DesignSprayable - Thermocromex®

General recommendations

General information
DesignSprayable (Thermocromex®) is a one coat render designed to be spray applied on most surfaces, including clay blocks and lightweight blocks.

On high suction surfaces it is recommended that these are well dampened the day before application and again just before. Bricks should be dampened with a slight mist 30 -60 minutes prior to application of the render.
Do not apply on gypsum, wooden boards, lath, cob, adobe, frozen or oversaturated masonry units, painted surfaces.

On existing waterproofed surfaces apply only if an adequate key is provided. On pre-cast units ensure that de-moulding oil has been removed (high pressure water jet). Apply the render in 2 passes, wet on wet. The first pass will be like a rough slurry and will contain 0.5 litres of SBR (Styrene-Butadiene Rubber)per bag of DesignSprayable (Thermocromex®). The same procedure applies on very smooth surfaces.

Backgrounds incorporating multiple elements will have to be prepared with a suitable mesh covering the areas were the different surfaces meet.

When rendering on masonry units with unfilled vertical joints, the joints with an over 5 mm width should be pointed. This should be fully dry before the render is applied.

To avoid shadows when rendering on masonry units with large joints either apply the one coat render in two passes (waiting 1 day maximum between passes) or apply a base coat and render on it after about 5 days.

On high suction surfaces it is beneficial to dampen, as previously described, but also to work in two passes (leaving no more than 2 to 4 hours between the two passes). The function of the 1st pass is to unify the suction. Tight floated finishes should be avoided unless the background is properly constructed with tight and well finished joints. Sponge finishing is preferable.

Test panels are recommended in all cases. In the presence of multiple or potentially problematic surfaces to render, a representative test panel will help the applicator decide the best method to use.

The minimum requirement to achieve water resistance is 10 mm (total finished thickness). If scratched or textured finishes are desired, leave a 12 to 15 mm thickness (or more).

The maximum thickness should not be over 25 mm. If more is required, DesignSprayable (Thermocromex®) can be applied in additional layers but total thickness should never exceed 40 mm.

Always use whole bags. Do not add any other material unless specifically agreed with the manufacturer.

Add 5.5 to 6 litres of clean water per bag. Always use the same water dosage for each mix (proper measuring devices should be used).
Mix for 5 to 10 minutes maximum. Always maintain the same mixing time for all mixes. Use the mixed material within 1 hour. Do not try and re-work the mortar.


1) Rustic (rough cast), partly smoothed rough cast and dragged finishes
Work in 2 passes. The first pass has to be at least 10 mm to guarantee the waterproofing effect of the whole work. If the second pass cannot be done within a 2-4 hours, dampen the surface before new application. In sprayed renders, make sure that the pressure and the distance of the spraying nozzle are constant.

In rough cast finishes the render is left as cast. Smoothing a rough cast finish is done once the render has slightly hardened. Dragged finishes are achieved by scraping the surface once sufficiently hardened.

2) Scratched finishes
The render is applied in 1 or 2 passes, depending on the background: the first will be cast on or sprayed (10 mm coat), the second should be applied after 2 to 4 hours, when the render is still plastic but hard enough to apply over. The total thickness should be a minimum of 15 mm making sure that at least 10 mm is left after scratching over the whole surface. Rule the second pass immediately after application.

The scratching should be uniform and appropriate scratching tools should be used (devil floats etc.). It can be done from 3 to 24 hours after ruling, depending on weather conditions.
Remember that scratching will cause a different visual effect in the colour of the product from the colour of the same product with a smooth finish.

Deep scratched surfaces are more sensible to rapid drying and therefore more attention should be paid to curing with light water mist. This should not be done in full sun or on sun baked surfaces (cure in advance and later on in the day).

3) Sanded finish
Proceed as per scratched finish. When the surface is hard enough, usually 48 hours but could be longer.

4) Sponged finish
Can be applied on various types of work, using different sponges texture or hardness when the work is sufficiently dried.

5) Smooth floated finishes (floats, sponge, trowel)
The render is applied in 2 passes of 5mm each,ruled and floated when sufficiently dry. The minimum thickness has to be 10mm after floating.Note:on large surfaces without joints it might be necessary to introduce joints. In all cases, if joints are present in the background, these should not be bridged.

6) Dry dashing
Apply the render in 2 passes to achieve a 15mm overall thickness.
Dry dashing is possible on the second pass when still fresh

7) Lines finishes
Lined finish, simulating stonework, is achievable with the appropriate tools.
Limit the line to a maximum thickness of 10 mm.

Protection and curing
Protect fresh work against adverse weather conditions (rain, wind, frost etc…). To avoid blooming, do not apply one coat renders with strong colours at temperatures below 8oC and high humidity. In hot weather or windy conditions, cure the work repeatedly with light water mist for at least 2-3 days.

Climate conditions
Not to be applied in temperatures below 5oC or above 30oC unless the appropriate protection and curing practices are followed.

Further guidelines on the application
On a suitable background, offering adequate key and, if required, suitably dampened, spray Thermocromex to various thicknesses (depending on the finish required). Rule immediately after spraying. Float to finish few hours after ruling out. As compaction has been achieved by spraying, do not float exercising a lot of pressure as overworking might produce patches. Smooth finishes can be achieved using the TF grade (0-1.3mm). If using a sponge, use a fine texture sponge, semi dry. Single floated finishing coats should not exceed 5mm thickness, they will not therefore achieve the minimum waterproofing thickness of 10mm.

Spraying equipment
Pneumatic Hopper Guns (3 holes) – pressure should be between 3 and 4 bars.
Spraying machines (for example Putzmeister, Lancy…)
Continuous spraying machines (i.e. plaster sprayers)

When using spraying equipment it is essential to respect the Manufacturer recommendations for water addition and mixing time. It is also essential, as for all rendering/plastering work, that the background is correctly prepared (protection of windows, doors etc…).

The information contained in this document does not constitute a specification but is given as a general recommendation. Please consult your St. Astier Distributor for site specific issues.