Mortar Mixes

[Spinal]

Right,
so first and foremost - let me get this out of the way:

I realise this is excessive and most people have had great results with portland mixes to bind their fire bricks.

Being a nerd/geek - I tend to over-engineer things if I can.

So I'm looking for the most refractory mix I can find; and after some research (many thanks to kerneos and cimentfondu) it would appear that they would recomend mixes of 6:4-6:6 of chamotte (or crished firebrick) to HAC. Also, they don't suggest using sand over 500C.

Has anyone tried this?

Similarly, I was planning on changing the recipe slightly and replacing the pure chamotte with equal measures of chamotte and fire clay. Idea being that the fire clay should act as a binder if the heat gets hot enough, right?

M.

Sources:
http://www.cimentfondu.com/gb/artisa...arConcrete.pdf
http://www.kerneos.com/IMG/pdf/CF_GB.pdf (last page for high temp applications)

[nissanneill]

Re: Mortar Mixes

Don't waste your time with special mixes and preparatory mixes. Use the poor man's mortar an you will get the best result at the cheapest price. with the least problems.

Neill

[Mistertoy]

Re: Mortar Mixes

I used 4:1

For mortar the CF_GB.pdf indicates 4:1

To be a workable mortar, I found that I had to use more water than this data sheet states. I read than someone else had similiar experience. I did quite a few small trial mixes to compare consistency and setting time.
With only crushed firebrick (3) and fireclay (1), it was a very dry and stiff mortar. I found that the sand made it much more workable mortar.

So I suggest you make up some very small batches and then you can get an idea of the amount of water, consistency and setting time.

Brett

[Spinal]

Re: Mortar Mixes

nissanneill:
It's a bit like cars - while a Daewoo Matiz will get you from point A to B, I would prefer not to be driving a matiz... a bit of an extreme example as a matiz is utter cr*p - and the OP mortar mix I'm sure works... let's say the 3111 OP mix is more of a fiat... it works, is cost effective and most people use it. I would rather be in something a little more... "specialised"

Misterytoy:
Cool - thansk for the info! How much sand did you end up putting? I presume you did 3(grog):1(fireclay):1(hac):??(sand). I'm having a luau party, and have ordered 3 tons of sand to convert my patio into a beach... so sand wont be missing...

M.

[Mistertoy]

Re: Mortar Mixes

I found that 2 sand;1 grog;1 fireclay; 1 ciment fondu gave a workable mix, but I have not fired my oven yet. I figured that if the poor man's mortar uses sand then ciment fondu is going to work fine with sand and replacing one part of sand with grog is a bit of me being geeky myself.
I also wet my grog and fireclay with some of the water first and let stand for 10 minutes or so so it absorbed water before doing final mix with ciment fondu and last amount of water to get the texture right.

Hope that helps
Brett

[shuboyje]

Re: Mortar Mixes

Your analogy is all wrong. Hombrew mortar is like having someone give you the perfect car for your needs. Refractory mortar is like someone giving you a super expensive luxary sports car that seats two, gets 4 miles to the gallon, and is always broke down.

Home few mortar has proven many times to be superior. It is cheaper, easier to work with, and leads to a better result with less cracking. And as a guy who has demod an oven built with it I can tell you it's strong as heck and bonds great to the brick.

nissanneill:
It's a bit like cars - while a Daewoo Matiz will get you from point A to B, I would prefer not to be driving a matiz... a bit of an extreme example as a matiz is utter cr*p - and the OP mortar mix I'm sure works... let's say the 3111 OP mix is more of a fiat... it works, is cost effective and most people use it. I would rather be in something a little more... "specialised"

Misterytoy:
Cool - thansk for the info! How much sand did you end up putting? I presume you did 3(grog):1(fireclay):1(hac):??(sand). I'm having a luau party, and have ordered 3 tons of sand to convert my patio into a beach... so sand wont be missing...

M.

[deejayoh]

Re: Mortar Mixes

There is over-engineering, and there is over-thinking. They aren't the same thing - but people often confuse one for the other.

In this case, I think it's overthinking.

[Spinal]

Re: Mortar Mixes

Here's a query for the portland supporters (didn't want to get into this debate, but seems inevitable :P) - has anyone used a high-alumina refractory mix as mortar? Similarly, have you made a cast oven? (the mix I'm aiming for is very similar to a cast oven mix - bar the sand).

If homebrew is the perfect mix, have you tried making an entire oven out of it? I.e. a cast oven (like a clay/cob oven) from it? How did it react?

Regarding price differences, I don't know prices in the US - but in the UK it's not so different between the two mixes. I found a place selling cheap reclaimed crushed firebricks (36% minimum alumina content) which should work quite well. Fireclay is dime a dozen here (currently at a client in the area that used to run the entire ceramic industry in the UK) and actually works out cheaper than silica sand if I order it by the tonne (cheapest sand I can find with delivery is ?44 for 850kg (or from another company, ?38 + ?25 P&P); while the cheapest fireclay is ?12 + ?25 P&P for a 1000kg - but they're only a few miles from my house... so may be able to negotiate a cheaper dropoff when they deliver to another client). Yes, HAC is about 4x the cost of OP - but then again, I only need 2 bags or so, thus the price difference here is minim`al.

Finally, how long did you wait before starting a curing fire? The oven in case needs to be comissioned in 7 weeks - and most suppliers seem to take about a week to deliver. Given that I work Mon-Fri, it probably wont be ready for its first fire until 1-2 weeks before when it needs to go live. According to kerneos, I should be able to run a curing fire after 48 hours, and have it operational at full temperature 3 days after that.

