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Re: Render cracks
From the WFO board
Posted by Rado (126.96.36.199)
In Reply to: Render cracks posted by Ed
Write in more about the oven type, please describe dense part and insulation layer thickness and what it's made of, also the render. When oven is covered with render as per weather finish;
it's fired with first insulation thinner layer on top (you can cook now), then it cools down, then second insulation layer is put on (if there was a second insul. layer) and cooking heat up goes on again.
And so on with more thin insul layers even 3-4 for better result - this way layers better adjust to heat expansion movements avoiding cracks. Few types of insulation can be used for the job each works differently. Then render, if using sand/cement it should be mixed not too wet (when water later escapes mix will lessen on volume and shrinks), after it's applied and as it sets smooth it with metal trowel till it's touch dry -> this is important as smoothing avoids drying crack too, same like with concreting if the area is bigger it needs it, then covered with plastic. If the oven is boxed inside e.g. brick walls etc. there isn't render only roughly poured in insulation over the oven and in sides. If covering oven into a shape without a roof over it, main is to prevent expansion pushing onto the last weather layer when it opens cracks when hot and these close when cold.
it's different if expansion cracks are not present; if the render develops only not moving stable cracks as it dries, also in mud/clay ovens, you can just fill these with cement and paint the structure with lime/sand wash. r
PS We talked about insulations and renders in here few times, also help is in the "building details" page, link below.
Re: Render cracks
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