Asbestos in fireplaces and stoves: gaskets, heat shields and flue joints

In a fireplace or stove, asbestos is most likely to be found in the gaskets of doors and glass panels, in heat shield boards behind and around the appliance, in the sealant where the flue pipe joins the chimney, and in mortars used for repairs. Ordinary bricks and stones are usually not the concern; the materials between and around them are. If a fireplace, masonry heater, stove or wood-burning cooking range was installed or repaired before 1994, it is worth having the parts you plan to remove analysed before you touch them, because asbestos cannot be identified by eye.

Sauna stoves and the walls behind them are covered separately in the article asbestos in the sauna.

Which parts of a fireplace can contain asbestos?

Asbestos was used because it withstands heat, so it turns up exactly where fire, hot flue gases or hot surfaces meet the rest of the structure.

Door and glass gaskets

The rope seals on the firebox door, the ash door and the soot doors, and the gaskets around a fireplace glass, are the most common asbestos suspects in a fireplace. An old seal is often a grey or white braided rope that has hardened or become brittle from the heat. Today's replacement ropes are asbestos-free but can look exactly like the old ones, so appearance settles nothing. Insulating tapes and braided seals in general are covered in the article asbestos in mineral wool and insulation.

Heat shield boards behind and around the fireplace

Boards were often fixed to the wall, and sometimes the floor, behind stoves, cooking ranges and fireplaces as fire protection. A hard grey board may be asbestos cement, which is described in the article asbestos cement boards. A light, softer insulating board that scratches easily is a more delicate material, because it can shed dust just from being handled. The board may be painted, tiled or hidden behind a metal sheet. Fire protection boards elsewhere in the building are covered in the article asbestos in fire protection.

Where the flue pipe joins the chimney

The flue pipe of a stove or cooking range enters the chimney through an opening in the masonry, and the joint has been sealed with rope, sealant or mortar. Old heat-resistant sealants and joint ropes may have contained asbestos. Ventilation flues and pipes were also made of asbestos cement, so a grey, cement-like pipe connected to the chimney should be tested as a separate sample.

Mortars and repair compounds

Over the decades, fireplaces have been patched, re-rendered and re-pointed. The heat-resistant mortars, renders and joint compounds used in these repairs can date from a different period than the original masonry, and they may have contained asbestos. Asbestos was sometimes added to indoor masonry and plaster mortars, so in a tiled stove it may be worth testing the joints and masonry mortar too. Mortars in general are covered in the article asbestos in mortar.

Inside the appliance

Older ovens, such as baking ovens and sauna ovens, used asbestos paper as fire protection, and it may sit inside the appliance or between its parts. It usually only comes to light when the appliance is opened, repaired or dismantled.

When should a fireplace be tested?

An intact gasket or board that nobody touches does not release fibres. With fireplaces, the risk usually comes with maintenance and repairs, when old material is pulled out, scraped off or broken. Test the material before the following jobs:

• replacing the rope seal on a door or around the glass, when the old rope is pulled out and the channel cleaned
• replacing a stove or cooking range and detaching the flue pipe from the chimney
• replacing a fireplace insert or dismantling a fireplace
• removing a heat shield board, drilling into it or fixing a new surface on top of it
• rebuilding part of a masonry heater or chimney, re-rendering it or repairing the joints of a tiled stove
• demolishing the whole fireplace or chimney as part of a larger renovation

Heat and years of use make gaskets and soft boards brittle. A crumbling gasket or a dusty board is a reason to be especially careful even before the actual work starts. Typical locations in older Finnish detached houses are covered in the article asbestos in a Finnish post-war house.

Where on the fireplace should the sample be taken?

• Take a separate sample of each different material: the gasket, the board and the sealant. That way you know which part has to be treated as asbestos-containing.
• If the fireplace has several doors and their gaskets look different or were replaced at different times, test them separately.
• Take the board sample from an edge or a corner so that the layers on top of the board, such as paint, mortar or tiles, come with it.
• Take the sealant or mortar sample from the spot you plan to remove or repair.

How to estimate the number of samples is explained in the article how many asbestos samples are needed.

How to take a sample from a fireplace

1. Make sure the fireplace has cooled down completely and there are no embers in the ash.
2. Wear disposable gloves and a respirator of at least class FFP3.
3. Lightly mist the sampling spot with a spray bottle to keep dust to a minimum.
4. Gasket: with a sharp knife, cut a piece of about 2–5 centimetres, for example from the bottom edge of the door or where the rope has already come loose. Do not pull the whole rope out of its channel.
5. Board: with a chisel or knife, remove a piece of about 2–5 centimetres from the edge of the board so that every layer through the board comes with it.
6. Sealant or mortar: with a chisel, remove a small piece from the joint or repaired spot through the full thickness of the layer.
7. Drop each piece into its own zip-lock bag, seal it and put it inside a second bag.
8. Mark the bag with the fireplace and the part, for example "living room, stove, firebox door gasket".
9. Cover the sampling spot with tape and wipe the area with a damp cloth.

If you took the sample from a door gasket, the door may no longer close tightly, so do not light the fire until the gasket has been replaced. If the board or gasket crumbles in your hands or gives off dust, do not take the sample yourself; leave it to a professional. General instructions on tools and packing are in the article how to take an asbestos sample.

What does the result of a fireplace sample mean?

Onelab analyses the sample with a JEOL SEM-EDS electron microscope in accordance with ISO 22262-1, and the result is sent by email, typically on the day the sample arrives. The result tells you whether asbestos was detected in the sample you sent.

• No asbestos detected: the result applies to the part you sent, for example the gasket of one door or the board behind the fireplace. The other parts of the fireplace are tested separately.
• Asbestos detected: that part is treated as asbestos-containing. Replacing the gasket, removing the board or dismantling the fireplace is planned as asbestos work, and the removal is carried out by a company authorised for asbestos removal work.

If the fireplace is part of a larger renovation or demolition that requires an on-site asbestos survey, the survey is carried out on site by a qualified surveyor. Onelab is a laboratory, and on-site surveys are handled by our sister brand AsbestiPro.

How much does the analysis of a fireplace sample cost?

The analysis costs €39.90 + VAT per sample, and the price is the same for 1–100 samples. Orders of more than 100 samples can be priced separately. Postage is not included. If you test the gasket, the board and the joint sealant of the same fireplace, that is three samples. You can order the analysis online and send the samples to the laboratory by post.