Thermalite blocks for external skin?

R

RedHerring2

Quick question.
Specification for our extension to bungalow is render on 100mm blocks, 50mm partial fill (25mm Kingspan K8 ), 100mm Besblock Cellular Insulite blocks for internal skin with 25mm (K17) insulation and 12.5mm pb on internal.

I've substituted 25mm Kingspan K8 for 30mm Xtratherm and I was intending substituting Besblock Cellular Insulite for 3.6N Thermalite Shield blocks for internal skin.

1. Can I use same Thermalite blocks for outer skin?

2. Bearing in mind the speed I work, it'll be next winter before I render. Is it advisable to leave Thermalite blocks open to the elements for that long?
 
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Aerated blocks are more prone to cracking and give less adhesion for render than concrete blocks. Also they are more susceptible to showing the bond/block pattern through render.

They can be used but need more care, so follow the makers guides precisely

The problem with leaving aerated blocks exposed is that they can change rapidly from hot to cold and wet to dry, and so experience severe vertical thermal cracking if changes are not adequately controlled
 
R

RedHerring2

Cheers Woody, It's mainly the south facing side so it gets the full sun and seems to suffer the worst of the rain, so it looks like a no, then.
Thanks again.
 
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Celcon have plenty of info on their website.

They say it's fine to use their blocks for the external skin (but they would, wouldn't they?!)

There is a factsheet which you will find here,
http://www.hhcelcon.co.uk/c/document_library/get_file?folderId=54610&name=DLFE-14123.pdf , which lays out the recommended method for rendering onto their blocks, might be helpful...
Exposure conditions have a big bearing; and their solar blocks are more difficult to render onto, although still possible as long as you follow their guidance.

My extension was built three years ago from aerated blockwork inner and outer, and fingers crossed, no issues yet :D
 

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