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Appendix E 1.2 Aggregate Precoating

It is important to only use aggregate of good quality that is dry and free from dust. This applies to all PMB seals, including those applied on lower traffic volume roads. It is not uncommon for seals using PMB classes with relatively high polymer contents to perform satisfactorily in dry and warm weather but lose a considerable portion of the aggregate during the first wet and/or cold weather if precoating and work practices are inadequate.

With PMB seals, aggregate precoating is most important and a bitumen-based precoat, containing about 1% of adhesion agent, is recommended at all times to ensure both initial adhesion with, and longer‑term retention of the aggregate.

The PMB/adhesion agent/aggregate/precoat system must be evaluated well in advance of the work, using both initial adhesion and plate stripping tests. Check with the adhesion agent supplier if unsure of the dosage details. It is also recommended that the user check with the local road agency regarding adhesion agents and/or precoating materials.