Refractory Coatings

Selecting a Refractory Coating by Substrate and Process

A refractory coating is a thin mineral layer applied to an existing heat-resistant substrate. Its purpose may be to reduce surface wetting, resist alkali or slag attack, seal open texture, form a glazed face or limit direct exposure of the underlying refractory. It does not supply the structural thickness of a brick or castable lining, and its maximum temperature must never be treated as a rating for the complete furnace.

The products in this category use two distinct chemistries. Zircon-based coatings are intended for severe duty up to 1750°C, including selected contact with molten aluminium alloys, glass and metal slags. Silcas RGW is a silica-rich thixotropic glaze wash described for service up to 1000°C and develops its glazed surface during the first high-temperature firing. Product choice must reflect the process chemistry as well as temperature.

Product Comparison

Product	Supplied form	Service temperature	Compatible substrate or duty	Preparation and application	Published coverage
Zircon refractory coating	Ready-mixed beige liquid or creamy coating; 5kg	1750°C / 3180°F	Refractory brick, alumino-silicate monolithic lining and compatible ceramic-fibre blanket, board or module; selected molten-alloy, slag and glass duties	Stir thoroughly; apply directly by brush or thin with water as required for spraying, warm surfaces or porous fibre substrates	Product listing states approximately 3m² per litre
Zircon coating dry powder	Water-activated powder; 5kg	1750°C / 3180°F	Refractory bricks and alumina-silicate monolithic linings in aluminium, molten-glass, slag and ceramic-fibre applications	Mix with 300ml water per kilogram of powder; apply by brush or spray to a suitably prepared refractory surface	Approximately 3m² per kilogram
Silcas RGW refractory glaze wash	Ready-to-use off-white thixotropic paste; 5kg	1000°C / 1830°F	Refractory bricks, castables and other monolithic linings requiring a dense silica-rich glazed face	Stir and apply by brush, spray or trowel; brush application is identified for maximum bond strength	Approximately 5kg per m²

Ready-Mixed or Dry Zircon Coating?

The ready-mixed zircon coating reduces site preparation and can be brushed directly after thorough stirring. Water may be added when spray viscosity is required, when the refractory is warm or when a porous ceramic-fibre surface would otherwise draw liquid too quickly. Because no universal dilution ratio is published for this version, add only the amount required by the approved application method.

The dry version provides a controlled water-addition instruction of 300ml per kilogram. A mechanical paddle helps disperse the powder uniformly and avoid dry pockets. Prepare a batch sized for use within the working period stated on the current packaging or data sheet. Do not compensate for stiffening by repeatedly adding unapproved quantities of water.

Both zircon products carry the same 1750°C rating, so the choice is primarily about preparation, logistics, application control and project preference. Supplied form does not change the need to confirm substrate compatibility, molten-material chemistry or the required final film.

Zircon Coatings in Aluminium Processing

Zircon coatings are used as non-wetting barriers on suitable refractory surfaces in furnaces, ladles and transfer launders handling molten aluminium alloys. They can reduce adhesion and corundum build-up at the refractory interface, helping maintenance teams keep working surfaces cleaner and limit progressive penetration.

“Non-wetting” is not the same as permanent immunity. Alloy composition, magnesium content, flux, cleaning tools, melt temperature, dwell time and coating damage all influence performance. Trial the system under representative plant conditions and inspect high-wear areas regularly. A coating cannot make an unsuitable base refractory chemically compatible with every aluminium alloy.

Molten Glass and Slag Exposure

The zircon products are listed for refractory surfaces exposed to molten glass and metal slags. Their zirconium-silicate chemistry provides a barrier against selected alkali-rich and reactive environments. The underlying brick or monolithic lining must still be chosen for the glass composition, furnace zone and expected penetration.

Separate tank, throat, melt-line, splash, crown and superstructure conditions during specification. Temperature, movement and corrosion mechanism vary substantially between these areas. Carry out production trials where a coating could affect glass colour, seed, blistering, inclusions or another quality-critical parameter.

Silcas RGW Glaze Wash

Silcas RGW is a high-silica, thixotropic refractory coating. At rest it retains a paste-like consistency, but shear during brushing, spraying or trowelling allows it to flow across the substrate. This behaviour helps it cover brick, castable and gunned or other monolithic surfaces without immediately running from vertical areas.

