30" cast dome design

[david s]

Do not use a concrete mix for your render/stucco mix. Concrete is that hard thick stuff containing large aggregate and usually 100 mm thick, composed of sand, water cement and aggregate. What you are talking about is a cement based render/stucco comprised of sand water, hydrated lime and cement to be troweled on in around 2 or 3 5mm layers (I do mine in one 10-15 mm layer reinforced with AR fibreglass fibres).

[sergetania]

David

I meant a commercial base/brown coat mix,not just a concrete mix. I think that's what you are talking about. I also ordered an acrylic bonding agent that I will use for part of the water in the mix. Now I will also get the AR fiberglass fibers like you said for reenforcement and do it one layer. Thanks!

I understand that I need to dry/cure the oven first. Thanks again!

[david s]

Yes, now you’re on track.

[sergetania]

I feel like I am! Be patient,cure,mix stucco with all kinds of hi-tech stuff and smear it on...in layman's terms

Thanks, David, hope you are out of the hospital and back to normal... Whatever that is these days!

[sergetania]

Watching perlite concrete dry is so exciting... So I made a (semi)shiny door. I think the fit is pretty decent and it should be able to extinguish the fire when shut.

[Gulf]

.........it should be able to extinguish the fire when shut.

Be careful! I haven't found much reason to extinguish a fire in a WFO other than making lump charcoal. But, If you do, don't open the door for at least a week. Underwear is replaceable and hair will grow back, but the smell will stay in your memory for a lifetime .

[sergetania]

Haha! Got a ceramic egg grill, similar risk. Considering that hair have become somewhat sparse, definitely nothing to be taken lightly

[sergetania]

I have to admit - the first fire is a sight to behold! Enjoyed it a lot!

[sergetania]

Do not use a concrete mix for your render/stucco mix. Concrete is that hard thick stuff containing large aggregate and usually 100 mm thick, composed of sand, water cement and aggregate. What you are talking about is a cement based render/stucco comprised of sand water, hydrated lime and cement to be troweled on in around 2 or 3 5mm layers (I do mine in one 10-15 mm layer reinforced with AR fibreglass fibres).

David

How much fiberglass fibers do you add to stucco mix? I got a small bug that came without directions. Thanks!

[danhem]

David

How much fiberglass fibers do you add to stucco mix? I got a small bug that came without directions. Thanks!

Hi,

I followed David's advice also and use the AR fibers, I just mixed up a bucket of stucco and threw a couple of handfuls of the fibers in. I'm Sure David will come back with a more precise formulae, but my stucco has set really well and after a couple of full blown fires no cracks have appeared.

I did the scratch/brown coats and wrapped the dome in plastic for about 8 days until the condensation was no longer visible on the inside of the plastic. I think this process along with the AR fibers helps the stucco to cure and set strong. Providing you have driven all moisture out of the oven and perlite your stucco will be crack free.

Being patient is the real killer here, especially as you have now seen your first fire. In all honesty I am addicted to lighting and watching fires in the oven. As you progress through the curing and the fires get bigger....boy you are in for a real treat there .

Good luck.

[sergetania]

danhem Thanks!
Wrapping in plastic usually leaves an imprint on the surface, doesn't it? Also, did you moisten the perlite layer before applying the stucco? That adds some water back in but I guess not that much.
I don't mind just watching the fires at all(a beverage of choice helps). It's quiet time. Once the oven is ready and you have to make pizzas it's over!

[danhem]

danhem Thanks!
Wrapping in plastic usually leaves an imprint on the surface, doesn't it? Also, did you moisten the perlite layer before applying the stucco? That adds some water back in but I guess not that much.
I don't mind just watching the fires at all(a beverage of choice helps). It's quiet time. Once the oven is ready and you have to make pizzas it's over!

I didn't have an issue with an imprint. The plastic is naturally smooth and I didn't pull it too tight - just made sure that no moisture could escape. At the end of each day I smoothed the plastic back over the surface and any condensation went back onto the stucco - whether that helps or not I have no idea.

I used vermiculite instead of perlite and left the layer to dry out for around 4 weeks. With that in mind I didn't want to add moisture to the v-crete as it seemed counterintuitive. I guess that the v-crete will absorb some of the moisture from the stucco helping with the bond. David S warned that excess moisture would steam during a fire, which could cause some cracking so I was very cautions to keep the v-crete layer as dry as possible.

[fox]

I am a big fan of fibre reinforced cement for a base top layer, it is a hugely popular product where I live but I don’t see much evidence of its use on this forum.!

Basically a 2-1 mix of sand and cement with added fibres, it sets extremely hard, the high cement content makes is very weather proof and the fibres make it very crack résistent .
It sets fast and can be applied in thick layers up to 75mm (3’’) or more, however it still needs a top finish coat of 4-1 fine sand and cement and that need to be applied within 24 hours.
Fibre mix or rein fibre mix are both popular trade names and used extensively in the building trade.
My personal method to coat and weather proof the ovens i build (working on number 8 at the moment) is to apply a basic 4-1 sand cement mix in a thin layer over the ceramic fibre, not a heavy thick coat that will compress the insulation.
This is done in the morning so another thin coat can be applied in the afternoon.
(If you have used vermiculite mix then you dont need to do the two thin coats)
Then I apply a single fibre mix coat too get the shape I want, it is easy to build up a very thick single coat but not so easy to get a good finish so i then apply a top finish coat of 4-1 fine sand mix.
Rein fibre mix at 2-1 sets like sheet metal and you can watch rain bonce off it, you can make amazing shapes and build up a deep thickness, it sets very fast and hard.

[david s]

I’ve missed some of these posts, apologies, but would endorse what others have said. Sorry to disappoint, but I don’t have a precise measurement either, but it is pretty close to 700 ml AR glass fibres for every 10 litres of dry render/stucco mix.
As I’ve said many times there are many ways to skin a cat. To reduce labour I do the outer shell in one coat, around 10-15mm thick. Normally one would dampen the substrate before applying the render, but as the water removal is so important I prefer to cover it to hold the moisture in that outer layer instead. Anything containing Portland cement should be damp cured so maximum hydration takes place, generally for one week. Ferry concrete boat builders talk about 28 damp days. I think this is doubly important because the dry vermicrete is sucking moisture out from the inside.the presence of moisture beads under the clingwrap is evidence this is working.I also sponge finish the surface before wrapping which removes any troweling marks. The surface at this stage is quite hard and the plastic leaves no marks.
There is evidence to show that too high a cement content can produce a brittle render, also that each subsequent coat should be slightly weaker and that the addition of lime imparts some elasticity as well as self crack healing properties. I use a 4:1:1 sand, cement, lime mix combined 50/50 with a proprietary PM modified cement render. This works pretty well, the commercial render containing some waterproofing, imparting some resistance to moisture.
I’m a great fan of fibre reinforcement and use stainless steel fibres, macro and micro fibres and just recently added nano fibres to the armoury which work on a molecular scale using multi walled carbon nano tubes, expensive but increase strength by 50%

[sergetania]

David, hope you are feeling better and out of the hospital!

It seems you use much more than I planned so I have ordered more. I will just throw 1-1.5 lbs of fibers into 80lbs of dry stucco mix. Hopefully, it is not easy to add too much. After curing the render for 2-3 days under the wrap and drying it for a 3-4 days should I wait much longer before I can make pizza?