Insulated Pad question

[Abear]

Re: Insulated Pad question

.portland and vermiculite is good for the hearth insulation but I would recommend mixing vermiculite with "Type N" masonry mortar for the outside of the dome...type N is a bit softer and sticks better to vertical surfaces...
Dutch

Do you use the same ratio for above the dome (5:1 vermiculite: Type N mortar) as below the hearth just substituting the portland for Type N?

[Abear]

Re: Insulated Pad question

On that note, another question seeing I'm up to the insulated hearth phase: I bought 3 bags of vermiculite (12 cu. ft. total) and plan on filling a form 24 sq. ft. 6" deep. If all goes well, it should be enough but I fear compression and volume loss once the mixture gets wet. Should I buy more bags before I start or will I get a true 12 cu. ft. of material to use after mixing? Seeing it takes awhile to set, is it OK to add to it later if I due run short and need to make a trip to the store?

[boily]

Re: Insulated Pad question

I did my insulating layer yesterday and used 5.33 100litre bags. My hearth is 1500mm x 1800mm x 170mm. Sorry about the metric measurements but that is what I use.
I hope this helps.

[Wlodek]

Re: Insulated Pad question

Just to report (9 months later) that my hearth construction seems to be working well, there are no structural problems, and the insulation seems to work really well, with the oven hot enough to cook at 200C at noon the day after a dinner time pizza the previous day.

The refractory oven floor rests on some 2in of dry sand, followed by 2in of a high-temperature insulation board, which lie on 4in layer of breeze blocks. The breeze blocks rest on a cement board supported by a number of standard pre-stressed concrete lintels. The bottom of the cement board is always cool to touch even if the oven is a mad inferno.

Once again, many thanks to this community for your support and excellent advice. I am truly indebted to you all.

All the best,
W.

[Dutchoven]

Re: Insulated Pad question

Do you use the same ratio for above the dome (5:1 vermiculite: Type N mortar) as below the hearth just substituting the portland for Type N?

Abear
That recipe should work fine...some builders try to squeeze in more vermic for a better insulation but there comes a time when it would get very hard to work with on the outside of the dome.
Good luck and all the best!
Dutch