Quality Control & Testing of Decorative Aggregates

Posted on 18th February 2021

Most decorative slate aggregate purchased in the UK are transferred from quarries in large 30-ton loose loads across the UK road network to be handled by third-party wholesalers. The wholesaler will re-bag the slate aggregate into small poly bags typically sold through garden centres and DIY chains and larger bulk bags sold via the internet or builders merchants. This process usually means no further tests or grading are carried out by the wholesalers, resulting in proportions of dust being packed and often a broader range of sized material being sold to customers.

All the slate aggregate from Stone & Surfaces Direct are distributed directly from the quarry, and the slate aggregate is consistently tested to ensure our customers get the best value for their expenditure. We have transferred the knowledge, expertise, and practices of supplying slate aggregates to the civil and construction industries. The quality and specification requirement can be critical to managing and controlling the manufacture of decorative slate aggregate such as 10mm, 20mm and 40mm slate chippings.

To ensure good quality decorative slate aggregate is achieved, the best quality material must be selected from the quarry, which is crushed then screened into the correct size ranges. Factors such as the supply of the raw material, weather conditions, and wear and tear on the processing plant can influence the finished product quality. To maintain the highest standards and consistency of the decorative slate aggregate, each product is inspected and tested regularly to ensure it conforms to its size designation. This ensures the customer is only getting the size of the stone they have ordered.

Inspection and Grading Process

The material is visually inspected as it is being produced to ensure the slate's visual appearance meets the expected specification. Samples are also taken and tested to ensure the size range is correct, which means that no undersize or oversize stones or dirty materials are present in the designated slate chippings size. These factors are common faults in other materials that consumers can often buy.

To ensure all the material meets the expected specification, small samples are taken at regular intervals around the stockpile to ensure every batch of decorative slate chippings that are manufactured are tested to the following criteria:

1. The small samples are combined to form a bulk sample which is representative of the stockpile.
2. The bulk sample is then transported to the laboratory, where it is reduced to provide a single test sample.
3. The sample is dried to check the moisture content.
4. The sample is then washed to remove any dust or fine material below 0.063mm.
5. The sample is then dried again before testing.
6. Once dry, the sample is processed through a range of sieves with decreasing sizes.
7. The material retained on each sieve is then weighed and checked against the specification to confirm the correct number of stones.
8. The material or fines that were washed away are then factored into the calculation to ensure they do not exceed the permitted limits.
9. A grading report is then produced, which shows the full range of sizes in the sample.

The quality control that is often not carried out by third-party providers is essential to ensure that when our customers order an 850kg bulk bag of slate chippings, it is not partly filled with dust and that the slate provided is from a managed and controlled source that is transported to the gardens and driveways across the UK.