Fireclay? Refractory Mortar? In Utah?

[meco211]

Re: Fireclay? Refractory Mortar? In Utah?

Here is the instructions off the website

Sairset Instructions
1. Make the edges to be joined wet.

2. Spread some kiln repair cement on the joint. Smooth while wet, and try not to get any at all on the inside of the mold.

3. Wipe off the excess with a damp cloth or sponge.

4. Back up the repair with more of the product on the back. Wash all tools used immediately or it will never come off.

5. Allow it to dry a fair amount of time. It can be sanded with sandpaper if necessary.

6. When dry fire to about 1472 degrees Fahrenheit to set the material.

7. Wash the mold and you are ready to go.

Read more: Sairset Kiln Mortar

[Spunkoid]

Re: Fireclay? Refractory Mortar? In Utah?

I used a premix monolithic refractory clay called Super 3000 made by Vesuveus. Had no problems with it drying or "air curing". I mixed in the "fire clay that I had from cutting my fire bricks. No problems. Once the dome was built, I let it air cure for a few weeks then started lighting small curing fires. Sometimes 2 a day, one in the morning, one in the evening, and slowly built them up to larger fires. The dome cured just fine. I suggest talking to the dealer who is supplying your fire bricks to see what they supply.

[jcalcote]

Re: Fireclay? Refractory Mortar? In Utah?

The mortar was model KS 4V Plus. I didn't even thing to ask them about fireclay. I'll go back and get some this week.

KS 4V Plus is castable refractory cement - will it work as mortar between fire bricks also?

You know, here's the thing: I've been trying to find fire clay for a couple of weeks now. Both Lowes and Home Depot claim to have fire clay (Basalite H C Muddox) for 7.95 per 50 lb bag on their websites, but I went into Lowes in Lehi the other day and they couldn't even find the SKU from their own web site in their computer system. They told me they'd call their QuikCrete supplier (please!) to see what they could learn.

More recently, I found a quote on the Alsey Refractories Co (IL) web site indicating that job-site mixing of fire mortars is not recommended because it doesn't pass state or national building codes. What the heck! Alan Scot has been building ovens with sand/portland/fireclay mortars for decades - now they're trying to tell us our ovens will fall apart if we use fireclay mortars?

Anyone have any idea what's going on here?

[ExpatInNicaragua]

Re: Fireclay? Refractory Mortar? In Utah?

You can dig for clay. You are looking for light colored clay with no organic material.

[wotavidone]

Re: Fireclay? Refractory Mortar? In Utah?

More recently, I found a quote on the Alsey Refractories Co (IL) web site indicating that job-site mixing of fire mortars is not recommended because it doesn't pass state or national building codes. What the heck! Alan Scot has been building ovens with sand/portland/fireclay mortars for decades - now they're trying to tell us our ovens will fall apart if we use fireclay mortars?

Anyone have any idea what's going on here?

I bet the people of Pompeii never had this much angst over the mortar.
It is amazing, considering how many ovens there are in the world, how few companies have a mortar specifically for the job.

Many refractory mortars including the air dry ones, as you have discovered when researching the one you were offered, need to be heated above oven temperature to set properly. Hence they are not much use in an oven.

I believe that many people with opinions about the mortar are approaching the issue from standard masonry/building code experience.

Many masons/cement experts believe the FB homebrew mortar is wrong because, at one part clay to one part cement to one part lime to three parts sand, there is one part of binder for every one part of sand.
A bricklayer building a house would never use such a strong mix.

But, there is the oft quoted belief that the Portland cement "breaks down' over time. If that happens you have only the lime holding it together, since if you use raw fireclay, then it is unlikely to ever get hot enough to fire the clay.
Unless you use the fired clay brick dust from your cutting, as this apparently has some cementitious properties.

I know a bloke who made his oven with "brickies mortar with half the cement replaced by lime". i.e. 3 parts sand, 1/2 part cement, 1/2 part lime. This is what the old Greeks and Italians in my home town tell us to use.
His oven is still standing, and it would have to be at least ten years old. Not water proofed at all, the dome is unclad, so when it's fired up it has to cook out whatever rainfall has found its way in.

I used clay I gathered myself from the local wet lands. Standard FB homebrew mix. My oven has not fallen down, however the high shrinkage rate of the mortar as it dried out drove me nuts. I spent a lot of time keeping it wet until the Portland had set properly, and with the clay trying to shrink and the Portland trying to stop it, surely I have set up internal stresses?
I'm building one for my mate, and what we've done is cut the clay in half, so now my mortar is 3.5 parts sand, 1 part each of Portland cement and lime, 0.5 parts clay. Shrinkage cracks non existent.

