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Sanding epoxy resin – Instructions for the perfect surface treatment

sanding epoxy resin The sanding of epoxy resin is a very important step on the way to a perfect surface. In this guide article, we show what needs to be considered and which material you need for this.  




The pitfalls of sanding epoxy resin

Cured epoxy resin is relatively difficult to sand due to its hardness. The hardness of the resin makes the sandpaper dull relatively quickly. In addition, hardened epoxy resin can clog the abrasive paper relatively quickly, so that it must either be cleaned again first or replaced. With wet sanding, the clogging is significantly reduced and the abrasive paper can be used for longer.

Hint: Wait long enough for the epoxy resin to cure effectively. This happens after at least 48 hours, but may take longer depending on the product.



Sanding epoxy resin wet or dry?

Wet sanding with waterproof sandpaper is often the best approach to sanding cured epoxy resin. Wet sanding removes unevenness while you are sanding, reduces clogging of the abrasive paper and drastically reduces the amount of dust emitted into the air. The abrasive paper lasts much longer and you can see immediately what the sanding result is. Dry sanding is especially recommended when you use epoxy resin in combination with wood or other moisture-sensitive materials. Here the added water causes the wood to swell and can cause stains.    


Can epoxy resin also be sanded dry?

This is basically possible, but we recommend wet sanding. Why? Dry sanding by hand or with an orbital sander generates heat which could dissolve the epoxy resin. The surface is then matt and can only be restored with a lot of effort. The temperature point varies depending on the product used. It is therefore always safer to carry out the sanding process by wet sanding, as considerably less heat is generated here. In addition, epoxy resin dust, which is produced during dry sanding, is carcinogenic. Wearing a mask is therefore absolutely essential.


sanding resin  


Wet sanding of epoxy resin


Wet sanding Pros  


  • Wet sanding improves performance: Water improves cutting performance by flushing the cut material from the surface, which can come between the sanding surface and the substrate. In addition, water keeps the sanding surface free of dirt so that it does not clog or clog the grinding surface.
  • Wet sanding reduces dust formation: Since cut particles are wet during sanding, wet sanding releases practically no dust into the air. This reduces exposure to epoxy dust and is therefore safer from a health perspective.



Wet sanding Cons  

  • Wet sanding is a mess: The combination of water and sanding dust makes a mess. Therefore, make sure to cover the workplace accordingly with a plastic sheet or tarpaulin.
  • Wet sanding is not recommended in combination with wood: If you combine epoxy resin with wood, you should switch to dry sanding. The water makes the wood swell and the wood fibres stand up.



What is waterproof sandpaper?

Waterproof sandpaper usually consists of a closed layer of silicon carbide. Grit sizes from 60 to 1000 are available, although we recommend starting with a grit size of 120 to avoid making too deep scratches in the surface, which can only be removed with a lot of patience. If you want to polish the epoxy resin and thus achieve a shiny surface, you should sand up to grain size 1000.  

sanding and polishing epoxy resin 


The wet sanding – instruction



Wet sanding is usually done by hand. Do not use an electrically operated grinding machine if you are sanding wet, as you could otherwise suffer an electric shock. As an alternative, you can use an air-powered sander for large surfaces.

We use a hard rubber sanding block to keep the paper smooth when smoothing and sanding most surfaces. A curved or soft backing may be required on curved surfaces, but you can wet the sandpaper without the block or backing by simply folding the cloth to fit the shape of your hand and dipping the paper in water.

On very irregular or textured surfaces such as a sculpture, the somewhat rigid, waterproof sandpaper does not adapt sufficiently to the curves. Here you can use more flexible sanding pads, such as the 3m Scotch Brite, which can also be used wet.

The water can either be provided in a slightly larger container – warm water is also welcome if you are working in a cold environment. In the meantime, simply dip the sandpaper into the water and sand the surface in a circular motion until you see no more traces of the previous grain.  


Hint: Filling water into a spray bottle has also proven to be a good solution. Then simply spray the surface with some water.


Check the progress of the sanding process again and again by removing the sanding residues with a cloth. The epoxy resin surface should always be cleaned, especially when changing to a finer grain size. Otherwise there is a risk that the coarser, detached grains of sand will leave grinding marks again.


Hint: Any residues should be removed immediately after the last sanding process, as they are difficult to remove after drying.


To prepare the surface for subsequent epoxy coating or painting work, wipe the dry surface with a paper towel to remove any remaining deposits, then gently sweep the surface with a broom. Do not use rags – they could contaminate the surface. If you want to paint the surface immediately after sanding, use an electrostatic dust cloth afterwards. This will remove any dust particles that may still be present, which would worsen the result when painting.  


sanding epoxy resin between coats


Sand epoxy resin dry



The sanding of synthetic resin is useful when larger areas are involved or when the resin has been processed in combination with wood, which cannot tolerate moisture. An orbital sander has proven itself here.  

  • Protect your health, always wear a respiratory mask to avoid inhaling the toxic dust. Work in a ventilated room
  • Start with a grain size of 120 and work your way through to one grain size if possible (at least 1000 grain size is recommended).
  • If the sandpaper becomes clogged, there are special rubber sticks for this purpose, which remove the residue from the sandpaper surface.
  • Make sure to completely remove the traces of the previous grit


Hint: With pure sanding you will achieve at most a very slightly shiny surface. If you want a really shiny surface, it is necessary to polish the work pieces.



Video tutorial about sanding epoxy resin



Waxy surface with epoxy resin – Amine blush

During curing, especially at fluctuating temperatures, a slightly sticky, waxy layer may form on the surface. Its appearance changes depending on the moisture content of the air, but it is usually more noticeable in cool, humid conditions. It may be difficult to see at all, or it may appear as a thin, greasy or dull layer. However, this so-called amine redness can be removed and underneath it the epoxy resin should be intact. Due to the waxy surface, sanding with normal sandpaper does not work, as it will clog up immediately. Here only helps:

  • First try to remove the layer with some warm water, soapy water and a sponge
  • If this does not work, try to remove it with spirit and a cloth
  • Sanding with wet sandpaper and water is also a possibility



Why is the amine blush a problem?

Amine redness is not a problem in itself: it is the effect of it that is the problem. If you continue to work without removing this layer, it will prevent lacquers, other epoxy coatings and other substances from bonding effectively and ensuring adhesion. The surface should therefore definitely be cleaned.

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