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Post by james9 on Aug 7, 2018 20:41:28 GMT
Cement Render
I got a plasterer to look at the dome and whilst he worked with silicon render systems he thought cement was the way to go to avoid cracking at the dome-brick interface. I wanted a good finish to cover up the imperfections but he quoted £300 so I’m doing it myself.
Maradge (Cornish Pompeii) in 2013 went for: Scratch coat, 8:1:1, mix of sand types (I'll use plastering sand as a premixed alternative), hydrated lime, cement plus waterproofer, 15-16mm thick. Final coat, same mix but with plasticiser, 12mm thick
Some people also use reinforcing fibres.
I was going to follow this and use Sika waterproofing?
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Post by james9 on Aug 13, 2018 13:15:48 GMT
The intention was to fill in the holes and do a 15-20mm scratch coat but its probably averages about 5-10mm at the moment. The render (8+1+1+WP) was difficult in thin layers whereas 10mm or more gave more flexibility to smooth out, I assume the vermicrete sucked moisture out. We ran out of time on Sunday and will need to add a second scratch cost but this time I'm hoping the waterproof layer will bond without sucking water from the wet mix.
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Post by james9 on Aug 13, 2018 13:40:58 GMT
The best thing cooked by a long way was a "restaurant quality" side of brined salmon with fennel seeds & fresh fennel herb with lemon zest on a cedar plank which was put on top of a Tuscan grill with embers underneath. The cedar plank was soaked in water for a couple of hours but it was alarming when it caught alight due to fat coming off the salmon. I also added some soaked cherry chips for extra smoke in the oven.
Sourdough looked good but needed industrial cutting tools & more time to rise
Garlic bread worked a treat
Pizza was ok but needed a hotter floor.
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Post by james9 on Sept 17, 2018 18:55:57 GMT
I made 3 render layers (160kg of plastering sand) over 2 weeks and left it a further week to dry before applying 3 coats of sandtex. Total thickness varies 20-30mm but its very solid. 1st Layer onto vermicrete dried out very quickly Second layer was wetter and good thickness which made it easier to work Final layer Found a paint brush very helpful to smooth render.
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Post by james9 on Sept 17, 2018 19:11:36 GMT
Cooked pizza, focaccia, and a meatball dish on Sunday so a really hot burn. 28 hours later, its still 127c in dome and 103c on the underside of the floor But there are problems: Second photo is on the other side of the oven. The underside of the floor is 71.4c but the concrete slab under all the insulation is 77.6c (note the dome itself sits completely within the insulation layer so quite a bit of energy is penetrating the floor insulation (50mm) The concrete base and a slab underneath has cracked, not surprising if its getting to 100c on long burns Crack starts at the slab, goes down through a breeze block and up into the render The render has also cracked Also a small crack on adjacent side, hairline crack goes to joint. Small hairline crack near entrance This is an earlier photo, slab thermocouple on the left hand side under the insulation, the entire dome is on top of the 50mm insulation. In hindsight 100mm would have been better.
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Post by james9 on Sept 17, 2018 19:45:02 GMT
The slab shuttering is still in place as I couldn't get the supports out but given the cracking I'm thing about inserting 2-3 hollow block columns to strengthen the slab? Any advice or comments?
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Post by downunderdave on Sept 17, 2018 20:26:15 GMT
Do not attempt to get them out by hammering them. You are likely to damage the slab. The normal thing is to place wedges under the uprights so they can drop when the wedges are removed. You could try cutting them out with a reciprocating saw.
Regarding your cracking, it sounds like you have gone at the fire too eagerly too soon. Don’t worry you wouldn’t be the first to have an oven with cracks. The temperatures you describe indicate wet insulation. If it’s moist it won’t insulate properly. The underfloor moisture is the hardest to eliminate. A few holes drilled up through the supporting slab into the underfloor insulation will help the moisture to escape.
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Post by james9 on Sept 18, 2018 10:00:00 GMT
Dave, thanks for getting back.
Should I remove the shuttering under the slab? this would help moisture to escape and let it cool down quicker
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Post by downunderdave on Sept 18, 2018 21:41:21 GMT
Dave, thanks for getting back. Should I remove the shuttering under the slab? this would help moisture to escape and let it cool down quicker Yes it would. The holes drilled through the slab will do much to help remove the moisture too.
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