Thermasheet is the perfect mosaic substrate

Thermasheet is light, strong, 100% waterproof and can be cut to any shape with a craft knife. It is inert, and will not warp, shrink or expand over time. Being waterproof it is suitable for exterior as well as interior use. It is virtually identical to wedi board, which is commonly used as a mosaic substrate in Europe and America. It is also used in the European building industry as a backing board for ceramic tiles in bathrooms, saunas and steamrooms.

Thermasheet consists of an extruded, polystyrene core and is covered in a fibreglass mesh and polymer-modified cement coating. The glass mesh adds strength and rigidity to the panel.

Smalti Australia supply fixings that include special washers for protecting the surface, allowing bolts to secure D rings for a hanging mechanism. We can attach these for you. The D rings are rated at 12kgs each, so two of them can support a 24kg mosaic project. Instructions are supplied below for attaching the fixings, and preparing your board for a mosaic project.

Technical details

Thermasheet board is made up of three components: extruded blue Styrofoam, mesh, and mortar It is inherently waterproof as it provides a closed cell matrix. The foam is extruded under enormous pressure, creating a dense mass of tiny, closed cells so tightly packed together that water cannot penetrate the insulation, nor can the insulating air escape from the cells. The foam is then covered with a glass fibre mesh to add strength and rigidity, which in turn is coated with a polymer-modified cement coating. The cement coating allows for adhesion as a bonding surface.

Smalti Australia supply Thermasheet in 1cm and 2cm thicknesses with maximum size of 60 x 60 cms for posting. For a free sample email with your address and contact phone number.

Instructions for applying the T-nut wall hanging fixings

Make  a hole in the Thermasheet either by pushing through a wide screwdriver (about 8mm) or by using an 8mm drill.

On the front surface of the Thermasheet push the T-nut into the hole pressing the teeth into the Thermasheet. You can put the washer on top and press down to seat it firmly


From the back, put the washer on, lining up the holes. Then slip the D-ring onto the bolt, insert into the hole and hand tighten into the T-nut.


Tighten the bolt with a screwdriver until the T-nut pulls into the Thermasheet and becomes flush with the surface.


You can glue directly over the T-nut because it lies flush with the surface, and there is no need for a skim coat. If the board is to be unframed, the foam edges need to be protected in some way, especially if the piece is going outside. A thin layer of cement-based adhesive is good for this. For extra security you can cover the sides with alkaline-resistant fibreglass mesh tape before applying the cement-based adhesive. It is not advisable to use grout as it has no adhesive properties and will chip off over time. The edges of the board can then be painted if required.

For more information on Thermasheet (Marmox board)