APPLICATION GUIDE

WBS ASHLAR DETAILING
ONTO NEW / EXISTING BLOCKWORK

For Refurbishment Only Applications
If applying directly to existing brickwork /blockwork / render surface, the substrate must be brushed down to remove any friable material, algae or lichen and fungicidal wash should then be applied. Any ridges or protrusions should be removed and hollows filled to provide a smooth surface.

For Refurbishment & New Build Applications
Stabilising solution may be applied if required to help improve adhesion and offer uniform suction.

Install all beads and trims using approved WBS fixings at a maximum of 300mm centres (depending on the substrate – please consult WBS technical department for assistance).

Mix basecoat to a pliable consistency using approximately 4-5 litres of clean water per 25kg bag. A suitable measuring bucket ensures the correct quantity and accuracy each time. Ensure that the basecoat is mixed thoroughly - it takes at least 10 minutes to dissolve the powder additives. Note how the dryish mix becomes creamy after several minutes. Mix will normally be slightly sticky.

Note: Renders with a high polymer content should be left to stand for 10-15 minutes and be remixed to break the initial set.

Do not add anything to the mix other than clean water.

Trowel apply initial coat to substrate, dubbing out to a minimum of 8mm (or to architect's specification) until a level surface is achieved.

Bed in alkali resistant reinforcing mesh into top third of basecoat (if required), ensuring that an overlap of a minimum of 75mm is achieved.

When basecoat is dry, apply additional stress patches and corner reinforcements across all window and door openings at a 45° angle.

Tidy up base rails and profiles with a damp paint brush or similar to ensure a professional finish.

Lightly scratch basecoat surface with a scratch comb to provide a key for finishing coat.

Mix coloured mortar coat with clean water as per manufacturers instructions.

Apply render 16-20mm thick ensuring that it is finished proud of all profiles.

A darby or straight edged tool may be used to ensure a relatively uniform thickness, then smoothed out using a plastic float.

To achieve a smooth ashlar finish
When green (set but not fully hardened), form cuts in the render using an ashlar cutting tool (various types are available).

A minimum of 10mm of render should be left between the recessed ashlar joints and the substrate.

To achieve an open stone ashlar finish
Take care to avoid even small hollows, which make a good finish difficult to achieve. Hollows should not be filled out if a skin has formed, as it will spoil the finish.

Scratching should take place when the render is considered green (i.e. set but not fully hardened). The exact timing of this operation varies according to weather conditions and can be anything from 4-48 hours, however usually the next day is considered adequate.

When green, remove approximately 1-2mm of the surface with a nail float, in an even circular motion, to achieve the scratched texture finish. Render should be dry enough not to stick to the nail float.

When dry, brush down with a soft brush to remove any loose material. This will also highlight any unscraped areas which must be scraped at the same time to avoid colour variations.

If scrape patterns or marks are observed, they should be softened by gently scraping or brushing. Loose material that has been scraped from the wall may aslo be used to repair small blemishes at this stage.

Provided strictly for guidance purposes only. For technical support please call 08458 382380.