During the prescribed first firing, the coating vitrifies and forms a denser glazed face. This can reduce open surface permeability and provide added resistance to gas penetration, abrasion and selected slag or chemical exposure. Do not treat it as compatible with all kiln atmospheres, ware, glaze vapours or kiln furniture without testing.

Suitable Substrates

• Dense refractory brick: confirm surface integrity, remove contaminants and provide sufficient key for adhesion.
• Refractory castable: complete curing and dry-out must precede coating unless the current system instructions explicitly state another sequence.
• Gunned and monolithic linings: remove rebound, loose grains and friable laitance before application.
• Alumino-silicate refractories: both zircon versions are specifically identified for compatible monolithic linings.
• Ceramic-fibre blanket, board or module: use the ready zircon product with controlled dilution and a thin, even layer so the soft substrate is not overloaded.
• Metal: the ready zircon coating expressly must not be applied directly to metal; these products are not replacements for heat-resistant metal paint.

Surface Preparation

Coating performance is governed by the surface beneath it. Remove dust, oil, grease, soot, release agent, salt deposits and all loose refractory. Scrape or wire-brush deteriorated areas and roughen glossy surfaces with suitable abrasive equipment where the substrate can tolerate it. Use dust extraction and personal protective equipment appropriate to the refractory being prepared.

Open cracks, holes and missing sections require a compatible refractory repair material before coating. Current zircon guidance identifies a thick zircon-based paste for local defects. Allow repairs to set and dry as specified. Do not bridge moving joints or unstable cracks with a thin coating, because movement will transfer through the film.

Application Thickness

The ready zircon product is generally applied at approximately 1mm. Current guidance for porous ceramic-fibre blanket gives a thin layer of about 1–2mm. Apply the film evenly without heavy ridges, pinholes, runs or uncoated recesses. Multiple controlled passes may be preferable to one overloaded coat where the substrate is highly absorbent or geometrically complex.

Excess thickness is not automatically more protective. A heavy coating may dry unevenly, crack, detach or place unnecessary weight on a soft fibre lining. Insufficient thickness can leave an open, discontinuous barrier. Use wet-film checks, measured consumption or a representative sample to control the applied quantity.

Brush, Spray or Trowel Application

Brushing works coating into surface texture and is suitable for local repairs, irregular linings and smaller areas. The Silcas RGW information identifies brush application where maximum bond strength is required. Use clean tools reserved for refractory materials to avoid oil or incompatible pigment contamination.

Spraying can provide faster, more uniform coverage over large areas but requires suitable equipment, nozzle size and viscosity. Screen mixed material where permitted and prevent overspray from reaching burners, thermocouples, anchors, joints and moving parts. Trowel application applies specifically to the thixotropic glaze wash and must still produce the specified uniform film.

Coverage and Quantity Estimation

Published coverage is a planning figure rather than a guarantee. Surface profile, porosity, wastage, overspray, dilution and required film thickness all affect consumption.

Product	Published rate	Theoretical quantity example	Estimation caution
Ready-mixed zircon coating	Approximately 3m² per litre	Required litres equal coated area divided by 3	The pack is sold by mass, so do not convert a 5kg container directly to litres without confirmed product density.
Dry zircon powder	Approximately 3m² per kilogram	A 5kg pack gives about 15m² theoretically	Add allowance for mixing residue, substrate texture, spraying loss and the approved thickness.
Silcas RGW	Approximately 5kg per m²	A 5kg pack gives about 1m² theoretically	Confirm the unusually high consumption against the current data sheet before pricing a large project.

Drying and First Firing

The ready zircon coating is instructed to dry for approximately 24 hours at around 20°C before temperature is raised gradually in stages. The full lining, local repairs and any fibre substrate must be sufficiently dry. Rapid heat applied to retained moisture can blister the film, generate steam pressure or spall the base refractory.

Silcas RGW lists a 24-hour curing period and requires heating to 1000°C during the first firing to initiate glaze formation. The heating rate must suit the complete refractory construction, not only the coating. Follow the current technical data and the equipment's dry-out programme, particularly where new castable lies beneath the surface.

Ceramic-Fibre Surface Treatment

The ready zircon coating can seal compatible ceramic-fibre blankets, boards and modules and reduce direct fibre release from the treated face. Slight dilution helps distribute a light film without excessive build-up. The fibre lining must be firmly installed and capable of carrying the dry coating during gas flow and thermal cycling.

