Manufacturer of Ceramic Bodies and Clays for Modelling

Self-hardening Clay


Self-hardening Clay

General description and properties

SIO-2 PLUS® is natural self-hardening clay. No firing is necessary. After drying, it achieves high hardness, strength and solidity. It is a suitable material for the development of creative skills and plastic expression. Recommended for handicrafts and professional creative arts as well as it is suitable for children.

SIO-2 PLUS® clay has a soft, pleasant and fine texture to the touch. Its clay composition gives it excellent plasticity for detailed modelling. Can also be thrown on a potter's wheel. Odorless and not staining. The rest of the clay can be easily removed from any surface with a damp cloth. The presence of natural cellulose fibers allows safe drying without cracks or fissures, even in large pieces. Once dry, the clay can be painted or varnished with any type of paint or varnish. It can be also polished, carved or drilled.

Available in 5 naturals colours:

Available in 5 sizes: 500 g, 1 kg, 1.5 kg, 5 kg y 10 kg. The larger sizes are more economical and very practical to use in schools or workshops.

The product conforms to the European regulation EN-71 and to USA regulation (seal AP non toxic product). It does not contain food allergens.

What makes SIO-2 PLUS® clay different?

Compared to conventional pottery clays, SIO-2 PLUS® clay does not need firing. Once dry, the piece can be painted or varnished. This clay allows creating objects with difficult drying, free of cracks and fissures.

In relation to other air-drying clays, SIO-2 PLUS® is composed of minerals and natural clays, with plasticity noticeable at touch, but especially it is recognizable by the lack of smell. Unlike other self-hardening clays on the market, SIO-2 PLUS® clay can be thrown on a potter’s wheel.

How to use it
  • Very clean handling.
  • Use a cutting wire to slice enough clay to work with (Picture 1).
  • It is recommended to knead the clay SIO-2 PLUS® before working with it.
  • If clay loses its plasticity during modeling, just slightly moisten your hands to recover it.
  • The clay is easy to model, using adequate modelling tools. It can also be moulded (we recommend plaster moulds) and thrown in a potter’s wheel. Solid or very thin-walled objects can be made with optimal results.
  • To get an even surface, use a wooden roller and two slats of the same height (Picture 2).
  • A large wire-loop tool is used to extract large pieces of excess clay and to shape; for example, a bowl (Picture 3).
  • A double-face wire-loop tool is used to remove small leftover clay and refine details (Picture 4).
  • To join two pieces of clay together, previously scratch the parts to be joined with a spatula or awl (Picture 5) and with a brush moisten them with slip (clay previously mixed with water until a liquid texture is obtained). In the case of corner-shaped joints, reinforce the joint with the help of a noodle of clay along the angle and then press and smooth the joint with a spatula (Image 6).
  • To join two dry pieces, use conventional glue. It is not recommended to join a dry part with a wet part, as the union would crack due to shrinkage during drying of the wet part.
  • A wooden rib helps to remove small imperfections on flat surfaces (Picture 7).
  • A metallic rib is used to smooth out small imperfections on curved surfaces (Picture 8).
  • To smooth and polish surfaces to a very clean finish, use a damp sponge (Picture 9).
  • For modelling hollow items, flexible supports can be used.
► If the clay is used wrapping rigid interior supports, it is recommendable to cover the surface first with paper or cloth. The water in the mass evaporates during the drying process and causes a shrinking, which can lead to cracks. In order to avoid this negative effect, the solid surface is coated with a flexible and absorbent material to support the drying process of clay. This will also absorb the moisture on the inside of the object and prevent cracks.

How to preserve it.
  • Once the package is opened, SIO-2 PLUS® clay needs to be wrapped in plastic in order to be preserved.
  • As long as it contains a minimum of moisture, it can be recovered by wrapping it with damp cloths.
  • During work interruptions, cover the object with a plastic or damp cloth
► Keep the clay in a cool environment avoiding high temperatures. Do not store at temperatures below 0ºC (32 F). If clay freezes, it loses its properties.

