New build in Barnet

[cobblerdave]

G'day
The solider course should be on the insulation. When the dome insulation goes on it meets up with the hearth insulation effectively encapsulating the whole oven.
The hearth brick will sit in position by themselves no mortar required. If you have the solider course on the outside of the hearth floor mortar the sides of the solider brick but not bottoms. It will form a ring of brick to hold you floor in.
Regards dave

[kaneabel]

Thanks Dave,

All,

I am using CalSil boards as hearth insulation. How are these attached to the concrete base. Can I just use fireclay/sand/ water mix? I read somewhere that CalSil can't be exposed to water and gets destroyed if it absorbs too much water. Also, is the recommendation to cut the CalSil board in circular shape of the oven or just keep them square and build on it, leaving edges exposed to the elements?

Thanks,

[kaneabel]

So today was 'cut the bricks' morning. Got through 45 but found it difficult to get very smooth/precise cuts with a 9" angle grinder. I don't think I am holding the grinder at the correct angle. Need to get it right before I attempt trickier cuts. Any tips based on the attached photo? Don't worry about being rude if I am doing something totally silly.

[downunderdave]

Don't cut any more bricks with that grinder until you get a decent respirator. The dust created from cutting bricks is quite dangerous to your lungs, that's why brick saws have a water feed to reduce airborne dust.

[kaneabel]

Thanks Dave,

Valid point. I used a respirator for most of the 45 till the elastic gave way for the last few, but will fix it before embarking on the next round. Any thoughts/tips on how to get more precise cuts?

[albacore]

What strikes me is that you are trying to cut something that is nearly on the ground, so your back is bent over and you won't be comfortable and won't be cutting accurately. I would say try and get the workpiece up higher on some kind of supporting table. Obviously you need to make sure the workpiece in well secured - you don't wan't it flying past your ear, or worse!
Lance

[myke]

What blade are you using? Also try and get comfortable if I cut on the floor I kneel down and use knee pads. Its also a matter of control the additional handle on the grinder is usually better screwed in near the guard (90 degrees to where it is now) this allows you to hold the weight of the grinder better and therefore get control.
soak the bricks in a bucket for a while before cutting to reduce dust. I rigged up a small spray for mine but be careful as electricidy and water dont mix well.
Holding the bricks steady is helpfull I screwed a board at 90 degrees to another board and used a clamp to secure the brick to it.
Hope this helps Myke

[kaneabel]

Hello,

A quick update on the rather slow progress. Have done the first two courses. Decided to use my home made IT rather than a form. The finishing is turning out to be not so great but will have to do.

Am struggling s little bit with home brew. Am using 4:1:1:1 - sand:cement:fireclay:lime but it does not seem to hold too well and had to re do the first course after it dried out and cracked. Not sure about how strong the end result will be at this rate. Any tips?




Thanks,

[downunderdave]

Sounds like your mortar may be too dry. You could also try dunking your bricks in water and waiting around 30 secs for them to absorb the water prior to laying them, but don't have the surface wet or the mortar won't stick. It's best if they're about half way between bone dry and saturated.

[kaneabel]

Thanks Dave - let me try that this weekend

[kaneabel]

Hello,

I finally finished closing the dome today - see pics below. Hopefully it will hold once I remove the exercise ball support next week. I have a few questions about the next steps - appreciate your advice:

- I am planning to insulate using ceramic blanket. Do I need Vermicrete or is the blanket enough? Do I need anything between the dome and the blanket? How do I bind the blanket to the dome - is chicken wire on the outside sufficient?
- How is the chicken wire bound to the dome?
- I won't have a roof on the dome so need a water proofing solution that will take the English weather. Any suggestions, particularly if I end up not having a vermicrete layer?
- Finally, seems like I will soon run out of summer so may have to do the insulation next year. If so, is the oven safe ok to use the current form without any insulation?

Thanks for all your help as always - feels like the home stretch now!

Cheers,

[oblertone]

If you're using blanket then you won't need vermicrete; both are insulators but vermicrete is cheaper but can be tricky to apply. A good standard is 50mm of blanket, I used 25mm because of space constraints which is adequate but more is better. The chicken wire cage is to key the render without crushing the insulating layer, normally it's just laid on in sections and wired together using little twisted offcuts. K-Rend is waterproof and used by many, it's a two stage process. Before using any render consider how you will protect the exterior corners from water ingress and do that first, then your render coat will come down to cover the joints between the dome and the outer corners.

[bry]

I have seen some one push nails into the insulation board and then tie wire round them and run it over the dome back and forth bit like dot to dot, could be a good way to hold down you chicken wire and blanket. If you use good old fashioned sand and cement render you can get waterproof adatives that also contain plasterciser, they won't make the render completely waterproof but should be sufficient enough to prevent penetration from normal rainfall, alternatively you can get clear coat penatrive water sealers like thomsons, both readily available at most merchants

[downunderdave]

Sept 2, 2016 9:05:27 GMT oblertone said:

If you're using blanket then you won't need vermicrete; both are insulators but vermicrete is cheaper but can be tricky to apply. A good standard is 50mm of blanket, I used 25mm because of space constraints which is adequate but more is better. The chicken wire cage is to key the render without crushing the insulating layer, normally it's just laid on in sections and wired together using little twisted offcuts. K-Rend is waterproof and used by many, it's a two stage process. Before using any render consider how you will protect the exterior corners from water ingress and do that first, then your render coat will come down to cover the joints between the dome and the outer corners.

You can render directly on to the blanket, although it is a little difficult because it's not a firm surface to render against. In addition the surface form is somewhat lumpy and to achieve a nice spherical form then requires a much thicker render layer. A solution to both these problems is to apply a layer of vermicrete over the blanket which evens out the lumpiness of the surface and also adds additional insulation if the mix is made lean. I find a 10:1 mix works well and make the layer around 30 mm thick. Tapping the surface with the flat of a trowel achieves a perfectly spherical form.

[kaneabel]

Thanks Bry, Oblertone and Dave,

A couple of followups:

- any estimates on how many 100ltr vermiculite bags would I need for a 36" oven? Is this the same as garden centre vermiculite? Similarly how much K rend would I need?
- should I start doing the build up fires now or after the insulation goes up?

Cheers,