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Clean, Dry, Rough - Surface Preparation

Surface Preparation

The primary reason for surface preparation prior to application of a protective coating is to create a surface that will optimize adhesion of the coating. This is accomplished by maximizing each of the three requirements – Clean, Dry and Rough.

Let’s examine each of these items for each type of substrate:

Clean:

Definition: Free of contaminants, both visible and invisible.

On Metal:

Visible:

  • Rust, Scale - remove by grinding, wet or dry blasting or water blasting
  • Old Coating – remove by grinding, wet or dry blasting. NOTE: if prior coating is a 2-part system and is well adhered [withstands blasting] it may not be necessary to remove the coating, only texturize it – see “Rough” below]
  • Oils, Greases, Waxes, etc. – remove by degreasers. Apply final treatment with alcohol, acetone, MEK to remove any residue

Invisible:

  • Soluble salts [Chlorides, Sufates] – remove by hot water or steam. Flash rust is a concern.

On Concrete and Tile:

Visible:

  • Oils, Grease – remove by grinding, wet or dry blast or shot blast, followed by degrease as needed.
  • Old Coating – see Metal/Visible above

Invisible:

  • Clear Sealer – test by putting small amount of water on the concrete. If the water stays on the surface, a clear sealer has been applied. Remove by grinding, wet or dry blasting, shot blast.

Dry:

Definition: Free of surface moisture, condensation or moisture migrating from underneath the surface [concrete]

On Metal:

  • The surface must be dry to the touch. Also, the surface temperature must be 5° F above the dew point. This eliminates the possibility of moisture condensing on the surface during the coating process.

On Tile:

  • Dry to the touch

On Concrete:

  • In addition to being visually dry (not darkened by moisture), the substrate should be tested for migrating moisture due to hydrostatic pressure if there is a possibility of that happening.

Rough:

Definition: A surface that, versus a smooth surface, creates additional area that allows for:

  1. Additional bonding sites and
  2. Increases the mechanical adhesion of the coating.

On Metal:

  • Abrasive blasting [dry or wet] to an SSPC 10 near white metal blast is the first recommended surface preparation method. A minimum 3 mil profile is recommended. A hard blasting aggregate, Aluminum oxide, Slag [Black beauty], Garnet or other suitable aggregate is required. Consult your blasting contractor as to the system to achieve the required 3-mil profile.
  • When blasting is not an option, aggressive diamond grinding may be used.

On Tile:

  • Moderate grinding/sanding to break any existing glaze is recommended.

On Concrete:

  • Concrete finished by floating, especially magnesium floats, can have the surface pores closed to an extent that a coating will not well adhere without prior treatment. Grinding, high pressure water blast or shot blasting is recommended to open the pores and roughen the surface.