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Post by dave36 on Feb 19, 2017 13:49:54 GMT
Question on k render what type are people using for the base coat is it hp12 or hp14 !!!!! as it getting that time of year to finish off the pizza oven . I haven't done it yet, but I am planning on using HPX base coat as the website says it is best for unusual substrates (guessing fibre blanket fits into that category). I've seen at least one other this forum use HPX too. Downside is that it's twice the price. Out of interest, where are you getting it from. Has been difficult for me to find locally (London / Surrey)?
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Post by jagnut on Feb 19, 2017 14:42:43 GMT
Question on k render what type are people using for the base coat is it hp12 or hp14 !!!!! as it getting that time of year to finish off the pizza oven . I haven't done it yet, but I am planning on using HPX base coat as the website says it is best for unusual substrates (guessing fibre blanket fits into that category). I've seen at least one other this forum use HPX too. Downside is that it's twice the price. Out of interest, where are you getting it from. Has been difficult for me to find locally (London / Surrey)? Try this site www,rendit.co.uk
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Post by downunderdave on Feb 19, 2017 21:36:57 GMT
Question on k render what type are people using for the base coat is it hp12 or hp14 !!!!! as it getting that time of year to finish off the pizza oven . I haven't done it yet, but I am planning on using HPX base coat as the website says it is best for unusual substrates (guessing fibre blanket fits into that category). I've seen at least one other this forum use HPX too. Downside is that it's twice the price. Out of interest, where are you getting it from. Has been difficult for me to find locally (London / Surrey)? Rendering over ceramic fibre blanket is difficult because it's very water absorbent and quite springy. It is far easier if you cover the blanket with a 10 :1 vermicrete mix (10 parts vermicrete 1part cement and add a little powdered clay to help make it more workable), which will set nice and firm. This layer needs to be about a min of 35 mm to hold together properly. Another big advantage is that you can restore the spherical form of the oven because you can even out the lumpiness of the blanket surface. You just tap the vermicrete gently with the flat of your trowel.
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Post by dave36 on Feb 20, 2017 13:28:49 GMT
I haven't done it yet, but I am planning on using HPX base coat as the website says it is best for unusual substrates (guessing fibre blanket fits into that category). I've seen at least one other this forum use HPX too. Downside is that it's twice the price. Out of interest, where are you getting it from. Has been difficult for me to find locally (London / Surrey)? Rendering over ceramic fibre blanket is difficult because it's very water absorbent and quite springy. It is far easier if you cover the blanket with a 10 :1 vermicrete mix (10 parts vermicrete 1part cement and add a little powdered clay to help make it more workable), which will set nice and firm. This layer needs to be about a min of 35 mm to hold together properly. Another big advantage is that you can restore the spherical form of the oven because you can even out the lumpiness of the blanket surface. You just tap the vermicrete gently with the flat of your trowel. DownunderDave - thanks for the tip, but argghh, I don't think I have room for a 40mm Vermicrete layer. I have 16cm of space either side of the hearth - the plan was 8cm of clay, 5cm blanket (already bought) and 2cm of K-rend with 1cm of wiggle room.
Any thoughts on what to trim?
My thoughts - I'm nervous about going less than 8cm clay (the oven is 80cm diameter and worry the clay layer may become too thin, thus weak (?)), which means one of three options:
(i) reduce radius of over by 4cm across the base but keep 40cm radius high (arch already built, thus can't change height of dome), but then I end up with something that is not quite a hemi-sphere (any loss of strength associated with this?) (ii) reduce thickness of clay by 3cm, down to 5cm and use my 1 cm of wiggle room (iii) A combo of both the above - say 2cm off radius, 1cm off clay, use 1cm wiggle room.
thoughts gratefully appreciated!
D
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Post by dave36 on Feb 20, 2017 13:30:45 GMT
Rendering over ceramic fibre blanket is difficult because it's very water absorbent and quite springy. It is far easier if you cover the blanket with a 10 :1 vermicrete mix (10 parts vermicrete 1part cement and add a little powdered clay to help make it more workable), which will set nice and firm. This layer needs to be about a min of 35 mm to hold together properly. Another big advantage is that you can restore the spherical form of the oven because you can even out the lumpiness of the blanket surface. You just tap the vermicrete gently with the flat of your trowel. DownunderDave - thanks for the tip, but argghh, I don't think I have room for a 40mm Vermicrete layer. I have 16cm of space either side of the hearth - the plan was 8cm of clay, 5cm blanket (already bought) and 2cm of K-rend with 1cm of wiggle room.
Any thoughts on what to trim?
My thoughts - I'm nervous about going less than 8cm clay (the oven is 80cm diameter and worry the clay layer may become too thin, thus weak (?)), which means one of three options:
(i) reduce radius of over by 4cm across the base but keep 40cm radius high (arch already built, thus can't change height of dome), but then I end up with something that is not quite a hemi-sphere (any loss of strength associated with this?) (ii) reduce thickness of clay by 3cm, down to 5cm and use my 1 cm of wiggle room (iii) A combo of both the above - say 2cm off radius, 1cm off clay, use 1cm wiggle room.
thoughts gratefully appreciated!
