Here's the thing about refractory datasheets: the numbers that get buyers into trouble aren't the ones on the front page. Refractoriness gets the headline, but it's the least useful number on the sheet. Apparent porosity, refractoriness under load, cold crushing strength, and permanent linear change - those four tell you whether a brick will survive your kiln. Refractoriness only tells you where it melts. This guide explains each refractory property, what it predicts in service, and the typical values we see across brick grades. The numbers come from our QC lab in Qingdao, where every batch gets the same four tests before it ships.
What Are Refractory Properties and Why They Matter
Refractory properties are the measured numbers on a brick's datasheet: chemical analysis, refractoriness, density, strength, porosity, and the others. Most of them answer one question - will this material do the job in this kiln?
The four that matter most in practice are apparent porosity, refractoriness under load (RUL), cold crushing strength (CCS), and permanent linear change (PLC). Together they cover the four ways linings fail: penetration, softening, crushing, and dimensional change.
Buyers who read only the refractoriness number get surprised in service. The brick doesn't melt - it softens under load, or the slag gets in through the pores, or it shrinks and the joints open. Each of those failures maps to one of these four numbers. That's why a refractory properties review belongs before the purchase order, not after the reline.
One more thing about refractory properties: they drift. Raw material lot, pressing pressure, firing schedule - each one shifts the final numbers a little. That's why we test per batch, not per year, and why the COA on your shipment is the only number set that counts. Brochure values are the ambition; COA values are the fact.
Different refractory properties matter at different points in the buying process. Porosity and chemistry decide the grade. RUL and PLC decide whether it survives the duty. CCS decides whether it ships and installs without damage. Weigh them in that order and the datasheet reads like a roadmap instead of a wall of numbers.
Apparent Porosity: The Number That Predicts Failure
Apparent porosity measures the volume of open pores in the brick as a percentage, tested by water displacement under vacuum or boiling, per GB/T 2997 and ASTM C20. The test method is simple and the result is brutal: of all the refractory properties on a datasheet, porosity is the one that predicts failure earliest. The number is a doorway - open pores are how slag, metal, and alkali get into the brick.
High porosity predicts three failures. Slag penetration, which corrodes the brick from inside. Thermal shock damage, because pores conduct heat poorly and create stress. And low strength, because a porous body has less solid structure to carry load. That's why porosity sits at the top of the refractory properties list a buyer should check first.
Typical values by grade: silica brick runs 18-24% apparent porosity. Fireclay runs 20-25%. High alumina runs 18-23%. Dense magnesia brick runs 15-18%. Magnesia carbon brick is the outlier at 3-4%, because carbon fills the pores. Our earlier data on silica brick apparent porosity covers the silica grades in detail.
A common buyer mistake: treating porosity as a fixed grade property. It varies with pressing pressure, firing temperature, and raw material quality - two bricks with the same chemistry can differ by five porosity points. Read the number on the COA, not the number in the brochure.
Refractoriness Under Load (RUL): The Real Hot-Strength Test
RUL measures the temperature at which a brick under a fixed load - typically 0.2 MPa - deforms by a defined amount, per GB/T 5989 and ASTM C16. It's the refractory property that mirrors real furnace service: the wall carries load while it's hot. Refractoriness tells you the melting point of the material. RUL tells you when the brick stops carrying load, which is what actually happens in a furnace wall.
The gap between the two numbers is where buyers get caught. Reading refractory properties in pairs - RUL with refractoriness, CCS with RUL - is the habit that saves linings. A brick can be rated 1,790°C refractoriness and soften under load at 1,500°C. For a high alumina brick, RUL typically runs 1,420-1,500°C depending on grade; for silica brick, RUL sits close to the melting point, which is why silica holds so well in coke ovens. For fireclay, RUL runs 1,300-1,400°C.
Our rule: never buy on refractoriness alone. RUL is the number that predicts whether the wall stands, and it's the one buyers least often ask for. For a buyer comparing grades, RUL is the property that separates marketing from engineering. Two bricks with identical refractoriness ratings can differ by 150°C in RUL - that difference is the safety margin, and it's the refractory property most often missing from comparison tables.
