About Calcined Insulation Grade Diatomaceous Earth
Insulation grade diatomaceous earth is calcined diatomite intended for thermal resistance. Calcination in a kiln removes combined water and organic matter, stabilises the porous silica structure and gives the material dimensional stability when it is later fired or heated in service. The countless fine pores trap still air, which is what gives diatomite its low thermal conductivity and makes it far lighter than dense refractory fillers.
Manufacturers of insulating firebricks, calcium silicate boards, lightweight castables and insulating mortars use this grade to cut product density and heat flow. It is also used as loose-fill insulation in furnace walls and as a backup layer behind dense refractory linings in kilns, ovens and boilers. Because the material is already calcined, shrinkage during the customer's own firing is lower than with raw diatomite.
The white to pinkish calcined powder also finds use as a flatting extender in matt paints and coatings, where its porous particles scatter light and reduce gloss. Obsidian Minerals calcines and mills this grade in Gujarat, controls particle size and bulk density batch by batch, and supplies it with a Technical Data Sheet, SDS and Certificate of Analysis. As calcination can form crystalline silica, the SDS states the relevant content and handling controls.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| SiO₂ | 85–92 % | XRF |
| Loss on ignition (1000 °C) | ≤ 0.5 % | Internal method |
| Moisture | ≤ 0.5 % | Loss on drying, 105 °C |
| Loose bulk density | 0.25–0.45 g/cm³ | Internal method |
| pH (10 % slurry) | 7.0–10.0 | Internal method |
| Residue on 75 µm | ≤ 10 % | Wet sieve |
| Appearance | White to pink-buff powder | Visual |
Typical values for guidance. Maximum service temperature depends on the final formulation and is confirmed on request. Guaranteed limits are stated on the Technical Data Sheet and batch CoA.
Key features & benefits
Air-filled porous structure
Calcined diatomaceous earth keeps a high volume of fine pores that trap still air. This lowers thermal conductivity and density in bricks, boards and castables made with the grade.
Pre-calcined for stability
Combined water and organic matter are driven off before dispatch, so the grade shows lower firing shrinkage and fewer gas-related defects in the customer's kiln than raw diatomite.
Low loss on ignition
With loss on ignition typically below 0.5 %, the material adds very little volatile content to refractory mixes, which helps when tight control of fired density and dimensions is required.
Second role as a flatting extender
The same calcined powder reduces gloss in matt architectural and industrial paints, giving formulators a lightweight extender that also improves surface texture, touch-up and recoatability.
Applications
Insulating firebricks and boards
Used as the lightweight siliceous component in insulating bricks, calcium silicate boards and diatomite blocks for kilns, furnaces and heat-treatment equipment, where low weight and low heat loss are both needed.
Refractory backup and loose fill
Applied as a loose fill or mixed into insulating mortars and castables behind dense refractory linings, reducing shell temperature and heat loss in industrial furnaces and boilers.
Matt paints and coatings
Added to emulsion and solvent-borne paints as a flatting extender that controls sheen and improves touch-up behaviour. Particle size is selected to suit the target gloss and film thickness.
Usage & handling
- Insulating bricks and boards: typically 20–60 % of the dry mix, depending on target density and strength.
- Paints: typically 2–8 % on total formulation as a flatting extender, added during the grind stage.
- Dry-blend with other powders before adding water to avoid lumps and uneven density.
- Keep bags dry and closed; use dust extraction and respiratory protection as advised on the SDS.
Packaging & supply
- 25 kg or 50 kg HDPE or paper bags
- 1 MT or 1.2 MT jumbo (FIBC) bags
- Palletised and stretch-wrapped loads on request
Frequently asked questions
What temperature can calcined diatomaceous earth insulation withstand?
Diatomite-based insulation is widely used in kilns and furnaces at elevated temperatures, but the safe service limit depends on the final product: brick, board, castable or loose fill, and its other ingredients. We confirm guidance on request after reviewing your formulation and operating conditions rather than quoting a single figure.
Why use calcined rather than raw diatomite for insulation products?
Raw diatomite still contains combined water and organic matter, which are released during firing and can cause shrinkage, cracking or uneven density. Calcined insulation grade diatomaceous earth has already been through that change, so it behaves more predictably in the customer's process and gives more consistent finished dimensions.
Does calcined diatomaceous earth contain crystalline silica?
Calcination can convert part of the amorphous silica to cristobalite, a crystalline form. The content for this grade is stated on the SDS together with recommended exposure controls. Users should follow local occupational exposure limits and use dust extraction and suitable respiratory protection when handling the dry powder.
Can this grade be used in paints?
Yes. Calcined diatomaceous earth is used as a flatting extender in matt and eggshell paints. It lowers gloss, improves surface texture and can help recoatability. Paint makers should trial it at different loadings to balance sheen, scrub resistance and viscosity in their own formulation.