How to Finish and Paint Resin 3D Prints
A freshly printed resin part is not a finished part. It comes off the build plate sticky, slightly soft, and covered in support marks, layer lines, and surface artifacts. Finishing resin prints properly is what produces the smooth, painted results you see in professional builds and on display shelves.
This guide covers the full finishing process from initial cleaning to a final topcoat, including safety precautions that genuinely matter with resin.
Why Resin Needs Finishing
Resin prints have several characteristics that require attention before painting.
Support marks are the most immediately obvious. Every support contact point leaves a small nub or pit on the surface. These need to be removed or filled before any paint goes on.
Layer lines are finer in resin than in FDM printing, but they are still present and will show through thin or gloss paint. Resin layer lines are typically 0.025mm to 0.05mm deep, compared to 0.1mm to 0.2mm in FDM. They are subtle but visible, especially at shallow viewing angles under good lighting.
Print artifacts include print-through of the support structure showing as a grid on flat surfaces (known as peel marks), slight warping on large flat areas, and occasional blobs or zits from overexposure.
Surface stickiness from uncured resin on the surface will prevent paint from adhering properly and can transfer to your hands or painting tools.
All of these issues are addressable with the process described below.
Step One: Wash and Cure Fully First
This is not optional and cannot be skipped. Before doing any sanding or finishing work, the print must be properly washed and fully cured.
Uncured resin is a skin sensitiser and potential irritant. Sanding or cutting an uncured print creates dust and particles that contain liquid resin, which can cause allergic reactions, skin rashes, and respiratory irritation. Once resin is fully cured it is chemically stable and much safer to work with.
Washing
Remove the print from the build plate carefully using a scraper or removal tool. Place it in your wash station with isopropyl alcohol (IPA) at 90% concentration or higher, or use a dedicated resin wash solution. Wash for 3 to 5 minutes, agitating the part to expose all surfaces.
Remove the print from the wash solution, allow the IPA to evaporate fully (2 to 5 minutes in open air), then remove supports before curing. Supports are much easier to remove before the final cure when the resin is still slightly soft.
Curing
Place the washed, support-free print in a UV curing station or build a simple DIY station with a UV nail lamp inside a reflective box. Cure times vary by resin type and curing station power, but as a guide: 2 to 5 minutes each side for standard resins in a dedicated curing station.
A fully cured print will not be sticky to the touch and will have a slightly harder, more rigid feel than the fresh-from-printer state. If your print is still tacky after curing, either your cure time is too short, your UV source is too weak, or the IPA wash was insufficient.
Step Two: Remove Supports and Initial Cleanup
With the print fully cured, remove any remaining support material using flush cutters or small pliers. Cut as close to the surface as possible without gouging the print.
For support nubs that are proud of the surface, use a sharp hobby knife or scalpel to pare them down flat. Work carefully at a low angle to the surface to avoid cutting into the surrounding area.
Fill any pits or holes from supports with UV-cure resin applied with a cocktail stick or fine brush. Apply a small amount, press it into the pit, then cure immediately with a handheld UV torch. This produces a fill that sands and paints like the surrounding material.
Step Three: Wet Sanding
Wet sanding removes the remaining layer lines, light marks, and surface irregularities. It is the primary levelling step before priming.
Always wet sand resin. Dry sanding creates fine resin dust that is a respiratory hazard even from fully cured resin. The water lubricates the process and keeps dust particles in suspension, which is far safer. Work in a ventilated area and wear a P3 or FFP3 rated mask regardless.
The Grit Sequence
Work through the following sequence, spending enough time at each grit to remove the scratches from the previous grit before moving up:
200 to 400 grit - removes visible layer lines and support marks. The surface will look scratched and dull at this stage, which is correct.
600 grit - refines the scratch pattern from the previous grit. The surface begins to look more uniform.
800 to 1000 grit - removes the 600 grit scratches. Surface starts to look smooth.
1500 grit - the surface should look quite smooth at this stage, with only fine, even scratches.
2000 grit - the surface should look nearly gloss after this step. Fine sanding scratches will be visible but shallow.
You do not need to go to 2000 grit on every surface. For surfaces that will be primed and painted with an opaque colour, 800 to 1000 grit is sufficient. Reserve the finer grits for surfaces where the finish quality will be visible through the paint (such as skin tones on miniatures or gloss finishes).