  • Once the object is finished, let it air dry.
  • Maximum hardness and strength are obtained in 1 to 4 days at room temperature.
  • In small pieces, drying can be accelerated using a hand dryer, projecting the heat evenly throughout the piece. In this case, the time to obtain maximum hardness and strength is reduced to minutes (Caution: do not use hand dryers in the case of medium/large sizes or flat shapes).
  • Once the object has hardened completely, hardness can be further increased by ending the drying in a domestic oven between 100ºC and 110ºC (180-200ºF).
► During drying, SIO-2 PLUS® clay shrinks. The more water the clay contains, the greater its drying shrinkage. It is therefore advisable not to add any additional water to the modeling clay, otherwise cracks may appear! When modelling big size pieces or objects with a difficult drying, it is recommended, before modelling, to first leave the clay to dry for a while and then homogenize it by kneading.

► Let the piece dry on an absorbent surface (ideally wood or plaster). In case of non-absorbent surfaces (such as metal, plastic or glass), it is recommendable to place the piece over a sheet of paper to facilitate shrinkage of the clay during drying.

Finishing and Decoration.
  • Once dry, the object can be polished, carved or drilled.
  • It can be decorated with any type of paint, pencil or marker.
  • As it is not very porous, a single coat of paint is enough to achieve all the vividness of the color.
  • The use of varnish is recommended to enhance the natural color of the clay. The use of varnish also ensures greater durability of the object and allows an easy cleaning.
SIO-2 PLUS® clay is not water resistant. It is not advisable to create objects which get in contact with water (vases, flower pots, cups, etc.) even if they are protected with a waterproofing agent. In this case, we recommend using an inner plastic or glass container, so that the SIO-2 PLUS® piece is only for external decoration. In this context, please be aware of the last point in "How to use it".


How long does SIO-2 PLUS® clay take to dry?

SIO-2 PLUS® is essentially made of natural clays. Therefore, its drying speed is equivalent to that of other natural clays, with which the drying time ranges between 1 to 4 days. It further depends on the object size, on its shape and on the room drying conditions (temperature and ventilation, basically). In small pieces, drying can be speed up by using a hand dryer. In this case, the time for obtaining a maximum hardness and solidity is reduced to a few minutes (Caution: do not use hand dryers in the case of medium/large sizes or flat shapes).

Do I have to use all the clay once the pack is opened?

If not all of the clay is used, it can be kept for another time, keeping the excess in a tightly closed plastic bag. When using the clay again you may notice that it has hardened slightly. If so, simply moisten your fingers before modeling.

Why is SIO-2 PLUS® White clay light grey?

Natural clays are not really white because they usually contain organic matter, which gives them a certain grey hue when wet.

Does SIO-2 PLUS® clay stain?

SIO-2 PLUS® is a very clean clay. Cleans easily with water on hands and clothing. With a damp cloth, any clay residue on surfaces and furniture can easily be removed.

Can it be used for outdoor pieces?

It is not recommended to use SIO-2 PLUS® clay for outdoor objects. SIO-2 PLUS® clay is not water resistant. Although the clay is dry and hardened, if it is exposed to environmental conditions (rain, snow, ice) it softens and deteriorates. To make outdoor pieces it is recommended to use conventional SIO-2® ARGILA clay fired in a ceramic kiln.

Can SIO-2 PLUS® clay be fired?

Firing SIO-2 PLUS® clay is not recommended. For this purpose it is recommended to use a non-hardening natural clay (SIO-2® ARGILA). Even so, as it is composed essentially of natural clays, it can be fired in a ceramic kiln at 1000ºC.

► It must be taken into account that, when firing, the object significantly reduces its dimensions (firing shrinkage). In addition, during the firing of SIO-2 PLUS® clay, smoke is generated from the combustion of organic matter. The smoke gives off an unpleasant odor and appears from 130ºC. In the case of firing SIO-2 PLUS® clay, the area must be sufficiently ventilated or a good system for evacuating the kiln fumes must be provided.

Can it be a danger if a child ingests SIO-2 PLUS® clay?

Clay is not food. In case of accidental ingestion, it is a non-toxic product, in accordance with the European regulation EN-71 and the USA regulation (seal AP non toxic product). It does not contain gluten or other food allergens. Clay is not suitable for children under 3 years of age because accidental ingestion could cause drowning. Remove the packaging before giving the clay to a child.

Does SIO-2 PLUS® clay expire?

All available SIO-2 PLUS® formats remain unchanged in their original packaging conditions for a minimum period of 2 years.

Safety regulation

Material Safety Data Sheet is available upon demand.

Online info

Instagram: sio2.plus
Facebook: sio2.plusclay
Use our hashtag #sio2plus
► Other languages
T. +34 93 777 23 44 | info@sio-2.com
T. +34 93 777 23 44 | info@sio-2.com