Vermiculite or chamotte — and the cracks that are allowed

Firebricks, and which cracks actually matter

The lining of a firebox does two jobs: it protects the steel or cast body, and it holds heat in the fire so combustion stays hot enough to burn the gases. Two materials do it. Vermiculite board is light, insulates far better, is cut with an ordinary saw, and is soft enough to be gouged by a carelessly loaded log. Chamotte — fired clay firebrick — is heavy, hard, stores heat rather than reflecting it, and is what older and heavier stoves use. Neither is superior; they belong to different appliances, and fitting the wrong one changes how the stove burns. The figures are the thickness, which is fixed by the firebox and is usually 20, 25 or 30 mm, the dimensions of the plate or brick, and for vermiculite the density in kilograms per cubic metre, which is the number that predicts how long it survives. Then the practical question that decides the purchase: whether the product is a named-model replacement or a plate to be cut. A cut-to-fit board is the answer for any stove whose maker has stopped supplying parts, and the pages here say which listings offer it. Finally, the thing owners worry about most: a hairline crack in a lining that stays in place is normal and is not a failure — a piece that has moved or fallen is. We compare dimensions, thickness, material, density, quantity, temperature, working and stated uses.

These parts, set out figure by figure

1. 

   FIREFIX Moulded Fireclay Brick, 250 × 124 mm

   The only actual firebrick on this shelf — pressed fireclay, 20 mm thick, rated to 1,300 °C, in a family otherwise made of vermiculite board.

   Dimensions

   250 × 124 mm

   Thickness

   20 mm — the thinnest section in this family

   Material

   Fireclay (Schamotte), moulded under pressure — the only one in this family

   Density

   Not published

   Quantity

   One brick · Not published

   Temperature

   1,300 °C, stated

   Working

   Not stated — fireclay is cut with masonry tools, not wood tools

   Stated uses

   The maker does not state it.

   Amazon reference

   B01N7U8FXG (one reference across 6 Amazon marketplaces)

   EAN

   4017537851452

   • The material the family is named after, sold as itself rather than as a substitute
   • Fireclay stores heat and gives it back, which is what the lining of a masonry-style firebox is for
   • A single brick: a firebox lining takes several, and the listing sells one

   Best for: Replacing a cracked fireclay brick like for like, in a stove that was built around fireclay

   Check price on Amazon
2. 

   Feuerfest 123 GmbH Vermiculite Board, 300 × 200 × 25 mm

   A single vermiculite board with its weight published, sold openly as a fireclay replacement and rated at 1,150 °C.

   Dimensions

   300 × 200 × 25 mm

   Thickness

   The maker does not state it.

   Material

   Expanded vermiculite with inorganic binders, stated · A replacement for fireclay, said to allow higher firebox temperatures and reduced emissions · Stated that the shade may differ from the photograph

   Density

   The maker does not state it.

   Quantity

   Approximately 1.40 kg — the only weight published in this family · One board

   Temperature

   Stated to withstand up to 1,150 °C

   Working

   Stated rigid and stable, with electrical resistance and low thermal conductivity

   Stated uses

   The maker does not state it.

   Amazon reference

   B0CGVGQVKK (one reference across 5 Amazon marketplaces)

   EAN

   4262443450545

   • Publishes a weight, which is the figure that says how dense a board actually is
   • Names the binder system — inorganic — rather than leaving the board unspecified
   • Rates the same generic material at 1,150 °C where two listings here state 1,300 °C

   Best for: Replacing one cracked lining panel, in a stove already running vermiculite rather than fireclay

   Check price on Amazon
3. 

   H&M Germany SF600 Vermiculite Board, 2 × 500 × 300 mm

   Two large boards with a published minimum density — and the one listing on this shelf that says what vermiculite is really for: stoves with no spares left.

   Dimensions

   500 × 300 × 25 mm, two boards

   Thickness

   The maker does not state it.

   Material

   Vermiculite, grade SF600 · The SF600 designation is not explained on the listing

   Density

   At least 600 kg/m³, stated

   Quantity

   The maker does not state it.

   Temperature

   Temperature-resistant to 1,100 °C

   Working

   Stated easy to adapt with a jigsaw, circular saw or handsaw · Fireproof and heat-insulating, stated

   Stated uses

   Ideal as a fireclay replacement, and perfect for stoves for which no spare parts can be had any more

   Amazon reference

   B088FX6G79 (one reference across 1 Amazon marketplace)

   EAN

   4893243154342

   • The only listing in this family to say why somebody actually buys a vermiculite board: no spares exist for the stove
   • Publishes a minimum density, which is what decides whether a board survives a log rolling into it
   • Rates the material at 1,100 °C — the lowest figure published on this shelf

   Best for: An older stove whose original bricks are no longer made, relined from sheet material and cut to fit

   Check price on Amazon
4. 

