Elastomeric Coatings Over Render: When They Make Sense

An elastomeric coating is a thick, flexible film that goes over a rendered wall. It stretches with small movement, so hairline cracks in the render underneath stay covered and the wall keeps shedding water.

It is not a cure for a badly built wall. It is a finish choice that suits some homes and adds cost on others.

What an elastomeric coating does

Standard acrylic texture coats are flexible, but only up to a point. An elastomeric coating is built thicker and made to stretch further. That extra movement is the reason to use one.

Dulux lists elastomeric products in the Dulux Acratex range, including AcraShield 955. The current product data sheet sets out the primer, the film build, the number of coats and the recoat times. Those figures change from product to product, so we work from the sheet for that job and not from memory.

When a builder should consider one

These are the situations where we raise it with the builder:

• Walls with a lot of exposure to driving rain
• Lightweight substrates where some movement is expected
• Designs with large flat rendered areas and few natural breaks
• Owners who want a smooth, even look rather than a heavy texture
• Repaint jobs where fine cracking has already shown up

On a sheltered single storey home with a standard texture coat, it often adds cost without much benefit. We would rather say that up front than sell a product the wall does not need.

What has to be right underneath

A flexible coating only works on a sound base. Before it goes on, we check:

• The render or substrate has cured for as long as the data sheet requires
• Control joints are in the right places and have not been rendered over
• Loose, chalky or dusty surfaces have been cleaned and primed
• Existing cracks have been assessed, because a moving structural crack will come back through any coating

If a crack is structural, the builder needs to deal with the cause first. Coating over it only hides the problem for a while.

Weather on the day

Film forming coatings are sensitive to weather. Rain, heavy dew, strong wind and very hot walls in direct sun can all affect how the film cures. The data sheet gives the temperature and humidity limits. On a Brisbane summer afternoon, west facing walls can go well past those limits, so we plan the order of elevations around the sun.

Colour and maintenance

Elastomeric coatings come in a colour range like any other finish. Very dark colours heat up more in the sun, which puts more strain on any coating. We talk this through before the colour is locked in.

Owners should be told how to clean the wall and when to have it inspected. A gentle wash every so often keeps dirt and mould from building up, especially on shaded sides of the house.

Getting it specified properly

If you are considering an elastomeric system, put the product name and colour on the schedule and ask your renderer to confirm the system in writing. That keeps the product, the substrate and any warranty conditions lined up.

Send the drawings through our project portal or call 0452 295 212, and we will price the job.