FINISHING & POST-PROCESSING

Surface Treatment Techniques for FDM and SLA Printed Parts

Platform: https://3d.dglabs.cloud

What is post-processing?

Post-processing is the set of techniques applied to a part once 3D printing is complete in order to improve its appearance, strength, surface finish or functionality. A freshly printed part is just the starting point: through sanding, painting, coating or chemical treatment, it can be transformed into a professional-looking product indistinguishable from an injection-molded piece. Each technique has its own advantages, limitations and material compatibility.

General workflow

  1. 01

    Part removal and inspection

    Once printing is complete, the part is carefully removed from the bed and visually inspected to identify imperfections, supports and areas requiring treatment.

  2. 02

    Support removal

    Supports are removed with pliers, spatulas or scalpels. FDM parts with soluble (PVA) supports are soaked in water. SLA parts require fine cutting tools.

  3. 03

    Progressive sanding

    The surface is sanded with increasing grit (80 → 400 → 2000) to remove layer lines and burrs. For SLA parts this step is usually unnecessary.

  4. 04

    Specific treatment

    Depending on the goal, the appropriate technique is applied: primer + paint, acetone smoothing (ABS/ASA), epoxy coating, electroplating or other specialized finishes.

  5. 05

    Final finish and protection

    A matte, satin or gloss varnish is applied to protect the paint and provide the definitive finish. Functional parts may also receive lubricant or anti-corrosion treatment.

Available finishing techniques

Each technique suits different materials, aesthetic goals and finish levels. Combined, they can completely transform the final result.

Support Removal

Removing Temporary Support Structures

Any model with overhangs or suspended parts requires support structures during printing. Once finished, they are removed manually with pliers, spatulas or scalpels. Water-soluble supports (PVA) allow mark-free removal by soaking.

Benefits

  • Essential first step before any other finishing technique
  • Basic, low-cost tools required
  • PVA soluble supports leave no marks on the part
  • Compatible with FDM and SLA

Limitations

  • May leave marks or burrs at support contact points
  • Hard-to-reach areas can be difficult to clean
  • Risk of fracture in thin or fragile sections
  • Requires care and manual dexterity
ApplicationsAny FDM or SLA part printed with supports. It is the mandatory first step before applying any other finishing technique.

Sanding

Progressive Manual or Mechanical Abrasion

Progressive sanding is the most direct technique to remove the layer lines characteristic of FDM. It works sequentially: coarse grit (80–120) for major imperfections, medium (200–400) to smooth, and fine wet-and-dry paper (1000–2000) for a near-polished result.

Benefits

  • Visually eliminates FDM layer lines
  • Significantly improves paint adhesion
  • Result is proportional to time and effort invested
  • Compatible with most thermoplastics

Limitations

  • Tedious and slow on large or complex parts
  • Risk of losing fine details or sharp edges
  • Difficult access to internal cavities and complex geometries
  • Not applicable to SLA resin (already smooth)
ApplicationsPLA, PLA+, PETG, ABS, ASA. Presentation parts, cosmetic prototypes or any part intended for painting or display.

Primer & Filler

Surface Preparation with Primer and Filler Spray

Spray primer acts as a revealing and levelling base: when applied, it makes visible imperfections that the naked eye does not perceive, and prepares the surface for optimal paint adhesion. Polyester filler or filler spray fills deeper layer grooves. The optimal cycle alternates layers of filler, sanding and primer until the desired surface is achieved.

Benefits

  • Hides layer lines and surface micro-imperfections
  • Perfect base for high-quality paint finishes
  • Available in spray and brush-on formats
  • Compatible with airbrush and conventional paint

Limitations

  • Adds thickness to the part, may affect fit tolerances
  • Intermediate sanding required between primer coats
  • Mandatory drying time between applications (30–60 min)
  • Requires a well-ventilated workspace
ApplicationsFDM in general (PLA, ABS, PETG). Ideal as preparation before finish paint, presentation prototypes and collectible figures.

Painting

Spray Paint, Airbrush or Hand Brushing

Painting visually transforms a technical part into a finished product. It can be applied by spray (large uniform surfaces), acrylic brush (detail areas) or airbrush (gradients, textures and precision work). In all cases, prior priming is key to ensuring adhesion and durability.

Benefits

  • Fully customizable finish in color and texture
  • Wide range of effects: metallic, matte, translucent, aged
  • Can visually simulate any material (wood, metal, stone)
  • Compatible with FDM and SLA

Limitations

  • Requires prior priming for correct adhesion
  • Airbrush technique requires practice and specific equipment
  • Sensitive to handling before final varnishing
  • Drying time required between coats
ApplicationsFDM and SLA. Collectible figures, architectural models, product prototypes, cosplay accessories and decorative parts.

Acetone Smoothing

Chemical Surface Smoothing with Acetone Vapour

Acetone vapor smoothing is a chemical finishing technique exclusive to ABS and ASA materials. The part is exposed to acetone vapors in a sealed container for controlled minutes. The vapors lightly dissolve the surface layer of the plastic, which reflows and creates a smooth, glossy, injection-molded-looking surface without any sanding.

Benefits

  • Injection-mold-like smooth finish with no manual work
  • Very fast: the full process takes minutes
  • Unifies surface texture and highlights model details
  • Can superficially strengthen the part

Limitations

  • Exclusive to ABS and ASA (incompatible with PLA, PETG, Nylon)
  • Requires strict ventilation and PPE (flammable vapors)
  • Can dissolve fine details if exposure time is exceeded
  • Requires practice to control the result
ApplicationsABS and ASA only. Technical enclosures, figures and parts with smooth geometries where the smoothest possible finish is required.

Epoxy Coating

Two-Component Epoxy Resin Coating (XTC-3D)

Two-component epoxy coatings (such as XTC-3D) are brushed in a thin layer over the printed part. Once cured, they form a hard, smooth and glossy surface that completely hides layer lines and increases the mechanical strength, impermeability and chemical resistance of the part. Compatible with most thermoplastics and SLA resins.

Benefits

  • Fully smooth and glossy surface in a single application
  • Resistant to water and many chemicals
  • Increases the mechanical strength of the part
  • Compatible with subsequent painting
  • Compatible with FDM and SLA

Limitations

  • Adds noticeable weight and thickness to the part
  • Requires careful mixing of both components in exact ratio
  • 24–48 hour curing time
  • Vertical parts may drip if not rotated during curing
ApplicationsFDM and SLA. Parts requiring waterproofing, high-quality display figures, premium product prototypes and decorative moldings.

Don't have a 3D model yet?

If you're starting from an idea, a sketch or a broken part, our CAD design team can create the 3D model from scratch in Fusion 360 or FreeCAD before moving on to printing and finishing.

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