Refractory Concrete Tutorial - Recipe and Instructions
Mixing heat resistant mortar without using a concrete mixer
Heat resistant refractory concrete
There are two ways, two types of heat resistant concretes that can be prepared. Cheaper and more expensive - stronger and weaker. The first one is a high heat refractory concrete. This type will survive in real high heat and can be used in hot-face (What is hot face? Hot face is a wall facing the main heat from a source. Internal walls, floor and arches made from firebricks inside a pizza oven is hotface. Firebricks face the heat, the hot flames from wood fire and the red hot embers.) Refractory concrete can be mixed with heat resistant cement, or, can be purchased ready in bags (the packed one is most often referred to as castable.) But saying that, even though it's refractory, still it is not so straight forward to cast large hot face section/s out of it. It is different to fill holes and awkward spaces with castables. Large blocks tend to crack as a result of something called heat differences in material, or temperature differences in material in other words, which is a very powerful natural phenomena. But hey no worries Mate, we still have firebricks here luckily (firebricks those nice little fragments) for making the dome part properly (read more about heat differences in materials - basically it deals with shrinking of cooled down edges and also surfaces while middle's still hot expanded). It would be a wise idea to mix heat resistant cement, e.g. Calcium Aluminate cement, with firebrick grog. The grog comes basically from crushed firebrick/s. Companies who manufacture refractory material (like Claypave Pty. Ltd. in Dinmore, Qld. Au.), or those who only resell firebricks, usually sell also firebrick grog, ready premixed refractory mortars and fireclay. There are many different refractory cement types, some of them allowed to mixed in lime, plaster, or fireclay, but others cannot be mixed with these because their chemical properties don't allow it, rather they get contaminated by similar additives. Because they differ, read the usage instruction printed on a particular cement bag, also its producer will gladly give you print out on -it will tell you exactly how to or what can be done. Now, the second one heat resistant concrete type. It is a lower grade heat resisting concrete, lower grade in withstanding heat but still it can be applied successfully in many areas whose get pretty heated too. For instance layers such as those on the other side of firebricks, on the outside of firebricks, the slab under the heated floor made from fire bricks or cladding around the firebrick dome, chimney parts, etc.. Into this concrete type the common Portland cement goes in (portland is often also referred to as GP cement and this one is already a bit refractory) and of course lime. Both lime and portland are bonding agents and are described more further below. Instead of firebrick grog you can use river sand and river stones. Sand and stones that come from river. If buying it, it's easily recognizable; what comes from river is round and it isn't sharp as opposed to the mostly crushed stuff coming to us from stone quarries, otherwise either of them is a building material. With a help of a few extra hands (plus hydrating liquids and nutritional energy of your choice ... "would you like to know what's my pick?") you can mix either of these concretes by hand in a wheelbarrow or on the ground because in smaller jobs, such as family sized pizza ovens, not much of it goes in. See the following sequence with images. Ingredients:
Firebrick Grog (crushed fire bricks) or gravel from river with sand Refractory cement (e.g. Calcium Aluminate cement. If available in different grades choose the better one) Lime (lime is usually cheaper, about 80% of the cement price. Lime applies if you use Portland cement type) Water
With the heat resistant concrete type mixed with Portland you can add into this...
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