rendering on thermerlite block

[harleo]

hallo first time on, Could any one give there opinion, got to render extension week end, single story, thermalite block , What is the best mix 2 use for scratch coat and top coat. in these weather condition. Many thanks

 

[corrie]

Without knowing the newton value of block you wont go far wrong with 4 sand and 1 cement for both coats. I would add waterproofer to first coat which should be 10mm thick.Second coat 8mm. Give first coat a good scratch while wall is still soft enough. Don`t tear hell out of it but a good deep and neat uniform scratch This is important when using waterproofing as you are killing suction on the second coat so therefore need a good mechanical key.

Alex

 

[harleo]

thanks for your info, phoned, thermalite technical, they told me to use 6s, 1c, 1L. Both coats

 

[Micilin]

thanks for your info, phoned, thermalite technical, they told me to use 6s, 1c, 1L. Both coats

I'd go with Corrie's advice, but perhaps 5 :1: 1 , a weaker coat, for the second.

If Thermalite gave a toss about plasterers , they'd stop making the bleddy things

 

[harleo]

Under stand what your saying, Thanks for your advice.

 

[corrie]

Yeah it must be a softish block. I thought you were just using Thermalite as a genereic term as some people use the word "breezeblock" As we tradesman all know you use a render in proportion to block strength . When those soft block started getting used outside a lot of the render was too strong and it came off in sheets pulling a skin of ash with it That being said 6and 1 for external render? First of all it aint gong to weather great is it? Secondly you will need plenty plastisciser in it to make it workable with the low cement content. This tends so kill the strength of final render.

Think if I was forced to use 6 to 1 render I would compromise by using 5 sand 1 lime and one cement.........more workable but no significant increase in strength.

Alex

 

[harleo]

thanks for your help

 

[robgod]

I've been reading up about rendering. I'm amazed at the various opinions from people who appear to be professionals! I'm starting to wonder if its all a conspiracy to put off us amateurs and boost the trade!

I thought I had enough information ...until I saw this post. Does the block really make a difference? I've just had my extension built with "blocks". I didnt know there was more than one type let alone that it might affect the render mix!!

Its 8" wide and its concrete coloured. Apart from that, how on earth would I know wether to use 4:1, 5:1 or 6:1?

(I'm also getting the impression that plasticiser might make it easier to work with for a novice like myslef instead of lime. Is that right?)