Anyone Ever Try Mixing Homebrew and Refractory

[robi]

Hello fellow oven builders... On my first oven, I used all homebrew for the dome and flue and it appears to be working as expected, holding heat just fine on pizza night and for next day cooking, however, I was concerned about how hard the homebrew did not get once it was cured, I saved a big chunk of extra homebrew after I cast the dome and it was not as rock hard as I hoped it would be. I am not sure what I did wrong I did research and followed the recipe exactly... I guess now I worry about how long it will last. I always feel like I need to treat the dome as delicately as possible so as not to cause undue wear and tear.

So I am now building my second oven at my vacation house near the beach. I was only able to find five 25kg sacks of refractory for my 36" dome. As we all know our ovens will never reach the temps that refractory is capable of sustaining. So because I am thinking I don't have enough refractory for my dome plus flue... I was wondering if I were to "weaken" the refractory a bit with say 25% homebrew I might be able to stretch what I have to build a nice 2" thick dome.

So have you heard or tried mixing homebrew and refractory? I was also thinking it might make the refractory more workable timewise since the temps on mixing day will be around 80f.

Your thoughts would be greatly appreciated...

Rob

[david s]

This is an old thread and I missed the question, but the answer is definitely no. If you have already attempted it then you probably discovered that the interaction of the lime and portland cement with the calcium aluminate cement in the castable refractory acts as an accelerant. This results in the mix going off as soon as it has been mixed giving you zero working time for its placement. I suspect that you didn't achieve good strength in your original homebrew cast from insufficient damp curing. It must be kept quite moist for a minimum of 7 days (some would say 28) for the hydration process to have sufficient time to build strength. The calcium aluminate cement works by a different reaction and achieves its full strength in 24hrs, so does not require extended damp curing, although I always give it two days.

[robi]

Thank you sir, I have not yet proceeded, but will be in a couple of weeks... my plan now is for the dome to have a layer of refractory probably about an inch, then on top of that a layer of homebrew to increase mass... I will cast the flue with homebrew.

Thank you again for answering the question, hopefully, someone in the future will find it useful.

[david s]

That sounds like a better solution. In order to get a good bond between the two layers you should add the homebrew asap after laying up the refractory. Most castable refractory contains burnout fibres that assist in moisture elimination. This reduces the possibility of steam spalling. You can check to see if it contains these by sieving a small quantity. The homebrew however, needs to have these fibres added. The ones you need are the very fine (finer than human hair and usually around 19mm long) polypropylene fibres used for adding to standard concrete. They do require more mixing than you'd think to disperse throughout the mix, so mix really well.

[Poochdog12]

Hi robi, I bought some bags of grog ( crushed firebricks I guess) went to mix with cement,lime and water. It went hard in minutes so it was unworkable. Have you any advice on the mix I need. Cheers.

[david s]

It sounds like you may have used the wrong kind of cement. If you used refractory cement (calcium aluminate) it reacts strongly in conjunction with lime to go off almost immediately. The homebrew uses normal portland cement (calcium silicate) and when lime is added to it actually extends its working time.Using grog is a waste of money IMO because at the temperatures we fire to sand is quite stable. Taken up to 1000 C it is likely, in the presence of fluxes, to begin turning to glass.