Baumit Guide: Top Tips For External Rendering In Winter

Russell Judd, Business Development Manager at global building materials manufacturer Baumit, offers a guide to rendering in winter 

What are the challenges when rendering during winter? 

Baumit supplies its products to  more than 35 countries globally, including a considerable presence in Russia which experiences significantly colder winters than the UK. The biggest obstacle our applicators have to overcome is drying times, which vary throughout the year. This is particularly pertinent when there is higher humidity on cold damp days, as this prolongs drying times.  In some cases the temperatures can become too low to render, as our products contain a volume of water which will be affected by freezing temperatures. However, the UK’s temperate climate means such occurrences are rare. Personally, the biggest challenge I’ve seen during winter months is workers suffering cold hands and feet on site.

Does rendering in cold weather have any benefits in terms of application and finish?

Ultimately, cold weather means that the render may not dry rapidly enough. When this happens the render may retain moisture for too long and become susceptible to damage from the trapped moisture.

Which renders work best in cold weather?

Thin coat render systems dry more quickly than conventional render such as sand and cement. This is due to the finished system being thinner on the wall.

How do newly-applied finished surfaces remain protected during cold weather?

This can be achieved with a tin hat (tin roof) placed over the full project or simply having some protection around the scaffold (debris netting). Therefore, applicators will ensure the scaffolder’s design allows this. In harsher conditions experienced across parts of Europe, applicators will also look to have space heaters behind the debris netting to create a healthy drying environment. This works as long as the heat isn’t directed straight at the rendered surface.

What preparation should be given to external walls in lieu of rendering in cold weather?  

Keeping the walls dry is key to successful application in winter conditions. It’s a good idea if the walls can be covered to keep them as dry as possible, as a problem can occur if water gets behind the render which can potentially freeze. Often, applicators will check the walls are not going to freeze the render whilst it’s drying. The best way to test this is with a small amount of water, which should be brushed onto the wall prior to the application. If the water freezes on the wall it is time to go home for the day, unfortunately.

Baumit has a couple of products that are winter specific. Baumit SpeedTop is a ready-to-use additive for Baumit SilikonTop and Baumit GranoporTop.  It provides accelerated setting and enhanced durability on the façade with high humidity and low temperatures, as well as in fog. Baumit SpeedTop can be added in temperatures of < +1C and <15C and with relative humidity of <95% to help with drying times. Baumit can also offer StarContact Speed which is a Mineral adhesive and reinforcing mortar for manual and mechanical application. StarContact Speed is fast setting, frost-resistant, water-repellent and permeable and like all Baumit basecoats, is easy to apply. This gives the user an advantage in cold weather conditions.

Find out more about our range of renders here