Quality Control Records for Block Supply Contracts: What a Block Plant Must Keep

Quality control records for block supply contracts are the written proof that the blocks you delivered were produced the way the contract said they would be, and buyers examine them before they discuss price. A workable record set has six parts: a mix design sheet, material and batch records, a daily production log, a curing log, compressive strength test results, and a non-conformance log that shows what happened when something failed. If one of those six cannot be linked to a specific delivery, the buyer has to fall back on testing your blocks himself, and that is where payment delays start.

What records does a supply contract actually ask for?

Contracts rarely name one document. They name what has to be provable, and the records follow from that. In practice six documents cover almost every clause a buyer writes.

The mix design sheet states cement content, aggregate gradation bands, target water content, any admixture, and the mould the mix was designed for. It carries a revision number and a date, and it is reissued whenever a material source changes. A mix sheet that has not been touched for three years while the sand pit changed twice tells the buyer nothing.

Material and batch records sit behind it: cement delivery notes with the supplier batch number, aggregate gradation and moisture checks, and the water correction made when the sand arrived wet. Moisture is the usual blank spot. A plant that corrects mix water by eye cannot show why one day's blocks reached the specified strength and the next day's did not.

The daily production log captures running conditions: date, shift, mould, cycle time, the press pressure and vibration time actually used, pallets produced, and every stoppage long enough to matter. The curing log is the one buyers find missing most often. It states when curing started, how long it ran, and the temperature and moisture the blocks saw, because a block dried in the sun and a block cured wet for a week are not the same product even when they came off the same pallet.

Laid side by side, the six records answer six different questions. The mix sheet proves what went into the block, the batch records prove the materials were the ones the mix assumed, the production log proves the settings used, the curing log proves how the blocks were treated after pressing, the test results prove what came out, and the non-conformance log proves what was done when the answer was not good enough.

Which tests belong in the block testing log?

Compressive strength is the anchor of the log. Cast specimens at the start of a run and at fixed intervals through it, test at 7 days as an early warning, at 14 days to follow the trend, and at 28 days for acceptance, and keep the individual specimen values next to the average. An average on its own hides the specimen that broke low.

Add density, dimension checks against the drawing tolerance, and a visual note on cracks, chipped edges and honeycombing. Record the press pressure the machine was set to. For reference, our QST6-15 works at a working pressure of 25 MPa, and the QST1200 and QST1800 presses run at 31.5 MPa, so the setting is a number a third party can check against your log.

Write down the compression machine used and the date of its last calibration. A strength result from an uncalibrated press is an opinion, not evidence.

Sampling rate is a contract term, so read it before you design the log format. Buyers commonly ask for one sample per shift, per mix, or per fixed number of pallets, and some ask for one sample per delivery. Build the log so that a missing sample shows up as an empty line rather than as an absence nobody notices until the claim arrives.

How do you link a record to one specific delivery?

Use one identifier that appears on every document in the chain: sample number, casting date, mix revision, mould, pallet number, truck and delivery note. A format as simple as a date plus a mix code plus a pallet number is enough, provided everyone writes it the same way.

Keep the specimens themselves until the 28 day result is accepted, stored under the same conditions as the production blocks and labelled with the same identifier. Photographs of the pallets cost nothing and settle more arguments than any summary sheet.

Number the samples the moment they are cast, not at the end of the shift. Identifiers written hours later are where mix codes and pallet numbers get confused, and a confused identifier is the fastest way to lose an argument about a strength result you could have won.

Common mistakes that void an otherwise good record

Testing a special batch instead of normal production is the first. A buyer who suspects it will ask for the production log of the day the sample was cast, and the two rarely match.

After that come the small ones: reporting only the average and discarding the individual values, quoting a 7 day figure as the 28 day strength, leaving the calibration date empty, filling the log from memory at the end of the month, and forgetting to update the mix sheet after the aggregate source changed. Each of them is a paragraph the buyer can use to hold back a payment.

The non-conformance log does not expose you, it protects you. Write down what failed, how many pallets were affected, what you did with them, and what changed in the mix or the machine afterwards. A plant that can show a failed batch and its correction reads as reliable; a plant whose records show that nothing ever went wrong reads as careless.

How long should the records be kept?

Set the retention period in the contract instead of guessing. Common practice is to keep the full set for the duration of the supply plus the defect liability period the buyer asks for, and to retain the physical specimens at least until the 28 day result is formally accepted.

Whatever you agree, store the records where a buyer or an inspector can read them without your help: one folder per project, one file per delivery, scanned once and named with the identifier used on the sample. Records locked inside a foreman's phone are not records.

Send the contract clauses and we will confirm the record set

Send us the testing clauses from your contract, the strength class and sampling rate the buyer expects, your block sizes and moulds, and the delivery schedule. If third party testing is required, say who appoints the laboratory and who carries the cost.

We will confirm the machine configuration and the documentation set that goes with the quote, so the records and the equipment are agreed before production starts rather than after the first rejection.