Refractory bond or castable

[Odin]

Let me list the jobs I will have to do and help me to decide which product will be better for my needs

1 bond firebricks hearth with vermicrete base
2 bond precasted dome to firebrick hearth
3 fill inside dome cracks
4 render?

My question is if I can do all above jobs with castable refractory. Where I live I can source bonding and castable in 25 kg bags which is too much than my needs so I would like to buy just one 25kg bag. Castable is 48$ and bond is 65$ per 25kg.

from manufacturers webpage:
Grip- is an air-setting adhesive for bonding insulation products together, or onto refractory or steel surfaces.

Suitable for use with Ceramic Fibre, Insulation brick, Calcium-Silicate and Fibreglass textiles.

Cast- Low Cement and Conventional castables is extensive and is based on achieving the best user friendliness and performance properties. General purpose 1450 grade

[Odin]

Can I use castable to join elements in my premade oven?

[david s]

You should follow the recommendations of the manufacturer of the oven. However, generally the precast ovens are done in pieces so that assembly can be done with manageable sized pieces. The other reason is to allow some expansion to take place where the castings join. Just like conventional masonry the mortar should be weaker than the units it holds. This allows any expansion cracks to take place in the designed positions, just like the grooves in concrete slabs. If you use the same material (castable refractory) for your mortar you run the risk of cracks developing where you don't want them. I use home-brew to hold the casting pieces together for this reason, however, not knowing the oven you have or its design I suggest you contact the manufacturer. Probably not a good idea to fill any joints from the inside that might drop mortar crumbs onto your pizza, just fill from the outside.

[Odin]

thanks but it dos not help with my question.
I will get castable to bond dome to hearth and hearth to base

[david s]

Can I use castable to join elements in my premade oven?

Yes you can, but you may have trouble getting it to bond. The usual regime is to make sure that the surrounding refractory is slightly damp, then apply a thin slurry of pure calcium aluminate cement and water, wait about 10 mins then apply the refractory mortar (calcium aluminate cement and sand). Cover the area in damp sand for 24 hrs if possible Then keep your fingers crossed and hope for the best.

ps. Calcium aluminate castable or mortar does not require extended curing, it achieves full strength in 24 hrs.

[Odin]

I do not really need my castable bond too much as weight of the dome and gravity will do the job.

Is it worth replacing regular cement with castable for vermiculite/perlite mix over for dome insulation?

[david s]

No, a complete waste of money IMO. The temperature seen by the vermicrete is not high enough to warrant it. A better idea is to use at least 25 mm of ceramic fibre blanket over the dome first, then a layer of the vermicrete mixture. The CFB then acts as an expansion joint.

[Odin]

Thanks for clarification!

So I will stick to use castable to bond hearth to my vermicrete subfloor and between dome and hearth.