Portland cement way downstream?

Hi

I've wondered about this many a time, did many a search, and found nothing, soooo...

Would Portland cement be suitable way downstream in a J-tube system, like in bell #2's brickwork over here:



Obviously one wouldn't use it in the burn chamber or riser or anywhere near the top of a first brick bell, but the relevant brickwork in this design only starts after bell #1...

Thanks.

Hi David;
Indeed, you can use portland far enough away from the high heat areas.

I myself have used it in the bottom level's of a bell.
However,  why would you want to?  
The only reason I used portland in the lower levels was to confirm that nothing  could bang into the bell and have it fail.
After building the rest with clay mortar I can sure tell you which one is easier on your hands!  
Clay is worked bare  handed, for portland I must wear thick rubber mechanic gloves.
Properly made clay mortar)    One part dry fireclay , and 3 parts commercial grade medium sand  makes for an excellent mortar!
Quite resilient ,  if it cracks,  a simple wet finger with new clay mortar will fix it right  up!
Best part is your hand's are smooth and soft!

Your drawing is not quite what you described.
The smaller brick box is a core. It must be clay mortar or expensive refractory mortar (That will crack)
There is only one "bell" in your drawing .
The lower levels could be portland but from the core on up I would use only clay mortar.

Thanks for your reply, Thomas.

Why would I opt for Portland cement downstream? Because I really battle to source clay in my part of the world, namely South Africa. It really is the biggest hassle I have when building TMHs. Now I have a client who wants a quick build, and he will organise a brick-layer, bricks and cement. I just have to arrive with the core.

I've built several TMHs now. I did one very similar to the design. Here's a pic near completion. Note that I did use clay, and I enjoyed working with it, but I had the time to source the materials:



I am well aware of the terminology, especially when it comes to the core, and I make the burn box from CFB, as shown in left of picture (though I did not use CFB for the burn box in the previous pic, but rather fire-bricks):



When I used to spend more time at donkey32, I often used to see both the barrel-radiator and the brick thermal mass bell referred to as bells. I find it very useful to refer to bell 1 and bell 2 when discussing designs rather than 'barrel-radiator' and 'brick chamber' or whatever.  

So just to be clear:

I am using the term bell 1 to describe the barrel radiator.

I am using the term bell 2 to describe the brick bell.

In my first post, I wrote "Obviously one wouldn't use it in the burn chamber or riser or anywhere near the top of a first brick bell". Note the term "a first brick bell", which is a hypothetical first brick bell because my bell 1 is a barrel radiator.

So sticking with those terms, let me ask my question a little differently.

Considering that most of the heat will be emitted through bell 1 (the barrel radiator), and that the temps entering bell 2 (the brick bell) will be below 100 degrees C, and that the burn box in this design will be made from ceramic fibre board...

...will portland cement fail if used for all the brick-work?

Judging from your reply, Thomas, where you said "Indeed, you can use portland far enough away from the high heat areas", I think my question is answered. Many thanks.

Quick feedback on this topic.

I spoke to a very helpful rep for the cement (etc.) company called PPC here in South Africa.

Surprisingly, he said he had never looked into the maximum temperatures for the company's various cement products. After speaking to his technical people, he got back to me and said when used in a mortar mix, anything below 500C is fine.

He said that the data sheets don't contain temperature specs because structural integrity under high heat (and other conditions) will depend on what people do when mixing the cement, as well as on the quantities and quality of other materials used, like building sand.

He made it clear that he would advise against cement plaster that might be exposed to fire and high heat.

The example of regular fireplace brick chimneys came up. He said that in SA the brick-work is almost always done with their product, and that he has never heard of structural issues in this regard. Seems relevant for cement mortar that may be used downstream in a TMH.  

In SA, our version of barbecuing is 'braai-ing', and the bases of braai places are often constituted by a simple cement slab. Guys here tend to make large fires on these slabs. The rep pointed out that the slabs tend to last indefinitely, though of course sometimes they crack.

For my application, which I consider to be constituted by two bells - a metal radiator and a brick bell - I am now confident that cement is fine (though not preferred, because clay is much nicer to work with etc.) for use as mortar throughout the unit. It looks like 1 part cement to 4 parts sand will be fine.

Just in case it is not obvious, let me offer a reminder that the core for this unit is made from ceramic fibre board, and that no part of the brick-work will be exposed directly to flames or high temperatures. My assumption is that by the time the heat enters the brick bell, it will be down to roughly 100C. If my barrel radiator were to be replaced by a brick bell, obviously that bell's mortar would need to be clay/sand.

For the sake of accuracy, I must correct the mistake I've been making with bell terminology.

As you said, Thomas, there is only one bell in my drawing.

I went back to donkey32, did some reading, and found this post from Peter:

"The barrel is not a true bell because the inlet and exhaust aren't both close to the bottom. ...neither the barrel nor the bench qualifies as a bell".