Open Fireplaces

Choosing Materials for an Open Fireplace

An open fireplace combines several materials exposed to very different thermal and mechanical conditions. Products used directly around the fire need to tolerate high temperatures and repeated heating cycles, while backing insulation, decorative finishes and chimney materials perform different supporting functions.

For construction or restoration, assess the firebox, fireback, hearth, fireplace opening, surround and flue separately. This makes it easier to select the correct refractory product for each part of the installation and avoids using one material for functions it was not designed to perform.

Open Fireplace Material Guide

Fire Bricks & Refractory Firebox Construction

The firebox is exposed to flame, hot embers and repeated thermal cycling. Refractory fire bricks are used where the fireplace design requires a durable heat-resistant lining or replacement refractory components.

Dense fireclay bricks provide both refractory resistance and thermal mass. When restoring an existing fireplace, match replacement materials to the original firebox geometry and construction wherever practical rather than selecting a brick solely because it has a high temperature rating.

Small damaged sections can also be repaired or reproduced using a mouldable refractory material such as VITCAS Mouldable Firebrick where the application and required shape are compatible.

Firebacks & Backing Insulation

A fireplace fireback forms the heat-resistant surface at the rear of the firebox. The VITCAS Heat Resistant Concrete Fireback is available in nominal 16-inch and 18-inch sizes for compatible open fireplace installations.

Where suitable spaces remain behind the fireback, VITCAS Vermiculite Insulating Cement can be used as lightweight, non-combustible backing insulation and non-structural infill. The fireback itself should be correctly supported by the fireplace construction rather than relying on insulating infill as a structural material.

A compatible Heat Resistant Fireback Lintel can form part of suitable fireback arrangements where its dimensions match the fireplace design.

Heat-Resistant Hearth Construction

The hearth is exposed to radiant heat, hot fuel and falling embers and therefore requires a suitable non-combustible, heat-resistant construction. VITCAS Heatproof Screed is rated to 1400°C and can be used for compatible fireplace screeding and refractory repair applications.

For an open-fire hearth, VITCAS specifies Heatproof Screed at a minimum thickness of 25mm. The screed forms the heat-resistant layer; the supporting hearth structure beneath it must still provide the necessary mechanical support for the completed installation.

Heatproof Mortar vs Fire Cement

Refractory mortar and fire cement are used for different types of joint. VITCAS Heatproof Mortar is a ready-mixed, air-setting refractory mortar rated up to 1400°C for setting compatible fire bricks, brick slips and other high-temperature materials.

VITCAS Black Fire Cement, rated up to 1250°C, is better suited to fine joints, small cracks and compatible sealing or patching work. It can also be used for suitable joints around firebacks and internal fireplace or flue components.

The two products should therefore be chosen according to joint size and function, not simply by comparing their maximum temperature ratings.

Fireplace Render for Recesses & Surrounding Masonry

Ordinary decorative finishes close to an open fire can be exposed to temperatures considerably higher than those found on normal internal walls. VITCAS Fireplace Render is a heat-resistant base-coat render for compatible brick, stone, concrete and masonry surfaces and is rated up to 1400°C.

For open fireplaces and log-basket installations, the VITCAS product instructions specify a 25mm render thickness. Where a smooth decorative finish is required, Fireplace Render can form the base coat for a compatible heat-resistant plaster system.

Heat-Resistant Tiles Around an Open Fireplace

Tiles can be used to create traditional or contemporary fireplace surrounds where the substrate and fixing system are appropriate to the expected temperature. VITCAS Heat Resistant Tile Adhesive and Heat Resistant Grout are rated up to 1000°C for compatible high-temperature tiling applications.

Tile selection should also account for thermal expansion, substrate stability and the position of the tiled surface relative to the fire. The temperature rating of the adhesive or grout does not by itself determine whether a particular tile or substrate is suitable.

