Manchester Pizza Oven Build

[loumw]

Hi people, new to this forum which we’ve recently discovered and has been very helpful as me and my mate are currently in the process of building a pizza oven, photo attached of where we’re up too, (ignore the sloppy brickwork! First time doing so got the repointing to come later!). Basically we don’t have the budget, (or skills!), to do the dome out of firebricks so are planning on making the dome from what we’ve seen called a Homebrew mix which is, correct me if I’m wrong, a 3:1:1:1 ratio of Sand, Cement, fireclay and hydrated lime. Not completely sure of which sand is best which is why I’m here but for this mix is sharp sand, kiln sand, builders sand etc best for this? We thought kiln may be best as this dome is what takes the heat but have also read sharp sand so just want to be sure on which to use! Let us know if anyone has any past experience on this and other tips which would be helpful as hopefully starting on the firebrick base and then dome this week! Thanks, Louis & Oscar

[UtahBeehiver]

David S is our resident cast oven home brew guru. Look at his post and threads. He always is willing to guide our cast oven builders.

[loumw]

UtahBeehiver Thanks for the reply and guidance! Will look into David S’ threads and give him a message about it - a home brew guru sounds like the person we need! Thanks again.

[david s]

Hi people, new to this forum which we’ve recently discovered and has been very helpful as me and my mate are currently in the process of building a pizza oven, photo attached of where we’re up too, (ignore the sloppy brickwork! First time doing so got the repointing to come later!). Basically we don’t have the budget, (or skills!), to do the dome out of firebricks so are planning on making the dome from what we’ve seen called a Homebrew mix which is, correct me if I’m wrong, a 3:1:1:1 ratio of Sand, Cement, fireclay and hydrated lime. Not completely sure of which sand is best which is why I’m here but for this mix is sharp sand, kiln sand, builders sand etc best for this? We thought kiln may be best as this dome is what takes the heat but have also read sharp sand so just want to be sure on which to use! Let us know if anyone has any past experience on this and other tips which would be helpful as hopefully starting on the firebrick base and then dome this week! Thanks, Louis & Oscar

Hi Louis and Oscar,

I first came across the home-brew recipe on this site more than 20 years ago, but I suspect it has been around since the invention of Portland cement in the mid 19th century, where Portland cement quickly replaced the lime mortars used in building.
Because Portland cement is susceptible to degradation from high heat where it begins to fail over 300C, the lime which is more resistant, beginning its failure higher than 500C, takes over. This explains the over rich presence of cementious material in the recipe. A combination of cement and lime of 2 parts to 6 total (33.3%). The clay in the recipe is designed to take over from the lime after its failure, but as clay does not begin its chemical change making it permanent until around 600C, which is higher than the service temperature of a WFO, should only therefore be considered as an aggregate.
The home-brew recipe has received accolades for years as a mortar for brick built ovens, proving its longevity, workability, availability and cheap price, over proprietary refractory mortars. Because something is rated to withstand a far higher temperature does not guarantee its suitability for the purpose required.

Sand: In my view any sand should suffice, but sharp sand having sharper grains theoretically has greater holding power. On the other hand because builders sand contains a range of grain size (graded) is more suited as a castable (a range of aggregate size has been proved to provide greater strength in concretes), although fine grains are preferable if the sand is to be used as a mortar and these are usually sifted out if used for this purpose.. For the service temperatures we fire to there is no danger of the sand turning to glass in the presence of contamination by various fluxes, as would happen if used as a refractory mortar for a kiln.

cement: Normal builders general purpose cement should be used

Lime: Builders hydrated lime should be used, not agricultural lime, Be careful, like cement it is injurious to skin, but far more so, gloves are advised and quite dangerous if you get any in your eyes.

clay: powdered clay should be used, but be careful, We want the cheapest powdered clay available. in the US the building industry calls it "fire clay" but to a potter "fire clay" is a different animal. To them it is a refined pure clay able to withstand extremely high temperatures and therefore expensive, you don't need this although the cheaper "ball clay" would suffice.
Apart from the clay providing a refractory quality it also has the advantage of imparting stickiness to the mix which is of great assistance in the mix being nicely workable because it holds the other materials together really well. Unfortunately it also has a drawback in that it imparts shrinkage on drying. Industry has determined that it also improves strength if added to normal mortars, but not to exceed 7% of the total. (The 3:1:1:1 recipe would put it at 16.7%) The reason is that the shrinkage it imparts is excessive and I have observed this problem in its use as a mortar. Additionally if use as a cartable over a mould, it leaves nowhere for the casting to shrink to making shrinkage cracking a greater problem. For this reason I advise builders to reduce the recipe to 3:1:1:0.5 (halving the clay content) as well as removing the sand mould out of the mouth of the oven after 24 hrs or the casting has set a little and is in no danger of collapsing. This then allows the casting to shrink a little more.

Go the the Forum and look up cast builds under Other Ovens and you will find plenty of well documented home-brew builds, it is easy, fun and cheap. Might not be quite as good as a manufactured one, but we've had no reports of failures.

[UtahBeehiver]

I forgot that the build by Nick JC was a cast oven, done very well, and from the UK. He documented the build well and also listed where he procurred his materials. Look up his thread under Nick JC.

[loumw]

Wow. Thankyou so much for taking time to give us such an in depth response david s! That’s all very very helpful. Especially the fire clay and removing the sand mould after 24hr’s. We’re pretty new to this and trying to do on a budget, (without letting it affect the quality of the build!), so finding this forum has been a bit of a revelation haha, so we really appreciate you’re help. We want to keep posting our progress of where we’re up too because we’ve loved reading and seeing all the other builds. What’s the best forum/thread to do that in? I’ve realised we’ve gone in the materials one so probably not best for daily/weekly updates of our build. Another question we had, as just picked up the fire bricks today. When setting them on the sand, how would recommend us to set them in place? Does the sand just do that job or do we need to put a layer of refractory cement around them to hold them in place? Or the homebrew mix? We’ve seen people do different things again so not sure if the homebrew mix sits on top of the fire bricks or around. Also thanks UtahBeehiver for telling us about Nick JC, just been looking at his build, it’s amazing! Thanks, Louis and Oscar