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Application Guide - General Guidelines

Sanding and Sandpaper

Read all health and safety information contained in Material Safety Data Sheets.

Always thoroughly clean the surface before sanding. See the surface cleaning section.

  1. When sanding or grinding, work in areas with adequate ventilation, maintaining a continuous flow of fresh air.
  2. Do not breathe sanding or grinding dust.
  3. Keep sanding dust off skin and out of eyes.
  4. Wear a properly fitted chemical cartridge/mechanical filter respirator (such as 3M 6000 series or equivalent) during sanding, grinding and blowing off.
  5. Keep bystanders and unprotected workers out of sanding and grinding areas.
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Proper sanding promotes adhesion for the next coat. Excessive sanding or using too coarse a grit can open pores in the surface or create a sanding scratch profile too deep to be filled by the next product to be applied. This can cause porosity holes in gelcoat and sand scratch print–through.

There are four basic types of sanding and throughout this book, references are made to each type. All four types may be accomplished by hand, machine or block. The surface shape, size and quality requirements will determine the tools or combination of tools required.

  1. Scratch Sanding: Scuffing or scratching a smooth surface to create a profile to promote adhesion of another coating. 3M Scotch-Brite® Pads #’s 7447 or 7448 may be used to push stripe edges down or remove light overspray from primer. Caution is recommended when considering Scotch-Brite® for scratch sanding between topcoats as adhesion will be questionable. Sandpaper is recommended.
  2. Smooth Sanding: Sanding the surface smooth of orange peel or fine texture. This is usually done with small blocks, small pad machine or hand sanding using relatively fine grits. This type of sanding is not considered fairing.
  3. Block Sanding: Block sanding is used for fairing. Block sanding by hand-board or machine is used to level a surface. The depth and height of the highs and lows, and the width between them, will determine the size block as well as the amount of filler/surface products needed to fair the surface.
  4. Grinding: Grinding is used for the removal of material. Grits are coarse,24–36–60, with the primary purpose being removal of undesirable material and creating surface profile. Grinding would be used to brighten corroded metal, remove old coatings and to remove heavily oxidized or damaged gelcoat.

Sanding Grit Cross Reference

The finish sanding grits in this book are for 3M Tri-M-ite® Fre-Cut® sandpaper.

When choosing 3M Gold, or Wetordry® sandpapers, a finer grit choice will be necessary to match the sanding scratch profile or depth of the Tri-M-ite® Fre-Cut®.

Example:

Tri-M-ite® Fre-Cut®
Gold
Imperial®
Wetordry®
220
280
280
400
320
400
400
500/600



Clears and dark topcoat colors tend to show sanding scratches more than lighter colors. Using finer grits will help overcome this condition. Use the following grit choices to sand before applying clears or dark topcoat colors:

Tri-M-ite® Fre-Cut®
Imperial®
Wetordry®
220
280
400
320
400
500/600