We have performed many test with different abrasives from different manufacturers and suppliers at sanding and polishing epoxy tables. We achieved the best results with CRA Kowax products. We fine-tuned a detailed procedure of how to grind and polish the surfaces of epoxies and wood to achieve an exceptional appearance of the product with the company CRA KOWAX.
Manual sanding
For manual sanding of epoxy surfaces, we recommend using sheets of sandpaper with different grain sizes. The sheets must be attached to the sanding pads, and this can be done in three possible ways:
1) Use a small SUPER ASSILEX HAND BLOCK with an intermediate layer measuring 72x125 mm. This block fits well in the hand, is slightly flexible and the sanding format is easily attached directly to this block using the integrated velcro. For sanding of large and extensive surfaces, SUPER ASSILEX HARD INTERLAYER with a velcro is added to the hand block, which excellently ensures that the plane is maintained, which as a result ensures a higher quality and even surface.
2) Use the FLEXIBLE SUPER ASSILEX HAND PAD. Thanks to its flexibility, this hand pad is especially suitable for processing round surfaces, edges, and differently articulated and shaped castings. The abrasive format is simply attached to it directly using the integrated velcro.
3) Use a HARD SUPER ASSILEX HAND PAD, which is used especially for small areas. Abrasive formats are attached to it and then attached directly using the integrated velcro.
Based on the quality of the surface, we choose on the highest grain size (lower number on sanding medium) to start grinding. A high grain size will remove a larger amount from the surface, but then it is necessary to take more subsequent steps with other grain sizes to unify the surface. From the CRA KOWAX products, we recommend using tested SUPER ASSILEX self-adhesive formats for combined wood and epoxy surfaces – they provide excellently uniform and shallow sanding grooves formed by the innovative and unique grain structure. K240 or K360 grits are sufficient for majority of cases. Paper tension is important for sanding. You should sand with uniform movement and pressure in direction of the wood fibers. Cross grain sanding is only used in special cases or to achieve a special effect. We recommend the reverse method for small objects – put the sandpaper on a flat table top and move the sanded object along it. During sanding, we gradually alternate the sanding grits from a lower number to a higher number and do not skip grits in a row by more than one grit. The basic recommended procedure is in these steps for SUPER ASSILEX FORMATS: K240-K320-K400-K500-K600-K800-K1200-K1500. You should use BUFLEX DRY FORMATS with a grain size of K2000 and then K3000 attached with Velcro for effective fine sanding and polishing. Abrasives and surfaces clogged with sawdust can be cleaned with a microfibre cloth or an ordinary clean cotton cloth.
Mechanical sanding
Eccentric sanders with oscillating motion are used for machine sanding (for efficient use of the abrasive, a 5 mm range) as they ensure a perfect surface of the polished surface and are simple to use.
However, for grinding the edges of the casting, a belt sander or a hand planer is more effective, or if these devices are not available, it is necessary to reduce the speed of the eccentric sander and thus reduce the removal and heating of the material (care must be taken not to create an eccentric grinding curve). Don't forget to protect hearing, sight and respiratory tract!!! Use a suitable vacuum cleaner. We do not recommend a rotating machines for for grinding; their rotational movement causes poorer surface quality. It is very convenient to use sandpaper with holes, as the holes serve to extract dust particles during sanding (ideal are SUPER ASSILEX discs with 15 holes for a sander diameter of 152 mm or SUPER ASSILEX with 7 holes for a sander diameter of 125 mm). If the abrasive does not have holes or the sander does not have suction, the sanded surface and the abrasive itself must be cleaned more often. A regular cotton cloth or microfibre cloth is usually sufficient. We recommend SUPER ASSILEX INTERLAYER HARD (15 holes for sander diameter 152 mm) with micro Velcro (for sanding with grit K240-K1500) or SUPER ASSILEX INTERLAYER 7 holes for sander diameter 125 mm for effective sanding.
