One-coat lime renders

use and application

All Saint-Astier® products should follow the UNE-EN 13914-1: 2019 standard, regarding design, preparation and application of exterior and interior plasters.

One coat renders are principally used to protect external surfaces from water penetration but they are also suitable for internal use. They are normally applied in one coat, sometimes in two passes depending on the required thickness and type of background.

The choice of a one coat render is related to the following:
– background
– exposure
– use in communal and public buildings
– use in basements
– application method
– climate conditions during application
– type of finishing required
– application of further decorative elements or coats

One coat lime renders are suitable for the following backgrounds:

1) New build
– Concrete blocks
– Bricks
– Clay blocks*
– Lightweight blocks*
– Stone
*For these types of backgrounds we only recommend DesignSprayable -Thermocromex®).

2) Existing building
Bricks and blocks

3) Excluded backgrounds
– gypsum
– wooden boards
– lath
– cob, adobe
– frozen masonry units
– over saturated
– waterproofed (unless an adequate key has been provided)
– pre-cast units with presence of demoulding oils
– painted, unless paint has been removed
– background incorporating multiple elements unless a reinforcing mesh has been applied

Nevertheless, two main types of backgrounds are identified:
– for type A, high density masonry elements
– for type B, all types of backgrounds (including weak elements), see DesignSprayable (Thermocromex®)

Note: on type B, specifically on lightweight blocks, some products still need a stipple coat or a bonding coat. This is not the case with DesignSprayable (Thermocromex®). In all cases the background must be suitably dampened.

This is generally related to exposure to rain.
The choice of a product with low capillarity (< 2.5 g.dm2.min1/2) will be beneficial.

Capillarity on all Saint-Astier® one coat renders: < 2.5

In high rain exposure areas no one coat render should be applied on flat surfaces or on surfaces with an inclination below 10oC.

Use in communal and public buildings
The adoption of a product with high flexural strength > 2.7 MPa is recommended in these situations where abnormal impact and shocks could be experienced. A good elasticity is also required (between 5,000 and 10,000 MPa).

Saint-Astier® One Coat renders related data
> 2.5 MPa
4000 – 6000 MPa

Use in basement areas
In these areas, products with the following characteristics are recommended:
– dry mass density: between 1400 and 1800 kg/m3
– flexural strength up to 2.7 MPa
– capillarity: W2

Saint-Astier® One Coat renders related data
Dry density KG x m3
CAPILLARITY g.dm2.min1/2
1350 - 1550
> 2.5 MPa
< 2.5

Application method
There are 4 major application methods:
– manual application (please note that products especially made for spraying could present some stickiness when applied manually)
– using a pneumatic hopper gun: check that product is suited to this method. Take care of spraying distance and pressure to avoid too much thickness and a higher consumption than necessary.
– using spraying machines. Each supplier should give its approval on the suitability of their products for this type of application. St. Astier one coat renders are easily applied with machines such as Putzmeister and Lancy.
– using continuous spraying machines (i.e plaster sprayers). These are generally less powerful than the previously mentioned machines and require mortars with particular characteristics.

When using spraying equipment it is essential to respect the manufacturer’s recommendations on water addition and mixing time. It is also essential, as for all rendering/plastering work, that the background is correctly prepared. Do not exceed 10 bars of pressure when you use spray equipment.

Climate conditions during application
Apart from exposure to rain (as stated above), it is also important to consider hot weather, drying wind and the type of background.

In warm climates or in dry winds, in addition to correctly dampening the background and protecting the work, it is also beneficial to use products with a high water retention index (between 90 and 100%) to avoid excessive shrinkage.

Heavy renders (dry mass >1800 kg/m3) are normally stronger but tend to dry much quicker in warm weather. Apart from the potential shrinkage problem, this can also make a scratched finish more difficult, if this is the finish required.

In cold climates, light renders (dry mass >1400 kg/m3) can take longer to harden and therefore finishes longer to complete.

Saint-Astier® one coat lime renders have a medium weight dry density. They are therefore usable in all climatic zones subject to the correct working practices.

Do not apply in temperatures below 5°C or above 30°C.

Saint-Astier® One Coat renders related data
Hydration Water retention %
92 - 96

Type of finishing required
– sprayed or rough cast
– partly smoothed rough cast
– scratched
– floated
– spatter dash (dry)

> Please see relevant paragraph for each finish under Application recommendations.

Application of further decorative elements or coats
Cladding by applying tiles directly on the render is possible. Follow your supplier’s recommendations.
The suitable render will have a minimum flexural strength of 2 MPa and an elasticity moduli between 7500 and 14000 MPa.
The drying time and the cladding technique should be discussed with your supplier. Do not lay/apply tiles on a scratched surface.

If a decorative render coat is to be applied over the render, it should be at least 5 mm thick and of lower density, elasticity and flexural strength than the main render.

If the backing render is waterproofed, the bonding capacity of the decorative coat should be tested.