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Sanding, Buffing and Polishing, is not always necessary. Sometimes a dome coat or a flood coat of clear resin is all that is needed (and can sometimes be the easiest). In some cases a flood coat vs wet sanding and oil/polish is a matter of preference.
However, that is not always THE answer depending on project involved. Some projects do require a different finishing method, and sometimes their shapes make it difficult to flood coat effectively.
Many resin craftsman, say they will not leave dribbles down the sides, or attempt to spray coat with cloudy varnish. Sanding, cutting then polishing is considered the professional finish, by many. Yes, it is a ton of work.
If you have lipped edges on resin pieces you need removed, here is a blog you might find helpful for that: Removing lipped edge on resin
If you choose to flood coat after a bit of sanding, you can go to about a 220 grit so the resin has something to grip to.
You can use a wet/dry sandpaper (use it wet with a tiny amount of dish soap), in course grit, down to the finest grit you can get. You do need to go through each of the grits, because if you miss one, then it can be the one that leaves scratches. Dry sanding can have it's own problems, friction melts the epoxy and can leave swirls, also the dust is wicked if breathed in (wear a proper mask for particulates), better to wet sand and wipe between the grits. You are basically "scratching material off", at varying degrees of aggressiveness, so don't skip grits or you'll be there forever with an 800 grit (for example), trying to get out 100 grit scratches, and that's not viable. As you switch from one grit up to the next grit, while sanding, also switch direction. So for example, after sanding with 80 grit in one direction, go perpendicular (cross hatch) at the next grit up. Then switch back to opposite direction for next grit up. This enables you to better see if you've removed previous grits scratches. Then use a cutting (abrasive) compound, then finish with polishing compound to buff and shine the resin back to a glassy finish. Wipe it on with a cloth then hand rub it, or use with a buffing and polishing wheel.
There are many types of polishing compounds (these are just a few). Many people use vehicle headlight polish on their castings :
- Meguiar's PlastX plastic cleaner & polish, for automotive headlights.
- Blue Jewellers polish compound, often used on resin jewellry.
- Fabulustre
- Another one mentioned to give a lovely finish on resin jewellry is a piano polish.
- Hut Ultra Gloss Plastic Polish many pen makers use.
- Novus 7100 kit, 1 (Plastic Clean & Shine), 2 (Fine Scratch Remover), 3 (Heavy Scratch Remover).
- Flitz, Metal, Plastic & Fibreglass Polish
- Carnauba wax
- Turtle Wax 50935 Scratch Repair & Renew.
Different users have different preferences. Some artists find a polish paste works better then a polish liquid depending on their piece, and desired finish.
There are a variety of sand paper options as well:
- Wet/Dry sand paper
- Zona wet/Dry Polishing Papers
- Micro-mesh sanding buffing system goes much further up the grits (from 1500 up to 12,000 fine grit). This system is often preferred by jewellry artists.
- Paxcoo High grit wet and dry sandpaper. 9 x 11" assortment, 120, 240, 320, 400, 600, 800, 1000, 1500, 2000, 3000, 5000, 7000 for automobile -
These wet sandpaper are full size polishing papers in 9 x 11”, you also can cut it to any size as you need. The soft backing paper ensures a good fit to your hand and you can sands smoothly with only moderate effort, with high resistance to slippage during use
From rough to superfine sandpaper assortment helps to make easy polishing, fine grinding of flat and left the nice and smooth satin finish after polishing, which is fit for automotive, resin, metal, glass, auto, cars, plastic, stone, jade, leather, lacquer and wood
These ultra fine sanding paper sheets are made of silicon carbide, and nano-sand-planting techniques make the particles very fine and uniform on their surface. Can be cut to any size required.
There are hard cure & soft cure resins. If you're using a resin that can be dented with a fingernail, or softens with body heat, or gets bendy or soft in a warmer temperature, it is not a hard curing resin (the Shore Hardness rating for each resin should be available from epoxy resin manufacturers).
You have to sand to a fine grit first. Ideally you need to get rid of any scratches seen to the eye, before starting to polish. Work through the grits (from lower number such as 80), up through all to around 2500/3000 (or higher depending on project), then start polishing. Make sure scratches from previous grit are gone before moving to next grit. Wet/dry sand paper (or zona papers) is ideal for these projects.
Example:
You can shape your pieces on a 320 grit disc sander, then 400 grit dry (wear PPE designed for dust particulates). From there it's all wet sanding 600, 800, 1000, 1200, 1500, 2000, etc. up to 3000 (some kits go up to 10,000+grit).
