Plastering A Fireplace: All You Need To Know

Plastering a fireplace is a vital skill for homeowners who want to enhance the aesthetic appeal and functionality of their living spaces. Fireplaces, being central features in many homes, often face wear and tear over time.

A well-executed plastering job will not only restore the fireplace’s appearance but also improve its safety, durability and insulation.

This guide outlines each step involved in plastering a fireplace, from surface preparation to finishing touches, ensuring a professional outcome.

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Estimated reading time: 8 minutes

The Importance of Proper Fireplace Plastering

Properly plastering a fireplace, false chimney breast, or media wall with an installed wood-burning or gas fire is essential for both safety and aesthetics.

Plastering the right way ensures that the surface is heat-resistant and can withstand the high temperatures generated by the fire, preventing potential fire hazards.

It also helps create a smooth, durable finish that enhances the overall appearance of the space. Poor plastering could lead to cracks, peeling, or damage due to the heat, compromising the structural integrity and reducing the longevity of the installation.

Furthermore, professional plastering ensures compliance with building regulations, ensuring the installation is safe for use in a residential setting.

Different Types of Fireplace Plaster

There are a few types of plaster for fireplaces:

• Lime plaster: Great for older homes and natural aesthetics.
• Gypsum plaster: More common but not ideal for high-heat areas.
• Heat-resistant plaster: Designed specifically for areas exposed to heat.

Lime Plaster

NHL2 lime plaster is ideal for fireplaces because it is breathable, allowing moisture to evaporate and preventing dampness or damage to the structure.

It also has excellent heat resistance, making it durable in high-temperature environments.

Additionally, its natural composition is eco-friendly and compatible with traditional building materials, ensuring longevity and historical authenticity.

Gypsum Plaster

Gypsum plaster is not ideal for use around fireplaces where it may be exposed to high temperatures for several reasons:

1. Low heat resistance: Gypsum plaster has a relatively low thermal tolerance. When exposed to high temperatures, typically above 49°C (120°F), gypsum can begin to degrade, causing it to crack, crumble, or lose its structural integrity over time.
2. Moisture release: Gypsum contains water in its crystalline structure. When exposed to heat, it can lose this water (through a process called dehydration), which weakens the plaster and can cause it to break down, especially in high-heat areas like around fireplaces.
3. Risk of cracking: Repeated exposure to heat and cool cycles can cause expansion and contraction in the plaster, leading to cracks and weakening the surrounding surface. This makes the area prone to aesthetic damage and structural problems.
4. Flammability of additives: While gypsum itself is not flammable, some additives used in plastering materials (such as binding agents) might be more susceptible to heat, contributing to potential risks.

Because of these properties, materials specifically designed for high heat environments, like fire-resistant boards or cement-based plasters, are better choices for areas around fireplaces.

Heat-resistant Plaster

Heat-resistant plaster is an excellent choice for areas exposed to high temperatures, but it can be quite expensive.

Vitcas Heat Resistant Plaster

It’s ideal for surfaces around cassette fireplace openings, inset stoves, wood-burning stoves, and range cookers, where walls are subjected to intense heat.

Cracking From Heat Exposure

Cracking caused by heat from wood or gas fires can occur when materials such as brick, stone, or metal are exposed to high temperatures, leading to thermal expansion. When materials heat unevenly or rapidly, stress builds up, causing cracks to form.

This is especially common in fireplaces, media walls and chimneys, where the intense heat is concentrated in small areas. For example, bricks used in fireplaces may crack if they are not fire-rated, or if mortar deteriorates over time due to repeated exposure to heat.

Similarly, metal components like grates or fireplace doors may warp or crack if they are not made from heat-resistant materials. In the worst cases, such cracks can lead to structural instability, allowing gases or flames to escape and posing serious safety risks.

To prevent cracking, several steps can be taken. One key strategy is using heat-resistant materials specifically designed for high-temperature environments.

