Spot repairs and field joints are small areas with big consequences. A sound repair follows the same steps every time: remove oil and grease, check the conditions, clean to SSPC-SP 11 with a tool that creates a profile, verify, then apply the repair kit exactly as the data sheet says.
This checklist is based on the training our Thai partner ARKCO (Thailand) Co., Ltd. gives to contractors and asset owners on surface preparation for field joints and spot repairs.
1. Before you start: pre-surface preparation
- Remove grease and oil with solvent cleaning to SSPC-SP 1. Mechanical cleaning spreads oil; it does not remove it.
- Check the ambient conditions: relative humidity below 85% and surface temperature at least 3 °C above the dew point.
- If compressed air is used, check that it is clean and dry (ASTM D4285 blotter test).
- Remove weld spatter. Coatings do not flow over spatter, and spatter can break loose in service.
2. Clean to SSPC-SP 11 (power tool cleaning to bare metal)
SSPC-SP 11 is the standard written for field joints and spot repairs prepared with power tools. In short:
- All visible oil, grease, dirt, rust, coating, mill scale and other foreign matter is removed.
- A minimum surface profile of 25 µm (1 mil) is required, deeper where the coating specification asks for it.
- Profile is measured with ASTM D4417 (Methods B, C or D).
The catch: many power tools clean but do not profile. Grinders and wire brushes can polish or burnish the steel and damage weld seams. ARKCO's recommendation to its customers is the Bristle Blaster®, which removes contamination and creates the profile in one step. For heavy coating or rust, remove the bulk first with Tercoo®.
3. Inspect before you coat
- Visual inspection of cleanliness against the specified grade.
- Profile measurement (replica tape or depth gauge) against the minimum in the specification.
- Remove all dust and debris from preparation with a brush or vacuum.
- Feather the edges of the existing coating and roughen the overlap area so the repair coating has something to grip.
4. Apply the repair kit as the data sheet says
- Field repair kits are small packs of two-component coatings, often used for field joints and spot repairs. Mixing ratio, induction time and application method differ per product.
- Mix with a variable-speed drill and a mixing blade, base component first, then add the curing agent slowly while stirring.
- Apply according to the manufacturer's Technical Data Sheet (TDS) and remove masking tape immediately after application.
- Keep the Safety Data Sheet (SDS) on site at all times. It tells you which PPE is required and how to act in an emergency.
For the full method, see spot repair and surface preparation for field joints and corroded welds.
Why it matters
A spot repair done right once is prevention rather than cure; a repair done wrong comes back, and brings corrosion with it. Following the same steps every time protects the people doing the work through proper data sheets and PPE (People), avoids repeat repairs and the waste and material they consume (Planet), and shares know-how across our partner network so every crew gets it right (Power).
Training for your team? ARKCO and our partners run surface preparation training and tech days. Ask us for one near you.
→ Ask about training