Gap Filling on Resin Kits: Which Gaps Are Actually Yours

Most gap filling guides for figures were written for cast resin, and they carry a list of defects that a 3D printed kit physically cannot have. Mould lines, flash, release agent residue, air bubbles trapped in a mould. None of those exist on a printed part, because there was never a mould for them to come from.

That matters more than it sounds. If you go looking for a parting line down the side of a figure you will find something, because there is always something, and you will sand a perfectly good surface trying to remove a defect that is not there. So this guide starts by narrowing the problem rather than widening it.

A printed kit has a short and specific list of things that need filling, and depending on which finish level you ordered, some of them have already been dealt with here before the box went out.

Your kit has never been in a mould

A cast figure is made by pouring resin into a two part mould, which is why cast pieces carry the marks they do. A parting line is by definition the border between the two halves of a mould. Flash is excess material that has leaked out between those two halves. Release agent is a substance applied to the mould so the part will come out of it. Gas porosity, the small subsurface holes a foundry calls pinholes, comes from gas picked up by molten or liquid material inside a mould.

Every one of those requires a mould. Our kits are printed on MSLA machines, layer by layer, out of liquid photopolymer cured by ultraviolet light. There is no mould at any point, so there is no parting line to scrape, no flash to trim, and no release agent to wash off.

That last one is worth saying twice, because a lot of guides open with it. There is nothing on the surface of your kit that needs washing off. We wash the parts here as part of production, and they arrive clean and fully cured. If you find advice telling you to scrub a kit before painting, it was written for a different manufacturing process.

Printed parts do have their own defects, and some of them are hole shaped, which is where the confusion comes from. But the causes are completely different: a blocked light path, a dead pixel on the screen, or suction pulling on a wall during the peel between layers. Those are print failures, and a part with one does not leave here. What reaches you is the ordinary stuff below.

Where a gap on a printed kit actually comes from

Three things, and only three.

The part split. A figure arrives in pieces because someone deliberately cut it into pieces. Sometimes that is because the whole thing does not fit on a build plate, but just as often it is a quality decision made even when it would fit. Splitting a model lets each piece be oriented so that its most visible surfaces face away from the supports, and lets a cavity be positioned so it does not trap uncured resin. The seam you get afterwards is the price of a better surface everywhere else.

How well those pieces meet. Sculptors join parts in different ways. A peg and socket aligns precisely and can be fractionally tight or loose. A flat cut is more forgiving of any slight warp but gives you a visible line to deal with. Neither is wrong, and the difference decides how much filling a particular kit needs.

Support contact points. Where the supports touched, there is a small mark, between roughly 0.3 and 0.6mm, invisible at normal viewing distance but findable with a fingernail. On a Bronze kit those are yours to smooth. At Silver and above they are already sanded.

Notice what is not on that list. There is no random surface pitting to chase, no bubbles to dig out, and no seam running the full height of the figure because the mould halves did not close properly. The gaps on a printed kit are at the joins, and the joins are where the sculptor put them.

Key takeaways

• No mould means no parting lines, no flash and no release agent.
• Gaps live at the part splits, which were chosen for surface quality.
• Support marks are 0.3 to 0.6mm and already sanded at Silver and above.

Drainage holes are not defects

Larger parts are printed hollow rather than solid, which saves material and, more importantly, avoids the suction that builds up inside a sealed cavity every time the build plate peels away from the film. That suction is a real failure mode and it can pull a hole straight through a wall.

The way you prevent it is to design small drainage holes into the model so the pressure equalises and uncured resin can run out. They are deliberate, they are necessary, and they are usually placed underneath or behind where nothing will see them.

Occasionally one lands somewhere that would still be visible once the figure is assembled. Those are the ones we fill at Silver and above, before the kit ships. If you have a Bronze kit and you find a small round hole in an out of the way place, that is what it is, and filling it is a thirty second job rather than a sign that something went wrong.

Which gaps are yours, and which are ours

The three finish levels are not marketing tiers, they are different amounts of exactly this work. Finish levels explained has the full detail:

• Bronze, DIY Ready. Supports removed, washed, fully cured, checked. Sanding, gap filling and priming are all yours. Usually ships in 2 to 5 business days.
• Silver, Detail Ready. Everything in Bronze, plus support marks lightly sanded and any drainage holes that would be visible after assembly already filled. You still assemble, seal the seams, prime and paint. Usually ships in 4 to 8 business days.
• Gold, Paint Ready. Everything in Silver, plus all seams and joints pre-filled and sanded by us, and the figure primed in black, white or grey. You assemble and paint. Usually ships in 6 to 14 business days.

So the honest answer to how to fill gaps on a Remerlinds kit depends entirely on which one you bought. At Gold there is essentially nothing in this guide left to do. At Silver the holes are handled and the seams are not. At Bronze it is all yours, which is the point of Bronze and is why it is the cheapest.

If you are reading this before ordering rather than after, that is the more useful decision than any filler choice below.

Dry fitting decides how much filling you do

Everything that follows gets easier or harder based on one step that takes ten minutes and involves no glue.

Hold every joint together dry, before anything is permanent. You are looking for three things: whether the parts seat fully, where a gap remains when they do, and how big it is. A joint that closes to nothing needs no filler at all. A joint that leaves a hairline needs a completely different approach from one that leaves a visible channel.

If a peg is fractionally too tight the part will not seat, and the gap you see is not a gap in the sculpt, it is a fit problem pretending to be one. Take a little material off the peg rather than filling the space it caused. If a peg is loose the part will seat but wander, and that is worth solving with a pin or a thicker adhesive rather than by filling afterwards.

