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Demi Rustic Clayworks clay plaster on the spiral stair at Villa 515, Dubai
Specification and technical data

Clay plaster — specification and technical data

An unfired clay plaster, pigmented through the body, applied by hand over a primed substrate. It is a finish, not a waterproofing layer: it breathes, buffers humidity and is repaired rather than replaced. Interior walls and ceilings only.

The system

What sits against what, from the substrate outwards. Junctions, movement joints and edge details are project-specific — send us the drawings and we will mark them up.

Interior clay plaster on board or masonry

The standard interior build-up. Refer to the Clayworks Design Details sheet for junction and substrate detail.

BUILD ORDER — SUBSTRATE FIRST, IN SEQUENCE Substrate
Gypsum plasterboard, masonry, blockwork, wood fibre board, wood wool carrier board, or primed gypsum backing board. Joints taped and filled.
 Primer
Clayworks Wall Primer, or AURO Plaster Primer No. 301 on strongly or irregularly absorbent mineral surfaces.
 Backing coat
Where the substrate is uneven or outside the standard list. Confirm with the applicator.
 Finish coat
Smooth 2 mm in two 1 mm layers; Demi-Rustic 4–5 mm; Rustic 6–8 mm.
 Glaze
Clayworks Glaze where the surface must be sponged clean.

Performance data

Taken from the manufacturers' own technical data sheets, with the standard each figure was measured against. Product-level figures are on the product pages below.

PropertyResultStandard
Reaction to fire Euroclass A1 EN 13501 and EN 15824
Thermal conductivity 0.84 W/mK (Smooth, Demi-Rustic); 0.97 W/mK (Rustic) Clayworks data sheets
Moisture buffer value 1.28 (Smooth); 1.4 (Demi-Rustic, Rustic) Clayworks data sheets
Impact Impact diameter < 15 mm BS EN 520
Acoustics NRC 0.10 (Smooth) to 0.25 (Rustic), depending on backing board BS EN ISO 354
Light reflectance value 20.0 to 62.7 across the range, by colour and finish BS 8493:2008 + A1:2010
Embodied carbon 0.048 – 0.0677 kg CO₂e/kg (A1–A3) Clayworks EPD, stages A1–A3
Warranty 10 years manufacturer's warranty, subject to correct detailing, application and maintenance Clayworks v2.0 data sheets
Life expectancy 60 years interior; 25 years + exterior Clayworks v2.0 data sheets
Colours 89 standard, plus custom matching Clayworks v2.0 data sheets

Products in this family

One page per technical data sheet. Each carries the manufacturer's declared figures, the limits, a specification clause and the full document set.

Clayworks Smooth Finishes Natural clay plasters The closest, flattest finish in the Clayworks range: two 1 mm layers to a 2 mm total. It reads as a matt, even, hand-worked plane with the colour running through the body of the material. Clayworks Interior Demi-Rustic Finish Natural clay plasters A mid-texture clay finish at 4 to 5 mm. More aggregate movement than Smooth, more tonal variation, still an even plane at a distance. The most widely specified finish in the range. Clayworks Interior Rustic Finish Natural clay plasters The heaviest interior texture, 6 to 8 mm, with the coarse aggregate fully expressed. It carries the highest acoustic figures in the interior range and the most surface relief. Clayworks Exterior Demi-Rustic Finish Mineral exterior finish A three-coat mineral facade system for exterior walls, vapour permeable and cured over about two months. It is specified where an exterior elevation has to read continuously with an interior clay finish. Clayworks Exterior Rustic Finish Mineral exterior finish The coarser of the two exterior grades. Same three-coat build-up and same cure, with the aggregate more fully expressed in the top coat. Clayworks Tadelakt Hydraulic lime tadelakt A hydraulic lime, quartz sand and marble powder plaster, burnished and treated with polishing soap to give a water-repellent, seamless surface. Specified for bathrooms and humid rooms — with the maintenance regime written into the O&M. Clayworks Light Reflectance Values LRV data set, natural clay plasters The measured light reflectance value of every standard Clayworks colour, across Smooth, Demi-Rustic, Rustic and Tadelakt. Needed for visual contrast checks and for daylight and lighting calculations — the same colour reads differently at different textures. Cemher Cemher Claywash Clay paint A one-component clay paint for internal walls and ceilings, brushed on in two coats. Specified where a clay surface is wanted at paint thickness rather than plaster thickness.

Where not to use it

Specifying a material into the wrong place is the most expensive mistake on a finishes package. These are the limits we will raise at review whether or not they are asked about.

Interior walls and ceilings, and fixed furniture. Bathrooms and kitchens are appropriate. Not for wet or shower areas, and not for splash zones in direct contact with oils and fats. Not suitable for floors, standard doors, or elements subject to frequent movement. Not to be applied directly onto timber, plywood, MDF or OSB. Exterior grades are a separate specification with a separate build-up and a two-month cure. Custom finishes must be installed by an approved applicator.
Specification clause

Clay plaster: Clayworks [Smooth / Demi-Rustic / Rustic] Finish in colour [ref], applied to [2 mm in two coats / 4–5 mm / 6–8 mm] over Clayworks Wall Primer on the substrate scheduled, to the approved sample panel. Reaction to fire Euroclass A1 to EN 13501 and EN 15824. Substrate preparation and junctions to the Clayworks Design Details sheet. Supply and application by Earth Layers as approved applicator. Clayworks Glaze to surfaces scheduled to be wiped clean.

Square brackets mark the choices that belong to the project. Send us the finishes schedule and we will return the clause completed, with the sample and mock-up programme against it.

Document library

Every publishable document for this family, reproduced in full and unaltered under our cover. Free to download, no form.

Featured projects

Built with this material, by our own artisans. Open the project for the full set of photographs and the story of the installation.

Spiral staircase in Demi Rustic clay plaster at Villa 515, Dubai
Villa 515, Dubai Clay plaster — Demi Rustic and Smooth through the restaurant View the project →
Rustic clay plaster walls at The Makers Barn in the English countryside
The Makers Barn, UK Clay plaster — Rustic, English countryside View the project →

Related systems

Rammed earth In-situ rammed earth is a structural or non-structural wall built in lifts and compacted in place. Rammed earth finishes are a plaster system that reproduces the strata of a rammed wall at 7 to 10 mm on a conventional substrate. The two are specified differently and are not interchangeable. Lime plaster A one-component hydraulic lime plaster with marble dust, laid by trowel at 1 to 4 mm over a prepared base. It carries the hardness and the standards record of a mineral coating while reading as a hand-worked surface — tadelakt, marmarino or polished plaster, depending on how it is finished.

Technical support for the design team

We supply the material and we apply it, so the specification and the workmanship sit with one party. Send a finishes schedule, an elevation or a mood board and we will come back with the system, the build-up, the sample programme and a completed clause.

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