3:1:1:1

[david s]

Re: 3:1:1:1

Aren't we talking about clay used in the oven builds? Clay changes it's physical property after firing. And, I have never seen or heard of clay that was fired lose it's binding property from excess moisture. .

From ambient to 500 C which is the range we fire in, there is no physical change to clay and it will return to mud if soaked and abraded. An example of this is pottery fired in a sawdust kiln which typically reaches around 600C. On parts of the pots that did not receive quite enough heat, ie below 573 C the clay can be dissolved if soaked and scrubbed while the rest of the pot has been "fired" and made permanent. This change takes place during the firing not after it.

By the way do not be tempted to fire a WFO to over 600 C in an effort fire the clay in the mortar. There are lots of different thermal expansions of different materials that increase their expansion around these temperatures and it is not possible in a WFO to control a slow rise. Expect some cracking if you attempt this.

[Tscarborough]

Re: 3:1:1:1

The fireclay mix still has not set, so I think it is safe to assume that it is not hydraulic.

[stonecutter]

Re: 3:1:1:1

From ambient to 500 C which is the range we fire in, there is no physical change to clay and it will return to mud if soaked and abraded....

After this point, everything else is moot..because if you built an oven that gets wet enough to ruin your mortar, it was your fault not the physical properties of the material. And, it would take a lot of continuous soaking to reach that failure point too.

[stonecutter]

Re: 3:1:1:1

Ok, so if it's not cement or aggregate, it's somewhere in between and doesn't count. So lets just call it sticky stuff and move on.

Oh and the clay wasn't being called cement, but cementitious, having properties of cement.

Moving on... great idea. Maybe the new ratio can be called 3:1:1:? or 6:1:1:?

[david s]

Re: 3:1:1:1

After this point, everything else is moot..because if you built an oven that gets wet enough to ruin your mortar, it was your fault not the physical properties of the material. And, it would take a lot of continuous soaking to reach that failure point too.

Yes that's true. I told the pottery story to illustrate a point about clay not undergoing change in state from ambient to 500C Actually a modular oven that I built was subjected to a cyclone and was completely flooded. The whole thing was totally underwater from the tidal surge. After drying out it fired perfectly well and there was little erosion of the refractory mortar which was simply a mix of 50/50 sand, fireclay.

[stonecutter]

Re: 3:1:1:1

Yes that's true. I told the pottery story to illustrate a point about clay not undergoing change in state from ambient to 500C Actually a modular oven that I built was subjected to a cyclone and was completely flooded. The whole thing was totally underwater from the tidal surge. After drying out it fired perfectly well and there was no erosion of the refractory mortar which was simply a mix of 50/50 sand, fireclay.

Yikes. Well, it must have been a nicely built oven to survive that.

[david s]

Re: 3:1:1:1

Thanks, frankly I was amazed. It hadn't even budged the flue pipe. Their house was on the beach and they had a pool table on the same level as the oven in their rumpus room. All the furniture, fridge and freezer were swept about 300 metres inland but the pool table hadn't budged. But on closer inspection found it had done a neat 180 pirouette, or maybe spun around about six and a half times.

[stonecutter]

Re: 3:1:1:1

Thanks, frankly I was amazed. It hadn't even budged the flue pipe. Their house was on the beach and they had a pool table on the same level as the oven in their rumpus room. All the furniture, fridge and freezer were swept about 300 metres inland but the pool table hadn't budged. But on closer inspection found it had done a neat 180 pirouette, or maybe spun around about six and a half times.

Was it salt water that the oven was immersed in? I am wondering about efflorescence. That must have been one heck of a storm!

[Tscarborough]

Re: 3:1:1:1

Here is going to be your main issue with using fireclay and sand alone. It is cracked completely in half plus other small shrinkage cracks, and that is in a plastic cup which retards moisture loss. It does not have enough tensile strength to withstand the amount of shrinkage between wet and damp states, much less dry.

[david s]

Re: 3:1:1:1

TS, yes I agree. The oven I was referring to was built about four years ago. I no longer use the 50/50 clay, sand mix because there is too much shrinkage. I now use a much weaker mix of sand, clay and lime, which performs much better. However I was extremely surprised to see that the oven came out unscathed. I think because the mortar was well compacted and there was no abrasion on it that it survived immersion.
Stonecutter, yes it was salt water and there was no obvious sign of efflorescence.

[stonecutter]

Re: 3:1:1:1

Wow, and that's at 3:1 right? Another example of when sometimes leaner is better.

[stonecutter]

Re: 3:1:1:1

TS, yes I agree. The oven I was referring to was built about four years ago. I no longer use the 50/50 clay, sand mix because there is too much shrinkage. I now use a much weaker mix of sand, clay and lime, which performs much better. However I was extremely surprised to see that the oven came out unscathed. I think because the mortar was well compacted and there was no abrasion on it that it survived immersion.
Stonecutter, yes it was salt water and there was no obvious sign of efflorescence.

I think using/making mortar that is too strong is in the top 3 mistakes people make when building. Heck, most masons don't even pay attention to or understand proper mix design.

I would image that if it did show efflorescence, it wouldn't last long anyway.

[stonecutter]

Re: 3:1:1:1

That's just clay and sand, no cement or lime. The ultimate in "lean". No good at all.

Lean doesn't refer to how many ingredients are in a mix but to the ratio of binders to aggregates that are used in the design.

[david s]

Re: 3:1:1:1

Yet it works, same brew as under floor bedding. In a modular oven you are not trying to hold bricks together, but providing a joint where movement can take place if needed. Better for it to crack there where it's designed to rather than where it's not.

[Tscarborough]

Re: 3:1:1:1

Most architects and nearly all engineers specify mortar too strong for the units being laid. One thing I will give to our Southern brothers who dominate the rock laying trade here in Texas is that they do understand what mortar to lay with a particular stone.