clay or refractory cement?

[crowx]

I just finished laying the firebrick floor of my first attempt at a Pompei style oven.

Ive set the bricks on fire clay  (powder which I mixed 1:1 with sand before adding water).

Question is, is this same clay mix going to be appropriate for setting and (outer) cladding the bricks building the dome? I plan to use half bricks with a wedge to guide the angle, rather than taper each brick to get the dome shape.

I ask because I read somewhere it is better to use Refactory cement for setting the dome bricks... but then I also read it doesn't cope as well with the larger spaces.... but then I also read that the clay will shrink 10% when it dries out which doesn't sound like it's going to do much for structural stability of a heap of firebricks!

[downunderdave]

May 21, 2016 21:36:38 GMT crowx said:

I just finished laying the firebrick floor of my first attempt at a Pompei style oven.

Ive set the bricks on fire clay  (powder which I mixed 1:1 with sand before adding water).

Question is, is this same clay mix going to be appropriate for setting and (outer) cladding the bricks building the dome? I plan to use half bricks with a wedge to guide the angle, rather than taper each brick to get the dome shape.

I ask because I read somewhere it is better to use Refactory cement for setting the dome bricks... but then I also read it doesn't cope as well with the larger spaces.... but then I also read that the clay will shrink 10% when it dries out which doesn't sound like it's going to do much for structural stability of a heap of firebricks!

Most builders have found what we refer to as "home brew" is perfectly adequate for the temperatures we fire to and actually superior in workability and performance than a dedicated refractory mortars, which are typically designed for much higher service temperatures.



The recipe is 3:1:1:1 fine sand, powdered clay, lime and Portland cement. This mix is used for both the laying of the bricks, including backfilling the large gaps on the outside of the dome, as well as a parging layer over the whole dome.

[crowx]

Thanks. I had read on another site about 1:1 so just went ahead with it. I should have read more on this forum first - I can see there is loads written about homebrew.

Do you think my 1:1 mix to bed the hearth will give me problems then in the long run? Do I need to re-lay it?

[downunderdave]

May 22, 2016 7:12:07 GMT crowx said:

Thanks. I had read on another site about 1:1 so just went ahead with it. I should have read more on this forum first - I can see there is loads written about homebrew.

Do you think my 1:1 mix to bed the hearth will give me problems then in the long run? Do I need to re-lay it?

No the 50/50 sand, clay mix is normal and ok for under the floor because you want the floor bricks to be able to expand and contract freely as they heat and cool. Some builders use it dry rather than wet because it makes floor brick removal even easier. Use the home brew for the dome bricks though.

[crowx]

Thanks for the timely advice today.

Was able to pick up some lime first thing and crack on with the first brick course of the dome using the homebrew ratios recommended.

Nice to see it start to look like something more than a table.

Regretting building it tight in a corner though... I was careful to leave enough room to accomodate the insulation and render layers, but slightly underestimated how much room I'd need to manoeuvre a trowel round there...

[oblertone]

Thick rubber gloves are your friend, NOT the wife's marigolds but heavy industrial ones; remember that cement burns skin.

[SentencedToBurn]

Hey guys, sorry to hijack the post, I saw downunderdave mention the 3:1:1:1 recipe, and I went to look for some lime in my area. Is this what I'd be after? Or is this something else (not sure if you can tell from this description though): www.mitre10.co.nz/shop/garden_centre/growing_media/yates_gro_plus_lime_10kg_138361/

[oblertone]

You need non-hydraulic lime (preferably) which is commonly available in builders merchants in the UK. You can use hydraulic lime, but there is no point as you don't need it to set under water. Garden centres tend to be more expensive than builders merchants for lesser quantities.

en.m.wikipedia.org/wiki/Lime_mortar#Hydraulic_and_non-hydraulic_lime

[downunderdave]

May 30, 2016 23:40:51 GMT SentencedToBurn said:

Hey guys, sorry to hijack the post, I saw downunderdave mention the 3:1:1:1 recipe, and I went to look for some lime in my area. Is this what I'd be after? Or is this something else (not sure if you can tell from this description though): www.mitre10.co.nz/shop/garden_centre/growing_media/yates_gro_plus_lime_10kg_138361/

What you need is Hydrated Lime, it may also be called Builders Lime. Some Garden Lime may not be Hydrated and won't react to create a cement like mix the way builders hydrated lime will. Get it from where you would buy cement powder or bagged mortar and concrete products. Also get your clay from the same place, called Bricklayers Clay.

www.cementaustralia.com.au/wps/wcm/connect/website/packaged-products/home/our-products/trade-tools/hydrated-lime.html