Restoring Period & Cast Iron Fireplaces

Open fireplaces are found in Victorian, Edwardian, Georgian and later properties as well as modern interiors. Restoration may involve replacing damaged firebacks or fire bricks, repairing refractory joints, reinstating insulating backing and renewing heat-resistant finishes while retaining the original appearance of the fireplace.

For projects centred specifically on traditional cast-iron inserts and surrounds, see Victorian Cast Iron Fireplace materials. Material selection should respect both the historic construction and the thermal requirements of the fireplace when it is intended to return to service.

Chimneys, Flues & Fireplace Maintenance

The refractory construction around an open fire is only one part of the complete system. The chimney and flue must provide a suitable route for combustion gases and should be inspected and maintained according to the fuel, fireplace design and applicable local requirements.

VITCAS also supplies materials for flue and chimney installation and maintenance, including jointing, sealing, insulation and chimney-cleaning products. For ongoing repairs and cleaning, see Fireplace & Stove Maintenance.

Selecting Materials for an Open Fireplace

When planning a new fireplace or restoration, consider the function of each material within the complete construction:

• Direct flame and ember exposure: select refractory firebox and fireback materials designed for the thermal duty.
• Brick and refractory joints: match mortar or fire cement to the joint geometry and repair type.
• Hearth construction: provide both suitable structural support and a heat-resistant surface layer.
• Backing insulation: use compatible lightweight insulation where the fireplace design requires it.
• Recess and surround finishes: use heat-resistant render, plaster, adhesive and grout according to surface temperature and substrate.
• Chimney and flue: maintain a suitable combustion-gas route and follow the installation and maintenance requirements applicable to the fireplace.

Maximum temperature is only one selection factor. Substrate, joint thickness, mechanical support, thermal movement, exposure to direct flame and the position of the material within the fireplace are equally important.

Frequently Asked Questions

What material should be used for the hearth of an open fire?

VITCAS recommends Heatproof Screed at a minimum thickness of 25mm for compatible open-fire hearth applications. The screed provides the heat-resistant surface layer and should be installed over a stable supporting construction appropriate to the fireplace.

What is the difference between heatproof mortar and fire cement?

Heatproof Mortar is designed for setting compatible fire bricks and forming refractory masonry joints, while Fire Cement is better suited to fine joints, small cracks, patch repairs and selected sealing applications. Joint geometry and intended function should determine which material is used.

What should be used to fill the space behind a fireplace fireback?

Vermiculite Insulating Cement can be used as lightweight non-combustible backing insulation and non-structural infill behind compatible firebacks. The fireplace construction must still provide the required mechanical support for the fireback and surrounding masonry.

Can ordinary plaster or render be used inside a fireplace recess?

Surfaces close to an open fire can experience temperatures beyond those expected by conventional internal wall finishes. In heat-exposed fireplace recesses, use a purpose-designed system such as VITCAS Fireplace Render and a compatible heat-resistant finish according to the location and substrate.

Can a damaged fireplace brick be repaired instead of replaced?

Minor compatible damage may be repairable using refractory repair materials, while irregular missing sections can sometimes be formed using Mouldable Firebrick. Where a brick has significantly deteriorated or its integrity is important to the firebox construction, replacement with a suitable refractory brick may be the more appropriate solution.

Can tiles be fitted around an open fireplace?

Yes, where the fireplace construction and tile are suitable for the expected temperature. Use a heat-resistant tile adhesive and grout appropriate to the substrate and location, and account for thermal movement and heat exposure when designing the tiled surround.

Does the product with the highest temperature rating always make the best fireplace material?

No. Temperature capability must be considered together with material function, substrate, joint thickness, mechanical strength, thermal movement and exposure conditions. A fire cement, mortar, screed, firebrick and insulating material may have similar temperature capabilities but perform very different jobs within the fireplace.

What should be checked before using a newly built or restored open fireplace?

Confirm that refractory mortars, renders and screeds have been dried or cured according to their product instructions, and that the firebox, hearth, fireback and chimney system are in suitable condition. The flue, ventilation, clearances and fireplace installation should comply with the regulations and competent installation requirements applicable in the country of use before the fireplace is operated.