Cold Crushing Strength (CCS): What It Does and Doesn't Tell You
CCS is the compressive strength of the brick at room temperature, per GB/T 5072 and ASTM C133 - the force needed to crush a test piece on a hydraulic press. It's the easiest strength number to measure, so it's the one on every datasheet, and it's the refractory property that shipping damage reports are written about.
CCS predicts three things in service: resistance to abrasion, resistance to mechanical load, and handling strength through transport and installation. Dense high alumina brick runs 40-60 MPa, fireclay runs 25-40 MPa, and magnesia carbon brick runs 35-50 MPa. Our QC measures CCS on a 200-ton hydraulic press, and the COA numbers are the ones we shipped.
What CCS doesn't tell you: high-temperature strength. A brick with high CCS can still soften under load at 1,400°C - the CCS test happens cold. That's why these two refractory properties must be read together. High CCS with low RUL means a brick that handles well in the yard and fails in the wall.
Our QC runs CCS on every batch - target, average, and outliers all go on the COA. The reason is simple: of all the refractory properties we test, CCS is the one that catches pressing and firing problems earliest.
Permanent Linear Change (PLC): The Shrinkage Warning
PLC measures how much a brick's dimensions change after firing to a specified temperature, as a percentage, per GB/T 5988. Negative values mean shrinkage, positive values mean expansion, and both are dangerous in a lining - it's the refractory property most buyers discover only after their first mysterious joint failure.
Shrinkage opens the joints between bricks. Expansion buckles the wall and spalls the brick faces. Either way, the lining loses its structural integrity, and the failure shows up as gaps, spalling, and premature wear. Most brick grades hold PLC within ±0.5% at their rated temperature; a number outside that range means the brick isn't suitable for the duty it was fired for.
PLC also explains why first-heat behavior matters: a brick that shrinks on the first campaign changes the whole lining geometry. The test tells you before installation what the brick will do after firing, which is why it belongs on every COA. PLC is the least asked-about refractory property and the one that explains the most mysterious lining failures - a lining that loses its joint tightness over a campaign usually has a shrinkage problem that the COA showed all along.
How to Read a Refractory COA
A proper COA carries chemical analysis and the physical numbers: apparent porosity, CCS, RUL, PLC, and bulk density, each with the test standard. Read it in order, and read the four numbers together - the chemistry tells you what the brick is, and the physical refractory properties tell you how it will behave in your kiln.
First check the chemical analysis against the grade claim - alumina content should match the grade name. Then check porosity and CCS against the typical values for the grade; wide deviations mean a different production batch than the datasheet. Check RUL against your service temperature - if RUL sits below your hot face temperature, the brick is wrong for the zone regardless of anything else on the sheet. Check PLC for a value within ±0.5% at the rated temperature.
These four refractory properties belong on every COA because together they cover the four failure modes: penetration, softening, crushing, and dimensional change. A COA that lists all four, with test standards, is the minimum we'd accept from any supplier.
The shaped refractory range pages all carry these numbers per grade, so you can compare before asking for quotes. If a supplier can't produce a per-lot COA with all four, that's a signal - walk away or ask why.
Ordering: Lead Time, Payment & Packing
Lead time is 15-20 days from deposit for standard brick grades, 25-35 days for custom shapes. Payment is T/T with 30% deposit and 70% before shipment. Packing is wooden pallets with shrink-wrap and corner protection.
Every lot ships with the full COA - chemical analysis, apparent porosity, CCS, RUL, PLC, and bulk density - not a summary, the numbers. Every refractory property on it is the tested value, not the brochure value. We test every batch, and retained samples are kept on both sides.
Send us your kiln zone and service temperature, and we'll confirm the grade with its four numbers within 24 hours - and if the numbers don't fit your duty, our engineers will tell you before you order. Our quotes work from the same refractory properties the lab tests; there are no brochure numbers in our pricing.
Bottom line: the four refractory properties that predict lining life are apparent porosity, RUL, CCS, and PLC - read them together, against your service conditions, on every lot. A datasheet that carries all four is a datasheet worth trusting. Send us your duty, and we'll send the numbers.
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