Rendering a dome - advice please!

[flyingwild]

Hi All,

I was fortunate enough to pick up an Orchard Ovens Originale 100cm WFO off Freecycle last year. Benefits of living near the Cotswolds I guess  . I've finally managed to get round to building an outdoor kitchen and have got to the stage where I'm ready to render the outside. This is where I'm a bit stuck. I've used a square mesh to hold the insulation in place as I had a roll to hand, but wondering whether I ought to get some hexagonal chicken wire instead so it's more form fitting to the insulation? The other idea I've had is to put some concrete screws into the base and use some fine wire to pull the mesh tight against the insulation.

From reading up and looking at Youtube, I think I need to do a base 'scratch' coat to cover form the dome shape, smooth that down and then apply a finishing coat. Is there anything special with regards to the mixes I'll need? I've got plastering sand, hydrated lime and cement ready to go. Do I need a waterproofing agent in the base coat?

Advice appreciated.

Thanks
FW

[downunderdave]

May 6, 2022 19:38:08 GMT flyingwild said:

Hi All,

I was fortunate enough to pick up an Orchard Ovens Originale 100cm WFO off Freecycle last year. Benefits of living near the Cotswolds I guess  . I've finally managed to get round to building an outdoor kitchen and have got to the stage where I'm ready to render the outside. This is where I'm a bit stuck. I've used a square mesh to hold the insulation in place as I had a roll to hand, but wondering whether I ought to get some hexagonal chicken wire instead so it's more form fitting to the insulation? The other idea I've had is to put some concrete screws into the base and use some fine wire to pull the mesh tight against the insulation.

From reading up and looking at Youtube, I think I need to do a base 'scratch' coat to cover form the dome shape, smooth that down and then apply a finishing coat. Is there anything special with regards to the mixes I'll need? I've got plastering sand, hydrated lime and cement ready to go. Do I need a waterproofing agent in the base coat?

Advice appreciated.

The wire solution is difficult and time consuming. Applying it over a compound curve is not easy to get it even. One little trick you can employ is to grab the mesh, with the nose of some standard pliers,  in a spot that appears a bit loose and twist 90 degrees. This will tighten that area. This procedure can be repeated wherever it seems a bit loose. As this is such a laborious process I have developed an alternative method that I now prefer.
The blanket is too soft to act as a firm substrate to render against and the mesh does a good job of stiffening the surface and providing reinforcing for the rendered layers. But I find a layer of around 35mm of 10:1 vermicrete (see table for strength/insulation values) applied over the blanket will even out even extreme lumps and bumps of the blanket as well as providing a similar insulation value (for thickness) as the blanket. As it is far cheaper than blanket, some savings can be made here. It should be applied form the bottom up and to improve the stickiness a little powdered clay can be added to the mix to make the lean brew more workable. Allow to dry for a week then do the 7 fires in 7 days getting progressively bigger. Being very lean it’s not particularly strong, but firm enough to render against. To reinforce the rendered layer I add random mixed AR glass fibres to the render and apply it in one single layer around 12-15 mm thick to save time. Wet sponge to take out tooling marks and it’s done. To enhance the outer rendered shell strength I then wrap the whole oven in cling wrap to hold the moisture in that layer for a week.
After several firings I then coat the outer render in a waterproof acrylic product.
This method saves a lot of labour although there are more waiting periods to either remove or retain moisture in certain areas.

[downunderdave]

Here are couple of pics of a corner build 160cm internal diameter oven I recently built. As it was a corner build and access to the sides and back was limited the blanket insulation is only 2" at the sides but 5" on top. The pic shows how the vermicrete insulation restores the shape , evening out bumps in the blanket without the use of any time wasting wire mesh.

[flyingwild]

This is what I ended up with today. First coat. Thanks for the advice.

[downunderdave]

]This is what I ended up with today. First coat. Thanks for the advice.

That looks great. Don’t be in a rush to start any fires yet. Better to allow sun and wind to drive out the excess free water for a week first. A garden moisture meter is useful here before beginning your first fire.

[downunderdave]

Just taking a closer look at Orchard ovens Originale 100. According to their website their ovens are Valiorani imported from Italy. Yours looks nothing like a Valiorani. On a closer look at your posted pics it appears as if there's no underfloor insulation. This would not surprise me because a Valiorani 160 I built recently also came with no under floor calcium silicate insulation. I had to source it separately and put in two layers of 40mm thick each, between the supporting slab and the cooking floor. A lot of folk think that heat rises and it does by convection, but it doesn't care what direction to flow to by conduction.