Vertical Wall Overlay

The installation of vertical wall overlay follows similar principles to that of pattern imprinted concrete. However, because it is applied onto an existing surface in the vertical position, it has to be restricted to approximately 30 mm thick in order to avoid sagging or sliding down the wall.

The main stages of installation for vertical wall overlay are: –

Any cracks in the host wall should firstly be repaired with mesh tape and cement mixture to avoid them reflecting through to the new render surface.

Once that has been done the existing surface needs to be completely cleaned of all loose material.

The wall should then be thoroughly saturated with water and a bonding agent mixture firmly is applied with a brush, leaving it with a tacky finish.

This is a mixture of bonding agent, water and the proprietary powdered render and is trowelled onto the tacky surface to achieve a flat surface.

A scratching trowel is used to improve the mechanical key of the render coat into the scratch coat and the surface is left to dry completely.

A tacky surface should be created over the scratch coat in the same way as the existing wall was primed, before the lightweight render mix can be applied with a trowel.  A thin skim coat is applied first of all and this is built up to the required thickness, though unlike plastering an internal wall, a completely smooth finish is not important as the final pattern will be created with printing mats or texture skins.

The chosen pattern will dictate the thickness of the final render coat, with more rustic styles with deeper grooves requiring a thicker application.  A vertical wall overlay installer should not be too ambitious in the amount of the wall being covered at any one time, as the final render coat needs to remain workable in order to form the printed pattern.

The final render coat is sprayed with a liquid release agent and a flexible printing mat is offered up to the wall and pushed into the soft render, before being carefully removed. The next mat is then offered up in the same way to continue the stone or brick pattern.  ‘Squeeze ups’ of the lightweight render will form around the edges of the mats but these can be easily removed just before the render hardens.

Invariably the printed surface will need to be tidied up of any imperfections in the print or joint defects prior to colouring.  This can be done with a variety of tools including paint brushes, jointing tools or textured skins.  The render should then be left to cure for several days prior to colouring and sealing.

Although a pigment can be added to the render before it is installed, that would provide a consistent colour to the surface which would not necessarily reflect the varied appearance of the natural surface to be reproduced.  A water based stain is therefore used to colour the render after it has dried.  Manufacturers and suppliers of the lightweight cement render normally have a wide range of water based coloured stains for vertical overlay.

More than one colour is often applied to each wall surface in order to achieve the required effect.  Usually a base colour is applied, followed by one or more highlighted stains to created natural stone effects with mortar joints.  Just as with the installation of pattern imprinted concrete, the processes involved in vertical wall overlay are as much art as science and colouring the surface is no exception.

The surface needs to be completely dry before it can be sealed with an acrylic sealant otherwise the damp surface will prevent the sealant from penetrating the render and it may delaminate.

The sealer can be brushed on or applied with a sprayer unit and several thin coats are better than one or two thick ones, as an overly sealed surface can appear shiny and artificial.