Tom B
WFO Team Player
Posts: 148
|
Post by Tom B on Jan 1, 2013 22:18:40 GMT
I'll also agree here - I used a brick stack rectangle 2 bricks high, built around a stainless flue's base with a pot chimney over the top around the flue, sitting on the bricks. It works extremely well, considering it was a first build, and theory and guesswork combined.
|
|
|
Post by bookemdanno on Jan 2, 2013 13:17:13 GMT
I'd concur that best option is a stainless twin wall flue, with the next best option being brickwork to bridge between single walled flue of any kind and the render. The expansion forces due to the heat will crack any render away from the metalwork, which i've had to my regret. My single walled flue expanded and has caused cracking radiating from it out into the dome. I thought it looked the Mutts Sphericals when i finished the rendering, but this minor oversight of just how much heat and expansion which would take place spoilt it somewhat. Still...that means i get another summer of tinkering with the repairs!
|
|
petec
WFO Team Player
Posts: 232
|
Post by petec on Jan 2, 2013 17:21:02 GMT
All very helpful advice...
you know , I might just bite the bullet and buy a brand spanking new 1m S/S 6" flue. I found one for around £50 online for a 1m length.
I keep looking for second hand but none around where I live - seems to be loads in SouthWest and Scotland for some reason ?!
Rgds Pete
|
|
petec
WFO Team Player
Posts: 232
|
Post by petec on Jan 3, 2013 14:15:45 GMT
Bit the bullet and ordered a new twin 1m SS flue. Should be here next week. Will be a shiny chimney bit concerned about my last batch of mortar mixed for the external arch - even after 5 days its a little too soft and crumbly for my liking - The whole arch is pretty rigid but the mortar can be scratched relatively easily with fingernails. I think the cement may have gone damp in the greenhouse. Bugger ! I am loathed to tear it down and start again - I hope it toughens up as it dries out in next few days. I am going to proceed as though its not a major problem - It's not going to fall down anytime soon I guess. Time will tell .... Builders bags for vermicrete .... cant find one without a hole in it local skips !! - might have to bloody well buy one from wickes for 5.99!!! Cheers Pete
|
|
|
Post by turkey on Jan 3, 2013 19:31:36 GMT
builders bag is ideal but a tarp will do to roll the stuff together I suppose, line your bin with the tarp and you can roll it and keep it all together easier. But for 5.99 its cheaper than the chiropractor lol.
I just used a builders bucket and mixed by hand, was not all that bad as its so light and I only had 2 bags worth to mix.
|
|
|
Post by cannyfradock on Jan 3, 2013 21:00:18 GMT
Pete
I'm sure your chimney will look great and be well worth the investment. The mortar should be hardening after 5 days but I shouldn't worry too much. Even if it was a lean mix, any cement based mortars don't even start curing until 7 days after mixing.....keep your eye on it.
Best of luck with the vermecrete. It's a bugger to use but a little patience helps a lot. I added a bit of lime to my last mix to help it bind.....if you do that, don't forget to use gloves....marigold gloves are ideal.
Terry
|
|
|
Post by faz on Jan 3, 2013 22:52:55 GMT
And further to Terry's advice, also cover your forearms if you're using lime - I didn'tand ended up with burnt arms! That lime is lethal.
|
|
petec
WFO Team Player
Posts: 232
|
Post by petec on Jan 4, 2013 14:04:02 GMT
Hi,
checked the arch mortar again today and seems to be hardening up now pretty nicely - the arch wont have to come down. Just strange how this batch took much longer to go off - oh well maybe i just did cocked up on my mix ratio somewhere along the line.
Now trying to get my head around how to marry the vent to the 6" internal chimney before it arrives and cries out to be attached !
Ref the lime - I know what you mean - I've had a few close shaves where i got frustrated with the clumsiness of using gloves and worked bare handed only to find the lime was trying to turn my skin into soap. Aaarghh ! Lots of rinsing in clean water etc etc to get it off.
Do you use lime in the vermicrete mix - whats the recommended ratio ?
I was planning on just going 10:1 "Vermin" to OPC, with a little water added for damp consistency ?
Cheers Pete
|
|
|
Post by faz on Jan 4, 2013 18:10:06 GMT
I cant remember how much lime I used, not much, probably around a litre of lime per 100l of vermiculite, plus the OPC at approx 9 or 10ish to 1. It takes quite a lot of water before you get a consistency that sticks together enough to get in place on the oven. You need to have a bit of a play round and see how it works for you - every one seems to do it a bit differently!
|
|
|
Post by cannyfradock on Jan 4, 2013 18:26:37 GMT
Pete....the normal ratio for vermecrete is 6 parts vermiculite to 1 part cement by volume with water mixed to make a claggy porridge....
