fter curing, epoxy resin workpieces are not quite “finished”: without sanding the surfaces, in many cases they do not yet have the gloss that they could actually have. In this article, we would like to explain to you which materials you can use to sand epoxy resin and what you need to consider.
- 1 Possible Problems with Resin Sanding
- 2 Wet Sanding or Dry Sanding?
- 3 Wet Sanding of Epoxy Resin
- 4 Treat Surfaces by dry Sanding
- 5 Amine Blush – Wax on the Resin Surface?
Possible Problems with Resin Sanding
During curing, the initially liquid casting resin transforms into a very hard material after the specified curing time. It is therefore not at all easy to sand the surfaces of the completely dried workpiece. Due to the hardness of the resin, the abrasive paper used sometimes becomes dull very quickly. In general, the structure of sandpaper suffers greatly under the effect of the resin, so that it must be cleaned frequently or replaced quickly. To reduce the material consumption of the sandpaper, we recommend wet sanding of epoxy resin surfaces.
Tip: You should only wet sand your cast resin work pieces when they are really dry. As a rule, you should therefore wait at least 2 days after casting. It can’t hurt to consult the manufacturers’ labels of the products you use for information on the exact curing time: After all, there are also products on the market that take much longer than 48 hours to cure completely.
Wet Sanding or Dry Sanding?
Based on our experience, we recommend that you give preference to epoxy resin sanding with wet sanding with water-resistant sandpaper over dry sanding. There are also good reasons for this: The abrasive paper used for wet sanding usually lasts much longer than that used for dry sanding. The sanding process also removes minor unevenness immediately and much less dust is produced in the room air due to the moisture. Due to the binding of dust in the water, the respective condition of the surfaces is more visible during wet sanding than during dry sanding and can therefore be easily assessed at any time.
However, there may be exceptions where dry sanding gives better results. For example, we recommend dry sanding for workpieces that are partly made of wood or similar moisture-sensitive materials. The water used for wet sanding would make the wood swell unattractively and cause unaesthetic stains.
Nevertheless, there are a number of other reasons that speak more in favour of wet sanding and against dry sanding. Dry sanding with a random orbital sander (but also sometimes when sanding by hand) generates a lot of frictional heat. If this heat exceeds a certain value, the resin surface may be loosened, resulting in an unattractive matt surface.
If this is the case, it is difficult or even impossible to restore the shine to this damaged resin surface. With various products available on the market, this critical temperature point can vary greatly in height or depth. Therefore you should ideally play it safe if you are in doubt and decide to use wet sanding. After all, this method always generates considerably less heat than dry sanding.
Last but not least, the factor of dust formation also plays a role that should not be underestimated. In dry sanding, this dust is not bound by water, but is mostly swirled in the air. However, the dust generated during epoxy resin sanding is considered carcinogenic. For this reason, you should always protect your health when dry sanding by wearing a protective mask.
Wet Sanding of Epoxy Resin
What are the Characteristics of Waterproof Sandpaper?
To be able to sand resin by wet sanding, you first need water-resistant sandpaper. This special sandpaper is made of a closed layer of silicon carbide. Basically you can get the waterproof sandpaper in grits between 60 and 4000, but a very coarse grit can leave quite deep scratches in the material when sanding cast resin, which are very difficult to remove.
Therefore, when sanding epoxy resin, you should start with grit 120 and then slowly work your way up to a finer grit. Polishing epoxy resin is when a fine polishing paste with very fine particles is finally used. With this you can give your work a particularly elegant shine.
Important Tips for the Wet Sanding Process
The wet sanding of epoxy resin is mostly done by hand. You are playing it safe if you avoid using electrically operated sanding equipment with this method. Under no circumstances should you run the risk of suffering a dangerous electric shock from the water used. An alternative for working on larger surfaces is, however, a sander driven by compressed air.
As an aid for wet sanding, we recommend the use of a sanding block made of hard rubber. With this block you can keep the sandpaper nice and smooth while sanding. However, if the surfaces to be sanded have a curved shape, you should use a suitable backing. If you do not want to use a sanding block or pad, you can also place the abrasive paper in a suitable position in your hand before moistening it.
