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azpizzanut 10-25-2010 11:23 AM

Combine Mortars
This is probably a classic newbie question but maybe some of you can shed light on the question.

Is there a problem using Heat Stop 50 to hold the brick in place (Pompeii 36") then using homemade refractory mortar to fill the voids? I haven't started yet but would like to avoid buying a second bag of HS if it's practical to combine mortars.

My question is based on recommendations to keep the Heat Stop joints thin, yet the need to fill voids at the outside of the dome.


tusr18a 10-25-2010 07:56 PM

Re: Combine Mortars
I wish I had asked the question. My local masonry supplier only sold the Heat Stop in popcorn bucket size containers. I am embarrassed to say how many of those buckets that I used. I honestly think my mortar expense was higher than my brick expense. In hindsight, I should have ordered the 50 lb bags of heat stop. Even after calculating freight, I would definitely have been better off financially. Also, I should have considered tapering my bricks. This would have saved a lot of mortar. As to the homemade brew, I did not use it. If you are new to masonry, like I was, there is enough stress trying to get the bricks in place. I am not sure that I would want to add the stress of moving back and forth between the two mortars. Here is a link to my build: Picasa Web Albums - Daniel Woodruff - Wood Fired Oven

dmun 10-26-2010 04:16 AM

Re: Combine Mortars
The problem with this plan is the difficulty of filling all the voids. I saw a slide show of a professional oven builder who mortared the inner edges of the bricks together, then after the dome was done he filled the voids with some kind of refractory slurry.

As far as working two different kinds of mortar at once? Forget about it. Hard enough to manage one. My suggestion? If cost is an object, use the homebrew mortar, with fine sand.

And TUSR: 10 pound buckets? Wow. How many did you use? 15?

tusr18a 10-26-2010 05:14 AM

Re: Combine Mortars
Unfortunately, even more than that. I lost count. I am going to write it off to experience. As to the professional dome, I saw that video clip too. The professional used a sand dome. I would suspect that the mortar slurry would not work unless you used the sand-dome approach. Otherwise the slurry would end up on the hearth floor.

Neil2 10-26-2010 09:06 AM

Re: Combine Mortars
I used the mortar "neat" where the joints were small, typically the inner 1/3 or so of the brick. I filled the remainder of the voids with mortar extended by mixing 1:2 with mortar sand.

azpizzanut 10-26-2010 11:46 AM

Re: Combine Mortars

Wow, you took on a huge project. I don't think I've seen such a massive masonry effort for a wfo. I like the masonry base, red brick on the outside and you did a great job on the Pompeii too. more >


Nice approach to the issue. Did you fill the voids right away? How much time elapsed between laying the brick and filling, or did you do several, or wait 'til the end? more>


Thank you for your comments. I have materials at hand to do either method suggested. I'm at conflict with the manufacturers instruction for a thin mortar joint vs the huge volume of filling in the gaps. A less expensive and still suitable refractory mortar to fill the void seemed practical. You might have guessed that I think Heat Stop mortar is preferred over home brew and that is why I want to use it for the critical hot face joints. And, I'm over-thinking the "problem" a bit too.

What I've learned so far: compatibility of the different mortars is not an issue (unless someone with specific knowledge provides input to the contrary); Cost and degree of difficulty handling two mortars are important considerations (but not the only ones).

After seeing the humongus undertaking by tusr18a my problems seem small by comparison. If my build turns out half as nice as his then I'll be happy. I'll wait for more input on the mortars issue before I start. That will allow me time to consider everyone's input. I'm doing the insulation concrete a few days I'll lay my first bricks.


fxpose 10-26-2010 11:56 AM

Re: Combine Mortars
I forced home brew mortar into all the wide outer joints with my pinky and with a pointed trowel until they oozed out of adjoining voids. I usually did this the next day or the day after.
I was pretty confident that the mortar was solidly imbedded.

azpizzanut 10-26-2010 06:53 PM

Re: Combine Mortars

I like your thinking. That is the way I would approach the build.

The hearth insulation is finally done. arms are sore from mixing. 4 cu ft of perlite with Portland cement, 5:1 mix. The last inch on top was a dedicated insulating refractory left over from another project. Total depth is five inches. Next step is to review the plans and start cutting bricks....then laying bricks....then reviewing plans again. More Q's later.

Cheers, and thank you all for your comments.

dublintom 10-27-2010 03:40 PM

Re: Combine Mortars
1 Attachment(s)
I used 2 mortars while building the dome because my bricks were tapered between the layers. I used a high heat mortar between the layers of bricks which was very thin and to the front of the side of the bricks and after each row was completed i threw i in home brew mortar to fill the wedges at the side of the bricks. I did this because as you have said the high heat mortar should not be more than 3mm thick and therefore it is not suitable for filling up large areas. I used the trowel to literally fling the homebrew between the bricks and a slicing action with the trowel on the mortar to compact it. I had no problem dealing with two mortars as i only mixed small amounts in a bucket using a paddle and hand drill. Picture attached to illustrate

azpizzanut 10-27-2010 06:07 PM

Re: Combine Mortars
Thank you dublintom.

Nice workmanship on your oven.


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