   SENDEO Vermiculite Boards, 2 × 400 × 300 × 30 mm

   Two thirty-millimetre vermiculite boards rated to 1,300 °C, from a range offered in three thicknesses and two sizes — and no density figure.

   Dimensions

   400 × 300 × 30 mm, two boards · Offered in 25, 30 and 40 mm, in 400 × 300 and 500 × 300 mm

   Thickness

   The maker does not state it.

   Material

   Vermiculite, stated made from 100 % natural raw materials and fully recyclable

   Density

   Not published

   Quantity

   The maker does not state it.

   Temperature

   Stated heat-resistant up to 1,300 °C

   Working

   High rigidity, low thermal conductivity and high temperature resistance, stated · Higher firebox temperatures and reduced emissions against fireclay

   Stated uses

   Replacing fireclay panels, firebox linings, stoves and chimneys

   Amazon reference

   B0F9YB3727 (one reference across 6 Amazon marketplaces)

   EAN

   4255593628292

   • Three thicknesses on one range, so the replacement can match what came out rather than approximate it
   • Forty millimetres available, which is thicker than anything else published in this family
   • No density and no conductivity figure, where two listings on this shelf publish one

   Best for: Matching an existing lining thickness exactly, from a range that actually offers a choice

   Check price on Amazon
5. 

   raik Vermiculite Board, 400 × 600 × 30 mm

   A single large board at 400 by 600, thirty millimetres thick, published with a model code and nothing else at all.

   Dimensions

   400 × 600 mm — the largest single board in this family · V2-30

   Thickness

   30 mm

   Material

   Vermiculite, from the title

   Density

   Not published

   Quantity

   One board

   Temperature

   Not published

   Working

   The maker does not state it.

   Stated uses

   None — the listing carries no feature text at all

   Amazon reference

   B0721BF4J9 (one reference across 2 Amazon marketplaces)

   EAN

   4260518545219

   • The largest single sheet in this family, which is what a whole lining gets cut from
   • Thirty millimetres, matching the thickness most vermiculite linings on this shelf use
   • No published features whatever: no temperature, no density, no cutting note, no material description

   Best for: Cutting a complete small stove lining from one sheet, by somebody who already knows what board they want

   Check price on Amazon
6. 

   baustoffe-walter Vermiculite Boards, 4 × 500 × 300 × 30 mm

   Four boards with a fire classification published — and a seller that names its own better product for the hardest part of the job.

   Dimensions

   500 × 300 × 30 mm, four boards

   Thickness

   The maker does not state it.

   Material

   Vermiculite · Non-combustible to DIN EN 13501-1 A1, stated — the only classification in this family

   Density

   Not published

   Quantity

   Four boards — enough to line a chamber

   Temperature

   Up to 1,300 °C, from the title

   Working

   Stated to saw, drill, rout and sand with woodworking tools without difficulty

   Stated uses

   Recommends its Premium board instead for thermally highly stressed parts such as baffle plates

   Amazon reference

   B078YCBS6P (one reference across 3 Amazon marketplaces)

   EAN

   0791266091887

   • Names a fire classification standard, which no other listing in this family does
   • Tells buyers to choose a different, better board for baffle plates — against its own immediate interest
   • No density, no weight and no thermal conductivity figure

   Best for: Re-lining a whole firebox from sheet, with the baffle bought separately as the seller advises

   Check price on Amazon
7. 

   KS24 Vermiculite Boards, 5 × 400 × 600 × 30 mm

   Five large sheets with the fullest figures on this shelf — density, conductivity and melting point — and a temperature line that prints 110 °C.

   Dimensions

   400 × 600 × 30 mm, five boards

   Thickness

   The maker does not state it.

   Material

   Vermiculite · 0.06 to 0.07 W/mK — the only conductivity figure published here

   Density

   650 kg/m³ — the highest stated density in this family

   Quantity

   The maker does not state it.

   Temperature

   Stated high, at 1,315 °C

   Working

   Stated to be worked with wood tools without problems

   Stated uses

   Stoves, tiled stoves, open fireplaces, embers and blast furnaces — with the listing printing "bis 110°C" · Fire protection board, stove lining, and flue baffles

   Amazon reference

   DE B08B4325G3 · FR B08B3ZTYYR

   EAN

   4260286124753

   • Publishes density, thermal conductivity and a melting point — the fullest figures in this family
   • Five sheets of 400 × 600, the largest quantity of stock on this shelf
   • Prints a service temperature of 110 °C where the context calls for a figure ten times larger, and the listing does not correct itself

   Best for: Re-lining more than one appliance, or cutting several oddly shaped panels with material to spare

   Check price on Amazon