Anyhow, back to the point

Brett - thanks! Did you experience any shrinkage? Speaking to cimentfondu (they're amazingly helpful on the phone!) they suggest raising the amount of chamotte if shrinkage occurs... but I'm worried it won't be that workable.

Did you experiment with retardants/plasticisers? 0.2%-0.3% of trisodium citrate seems to work quite well with HAC; serving both as a plasticiser and a retardant. That said, I have no idea how it reacts under temperature... guess it'll be another call to kerneos!

M.

[david s]

Re: Mortar Mixes

If you have your heart set on using calcium aluminate cement you would be better off going to a refractory supplier and buying a few bags of mortar already made up. Personally, I think the home brew mix is a better option. Trying to make up your own formulation is fraught with problems and you will inevitably change your brew at least once during your build. The calcium aluminate castable I use, from the manufacturers recommendations, only requires 24 hr curing unlike Portland cement products which ideally need 28 days.Regarding workability of the mix, I use chilled water to retard setting. It is very temperature sensitive.The stuff is also really touchy with superplasticizers, another good reason to use the home brew IMO.

[Spinal]

Re: Mortar Mixes

wotavidone - by going to ceramic manufacturers, I've found prices vary quite a lot. i like the look of a brick oven, and fire bricks are quite cheap (medium duty, 230x114x76mm fire bricks, 42% alumina cost ?1-?1.29 a brick). They may not be heavy duty, but then again, I don't plan to smelt anything in the oven

The excess... not entirely sure. I'm considering coating the bricks to increase the thermal mass (before putting the blanket on)... also the enclosure I have designed is a little different from the norm; the flue, while 36" tall, will not protrude from the enclosure. So I may coat the steel flue with a fireclay/vermiculite/HAC mix before enclosing it all...

That said, with 900kg of clay left over or so I'm thinking I may just put it on freecycle. Or give it to my other half (art history major for her first degree) and see if she can make something useful A big clay sofa for the dog... at least he wont be able to tear it apart once it's fired... :P (I jest... freecycle probably to get rid of it)

Regarding prices - I did cheat a bit. The 4x ratio of the cements is based on retail prices. If I buy OP bulk (10+ bags) or HAC bulk (10+ bags again) I can get the ratio to 6x... so yes, HAC is more expensive... but given the small quantities... meh

Fireclay here is quite expensive if bought in small quantities. A 25kg bag is ?15-?30 depending on suppliers. But ordered by the tonne; the price is actually cheaper (odd, I know). I think it's because it comes from the old coal mines and they want to get rid of it... but I'm not sure.

david: I did consider ready made fire mortar, but it costs ?30 for a 25kg tub. Depending on the mix, I'm looking at a cost of ?0.50 per kg of HAC mix at the most... at which price I can afford to waste a few kilograms testing and trying.

M.

[shuboyje]

Re: Mortar Mixes

Now you have me confused. Are you looking for a mortar to use in an oven build from brick or a castable refractory? The two are very different things.

[GianniFocaccia]

Re: Mortar Mixes

Shuboyje,

At the risk of stepping on this thread, what is the viability of constructing a brick pompeii dome (quickly) by initially mortaring (homebrew) only the inside-facing joints, and finishing the backside all at once by pouring in a refractory cement 'slurry'?

I know there's a famous Italian oven-builder who does something like this. I was wondering if this is a viable approach for a home-built oven?

[shuboyje]

Re: Mortar Mixes

It's a speed thing. The italians feel the entire dome needs to cure together and to do so the dome should be built in one day(their logic not mine). I'm sure the speed is just as much a factor for economic reasons.

By using this technique and a sand form the dome can easily be built in a day. I used a modified version in my oven, and it really is lightning fast. To do it you do not mortar between bricks within the same course, you only mortar between the courses(I have a graphic I made to explain this somewhere). This leaves the dreaded triangular gaps that many Pompeii builder taper bricks to avoid as empty voids in the bricks work. Once the entire dome is formed this way a slurry of some sort of refractory material is poured over the dome to fill all the gaps and complete the dome. In the US I could not find a product on the market made to be mixed wet enough for this procedure, so I used a stiff mix of castable refractory and rodded it into each gap.

As for your question about facing the joints in homebrew and then back filling them with commercial refractory mortar, that is the opposite of what you would want to do in my opinion. One of the problems with commercial refractory mortars in dome ovens is that they are generally made for 1/8" mortar gaps. Homebrew mortar does a much better job with the larger gaps. So if you wanted to do a hybrid system commercial refractory mortar in the small gap inside the oven and then homebrew as the gaps widens at the rear would be a better option.

[david s]

Re: Mortar Mixes

An Italian friend of mine built a red brick oven using this technique. He used half bricks, roughly cut with a bolster, untapered, laid up against a sand dome. The bricks had lots of wooden wedges sticking out on the outside. Once he'd gone up a few course the bricks were back filled with home brew, removing the wedges at the same time. It is quick and easy and probably produces as good a result as meticulously cut individual bricks.
Unfortunately he did not take my advice and failed to insulate under the floor. He subsequently had to retro fit some insulation under it later.

[Bacterium]

Re: Mortar Mixes

David S .......speaking from experience on my first oven I tend to agree. Sure on my current build I will use my bricksaw to some degree to reduce the gaps inside the dome .... but plenty of homebrew elsewhere and homebrew "capping" the outside, before blanket insulation will give an oven a bit more mass. Reduce the airgaps and one whole mass that's effectively entomed by the outer insulating and render layer should be ample methinks.

Spinal I was thinking refactory mortar for a while but home brew seems to clinch it for me..and my first oven wasn't even homebrew and its results after 4years use was surprisingly minor cracking, no flaking etc......mmmmm.