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DBinnema 07-21-2014 04:26 PM

Wet premix mortar - crumble risk
I had three tubs of "premixed refractory mortar" (Clayburn set 50 DC is what they call it) sent up to me on a barge, along with a pallet of 200 fire bricks from BC bricks (an effort to make the most of the shipping cost).
A couple days ago I opened a tub of mortar and only then realized that it was premixed WET mortar... new to me; I didn't know that was an option...
I went ahead and mortar-ed my weekend away - I completed the arch and the first FIVE layers of bricks. Used up two of the three tubs. Long days, but looking pretty good.
I then read on this forum that a wet mix like this is best avoided.
I emailed BC bricks (where I ordered the mortar from) for more information (they have been most helpful) - they replied right away and said:
"You are not supposed to exceed ¼” thick. It is actually supposed to be laid 1/8” or 1/16” thick. It is fine for outdoors and it is air setting so you do not need to light a fire to cure it. If the gaps are larger than ¼” the mortar probably won’t dry properly and will start to crumble."

Many of my gaps are significantly larger than 1/4" thick on the outside (bricks touch on the inside of course). I had put small wedges of firebrick in between the bricks (between the rows), and cut the bricks in to wedge shapes to make horizontal gaps smaller - but not to fit tight - and larger than 1/4' gaps.
So, do I:
A) start over with a homebrew mortar like I should have done from the get go (but, this premixed mortar wasn't cheap, I put a lot of time in, and will take considerable effort to deconstruct and clean up all that work)
B) Keep on plowing ahead with periodic prayers to the goddess of fire.
C) What if I finished the dome and coated it in a homebrew mortar that would hold the crumbled mortar in place???
D) Other ideas? (Hint: "Don't worry, it will all be fine" is the answer I seek)

hodgey1 07-21-2014 04:52 PM

Re: Wet premix mortar - crumble risk
DB, I'm nearly certain someone here will have had experience with that product and give you good advice. I used a premix "wet" refractory mortar from a company called Onex, not being a refractory mortar expert I can only tell you that after two summers useing my WFO I haven't had any problem. I had many exterior gaps as large as 1/4".

I would wait to hit the panic button untill you get more input, hopefully from someone familiar with the mortar your useing.

DBinnema 07-21-2014 10:21 PM

Re: Wet premix mortar - crumble risk
Yes - I will hold off on panic. I'm going away for a couple weeks, and will see how things look and feel upon my return - and what the others out there in the great world of WFO makers have to say.
At this time I still hope to carry on as I am - will try to cut bricks to make smaller gaps from here on in.

Tscarborough 07-22-2014 05:01 AM

Re: Wet premix mortar - crumble risk
I would use homebrew or something similar on the exterior and proceed. At thicker quantities that type mortar has a large amount of shrinkage (very small aggregate and very wet blend). FYI, I laid the barrel vault of mine with a similar type and other than making sure the joints on the inside were as tight as possible, I did nothing else other than parge with regular refractory cement and then normal mortar.

kanoer54 07-22-2014 06:47 AM

Re: Wet premix mortar - crumble risk
I also used a wet premix refractory mortar for my dome. Most all of the bricks on the inside of the dome touch and have tight joints. The outside of the dome I used the brick shims and also have larger gaps similar to yours. I do not recall the brand of the mix but I contacted the manufacturer (not the supplier), who gave me the same story as you were told....1/4 inch max. They also told me their instructions error on the side of safety, so I should not have any problems with 1/4 inch or so joints. I did add a 1/2 inch or so layer of refractory mortar with stainless steel needles over the entire dome. I had one very small crack on the outside which I went over again with the refractory mortar and since have had no problems with the dome. There are others who have a lot more experience than I who may respond with different advise.


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