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Post by nickycat on Nov 28, 2023 14:11:37 GMT
hi there - I'm new to the forum, Hello! I installed a precast concrete pizza oven this summer and wanted advice on rendering it to make it hold the heat more.. I have bought the ceramic fibre fire blanket to cover it with and will use chicken wire to keep it in place but can I get advice on what render to use? Just sand cement or something else? Also as its been rainy here in Ireland as per.. do I need to dry it out again before I render? thanks in advance Nicky  |
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Post by enkindle on Dec 2, 2023 0:06:09 GMT
Hi Nicky, welcome to the forum. I used sharp sand and cement for my render. It's cheap and easy to use but likely to end up with a some cracks from all the expansion and contraction as you fire the oven. Mine developed a few cracks in the first year but these haven't grown any further. I've fired the oven hundreds of times and the crack between the top of the door opening and the chimney opens slightly when the oven is fired and closes as it cools but shows no sign of weakening the render. And in rainy Ireland under a tree it's also likely to grow a covering of moss which I personally like the look of but you can treat with a biocide such as Benzalkonium chloride to stop the growth if needed. I think I would fire the oven to dry it out before adding the insulation and render. If your oven has soaked up lots of water then that is likely to cause steam pressure and increase the chances the render will crack or fail completely. You probably want to wait for it to warm up a bit as your render wants to have several days to cure when there is no chance of temperatures getting close to freezing. Paul.   |
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Post by downunderdave on Dec 3, 2023 19:47:31 GMT
hi there - I'm new to the forum, Hello! I installed a precast concrete pizza oven this summer and wanted advice on rendering it to make it hold the heat more.. I have bought the ceramic fibre fire blanket to cover it with and will use chicken wire to keep it in place but can I get advice on what render to use? Just sand cement or something else? Also as its been rainy here in Ireland as per.. do I need to dry it out again before I render? thanks in advance Nicky Hi Nicky, It is far safer to do the drying fires after insulating, but before the outer render. The extreme temperature difference between the inner surface of the oven and the cold exterior, particularly in cold weather, can lead to a big difference in thermal expansion which can lead to thermal shock and cracking. Insulating over it helps even out this temperature difference. Regarding the outer render, it can be applied, once the drying fires have been completed and the inner oven surface turned white. A high lime content in the render layer imparts some elasticity, heat tolerance and also a degree of crack self healing. A good recipe is 4:1:1 of silica sand, hydrated lime and Portland cement.This mix does not have any waterproofing qualities and is fairly porous. If your oven is under a roof it is ideal because the layer will allow moisture to pass both in and out. If it is out in the weather you’ll need to give it a waterproof coating. Most commercial renders have a degree of waterproofing added to them so water is difficult to penetrate, but they’re still somewhat breathable. They usually don’t have a lime content, but you could add it to the commercial render to attain the benefits of the high lime content. I use 50% poly modified commercial cement based render and 50% 4:1:1. If any cracks develop in the outer shell they should be filled otherwise they’ll provide an entry for water which will be absorbed by the insulation layer, reducing its insulating capacity as well as creating potential steam expansion problems. |
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