How to Wet Sand
Keep a bowl of water nearby and dip the sandpaper frequently. Fold the sandpaper into a small pad and work in circular motions with light, even pressure. Rinse the surface periodically to remove swarf and check progress.
On curved surfaces, wrap the sandpaper around a soft foam pad to follow the contour. On flat surfaces, a small sanding block prevents rounding of edges.
Step Four: Filler Primer
Filler primer (automotive high-build primer) is applied after wet sanding and fills any remaining micro-scratches or imperfections that sanding alone did not resolve.
Shake the can thoroughly for at least two minutes. Apply from 25 to 30cm distance in light, even passes. Do not try to get full coverage in one coat. Apply two to three thin coats, allowing each to dry for 10 to 15 minutes before the next.
Allow the final coat to dry fully (30 to 60 minutes minimum, or longer in cool conditions) then sand back with 400 grit wet. This levels the primer and removes any orange peel texture.
Inspect under a raking light (a desk lamp held low to the surface works well). Any remaining pits or scratches will cast a shadow and be clearly visible. Fill deep marks with spot putty or a second application of primer. Repeat the prime and sand cycle until the surface is uniformly smooth.
For the cleanest result before painting, a final pass with 600 grit wet after the last primer coat produces an ideal surface for paint adhesion.
Step Five: Painting
With a primed, smooth surface, you can apply paint using any of the three main methods.
Rattle Can (Aerosol)
Aerosol spray paint is fast, accessible, and produces good results on larger pieces. Use paint labelled for plastic, or apply a plastic adhesion promoter first.
Apply in thin passes from 25 to 30cm distance, overlapping each pass by 50%. Multiple thin coats are always better than one thick coat. Thick coats cause runs, take longer to dry, and can lift the underlying primer.
Allow full cure between colour coats (at least 1 hour, ideally longer). For colour changes, 3 to 4 light coats with full drying time between each produces solid, even coverage.
Brush Painting
Acrylic model paints applied by brush give the most control for detailed work and small pieces. Thin the paint with water or acrylic medium to a consistency slightly thinner than whole milk. This produces smooth coats without brush strokes.
Apply with a soft flat or round brush and build up coverage in 3 to 5 thin coats rather than one thick coat. Thin coats dry quickly (5 to 10 minutes), preserve surface detail, and do not obscure fine textures.
Airbrush
An airbrush produces the most professional finish and is the best tool for smooth colour transitions, blending, and fine detail on miniatures and display pieces. Thin acrylic or dedicated airbrush paints to the consistency of skimmed milk and apply at 20 to 30 PSI pressure.
Airbrushes are the most technique-dependent option and have a learning curve, but the quality ceiling is significantly higher than rattle cans or brushwork for small or detailed parts.
Step Six: UV-Resistant Topcoat
A clear topcoat protects the paint from chipping, scratching, and UV fading.
For display pieces, a gloss varnish followed by a satin or matte varnish is a common approach. Gloss first seals the paint fully and creates an ideal surface for washes and weathering. The final satin or matte coat brings the sheen to the desired level.
For pieces used outdoors or in direct light, choose a topcoat specifically labelled UV-resistant. Standard varnishes do not prevent UV fading. Automotive clear coats with UV inhibitors are a good option for pieces that will see regular sunlight.
Apply topcoat in the same way as paint: thin coats, adequate distance, full dry time between coats.
Safety During Finishing
Resin finishing involves hazards that are worth taking seriously.
Resin dust - sanding resin, even fully cured resin, produces fine particles. These particles are not the same chemical risk as liquid resin, but they are still small enough to enter the lungs. Always wear an FFP2 or FFP3 dust mask when sanding resin. A basic paper dust mask is not sufficient.
Wet sanding significantly reduces airborne dust and is strongly recommended over dry sanding for all resin work.
Ventilation - all spray painting and priming should be done in a ventilated space, ideally outdoors or in a spray booth. Aerosol paints and primers produce significant VOC concentrations in enclosed spaces.
Gloves - wear nitrile gloves when handling uncured or recently washed resin prints. Once fully cured and primed, the sensitisation risk is much lower, but gloves are still sensible practice during any sanding that produces particles.
Dispose of resin waste properly - IPA used for washing, paper towels, and gloves that have contacted liquid resin should not go in general waste. Cure any liquid resin waste under UV before disposal. Check your local regulations for chemical waste disposal.
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