Render/stucco dome a little help needed

[OscarA]

Hi Guys/girls

I'm in the final stages of my oven build and need a little help.
I want to render/stucco my dome but not sure on the best way to do it. I have blanketed the dome, chicken wired around the blanket and then added 3-4" on vermiculite (mixed with cement) over the blanket and wire. I was going to render/stucco over the vermiculite but having done a little research on this site I see a lot of people putting down a layer of chicken wire to hold the render/stucco together and reinforce it. This is where I get a little confused as some say they do it in 2-3 layers so do you use chicken wire 2-3 times?
I have also read that some use reinforcing fibers in the mix but so far no luck in tracking a supplier of this stuff. they know about the product just don't know who sells it, frustrating.
Any advise will be greatly appreciated.
Almost forgot do you wet/hose down the vermiculite before putting the render on to reduce the vermiculite sucking out all the moisture out of the render. If so do you give the oven a quick spray with the hose or a decent spray.

Oscar

[Mike D]

Re: Render/stucco dome a little help needed

As far as I know the chicken wire is mostly for helping people form their round shape and to get a better connection to their blanket. I think you only use it once, then stucco from there.
-The fibers, I don't what people would be using them for, unless they are trying to make some strange shape. They do have fibers in surface bonding cement (sbc).
-I think one always wets down something before they put stucco on, to help it stick (with a sponge).
-where are the pics?

Mike

[OscarA]

Re: Render/stucco dome a little help needed

As far as I know the chicken wire is mostly for helping people form their round shape and to get a better connection to their blanket. I think you only use it once, then stucco from there.

-where are the pics?

Mike

Thanks Mike that helps

this is a link to my build which has pics scattered through the thread.

http://www.fornobravo.com/forum/f8/m...gun-15347.html

[rushhour]

Re: Render/stucco dome a little help needed

HERE are steel reinforcing needles I have read some people on the forum use.

[david s]

Re: Render/stucco dome a little help needed

you don't want/need stainless steel fibres for the outside layer. They are really only needed in the high heat inner layer for reinforcing castable refractory. I used to use chicken wire to help reinforce the outer shell, but it is difficult to form over the compound curve. I found cutting it into smaller more manageable pieces was much easier. You can overlap them which provides extra strength and they can be simply placed as you render over them. Adding fibres to the mix is even faster. Our local council use reinforcing fibres for all the footpaths rather than laying down mesh. They can be obtained from concrete suppliers. There are steel fibres, and lots of different plastic ones and even alkaline resistant fiberglass.
As far as wetting the vermiculite layer before rendering over it, yes you can. I don't because I don't want water in that layer which will create problems during curing.I prefer to render in one layer (about 15mm thick) in one go, then wrap the whole thing in cling wrap for a week to keep it moist and hope that not too much moisture is sucked away from it my the vermicrete. Other builders use a layer of al foil over the vermiculite to prevent this, but that has it's own problems in that it will also lock in any moisture under it. If you decide to use foil poke lots and lots of holes through it so moisture can pass through.

[OscarA]

Re: Render/stucco dome a little help needed

y I used to use chicken wire to help reinforce the outer shell, but it is difficult to form over the compound curve. I found cutting it into smaller more manageable pieces was much easier. You can overlap them which provides extra strength and they can be simply placed as you render over them. Adding fibres to the mix is even faster. Our local council use reinforcing fibres for all the footpaths rather than laying down mesh. They can be obtained from concrete suppliers. There are steel fibres, and lots of different plastic ones and even alkaline resistant fiberglass.
As far as wetting the vermiculite layer before rendering over it, yes you can. I don't because I don't want water in that layer which will create problems during curing.I prefer to render in one layer (about 15mm thick) in one go, then wrap the whole thing in cling wrap for a week to keep it moist and hope that not too much moisture is sucked away from it my the vermicrete. Other builders use a layer of al foil over the vermiculite to prevent this, but that has it's own problems in that it will also lock in any moisture under it. If you decide to use foil poke lots and lots of holes through it so moisture can pass through.