I've used the stuff on many occasions and I thought it was only me that added lime as I find it binds the stuff together better, until I re-read an old thread from Alf Armstrong (moderator on old forum "Armstrong ovens") which reads.....
****************
"Vermiculite is a bugger to mix, especially if using a normal cement mixer. The idea is to get the large vermiculite pieces sufficiently coated with cement / lime and then provide just the right amount of water to make the vermiculite concrete “go off”.
The mix for under oven vermiculite is usually eight vermiculite to one cement. For the vermiculite over the ovens dome its good to use a mix of eight vermiculite, half cement and one lime. This mixture is a little more sticky, so when trying to form your outer dome shape it’s a little easier to get it to stick to the thermal blanket.
Using a cement mixer this can be very frustrating as the whole mixture often gets stuck to the back of the mixers drum, or, one introduces more water than is required and the whole mess when dumped into a barrow just flows over the rim and onto the floor!
For small amounts of vermiculite concrete use this foolproof method. Using 100-litre bag of vermiculite, empty half the vermiculite out of the plastic bag. Add to the reaming half vermiculite still in the plastic bag the required amount of cement / lime. Close the top of the bag with one hand and then shake the whole bag using both hands, this will coat the vermiculite with the cement / lime. Then add around five litres water. Again close the top of the bag with one hand and then shake the whole bag using both hands; the result will be a good moist vermiculite concrete.
Alf"
***************
Myself, the day before I want to use the vermecrete I empty 2 100 litre bags of vermiculite into an empty 1 ton builders bag and add a couple of buckets of water and mix well by pulling the bag from one side to another. The next day I add 1 bag of cement and a shovel full of lime.....again pull the bag from one side to another to mix. The mix should end up sticky and claggy but not too wet.
Some members have bent a thin piece of board or 3 ply around the base of the dome to help them get to the stage where the vermecrete lies easy on the curved part of the dome. The first 8 to 12 inches is the most difficult to keep in place. The rest is plain sailing.....well sort of.
Hope that helps.
Terry
|
|
|
Post by cannyfradock on Jan 4, 2013 19:03:59 GMT
Pete
I couldn't find a general post on mixing vermecrete on the forum so if the last post is a good guide, then I will post it somewhere more prominent on the forum for new members to use as a guide.
I shall also wait for other responses in case anything can be added.
The chimney....and vent aperture.
Normally on a Pompeii build an oblong hole is left with "hit and miss" bricks at the top of the external arch. Mine is usually 7"x 4". Wedge shaped fire-bricks can then be laid on top of your curved hole to create a flat platform for your chimney. If you have bought a flange for the base of the chimney, sit the flange on the flat surface then slide the chimney into the flange. The flange stops the outer skin of the chimney from getting hot which is the main cause of cracking of the render around this area.
If you haven't bought the flange then fix the flue and carry on with the blanket and/or the vermecrete. When the final render coat is laid, wrap something like thin plastic or hardboard around the vent about 5mm thick and render to this. The next day twist the hardboard around and up.....then remove. When the render is dry fill the small gap with fire-cement.
I have seen so many different ways that people attack the vent fixing so the above are just my thoughts on how I go about it.
Terry
|
|
petec
WFO Team Player
Posts: 232
|
Post by petec on Jan 5, 2013 15:08:30 GMT
Thanks for the tips and advice as ever - much appreciated. Got a bit frustrated waiting on the chimney today , and weather has been the best its been for a few weekends so I grabbed the chance to get the ceramic blanket and chicken wire on the dome. Here are a few pics - I went mad with the camera today as its nice to see some dry weather and a bit of sun !!! Taking a gamble and have taken the gazebo down and resorted to just plastic and tarp over the top - just so much easier to see what your doing and move around the oven. Plan is to vermicrete next weekend. another small curing fire tomorrow i think to show it off when the in-laws come round for Dinner ! Cheers Pete
|
|
petec
WFO Team Player
Posts: 232
|
Post by petec on Jan 5, 2013 15:13:59 GMT
PS - forgot to add .... - yes, your posting on the vermiculite mix would make a good sticky post
As would the mix for HB mortar , and general brickwork mortar as well for newbies like I am ( err, was ! )
cheers Pete
|
|
|
Post by faz on Jan 6, 2013 8:10:16 GMT
And tips for using lime - especially the PPE and hygiene requirements!
|
|
|
Post by cannyfradock on Jan 6, 2013 12:41:41 GMT
|
|