I have a DIY manual from Adelaide Brighton Cement, the local cement manufacturer.
They say mortars for backyard incinerators (yes, 30 years ago we burned our paper and cardboard in the backyard - we have recycling now) and BBQ's should be 9 sand, 2 lime, 1 Portland cement. Note the 3:1 sand:binder ratio, even though conventional wisdom says the Portland will breakdown.

I know a bloke with a materials science/research background. His oven has sand, lime and Portland cement.

The more I think about it, the more I think the single most important thing is that there is one part hydrated lime for each three parts of sand.
If the Portland Cement and Clay add any long term strength, good. If not, by the time the Portland cement fails, if it fails, the lime should have sufficient strength to carry the load.
Note that, high strength mortars have lower adhesion to the brick, and many ovens that crack seem to have a failure of the bond to the brick, rather than a crack through the mortar itself. I reckon the Italians and Greeks here in my hometown must know a thing or two.

But it's all opinion and hearsay.
I can post my technique for processing wild clay if you want.

[Tscarborough]

Re: Fireclay? Refractory Mortar? In Utah?

It is important to understand the function of the various parts of a mortar.

The portland serves as a gauging material, i.e. it allows the mortar to set in a reasonable period of time.

The lime is the actual long term binder, as well as an air entraining agent and lubricant.

The clay is a filler like the sand, and fills the smaller end of the aggregate spread. Some clays may also work as a gauging material with the lime.

It is not debatable that portland cement hydrates disintegrate at temperatures above 500 degrees, that is simple scientific fact. If you were to make a straight 1-3 portland sand mortar, the mortar would not last long, although the oven would probably not fail for years. Mortar is used to hold the brick APART, not TOGETHER, and a hemispherical structure is self supporting.
I

[wotavidone]

Re: Fireclay? Refractory Mortar? In Utah?

It is important to understand the function of the various parts of a mortar.

The portland serves as a gauging material, i.e. it allows the mortar to set in a reasonable period of time.

The lime is the actual long term binder, as well as an air entraining agent and lubricant.

The clay is a filler like the sand, and fills the smaller end of the aggregate spread. Some clays may also work as a gauging material with the lime.

It is not debatable that portland cement hydrates disintegrate at temperatures above 500 degrees, that is simple scientific fact. If you were to make a straight 1-3 portland sand mortar, the mortar would not last long, although the oven would probably not fail for years. Mortar is used to hold the brick APART, not TOGETHER, and a hemispherical structure is self supporting.
I

Damn right.
IMO the most important part of the mortar is the lime as the long term binder.

Not 100% sure what the clay does, but I've always thought it could be as simple as filler. Is that 500 degrees C or F for the disintegration of the Portland?

[cobblerdave]

Re: Fireclay? Refractory Mortar? In Utah?

Gudday
It's the stuff that makes it " plastic" a stick able and squishy mortar. Using " brickies loam" sand with a clay content ,produces the same effect. Using a commercial plasticizer is the modern way, but a " squit " of mums dishwashing liquid will do. But in all deference to Tsar is the homehandyman way and shouldn't be used on a commercial job.
Regards dave

[david s]

Re: Fireclay? Refractory Mortar? In Utah?

There is some confusion regarding Fireclay. In the refractory or ceramics industry it is a clay that can withstand extremely high temperatures. In the building industry it is just a powdered clay added to mortar to improve plasticity but is usually not a true Fireclay. We do not require a true Fireclay for the temperatures our ovens are fired to, a bricklayers clay will suffice, but remember that a high proportion of clay wil contribute to excessive shrinkage therefore tending to to create shrinkage cracks, so use it sparingly.

[stonecutter]

Re: Fireclay? Refractory Mortar? In Utah?

Something worth noting about using Portland in the mortar for ovens, is the fact that almost every oven built on this site is non-commercial. Recreational ovens never receive the same amount of usage as a commercial ones, which you would be hard pressed to find some that were built with a high ratio of OPC in the mortar. 3:1:1:1 is not a new mix design.... Masons have been using that and similar mortars in fireplaces for decades, and they are always site mixed. The similarity between a fireplace and a recreational oven? The mortar is not subjected to super high ( higher than 1200*), constant temperatures. It does last, but how long has to do with many, many variables...so, back by what is already known by ceramic & refractory engineers and masonry heater/fp/oven builders...limit the mortars dependance on OPC.

As mentioned on this thread and many others, OPC is not a refractory material, and needs to be treated as such when designing a mortar mix. Additionally, every component of a mortar design should be suited to the application, according to what is the best material that is available to the builder.

[stonecutter]

Re: Fireclay? Refractory Mortar? In Utah?

Is that 500 degrees C or F for the disintegration of the Portland?

Starting at 500 degrees Fahrenheit

[cheftai]

Re: Fireclay? Refractory Mortar? In Utah?

The Home Depot has 50lb bags of fire clay
For $5.00