After sanding use a cutting (abrasive) compound to get out any micro scratches, then a polishing paste. Then polish with a buffer wheel on drill with choice of polish.
For tables, If you want a gloss finish, stop at about 3000 grit, then use polishing compounds for the rest. If you want a matte finish, 1000 grit sanded finish will be fine with oil or whatever finish you're using. Honing oil can also help with various sheen finish levels. Here's a separate blog post about honing oil.
Note: Putting a wax or polishing compound on unsanded resin doesn't really accomplish much, you have to get the finish to a minimum 3000 grit polished sanding. It's worth the work. You just lightly sand it with each grit. And you don't need to spend hours on it with each stage, just enough so that the higher grit removes the scratches from the previous grit. Once you're done sanding the resin will pretty much be back to shiny again, then the polish will gloss it up beautifully.
You can polish hard curing resins with a buffing wheel and a polishing compound. Use a cotton buff and polishing compound appropriate for resins (plastics). Get the buff spinning, and use it to pick up compound, then press onto the resin piece. You can use a dremel tool or flex shaft for small projects like charms, but a large buff makes quick work of polishing something larger like a pyramid, floral blocks, trays or coaster. Keep the piece moving. You don't want to buff any one area more than a couple of seconds at a time. You also do not want to press the piece into the buff. Let the buff do the work; let it run over the resin piece or charm, but don't use too much pressure. Go over the entire piece as needed. When done clean with mild soap and water, to remove any polishing compound residue.
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Another method I've heard mentioned for sanding resin projects, (but I have not yet tried), you might find helpful, is:
- sand with 800 Abranet. Abranet is a dust-free sanding material. On a random orbital, on high speed.
- then use the 1200 - 1500 - 3000 Trizact clear coat sanding disc abrasives. Wet on the same random orbital. Only water, no soap needed.
- Then wool buffing 1st cut 1500-2000 rpm.
- Then finish piece with 3M Perfect-It machine polish.
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When it comes to sanding floral blocks, some artists say they won’t go any lower than 800 grit, to remove any large burrs or defects and the lip around the edge. Then go to 1000, 1500, 2000, 3000, then swap to polishing papers of 9, 3, 2, and (sometimes) 1 micron, with Maguire’s Ultimate Polishing Compound on the last 2 or 3, then a final buff with a microfiber pad and more compound.
They suggest if you go to a lower then 800 grit on the resin floral block type art, it makes it much harder & takes longer to get those deeper grit grooves out. And they feel it's unnecessary in most cases to go lower then 800 grit on those resin blocks.
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According to some of the best casting epoxy artists, when resin is polish sanded, it has such a different feel to it then unpolished resin. It feels like glass and looks amazing. They swear it is worth the extra effort.
- If your piece has wood, and you're trying to keep the wood dry (which you don't have to), or keep the wood from too fine sanding, tape it off. That way, a little water under the tape isn't a concern, but you can sand the epoxy to a really fine grit, and keep the wood closer to 320-400 for a finishing product. You can always dry the wood quickly after sanding with a blowdryer or heat gun on low (and keep it moving).
- Another option, depending on desired finish, is to sand both epoxy and wood up to 4000 grit, and use Odies oil as it can be used after any grade of grit, unlike Osmo or Rubio etc, which are meant more for 180/240 ish grit.
- If you have wood involved that will not be coated with resin, you may want to put several coats of sanding sealer on the wood before wet sanding If the wood absorbs too much water, it could split the wood, or cause it to separate from the resin.
Some people will dip the sanding disc in the water, as opposed to letting the piece sit in a wet tub. Have plenty of paper towels or an old towel handy to wipe the residue as you go, so it doesn't gum up the paper or scratch your piece with little pigtails.
For a satin finish on wall art (or other pieces) where high gloss is not desired:
Use 0000 steel wool and rub in a circular motion. Allow at least 36 hours cure (brand dependant) before rubbing the coating, or it may scratch or mar rather then resulting in a satin finish. A good spray finish to put over this, is Liquitex Soluvar Spray Varnish for the satin finish. Some spray varnishes can react with cured resin, but this one has been used by numerous resin artists successfully. If your painting is going to be hung in a spot where light over high gloss is an issue, or someone prefers non high gloss finish, this is a possible alternative solution.
Another option to bring the shine level down is to use a honing oil & buff it in.
