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Applying Render to Metsec Steel Frames

When it comes to rendering Metsec steel frame buildings, the external surface of the building needs to be taken into consideration. At EWI Store, we provide coloured render and external solutions for a wide range of substrates, and today we’re going to be discussing in detail the exact process of how to go about rendering a Metsec frame. Metsec is a company that sells cold-rolled steel for structural frames; essentially the building is constructed of a lightweight steel frame (produced by Metsec) and a variety of materials are anchored to the frame to create the buildings’ exterior skin.

There are many materials that can be used for the outside of the Metsec frame, but typically a sheathing board is secured to the steel frame. For non-residential buildings, Mineral Wool insulation is fixed to the sheathing board and the thin coat render system is applied on top. For residential projects, Mineral Wool insulation is installed within a cavity, before a render carrier board is secured to the steel frame on the outside. Quite often you can find steel frame buildings with a brick cladding forming the exterior surface as well.

We’re going to be taking a look into how you can render different substrates on a steel frame building!

Render Carrier Board: Rendering Metsec 

Once the render carrier boards have been secured to the steel battens, there will be a spacer gap of a few millimetres between each edge of the board. This is to give the boards space for ventilation and to compensate for any movement. However, these gaps need to be covered over using an appropriate render tape, or Pavatex Render Carrier Board Joint Tape; both are suitable, however the Pavatex tape acts as a vapour permeable membrane so has that extra level of breathability.

After you’ve joined the render carrier boards together using either of these methods, you can apply the EWI-225 Premium Basecoat to the surface of the render carrier board – no primer needed. Premium Basecoat is our strongest basecoat-adhesive, so we really advise using this as a basecoat for a secure render installation. The Premium Adhesive needs to be mixed with 6.5L of water and applied at a thickness of 6-8mm, before Fibreglass Mesh is embedded within the basecoat using the flat edge of the notched trowel. Each strip of Fibreglass Mesh should overlap its neighbouring strip by approximately 10-15cm.

Leave the basecoat to set for 24-48 hours, then prime the basecoat using an EWI Pro render primer. If you’re using our Silicone Silicate Render then the SiSi Render Primer is the ideal primer; simply paint it onto the basecoat and leave it to dry for 12 hours. After this, you are ready to apply your Silicone Silicate Render; this is the final layer that ensures the system is entirely waterproof and resistant to weathering. You can apply the Silicone Silicate render straight out of the bucket and trowel it on at a thickness that corresponds with the grain size; after this, rub up the surface of the render using a plastic render float to get a textured effect.

External Insulation: Rendering Metsec 

When rendering Metsec, architects will often look to create an insulated render system using a Metsec steel frame building. With this kind of construction, sheathing board is applied to the lightweight steel frame leaving a ventilated cavity in front, and then a render carrier board.  Following the manufacturer’s guidelines insulation is applied to the render carrier board using the appropriate adhesive and mechanical fixings. Once the insulation is in place, the Premium Basecoat can be used once again as a basecoat, before priming and rendering using Silicone Render.

It is commonplace to install a ventilated cavity within these residential systems, as it is a requirement for several insurance companies, although they have recently come under criticism from the general public and within the industry itself since the Grenfell tragedy. We advocate the use of Econic boards and Rockwool Mineral Wool insulation in these circumstances because they are A1 fire rated and non-combustible.  Products such as the Dupont Tyvek Firecurb Housewrap can also be introduced for extra vapour permeability and fire resistance.

And there you have it, rendering Metsec steel frames! We upload a new blog post every Tuesday and Thursday, so stay tuned for more content.


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