonded silicon carbide. The main problem with silicon carbide is that it oxidizes to silica. The alumina bond reacts with the silica to form a mineral called mullite, which has a needle like structure and imparts high strength, and has a melting point of 1850øC. Kerasic mortar is not as electrically conductive as silicon carbide brick.

Kerasic mortar is a fine grained material (maximum particle size 600æm )

Chemical analysis:

Al2 O3 34%
SiO2 2%
SiC 58%
CaO 6%

Water addition: Use +10 to +16% for putty consistency through plaster to butter consistency.

Packaging: 25kg plastic bags.

Kerasic glue is also available for delicate repair of kerasic castings.

Kerasil Mortar

Kerasil mortar is supplied wet in buckets, 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.

Kerasil mortar can be smeared, trowelled or buttered, and has particularly good penetration and adhesion. 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 mortar 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 20kg plastic buckets with liners. Some liquid may be found separated on the top. Mix it back into the paste. Keep the lid closed when not in use. Wash hands well after use and apply a moisturising cream.

Caution: Spillage on the bucket dries very hard and may develop sharp edges which can cut your hands.

Shelf life: About 4 years in sealed buckets.

Pilot plant code: PHJ

Shorten Glue

An adhesive or sealant with extreme penetration properties. It was developed for anchoring wires in 2mm diameter ceramic tubes. It will penetrate a 1mm hole to a depth of at least 100mm. Can be used as a mortar for ultra thin joints.

Chemistry: Alkaline aluminosilicate.

Maximum particle size: 0.3mm

Consistency: Soft paste with a low yield value but no flow without pressure. Similar to soft toothpaste.

Colour: Grey.

Set: Air setting, very hard.

Strength: Will break brick before breaking bond.

Packaging: Mastic tubes, 540grams, like hardware store silicone sealer. Boxes of 15 tubes.

Shelf life: About 8 months.

Development no. 16929.

Water Based High Temperature Tile Grout

Description: A high density plastic alumina refractory. It has high strength and abrasion resistance and good adhesion generally.

Applications: Mainly used to glue alumina tiles into pipes which are to be used at high temperatures. The maximum service temperature is 1700°C.

Installation: Supplied as powder, to which +12 to+13% water must be added for a stiff putty consistency, or more water for a softer embedding consistency. Typically you place far too much in a corner between tiles, then push and wiggle the next tile into place as tightly as you can, pushing out a large amount of excess material. Scrape the excess material into the corner for the next tile. It sets in around 2 to 3 hours.

Chemical Analysis:

Al2 O3 89.0%
Fe2 O3 0.1%
SiO2 2.0%
CaO 9.0%
Na2 O 0.3%
P2O5 0,07%


Colour: White

Maximum particle size: 1mm

Packaging: 25kg plastic bags

Project no. 1396

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