01Initial state of the steel
ISO 8501-1 describes four rust grades of uncoated steel. They decide how much work the chosen cleaning grade will take.
| Grade | Description |
|---|---|
| A | largely covered with adherent mill scale, little if any rust |
| B | has begun to rust, mill scale has begun to flake |
| C | mill scale has rusted away or can be scraped, slight pitting visible |
| D | mill scale has rusted away, general pitting visible |
02Cleaning grades
| Grade | Method | What remains on the surface |
|---|---|---|
| Sa 3 | abrasive blast cleaning | visually clean steel with a uniform metallic colour |
| Sa 2½ | abrasive blast cleaning | only slight stains and streaks of mill scale and rust |
| Sa 2 | abrasive blast cleaning | most mill scale and rust removed, residues firmly adherent |
| St 3 | hand and power tool cleaning | no loose mill scale or rust, metallic sheen |
| St 2 | hand and power tool cleaning | no loose mill scale, rust or old paint |
| Wa 2½ | water jetting | no visible rust or old paint, dark pitting stains allowed |
Mill scale, rust and paint count as loose if they can be lifted with a blunt putty knife. After water jetting flash rust is also graded: light FRA, medium FRB or heavy FRC (ISO 8501-4).
03Cleaning required by Teping® products
- Teping EP-Coat Primer Zinc — only on blast cleaning to Sa 2½ with a 30–50 µm profile: a zinc-rich primer never goes on smooth steel.
- Teping EP-Coat Primer — best on blast cleaning to Sa 2½; where blasting is impossible, power tool cleaning to St 2–St 3 is allowed.
- Teping EP-Coat Mastic tolerates power tool cleaning to St 2–St 3, tightly adhering rust and sound old coatings.
- Teping PU-Coat Primer RP penetrates tight rust and suits cases where ideal preparation is impossible.
- Check compatibility with an old coating on a test area.
04Cleanliness, profile and timing
- Degreasing — to degree 1 under GOST 9.402, before blast cleaning.
- Welds, edges and imperfections — to ISO 8501-3, usually grade P2; sharp edges are rounded to a radius of at least 2 mm.
- Profile after blast cleaning — to ISO 8503 within the range given in the primer TDS.
- Soluble salts — no more than 50 mg/m² (ISO 8502-6, -9); dust — class 2 or better (ISO 8502-3).
- Prime cleaned steel within 24 hours, before flash rust appears.
05Shop primer, galvanizing and repair
- Steel with shop primer is pressure-washed and rust and damage are spot-cleaned; the shop primer stays only if it is compatible with the system.
- Hot-dip galvanized steel is cleaned of zinc salts with an alkaline detergent and, for long durability, roughened by light sweep blasting.
- Aluminium and stainless steel are washed and roughened with a mineral abrasive.
- In repair, the old system is assessed, unsound areas are cleaned to St 3 and the coats are rebuilt with an overlap onto the sound coating.
Sources. ISO 12944, ISO 8501, ISO 8502, ISO 8503, ISO 19840, GOST 9.402, SP 28.13330 and the technical data sheets of Teping® products on tnpgroup.ru. Check project values against the current TDS.