Waterproof sandpaper unfortunately has the property of being rather rigid and difficult to bend. This is particularly problematic if you want to use it to work on the possibly quite irregular or even structured surfaces of sculptures and similarly complexly shaped pieces made of epoxy resin. On these surfaces it is usually difficult to adapt the shape of the abrasive paper to the curves in the material. However, suitable alternatives are also available for such cases: With a sanding pad that can also be used wet, such as the 3m Scotch Brite, you can also work on this type of project without tedious difficulties.
For wet sanding you should provide a sufficiently large water tank as close as possible to your workplace. Hot water can also be used if the ambient temperature is very cold. For epoxy resin sanding with water, you should use the sandpaper to sand the resin surfaces in a regular circular motion, dipping the special sandpaper into the water frequently enough. When sanding with epoxy resin, the grit should only be changed to the next finer grade when no traces of the previous grit are visible on the resin surface.
It is not absolutely necessary to immerse the abrasive paper in a water container to constantly remoisten it. Alternatively, you can moisten the surface of the sandpaper with the help of a water-filled spray bottle.
In addition, you should regularly wipe off the sanding residues bound in the water with an absorbent cloth when working. This will also give you a much better view of how the resin is being sanded. At the latest when changing to a finer grained sandpaper, the resin surface must be cleaned, otherwise the coarser grains of sand from the previously used sandpaper can cause new sanding marks.
Tip: When finishing your sanding work, you should wipe off the sanding residues adhering to the workpiece as soon as possible. After drying, it is much more difficult to remove them from the surfaces.
Afterwards you can use a paper towel to prepare the dry cast resin surface perfectly for further steps like painting or an additional protective layer of epoxy resin. If loose particles still adhere to the work piece, they can be removed with a paper towel or by sweeping with a fine broom. It is essential to use a paper towel for this purpose, as a cloth cloth could sometimes soil the surface again.
In case of an immediate application of paint after sanding, it is worth using an electrostatic dust cloth. This prevents negative influences on the final result by effectively removing even the smallest dust particles.
Treat Surfaces by dry Sanding
Dry sanding offers advantages over wet sanding in terms of effort and time required when relatively large areas are to be processed, for example for Epoxy Resin Tables. Dry sanding should also be chosen if you want to process epoxy resin and wood. We advise you to use a commercially available random orbit sander for dry sanding.
- Dry sanding produces a lot of dust, which can be toxic if inhaled. Therefore, to protect your health when dry sanding epoxy resin, you should always wear a breathing mask. In addition, you should also carry out the work in a well-ventilated workplace.
- When dry sanding epoxy, start with a 200 grit size and work your way up to a fine 1000 grit size (or higher).
Dust abrasion can quickly dull the abrasive paper during dry sanding. However, with a rubber stick designed for this purpose, you can clean the sandpaper and use it for longer.
- Before changing the grit used, you should have completely removed any visible sanding marks from your work piece.
Tip: For a truly perfect surface with an impeccable shine, it is essential to polish the epoxy resin with at least a 1000 grain. When sanding with coarser grains, only half satisfactory gloss effects can be achieved.
Amine Blush – Wax on the Resin Surface?
It can sometimes happen that when epoxy resin hardens, a layer forms on the resin surface that feels slightly sticky and like wax. This phenomenon is generally referred to as amine blush. The formation of such a layer is usually favoured by significant temperature fluctuations during the drying phase. The amine blush may sometimes be relatively difficult to see with the eye, as its appearance may change.
Amine blush is most noticeable in humid and rather cool air conditions when it can be felt and seen as a dull or greasy layer on the surfaces. The good news, however, is that the resin under the amine blush is generally undamaged. Nevertheless, this amine blush must be removed in any case, as the waxy and unpleasantly sticky consistency makes sandpaper dull very quickly.
Amine Blush can be effectively removed with these Agents:
- Amine blush should be relatively easy to remove with a little warm water, ordinary soapy water and a sponge.
- More stubborn layers can be removed with a cloth and commercial spirit.
- A layer of amine blush can also be removed by wet sanding.
Reasons for Removing Amine Blush
In principle, a layer of amine reddening has no harmful effect on the cured casting resin. However, the sticky layer should definitely be removed if you want to further refine your work piece with a coating of epoxy resin or with special paint. If you do not remove the amine blush, the substances used as a coating cannot bond with the cured resin with sufficient stability.