The authoritative public forum
  for Metal Finishing since 1989
-----

Is "Sweep Blasting" Supposed to Remove Existing Primer?

September 30, 2008

We have a real situation on hand. A contract with the ship builder includes Painting after preparation of External Hull Surface to SA 2.5.
The Shipbuilder had blasted the plates to SA 2.5 prior to assembly (just after getting them from stockyard). That happened a good nine months back. Now that all the Blocks have been assembled, enormous amount of welding has gone in, and the ship is ready for launching, he intends to "Sweep Blast" the surface and then apply balance underwater paint coats, including primer, wherever it gets removed due to the sweep blasting operation.
My query is .. should this "Sweep Blasting" remove the existing Red-oxide Primer? If one is recommending removal of only loose, damaged primer, then please consider that in the past 9 months, to show that the plates are being preserved, primer was re-applied on rusted areas, "paint-burnt" areas without any great surface preparation. What happens to these areas... if the primer does not come out by sweep blasting?
We are planning to insist "Sweep Blasting" to ensure complete removal of the existing primer.. followed by full paint scheme application. We therefore are looking forward to a stand-off!
Requesting for suggestions please.

Dhekhar deshpande
Regulator, overseer - Mumbai, India

---

What is the reference standard for "Sweep Blasting"?

i.e. ISO, SA, SSPC, NACE.

Jake McCann
- Vancouver, BC, Canada
January 12, 2009

Good point, Jake. Here we have an initial blasting done to a recognized standard, Sa.2.5, and that's fine. Then for a followup blasting we start using the apparently colloquial term "sweep blasting" with apparently no recognized standard considered applicable, and questions are raised about what this "sweep blasting" is expected to do and expected not to do :-)

Jake is right, Dhekhar: someone needs to spec out this "sweep blasting". Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 3, 2009

Overcoating of zinc epoxy or acrylic based holding/temporary primers should not be done and these primers should be removed by blast cleaning prior to the application of specified primer /first coat to original blasting state. Sweep blasting should only be allowed when it is ensured that there is no reduction in system adhesion or performance.

Sajid Aslam
- Lahore, Pakistan
October 11, 2011