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Tools and Materials Required for Fireplace Plastering

Essential Tools:

• Plastering Trowel: Used for applying and smoothing plaster.
• Hawk: A flat board used to hold plaster.
• Mixing Bucket: For mixing the plaster.
• Angle Bead: Provides straight, clean edges.
• Plasterer’s Float: Smoothens the surface for a flawless finish.
• Plastering Sponge: For refining the finish and controlling moisture.
• Jointing Knife: Used for tight spots and precise work.

Necessary Materials:

• Bonding Coat: A base coat that adheres well to uneven surfaces.
• Finishing Plaster: For the final smooth layer.
• PVA (Polyvinyl Acetate): Used as a bonding agent between layers and on surfaces like brick.
• Corner Beads: To create strong, clean corners.
• Sandpaper: For smoothing the surface before applying finishing plaster.

What’s Recommended

For a heat-resistant plaster job, its recommended to use heat resistant rated board. Plaster using a sand, cement, and lime mixture as the backing coat. This combination creates a strong, durable base capable of withstanding high temperatures.

After applying the backing coat, use VITCAS Heat Resistant Plaster for the final finish. While it may be pricier, it’s worth the investment due to its superior performance in high-heat environments.

When working with VITCAS, make sure your application is precise because the plaster is very sticky and takes longer to dry than standard multi-finish plasters.

• Do NOT use plasterboard
• Do NOT use fire rated board
• Do NOT use any combustible materials (wood, paper, plastics etc.)

Once it sets, it becomes very hard and cannot be sanded, so ensure the surface is smooth and accurate while it’s still workable. Attention to detail during this stage will save you from any future issues with uneven finishes.

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Smoothing and Finishing

Use a plastering sponge or a lightly wetted trowel to achieve a perfectly smooth surface. Lightly mist the surface with water if necessary and run the trowel over the surface to polish the plaster.

For intricate areas or curves, take extra care to refine the finish, ensuring a professional result. Inspect the entire surface and remove any small imperfections while the plaster is still pliable.

Smoothing and rubbing down a chimney breast is much like working on a standard wall, but it requires a bit more care to avoid damaging the heat-resistant plaster.

Use fine-grit sandpaper and apply gentle pressure to ensure a smooth finish without compromising the surface.

Drying Time and Curing Process

Allow the plaster to dry naturally. This can take anywhere from 48 to 72 hours, depending on the room’s temperature and humidity. Avoid using any heating methods to accelerate the drying process, as this may cause cracks or uneven curing.

Once dry, the surface will appear pale and firm to the touch. At this point, you can paint the plaster, but it’s best to wait at least 7-10 days before applying any paint to allow full curing.

Maintenance and Troubleshooting

Common Issues:

• Cracks in the Plaster: If cracks appear, they are likely due to improper drying or uneven plaster thickness. Fill small cracks with a fine layer of finishing plaster and sand them smooth.
• Uneven Surface: Uneven surfaces can be corrected with light sanding using fine-grade sandpaper.
• Discoloration: If the plaster dries with discoloration, ensure that the bonding coat was applied correctly and evenly, or consider reapplying PVA to areas where bonding failed.
• Angle Beads moving: As metal expands and contracts, metal angle beads should be stapled to prevent this.

Fireplace Plastering Safety Tips

1. Wear Protective Gear: Always wear gloves, goggles, and a mask to protect yourself from dust and debris.
2. Ventilation: Ensure that the room is well-ventilated to prevent exposure to dust and fumes.
3. Fireplace Preparation: If the fireplace is still operational, ensure that it is turned off and cooled before starting any plastering work.

Conclusion

Plastering a fireplace requires patience, the right tools, and a methodical approach. By following the steps outlined in this guide, homeowners and professionals alike can achieve a durable and aesthetically pleasing finish.

Proper surface preparation, attention to detail, and choosing the right materials are key to ensuring that the plastering job lasts for many years without cracking or discoloration.

Bonfire cannot be held responsible for any issues or damages that arise from attempts to replicate these methods or techniques; all actions are undertaken at your own risk. It is essential to follow safety guidelines and professional advice to avoid potential hazards.