Rendered Dome Finish - Waterproofing

[fornoa]

Hi David S

I am in the process of building my oven and I was intrerested in your comment that adding lime to a render increases its flexibility.
What ratios of lime to other components would you use?

Also I have been told that adding fireclay to a mortar mix also increases flexibility of the mortar. Do you have any experience with this also?

Look forward to hearing from you.

[fornoa]

Originally Posted by david s

Hi Poops,
I think you should cover the finished render coat for a week to keep the moisture in it so that it cures nice and strong. Probably then wait a few more days for it to dry out before firing again.you may also want to consider adding lime to the render mix as it increases flexibility. A render with cement and sand only is more brittle and does not have any flexibility.

Hi David S

I am in the process of building my oven and I was intrerested in your comment that adding lime to a render increases its flexibility.
What ratios of lime to other components would you use?

Also I have been told that adding fireclay to a mortar mix also increases flexibility of the mortar. Do you have any experience with this also?

Look forward to hearing from you.

[david s]

I use 4:1:1 silica sand,cement, lime in one coat about 15mm thick. If you do more than one coat each subsequent coat should contain more lime than the previous one. Not sure about the addition of fireclay. It may have a similar effect to that of lime, but it may also create problems re shrinkage as clay always shrinks on drying.

[fornoa]

Hi David,

Thanks for the advice.

Your thoughts on using clay makes sense.

Considering you have experience with the mixture you suggest, I thinks I will go with that.

Also as I intend applying a number of layers, would increasing the lime by say 20% each time, be too much?

Cheers

[david s]

I think more like 10%

[fornoa]

Thanks for that David.