A surface coating does not remove all fibre-related obligations. Cutting, repair, removal and damage can still release dust or fibres. Use the applicable safety data, exposure controls, respiratory protection, waste procedure and local regulations for the exact fibre product.

Industrial Applications

• Aluminium foundries and casthouses: furnaces, ladles and launders requiring a non-wetting zircon barrier and reduced corundum build-up.
• Glass manufacture: selected refractory zones exposed to molten glass, alkali vapours or chemically aggressive furnace conditions.
• Ceramics and pottery: tunnel kilns, shuttle kilns and fibre-lined chambers requiring surface sealing or a compatible glaze wash.
• Iron, steel and general metal processing: refractory faces exposed to slag, heat and process deposits.
• Cement and lime: selected rotary-kiln and high-temperature lining zones after abrasion and chemistry assessment.
• Boilers and combustion plant: brick or monolithic surfaces where the selected silica coating matches gas, ash and operating temperature.
• Petroleum and petrochemical processing: refractory-lined hot equipment requiring project-specific chemical verification.
• Pulp, paper and sugar processing: kiln and thermal-process linings where coating compatibility has been demonstrated.
• Marine thermal equipment: refractory-lined systems selected to the vessel's operating, vibration and certification requirements.

Coating, Repair Material or Insulation?

Requirement	Appropriate product type	Why
Chemical or non-wetting surface barrier	Compatible zircon or silica refractory coating	Changes the exposed surface chemistry without rebuilding the full lining.
Deep crack, missing refractory or eroded joint	Refractory repair compound, mortar, castable or replacement brick	A thin coating cannot restore section thickness or structural continuity.
Reduced casing temperature or heat loss	Engineered back-up insulation or a redesigned lining	Coating thickness is too small to replace bulk insulation.
Steel stove, flue or equipment exterior	Compatible heat-resistant metal paint	The refractory coatings in this category are formulated for mineral refractory substrates, not bare metal.

Energy and Service-Life Claims

A continuous coating can seal minor surface texture and help protect the lining from a specific attack mechanism. This may reduce maintenance or slow deterioration when the correct product is applied correctly. Results vary with process conditions, and a fixed service-life multiplier or energy saving should not be assumed for every installation.

Refractory coatings are not thermal-insulation layers. Any reduction in heat loss depends on sealing defects, maintaining surface integrity and the behaviour of the complete lining. Casing temperature and energy performance require a heat-flow assessment of brick, castable, fibre, back-up insulation, joints, anchors and shell.

Inspection and Maintenance

• Inspect the coated face for blistering, crazing, flaking, worn-through areas and loss around joints or penetrations.
• Record alloy, flux, slag or glass changes that coincide with accelerated coating failure.
• Remove loose coating and unsound refractory before recoating; do not bury deterioration under another layer.
• Repair the substrate with a compatible material and restore the specified dry-out procedure.
• Use maintenance samples or marked reference zones to compare coating wear over time.
• Keep containers sealed and store them in accordance with the label and safety data, protecting water-based products from unsuitable temperatures.

Important Limitations

• The 1750°C rating belongs to the zircon coating, not automatically to the coated brick, castable, fibre, anchors or furnace shell.
• The ready zircon product must not be applied directly to metal.
• Silcas RGW should be specified at 1000°C unless current technical documentation resolves the conflicting 1260°C attribute.
• Non-wetting performance is process-specific and must be confirmed for the actual alloy, glass, slag and flux.
• A coating cannot stabilise a loose, deeply cracked or structurally failed refractory lining.
• No product in this category should be assumed suitable for food-contact surfaces or domestic cooking chambers without explicit approval.
• Application onto hot equipment requires a safe method statement, ventilation, access control and compliance with the current product instructions.

Frequently Asked Questions

What is a refractory coating?

It is a thin mineral surface treatment for refractory bricks, castables, monolithic linings or compatible ceramic-fibre products. It can provide a glazed, chemically resistant or non-wetting face but does not replace the underlying refractory.

Which refractory coatings are available?

The range contains a ready-mixed zircon coating, a water-activated zircon powder and Silcas RGW silica glaze wash. The zircon products are rated to 1750°C, while the conservative listed limit for Silcas RGW is 1000°C.

Which product has the highest service-temperature rating?

