Heat resistant mortar - hydraulic or ceramic drying??

[Frances]

I have been looking in the forum, but didn't find any mention of this:
When I went to get my firbricks, the guy asked me if I wanted hydraulic drying mortar (I gather this is cement based and hardens as it cures) or ceramic drying mortar (which reaches its final strength through heat and only after the oven is fired). The Pompei plans obviously use cement based, but will the other stuff work too?

The thing is, this guy gave me an I-was-building-ovens-when-you-were-still-wearing-diapers look and I ended up with the ceramic sort. He said it was better, because it expands and contracts with the rest of the oven when heating up, so you don't get cracking others have mentioned. He also assured me that it was easy to build with. So what is the down side? Has this been discussed on the forum before? What have I bought???

Frances

[DrakeRemoray]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Is one type premixed in a tub and the other a dry powder to be mixed with water?

[nissanneill]

Re: Heat resistant mortar - hydraulic or ceramic drying??

One has to ask.
Does it really make much, if any difference, provided that they both do the job as required?
The only factors which might sway the consumer is:
? price
? workability
? freshness (or useby date whether premixed or powdered)
? accessibility/availabilty
? characteristics (maximum recommended thickness, etc).

Neill

[Hendo]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Frances,

I wonder if we're getting tied up with nomenclature, across cultures? Perhaps the 'hydraulic' drying is an air-set mortar and the 'ceramic' a heat-set mortar. I'm just guessing here, but it may explain it.

My brickie said most industry kilns etc use a heat-set mortar, the bricks laid on a form (like a gigantic Alan Scott barrel oven), and when the forms are removed, the bricks are quite stable as they are self-supporting. When the kiln is ramped up, the mortar sets/cures/hardens thoroughly.

For ease of assembly, my supplier recommended I use an air-set mortar, as it sets up more quickly and you can get on with the next brick sooner.

Here, air-set mortars are generally available both wet or dry, and are available in a range of alumina contents, and heat-set mortars mostly dry, with higher alumina contents (hence their use in kilns etc).

Hope this helps.

Paul.

[Frances]

Re: Heat resistant mortar - hydraulic or ceramic drying??

The stuff I bought is not premixed, and I can add 20% of cement to it for areas which need to hold especially well (like the top of the dome, I guess - but any other recommendations are welcome).

Yep, heat-set and air-set, that sounds about right :-) (and I thought I was good at translations...) Good to know I can use either one, too.

Workability, no idea, but I'll find out when I get that far. The price is good (about 10 USD for 25 kg). And once its mixed, without cement obviously, you can continue working with it for hours. He said I need pressure joints of a couple of mm max, but only on the inner surfaces. Cos there's no way I'll get small joints on the outside!

Thanks for the help,
Frances

[maver]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Frances, a few thoughts on workability and holding. If you have mason's lime available, it really helps to make the mortar plastic and sticky. It is supposed to hold up with thermal cycling better than portland cement as well. The tradeoff is it does not harden as much as portland and not as quickly (but for those upper dome bricks stickiness may be more important than a quick bond). If you don't have to modify your mortar for stickiness or workability then don't - I'm sure mortar you have will have better performance as is than as modified.

[Frances]

Re: Heat resistant mortar - hydraulic or ceramic drying??

I have FINALLY (Hooray!!) stared work on my dome today - pictures will follow. The mortar is reall good to work with. It must have lime in it, because its really sticky stuff.

I have two more questions though:
As its heat-dry mortar, am I right in thinking that it doesn't have to be kept wet? Should I cover it if the sun is shining on it?
And seeing as it doesn't form a chemical reaction with the water, would it be ok to wash my tools in water afterwards? Rubbing them down with newspaper sure doesn't work...

Thanks for all your help.
Frances

[Frances]

Re: Heat resistant mortar - hydraulic or ceramic drying??

One last thought: if rain gets on my half finished dome, will it collapse? I have this horrible picture in my head of the tarp blowing off and all the mortar melting away in the night...

[Frances]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Hello? Anybody?

I've been reading past threads on similar subjects, but didn't find any that give tips on working with heat dry mortar. Cement based mortar I'm used to, but this is a bit different. Isn't it?

I mean obviously I'm going ahead with building the dome, but it would be nice to know what I have to watch out for sooner rather than later.

Frances

[aureole]

Re: Heat resistant mortar - hydraulic or ceramic drying??

I've got a very similar question myself: how did you get on with the air-drying mortar?

According to the link below and some other stuff I've read, "hydralic" means the more tradition portland cement-like action: it needs water to set.

Build Masonry Fireboxes

I've been offer the stuff that comes wet in a tub and dries out - but this, apparently, isn't good for exterior builds or big gaps.

[Breven]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Frances-
Can't help with with your motar question. I mixed my own using fine sand, portland cement, and fireclay. Seems to be workign great. As far as your question about your dome colapsing if it rains- I don't think so, as long as you do a full course and don't leave the course half complete. The laws of gravity and the 2,000 year old arch design (which is the basis of a dome shape) won't allow the bricks to colapes as long as they are wedged together in a circle tightly. Unless your mortar completley breaks down in water.

[aureole]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Sorry, it was me resurrecting an old post: Frances finished his build a while ago (and hasn't AFAIK, fallen down!) - mine is still very much an ongoing project!

[Breven]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Well, I guess the heat cured mortar works.
Are your pics current? Looks like you're about ready to start the floor and dome eh?

[aureole]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Yeah: I'm all ready to go. Hopefully going to order the bits today, and get them soon so I can go make the dome as soon as the english weather sorts itself out!

From my scraping of the forums, I think it's the case that Hendo and Frances have definitely used the heat-drying wet stuff. I think other UK builders have used a fireclay and lime mortar. I'm going to get 60 kilos of fireclay and 100 of air drying wet-mix mortar and have every angle covered!

[dmun]

Re: Heat resistant mortar - hydraulic or ceramic drying??

Frances used fireclay-and-sand only mortar (no lime or portland), on the advice of local masons, and it seemed to work out fine.