SSPC-SP 6 vs. SP 10: What Is Actually Different

Wally Bates

Sep 26

2 min read

Two abrasive blast standards appear in most steel coating specifications: SSPC-SP 6 (Commercial Blast Cleaning) and SSPC-SP 10 (Near-White Metal Blast Cleaning). The names are close. The results are not.

What they share

Both remove all visible rust, mill scale, old paint and dirt.

Where they differ

The difference is how much staining may remain. Staining means the light shadows and streaks of rust or old coating left in the profile after blasting.

SP 6: staining allowed on up to 33 percent of each unit area, roughly a 3-inch square.
SP 10: staining allowed on up to 5 percent.
SP 5 (White Metal): no staining allowed.
SP 7 (Brush-Off): removes only loose material; tightly adhered material may remain.

SP 10 is much closer to white metal than to commercial blast, and the labor and abrasive needed to reach it reflect that.

Which one the job needs

Atmospheric service on a bridge or structural frame usually performs well over SP 6. Immersion, potable water, wastewater and anything with chemical exposure typically call for SP 10 or better. Any contamination left behind in those services is a blister waiting for water to find it.

SSPC-VIS 1 provides reference photographs so the owner, contractor and inspector can agree on what each grade looks like on the actual steel.

A note on bidding

SP 10 costs more than SP 6, and a contractor who bid SP 6 will deliver SP 6. If the service is immersion and the specification says SP 6, the time to correct it is before bids, not after the blast.

What to check in your spec

Match the blast grade to the service: SP 10 or better for immersion and chemical exposure.
Reference SSPC-VIS 1 for visual acceptance.
State the required profile depth range.
Make surface prep an inspection hold point.

Further reading: Tnemec Technical Bulletin 06-58, Normal Transition Zone on Steel. Standards: SSPC-SP 5, SP 6, SP 7, SP 10, SSPC-VIS 1.

Talk to a consultant. Atlantic Coating Consultants helps owners, engineers and contractors in PA, NJ, DE, MD, DC, WV and OH with specification writing, on-site condition assessment, training, product recommendations and field support. Call 484-644-5303 or email atlantic@tnemec.com.