The two zircon coatings have the highest listed service temperature at 1750°C / 3180°F. Every substrate and component behind the coating must be rated separately.

Why are two temperatures shown for Silcas RGW?

The main description and category state 1000°C, while a separate product attribute displays 1260°C. Use 1000°C unless the current technical data sheet and supplier confirmation approve another limit for the intended duty.

What is the difference between ready-mixed and dry zircon coating?

The ready version can be brushed after stirring and diluted as required for spraying or porous surfaces. The powder version is mixed with 300ml water per kilogram. Both are rated to 1750°C.

Can refractory coating be applied to metal?

The ready zircon product expressly must not be applied directly to metal. Use a coating formulated for the particular metal and temperature instead of a mineral refractory wash.

Can zircon coating be applied to fire bricks?

Yes, it is intended for suitable refractory bricks and alumino-silicate monolithic surfaces. The brick must be sound, clean, dry and compatible with the process chemistry.

Can the coatings be used on refractory castable?

Silcas RGW is listed for castables and monolithic linings, while zircon coatings suit compatible alumina-silicate monolithics. Complete the castable's prescribed cure and dry-out before coating unless the approved system procedure states otherwise.

Can zircon coating seal ceramic fibre?

The ready zircon version is identified for compatible fibre blanket, board and modules. Apply a slightly diluted, thin and even layer without overloading the soft surface, and retain all required fibre-handling controls.

Is zircon coating suitable for molten aluminium?

It is listed as a non-wetting barrier for suitable refractories in contact with molten aluminium alloys and can help reduce corundum formation. Confirm performance with the actual alloy, flux, temperature and cleaning practice.

Can the zircon products contact molten glass?

They are listed for selected molten-glass contact. Test compatibility where glass quality is critical and ensure that the base refractory is suitable for the furnace zone and glass composition.

What preparation does the refractory surface need?

Remove dust, grease, oil, soot, loose grains and unsound coating. Roughen glossy refractory where appropriate, repair cracks and holes with a compatible material, and ensure the surface meets the product's dryness and temperature requirements.

How thick should zircon coating be?

General ready-mixed application is approximately 1mm. Current guidance for ceramic-fibre blanket gives about 1–2mm. Avoid both discontinuous coverage and heavy build-up.

Can refractory coating be sprayed?

Yes, the zircon products and Silcas RGW can be sprayed with suitable equipment. Adjust only as permitted, control overspray and verify nozzle, viscosity and film thickness on a test area.

How much water is added to the dry zircon powder?

Add 300ml of water per kilogram of powder and mix thoroughly, preferably with a mechanical paddle. Maintain the stated ratio unless current technical instructions specify otherwise.

How much area does a pack cover?

The dry zircon powder is listed at approximately 3m²/kg, giving about 15m² from 5kg in theory. Silcas RGW is listed at about 5kg/m². Actual consumption depends on porosity, profile, application loss and film thickness.

How long must the coating dry?

The ready zircon and Silcas RGW information specifies approximately 24 hours under the stated conditions. Repairs and the underlying lining may require additional drying before commissioning.

How is Silcas RGW vitrified?

The coated refractory is heated to 1000°C during the prescribed first firing so that the silica-rich surface forms a glaze. The temperature rise must also comply with the dry-out limits of the underlying lining.

Does refractory coating provide insulation?

No. It is a thin surface layer and cannot replace insulating brick, fibre or another back-up insulation system. Any energy benefit depends on the condition and design of the complete refractory lining.

Can a coating repair large cracks or missing refractory?

No. Rebuild deep defects with a compatible repair compound, mortar, castable or replacement unit. Apply coating only after the substrate is stable and the repair has been cured and dried as required.

Is refractory coating suitable for a domestic stove exterior?

No. These coatings are intended for mineral refractory linings and the ready zircon product excludes direct metal application. Use a suitable heat-resistant metal paint for a stove body or flue exterior.

Can these coatings be used in a pizza oven?

Do not assume suitability for a cooking chamber or food-contact surface. Use only where the exact product has explicit approval for the intended location and cannot contaminate food, fuel or combustion gases.

How should a coated lining be commissioned?

Allow the coating and all repairs to dry, then increase temperature gradually according to the approved schedule for the complete lining. Avoid rapid heating that could trap moisture, blister the film or damage the refractory beneath it.