Although it will be a lot of work, we have developed a 5 step sanding and polishing process that gives good results:
1. Planing wood/epoxy to achieve flat surface – what to take off the top? We advise a minimal cut of 1/32” (0.08 cm) or less. Be careful; if you cut too thick, the epoxy will grab the planing knives and throw the piece. A thicker cut can also generate excessive heat that will affect the surface finish.
2. Drum sanding – can even out the top or both sides of the piece, depending on the machine. Feeds should be quick with grits of less than 120. Finer grit paper of 220 or higher should be used at slower speeds. Sanded depth will vary, but 1/64 - 1/32” (0.04 – 0.08 cm) per pass should be the maximum. Be careful to make sure sandpaper is clean and free of material as the epoxy can leave a residue on the paper and gouge the material on the next pass.
3. Random Orbit Sanding – a) use a step up dry sanding method beginning at 60 open grit and proceeding in finer open grit paper increments; 80, 100, 120, 180, 240, 320, 400, 600, 800, 1000. b) wet sand using closed face or solid paper at medium speed beginning at 1200 grit and proceeding in finder closed grit paper of 1500 and 2000. Clean all residue between sanding steps. c) Wet Sand at low rpm using 3000 & 4000 foam backed sanding pads, using plenty of water at all times.
Material should be clear and slightly hazed. Do not over work or overheat.
4. Polishing – use a variable speed, 2000 rpm polisher. High quality plastic polishes are formulated to be used at specific speeds. We recommend Mirka Polarshine 10 medium-coarse compound. At each step, taking time to polish and keep pads lubricated with Mirka compound. a) Using a lamb’s wool polishing pad, buff at 2000 rpm until surface imperfections disappear, b) using a 2000 grit foam polishing pad, buff at 1800 rpm and c) using a 3000 grit foam polishing pad, buff at 1600 rpm.
5. Finishing – apply Mirka Polarshine-UF3 using a clean, new 3000 grit foam applicator pad at 1500 rpm, buff to a brilliant finish.
Important: Follow safety precautions on the technical bulletin when mixing and pouring Epoxacast™ 690.
When machining, sanding or polishing fully cured epoxy, wear a NIOSH approved respirator, protective eyewear and clothing to minimize skin contact. Results may vary depending on how closely directions are followed, quality of equipment and aptitude/experience of artisan. In all cases, Smooth-On is not responsible for the outcome due to the above variables. If results are in question, we recommend testing on a small test epoxy casting before scaling up to a large project.