Our assembly guide covers dry fitting, gluing and pinning properly, and the assembly troubleshooting guide goes through pegs that are too tight, pegs that are too loose and parts that arrived bent. This article is about what is left once the joint is closed as well as it is going to close.

Choosing a filler by the job, not by the brand

We do not sell fillers and we are not going to send you a shopping list. What decides the choice is the shape of the problem, and there are three shapes.

A hairline you can see but not feel. The join is closed and there is a visible line. You need something thin enough to run into it and hard enough to sand flush. Very little material is involved and the strength of the fill is irrelevant, because the joint itself is already holding.

A visible channel with two clean walls. A gap you can get a tool into. You need a filler with body, that you can press in, level off and sand back, and that will not sink below the surface as it hardens.

Missing volume or lost detail. A gap that interrupts a fold, an edge or a curve that has to continue across it. Here you are not filling, you are sculpting, and you need a material with a long enough working time to shape and blend before it sets.

Two part epoxy putties cover the second and third cases well. Thin filler materials cover the first. That is the whole decision, and any product on a hobby shelf that fits the description will do the job.

Key takeaways

• Diagnose the gap by shape: hairline, channel, or missing volume.
• Only the third case needs something you can sculpt.
• The fill is almost never doing structural work; the joint is.

Why some fillers shrink and others do not

This is the one piece of chemistry worth understanding, because it explains a failure that catches everyone once.

A filler carried in a solvent is a mixture of solids and a volatile liquid. When it dries, the volatile part leaves, and the volume that leaves is gone. If a filler is half solids by volume, a fill sets at roughly half the height you applied it at. On a flat panel that is a nuisance. In a deep gap it means the fill sinks below the surface and the seam reappears after you thought you were finished.

A two part epoxy putty works differently. The two components react with each other chemically when you knead them together, and the material is all solids with no volatile fraction to lose. Datasheets for epoxy fillers state one hundred percent solids by volume and describe them as non shrinking. What you shape is what you get.

The practical rule that falls out of this: for anything with depth, use something that cures by reaction rather than by drying. For a surface skim where the fill is a fraction of a millimetre deep, shrinkage barely matters and the easier material wins. And with anything that dries by evaporation, expect to need a second pass, and let the first one dry completely before you judge it, because a fill that looks flush at ten minutes can be dished at an hour.

Superglue is an adhesive, not a filler

Cyanoacrylate gets used as a gap filler constantly, and it is worth being clear about what it is and is not good at.

It cures by reacting with tiny amounts of moisture on the surfaces it touches, which is why it grabs so fast. Manufacturers are candid that in its standard form it is not especially impact resistant, and gap filling capability on a purpose made gel grade is quoted in fractions of a millimetre. It is an adhesive with some tolerance for a gap, not a material for filling one.

Where it genuinely shines is the hairline. A drop at the end of a closed seam will draw itself along the line by capillary action without any pressing or spreading, and it sands hard and flush. That is the first of the three cases above, and nothing does it better or faster.

Where it goes wrong is when it is asked to be a putty. A thick fill of it is brittle, it does not replace lost volume in any controllable way, and it cannot be shaped. The common workaround of mixing it with a powder to bulk it out and set it instantly is widely used and works well enough, but there is no technical literature behind it at all, only manufacturers' own blog posts, so treat any confident claim about how strong the result is with suspicion.

Sanding a fill without eating the sculpt

More detail is lost at this step than at any other, and the reason is that a filled area and the sculpt around it sand at different rates.

Work only on the fill. A sanding stick or a small pad keeps the abrasive where you put it, whereas a folded sheet of paper flattens whatever is adjacent, and on a figure what is adjacent is usually the thing you care about. Wrap the paper around something curved for a shoulder or a helmet, and use something narrow for a fold or an armpit.

Start no coarser than you have to. Coarse grit leaves scratches that then need finer grit to remove, so an aggressive start costs you two extra stages. Overfilling slightly and taking the excess down gently is easier than filling twice, but only slightly, because every pass over the fill is also a pass over its edges.

Feather outward at a shallow angle rather than sanding straight down onto the fill, so the join between filler and resin disappears instead of becoming a step. And check under a single light held low across the surface, which throws shadows off anything proud or dished that direct light hides completely.

Wet sanding gives finer control and keeps the dust down, which matters for the reason in the next section. Our painting guide covers what happens after this, and choosing a primer covers the coat that will show you everything you missed.

The dust nobody warns you about

Guides to this cover resin dust and stop there. There is a second one that is better documented and gets no attention at all.

Epoxy manufacturers are explicit that breathing dust from partially cured epoxy increases the risk of sensitisation, and that the window is much longer than it feels. Epoxy putty becomes sandable within hours, but full cure at room temperature can take more than two weeks. So the material you sand the same evening you applied it is, chemically, not finished, and that is exactly the dust the warning is about.

Sensitisation is worth avoiding once rather than managing repeatedly, because it does not wear off. The practical answer is easy: leave epoxy fills as long as you reasonably can before sanding them, wet sand where you can, wear a particle mask when you cannot, and do not do it over a desk where you then eat.

Nothing comparable is documented for sanding cured cyanoacrylate. Two adhesive safety data sheets treat the cured material as non hazardous and say nothing about dust from it. The ordinary particulate case still applies. Our guide to working safely with a resin kit covers the bench side of this properly, including why the aerosol primer is a bigger deal than any of the dust.

Recommended reading

• Assembling your first resin figure, for dry fitting, gluing and pinning from the beginning.
• Assembly troubleshooting, for pegs that do not fit and parts that arrived bent.
• Finish levels explained, for deciding how much of this you want to do at all.
• Tools worth owning, which covers the sanding side without naming a shopping list.

The rest of the range is in the full Remerlinds catalogue, and every product page carries all three finish levels with their prices side by side.