D
Just realised there is a 4th option - cover the blanket in heavy duty tinfoil or similar (beneath the planned chicken wire) and stick to just K-rend rather than try to insert the Vermicrete layer.
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Post by downunderdave on Feb 20, 2017 21:07:04 GMT
You could also make the inner shell from castable refractory rather than clay. This would make it far more durable and the usual thickness is 2". The downside is that it's way more expensive than clay you dig yourself, but you don't need to process it, just add water. Regarding the foil over the blanket, be careful as it creates a moisture barrier which will lock in moisture beneath it. If you go that route perforate the foil lots or get pre-perforated foil if you can find it.
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Post by chas on Feb 21, 2017 8:44:39 GMT
Question on k render what type are people using for the base coat is it hp12 or hp14 !!!!! as it getting that time of year to finish off the pizza oven . I haven't done it yet, but I am planning on using HPX base coat as the website says it is best for unusual substrates (guessing fibre blanket fits into that category). I've seen at least one other this forum use HPX too. Downside is that it's twice the price. Out of interest, where are you getting it from. Has been difficult for me to find locally (London / Surrey)? I see several posts after this, but thought I'd risk going back to it... 2 coat Krend works fine over a wire mesh key and will save the space you seem to lack for thicker vermicrete. A call to Krend will get you contact details for their Agent nearest to you who will in turn direct you to the nearest stockist. If he/she likes pizza, they might even arrange a discount for you... Chas
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Post by dave36 on Feb 21, 2017 9:00:44 GMT
You could also make the inner shell from castable refractory rather than clay. This would make it far more durable and the usual thickness is 2". The downside is that it's way more expensive than clay you dig yourself, but you don't need to process it, just add water. Regarding the foil over the blanket, be careful as it creates a moisture barrier which will lock in moisture beneath it. If you go that route perforate the foil lots or get pre-perforated foil if you can find it. Thanks dave, think I will go down the heavily perforated foil route as I've bought the clay already, albeit I will try to eke out enough space for vermicrete later if needed (guess it will depend on how spherical the dome looks after fire blanket and how the K-rend seems to stick). Would be interested to hear of anyone else's experience of putting K-rend or similar straight onto a fire blanket covered in chicken wire.
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Post by dave36 on Feb 21, 2017 9:11:10 GMT
I haven't done it yet, but I am planning on using HPX base coat as the website says it is best for unusual substrates (guessing fibre blanket fits into that category). I've seen at least one other this forum use HPX too. Downside is that it's twice the price. Out of interest, where are you getting it from. Has been difficult for me to find locally (London / Surrey)? I see several posts after this, but thought I'd risk going back to it... 2 coat Krend works fine over a wire mesh key and will save the space you seem to lack for thicker vermicrete. A call to Krend will get you contact details for their Agent nearest to you who will in turn direct you to the nearest stockist. If he/she likes pizza, they might even arrange a discount for you... Chas Cheers Chas, that is good to know! re K-rend, I think it was you who recommended Amaroc and if so, thanks, put an order in yesterday.
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Post by oblertone on Feb 22, 2017 10:39:10 GMT
I think the K-Rend will be fine directly on top of your chicken wire; I was stuck for room so did a similar thing but used waterproof tile cement as a base layer before a mosaic layer, just be careful not to compress the blanket layer too much during the process.
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Post by jagnut on Mar 19, 2017 20:23:09 GMT
Question on vermicrete can I add fibreglass (ppg) to strengthen or is it a waste of time !.
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Post by downunderdave on Mar 20, 2017 10:41:45 GMT
Question on vermicrete can I add fibreglass (ppg) to strengthen or is it a waste of time !. I throw some random 25 mm AR fibres into a 5:1 vermicrete brew, but I'm doubtful of how much difference it makes. For a 10:1 brew it's so loose that there are air spaces between the grains anyway, so I feel any fibres would not do much. Probably be a waste of $ as they're expensive. You must use AR (alkaline resistant) or the cement will corrode them. I find a little powdered clay added to a lean vermicrete mix is far better to help it be more workable and stick together.
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Post by jagnut on Mar 25, 2017 20:30:31 GMT
Nice day oven dried out template made for vermiculite cement.
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Post by jagnut on Mar 25, 2017 20:36:53 GMT
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Post by downunderdave on Mar 25, 2017 21:13:07 GMT
Hi jagnut. Your build is progressing. You said way back in your thread that you intended to build a dog kennel style rather than an igloo. If you still intend doing it this way then vermiculite insulation is best added dry over the blanket. To avoid extra use of vermiculite you can fill the corners with empty plastic containers. Adding the stuff dry eliminates the problem of having to dry the vermicrete layer as required with an igloo style.
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