Refractory Mortar Poll

[berryst]

Re: Refractory Mortar Poll

I used:

10 sand
6 fire clay
2 portland cement
2 lime

I have been using the oven for over a year. I like using it in winter here during the long and rainy seattle/north west winter.
I have no spalling or cracking of any kind. Seems like a lot of you like the spendy heat stop . Seems like its not a bad Idea but my mix works just fine and its a lot lot cheaper
berryst

[splatgirl]

Re: Refractory Mortar Poll

I used Sairset premixed, air drying. I'm not sure i'd recommend it, but it sure was a time/waste saver not having to mix mortar every time and it was very easy to work with otherwise as well. I did get some cracks, but no more so than what I would have expected with any other product and no worse than what I've seen posted here. My joints are not very tight. I used 3 pails for my 36" ID oven at a cost of $52 for 55 lbs.

What I think is questionable about it that I didn't consider beforehand is that it needs to be fired to cure which is presumably not a problem for the dome, but...I have no idea what the curing temp is, and I'm fairly certain the front of my arch and vent would never get up to that temperature anyway, so basically I'm assuming those parts are never going to "cure". I didn't think about this until after the fact. I'm not sure it's an issue, but talk to me in five or ten years and we'll see. Right now, I can't say I'd have chosen differently even if I had considered the above, because not having to mix and adhere to the timing of cementitious mortar was a HUGE benefit, IMO.

[ThisOldGarageNJ]

Re: Refractory Mortar Poll

Seems like a lot of you like the spendy heat stop . Seems like its not a bad Idea but my mix works just fine and its a lot lot cheaper
berryst

Hi Berryst... It really wasnt a matter of liking the heat stop 50,It did work well but, It was readily available and a known used product, Being an amateur mason I prefer to remove as many variables as possible.... and sourcing fireclay wasnt working out too well, There were no shipping charges on the heat stop either as they had it where I got my fire brick

[jmhepworth]

Re: Refractory Mortar Poll

Hi Berryst... It really wasnt a matter of liking the heat stop 50,It did work well but, It was readily available and a known used product, Being an amateur mason I prefer to remove as many variables as possible.

Exactly. That's why I used Heat Stop. It was rather expensive, but it worked.

Joe

[Lars]

Re: Refractory Mortar Poll

My mix, very similar to BerryST... 3:2:1:1/2 ( Fine sand, Fire clay, Portland, Lime)

Oh what a wonderful mix. The Portland holds it together so tight while under construction, then burns out when you cure the oven (AFTER you have a waterproof dome, right?)

When you fire it up to full temp, the fireclay becomes brittle and non-absorbent. Any gaps in there filled with fireclay mortar simply become like more firebrick over the years.

A joy to work with, not exorbitantly priced, classic fireplace mortar.

I mixed it up in the buckets I got from a kiln supply place here ( that had a few inches of high test ==water soluble== heat resistant mortar) hold the fancy expensive stuff that NEVER would have worked on this oven, out doors...

Just scoop 6 sands, 4 fireclays, 2 portlands, and 1 lime, pour it into a hod and mix for maybe 5 minutes, pour it back into the big plastic bucket with the sealing lid, and then mix up enough for a 1/2 chain at a time. Then next day your work is stuck down like a rock.

[kebwi]

Re: Refractory Mortar Poll

Thanks a lot. Maybe I'll use homebrew for most of it and buy one bag of HeatStop for the arch, or something to that effect. I don't really know.

I need to get the "right" homebrew ingredients I suppose. Is there variation in fireclay or lime? I honestly don't know. As to sand, my understanding is really fine white sand is my goal, finer than normal playground sand.

Is that right? What about lime or fireclay? Is there variation in those?

[Lars]

Re: Refractory Mortar Poll

I am sure in the Seattle area you have many clay artists and fireclay suppliers. The sand is often called silica sand, ( about 4-5$ at Lowes or Home Depot)

Lime is lime... Portland come is 90lb bags for about $12
So, to get started, you will only spend about 12+20+12+12.~ $56 for 150lbs of sand, 80lbs of fireclay, 90 lbs of Portland, and 90 lbs of lime... enough to do most of the oven, if not the entire thing.

[DimTex]

Re: Refractory Mortar Poll

I used the home made formula from the plans. For me it worked out well and I felt I had a little more control in how it worked (sand particle size, amount of fireclay). Building this oven in Texas during the hottest summer I can recall made this control all the more important. Besides the cost of buying sand, fireclay, lime and Portland cement locally was so much cheaper I would probably do it again.

[cynon767]

Re: Refractory Mortar Poll

I am only on the third chain up, but have been using a homebrew mix slightly higher in sand and clay than the one in the plans, of 4:2:1:1. So far, anyway, it is going well.

[kebwi]

Re: Refractory Mortar Poll

@cynon767: May I ask your reasoning for altering the ratios? I'm unclear on the motivation for the original ratios.

[cynon767]

Re: Refractory Mortar Poll

kebwi- Initially, it was an accident. I had extra clay/sand left over from leveling the floor, and mixed it into the rest of the ingredients at the incorrect proportion. After reading up on the forum out of fear that I had done something terribly wrong, I came to the conclusion that it was probably fine. The word around the forum is that portland burns out at higher temps, so it's basically just there to harden up and hold things together until the clay/lime/sand can fire into dozens of little keystones. With extra fireclay, the mix was very creamy, spreadable, and sticky. The extra sand seems to balance out the clay and I haven't had any real cracking from shrinkage. I did end up with a few cracks in the soldier course while setting the second in place, but I'm pretty sure that was from a combination of having set the soldiers too dry and too-vigorously tapping the bricks in the second course to fit into place.

Upon reflection, the mix was more like 3.5:2:1:1 (3 1/2 sand, not 4 as previously stated.) Very similar to both Lars and Berryst.

If I remember correctly, the original mix was based on a low-portland mortar with fireclay added for thermal stability.

[papavino]

Re: Refractory Mortar Poll

Heatstop 50. It was readily available, albeit about $76 a bag. Used about 3 1/3 bags for my 36" pompeii.

[philiph4@ameritech.net]

Re: Refractory Mortar Poll

I used Plibrico Super Demon pre-mixed mortar. Has anyone else used this stuff?

[dmun]

Re: Refractory Mortar Poll

I used Plibrico Super Demon pre-mixed mortar.

Is this the wet stuff in tubs? This has a bad reputation around here (won't dry, isn't waterproof etc) but let us know about the brand you're using.

[ThisOldGarageNJ]

Re: Refractory Mortar Poll

is it refractory ?