Thanks David your advise has been most helpful.
I will be on the phone tomorrow trying to track down some of these fibers you talk about. I do believe they are used down here as well as we also had our footpaths done about a year ago and there was no mesh used which I thought was strange at the time. Reading how your council uses fibers to reinforce footpaths makes me believe ours must have used something similar as well.
If however I have no luck finding a supplier I will resort to chicken wire and your tip of cutting it to smaller pieces is a good one. I also like the idea of doing the dome in one hit then clinge wrapping it for a week.
You say you make your dome 15mm thick is there a reason for this as I was planning on doing mine 25-35mm thick to make sure I have a nice round finish.
I also have a concrete sealer for water proofing concrete floors and to prevent stains from oi leaks etc.
I coated a poures terracotta tile in this stuff and it made it water proof and stain resistant. Would this be ok to use on the oven or would I be better of using a special sealant paint to seal the dome once properly cured and after a few good firings.
What sealant do you use?
Last question, what is your render mix I was thinking 1 part cement, 1 part lime and 3 parts washed fine sand.

Thanks.. Oscar

[david s]

Re: Render/stucco dome a little help needed

The outer shell is simply a weather thing to prevent water entry to the inner layers. I don't see much merit in making it thicker than it needs to be. 15 mm works for me, others will no doubt disagree.
On the waterproofing aspect of the outer shell I believe that it's best to wait until the oven is perfectly dry (this takes about 10 decent cooking firings after the initial curing in my experience) before making the outer shell waterproof, otherwise you are creating a barrier which also prevents water getting out.

[OscarA]

Re: Render/stucco dome a little help needed

Thanks for your help David.
Well I was at my local Bunnings the other day inquiring about these fibers with no luck. Bunnings used to sell them but stopped a few months back due to poor sales. Well today I was was over at the other side of town and decided to give the Bunnings on Plenty Road Mill Park a try. You never know different suburbs might have slightly different stock or they could have some old stock. Well I was in luck and got myself some Multimesh Concrete reinforcing fibres.

Multimesh Australia - Home

This stuff looks easy to use and best of all was cheap, $7 for a bag of 6 - 30gram sachets and each sachet is mixed with roughly 40kgs of premixed cement or in my case 40kg of render.

Thanks so much for the tip David, now to get this oven finished.

[david s]

Re: Render/stucco dome a little help needed

Oscar,
I forgot to also mention that I use 50% more fibres than what they recommend. Make sure you mix it well (about twice as long as you would think) for full dispersion.

[OscarA]

Re: Render/stucco dome a little help needed

Thanks David I'll do just that. I'm not sure how much Render will be needed to cover the oven but I'll do as you suggest and go back to Bunnings if more fibers are required. Better to play it safe.

[david s]

Re: Render/stucco dome a little help needed

Oscar ,
Sorry I didn't answer your last Q. Re render mix. I use 4:1:1 silica sand, Portland cement, lime mixed by volume.
Dave

[OscarA]

Re: Render/stucco dome a little help needed

Thanks David much appreciated.

[Neil2]

Re: Render/stucco dome a little help needed

You may want to consider an acrylic stucco outer layer to improve "water resistance".

Note that you can never expect a stucco based outer shell to be 100% water proof.

[OscarA]

Re: Render/stucco dome a little help needed

Hi Neil2

I am going to cover the dome with an acrylic sealer to help waterproof it as best I can. The acrylic layer will completely cover the dome and stand. Then I will lay down terracotta tiles on the stand and do a brick tile border (same tiles as the arch). When all done I will then cover the tiles, bricks and arch with a concrete sealer. So in short the dome will have an acrylic flexible sealer and the tiles, brick will have a concrete sealer.
I will never make it 100% waterproof I realise but water resistant it will be.
If down the track I find I'm having water issues then the whole thing will be inclosed but as I like the dome look I'm hoping that wont be necessary.

[cobblerdave]

Re: Render/stucco dome a little help needed

Dear Oscar
I believe you have it all covered......98 per cent is close enough

Regards dave