Epoxies should be cured before sanding, so sanding should be done after proper time. The longer the curing time, the harder the materials become and the easier they are to work. We recommend starting sanding epoxy surfaces ideally 14 or more days after casting, but at least one week. Epoxies generally do not like high temperatures ar sanding, so we recommend choosing lower speed and pressure to avoid excessive heating. Just as we don't put pressure on the saw, we shouldn't put too much pressure when sanding. The processed materials soften at a high temperature, the abrasive clogs more and it is harder to sand or polish. In extreme cases it can even start to form polymer fibers. It is important not to stay in one place for too long when sanding the resin, as there is a risk of overheating and subsequent melting (the resin will return near the transition temperature to the gel), excessive sanding of the abrasive and formation of the fibers of the molten resin. Optimally, the sander should be moved continuously with slow movements. It is also necessary to pay attention to the variety of sanded materials and to stay more on harder or stiffer material, in this case wood. This carefull procedure will prevent depressions at the point of contact between the two dissimilar materials. When the sandpapers are clogged with epoxy dust (especially with higher grits), papers can be cleaned from time to time with a cotton cloth, microfibre or knocked out.
We sand the hardened epoxy in individual steps from the coarsest grain to the finest. In the first phase, you should use rough sanding with abrasives (ideally with products from the TRI-PRO or PREMIUM series, both with 15 holes) with grain sizes from P120 to P600 with steps P120-P240-P320-P400-P500-P600 using eccentric sander with velcro. You should choose the individual sanding steps according to the quality of the surface, but do not jump in grain size by more than 120, because otherwise traces of the previous step will be visible on the surface. More grinding steps bring the better the quality of the work. You must thoroughly check the sanded surface to see if there is a deeper groove somewhere when you go to finer grain of sandpaper; finer sandpapers will be not able to remove it and it will be visible even more after the final polishing.
In the second phase, you will perform fine sanding. You should use SUPER ASSILEX discs, again with 15 holes, grits K600, K800, K1200 and K1500 also with SUPER ASSILEX INTERLAYER HARD (15 holes) with velcro. Then you should use a soft SUPER ASSILEX INTERLAYER SOFT (with 15 holes) with velcro to eliminate scratches, and gently sand and polish the castings using the attached BUFLEX DRY DISC with K2000 grit and then K3000 grit. You should follow follow the same principles as for coarse sanding.
Polishing
Polishing the epoxy table is a very important step, as it is the key improvement of final appearance. Surface treatment sells, so this step must also be included.
The best start is the surface previously sanded with fine grit paper. If you ended sanding process with 1500 grit, you have to continue up to 3000 grit to finish fine sanding. You should use Buflex 2000 abrasive on a soft intermediate pad. It is necessary to wipe the abrasive from dust from time to time with a microfiber cloth or cotton cloth, or use suction. You should continue with Buflex 3000 on a soft intermediate pad and vacuum or wipe the abrasive again. Now the surface is prepared for final polishing.
It is also necessary to have a proper tool – i.e. a rotary polisher with a buffer between the layer and the polishing disc. An eccentric sander is not used for polishing, because it forms micro scratches even at using of polishing pastes. The appearance is then "holographic" due to the small regular micro scratches. It is also possible to use a drill with a polishing attachment for once, but the work is much harder, it is not performed in the best way, and it also harder to regulate pressure and RPM. We do not recommend this procedure, because it can ruin all your previous effort. It is better to borrow a polisher if it is possible. When choosing polishing pastes, it is better to choose product based on oils with the finest grain as possible – they dry more slowly. Don't underestimate the choice. We recommend using the Finixa POL10 polishing paste, a one-step nanotechnology-modified paste that polishes from the coarsest grain to the finest and provides a high gloss of 95 %. Another great advantage of this paste is that it remains moist for a long time and reduces the risk of dry powder residues. You should apply the Finixa POL10 paste to an orange POP 714 polishing wheel with a diameter of 150 mm, set at a maximum speed of 700 RPM (the less the better), and rub it over the polished surface. At lower speeds (up to 700 RPM), the temperature of the surface is controled and prevent possible local softening. You should press only slightly and proceed with a slow and even movement over the surface of the table. Do not stop short. At the end of the polishing process, clean the surface either with a polishing cloth or with a black POP 914 disk with a diameter of 150 mm, attached with velcro asymmetrically, in order to obtain the so-called orbital movement. Then wipe with a microfiber cloth.