Seam lines are often the second most glaring issue on the kit – right after nub marks. Whether painted or not, a seam line running down the middle of an arm or a leg never looks good.

Nowadays we see less and less seam lines on Gunpla kits, thanks to Bandai’s ever improving engineering. That said, they’re still present on many cheaper kits – SDs, HGs, as well as some NGs. Those do not warrant the same design effort as RGs, MGs or PGs. As such, seam line removal is a skill that’ll probably never go out of fashion.

Removing Seam Lines

Before we jump into removing seam lines, we should take a moment to plan the process. Inspect the parts carefully, see how they go together. Can you reassemble them after gluing or do they require some extra mods? Last thing you want is fixing the seams, only to realize you can’t put the part back on the kit.

Later on I’ll show you some example mods that help when dealing with those tricky parts. Before we get there though, let’s take a look at the tools we’ll need, as well as three basic seam removal techniques. Those are: gluing, scribing and covering.

Tools we’ll need:

  • Plastic cement;
  • Some clamps to squeeze the parts (not pictured);
  • Your favorite putty;
  • Hobby knife;
  • Sanding sticks, sponges or sandpaper;
  • Flat file;
  • Nippers;
  • (Optional) Your preferred scribing tools;
Tools for removing seam lines.


Removing Seam Lines – Glue & Putty

Using glue is the most common method of seam removal. Plastic cement will fuse two halves into a single part. This is also the only method which physically removes the seam lines, while the other two only hide them. While most common, it’s also the one that requires most modding to make sure the parts can be reassembled.

Step 1 – Apply Glue

First off, we need to apply glue to the parts. You can apply it to each part separately, but keep in mind that thin cement dries rather fast. This method allows more precision, letting you avoid applying glue onto details, which may ruin them.

As you can see, I leave some polycaps inside. It’s usually a good idea when one or both ends of the part have a female polycap. Also saves a lot of time, as you don’t have to worry about modding the part to fit them in later. It’s perfectly safe, as the plastic they’re made of doesn’t react with cement (and most other chemicals).

Another way to apply glue is to put the part together first and then drop it into the gap. It’s faster, at the cost of precision.

For bigger surfaces, consider using thicker, slower drying glue instead. It gives you much more working time, so you can apply it over the entire area before it starts to dry.

Applying glue.Applying glue - again.Applying thicker glue.

Step 2 – Squeeze!

Next up, squeeze both halves together. Don’t worry, if the plastic runs out of the seam line. This plastic lip is something we actually want, as it shows the parts have joined together well and there won’t be much need for putty later.

Use the clamps to hold the part together until the glue dries.

You might be tempted to clean this plastic lip right away, especially in panel lines and other detail areas. Leave it be. Dragging melted plastic across the surface is a rather bad idea. It might cause some serious damage.



Step 3 – Sanding

Next step is to sand the part flush.

To save yourself some time, you can use the back of your hobby knife (or mould line removal tool) to scrape off the plastic lip.

As with nub removal, use a stiff sanding stick, fine flat file or a sandpaper wrapped around a file/piece of plastic for flat surfaces. For rounded ones use a circular motion and, preferably, a soft sanding sponge.

Scraping off the plastic lip.Sanding the part.

Step 4 – Fixes

With seam lines removed, we must now inspect the parts for any obvious mistakes.

Most common ones will be the gaps and other imperfections where seam lines didn’t close properly. We’ll need to fill those with putty. My choice is a homemade plastic putty. If you don’t want to paint your kit, you can make it from spare runners to match the color of the piece. Once dry, sand it flush and repeat this step if needed.

Another issue you might come across are removed panel lines. They often get filled if a seam goes across them and need to be rescribed. Since scribing is a huge subject, which requires its own tutorial or two, I won’t be covering it here in detail. Basic idea is to place the guide (usually plastic tape) along the panel line and lightly drag your scriber along it. Apply very little pressure and repeat it until the panel line has a uniform depth once again.

If you’re going to paint your kit, spray some primer on the parts to help you spot mistakes.

Filling remaining gaps.Some panel lines might need re-scribing.Priming helps with finding mistakes.
This was one of the most annoying parts of HGGT Gundam Ground Type-S build. After removing the seam lines, I had to rescribe the vinyl cover texture on all the major joints. Rescribed texture.
With some effort, the parts will look like they were a single piece from the very beginning. No trace of the seam.

Removing Seam Lines – Scribing & Covering

Some pieces simply cannot be glued together, usually because keeping them separate is essential for assembly. It’s common when they have other parts mounted inside them. One way to deal with them is to paint the parts and assemble them. Afterwards we can glue the outer piece together, remove seam and repaint the sanded areas. Sometimes it’s unavoidable.

In most cases though, it’s much easier to hide those seam lines rather than remove them. We can do so by scribing panel lines into them, or by covering them up with extra plastic.


Scribing is rather straightforward. Drag your scriber lightly along panel line a couple times and you’re pretty much done.

It gets tricky, when both sides of the body use the same pieces, rather than mirrored ones though. As you can see on the picture, shoulder armors on HGGT RX-79[GS] are identical. When assembled, one seam line will be at the front, while the other in the back.

To deal with it, I had to measure the distance from the seam line to the edge of the piece, and then scribe a symmetrical panel line on the other side.

I can't glue those shoulder pieces, so I will scribe some panel lines instead.Shoulders with new panel lines.
With some cleanup and a pin wash, it’s impossible to tell one of those panel lines houses a seam line. Seam line is completely hidden.


Another way of hiding a seam lines is adding extra piece on top of them.

The trick to this technique is gluing only half of this extra piece, on one side of the part. Leave the other half hanging over the edge. When the part is assembled, it’ll sit right over the seam line, hiding it from view.

I combined scribing and covering methods to hide the seam line on the head of my Barbatos Nemesis.

Gluing extra details on one half of the piece.I used scribing and covering to hide the seam line on Barbatos' head.

Removing Seam Lines – Mods

Main purpose of these mods is retaining the ability to disassemble the kit for painting after seam removal. Usually they involve altering the way the parts connect, without affecting kit’s appearance or articulation.

Remember – these are just examples. Construction varies from kit to kit, so usually there are no prescribed solutions. Most of the time you’ll need to figure them out for yourself. Obviously it becomes easier with experience – eventually you will be able to figure them out rather easily.

Hopefully the examples below will give you some idea how to approach and think about these mods. 


Many HG Gundam heads come in two pieces – front and back, with the face mounted from the inside. Big downside of those is obviously a giant seam line, running across the entire head.

Problem is, they need to be separated to mount the face in. So we have to either paint and install the face first, or mod it, so it can be mounted from the bottom instead.

To do so, we’ll need to turn the T-shaped piece into a peg, as well as cut out any obstacles which might block the movement – both inside the head and on the face piece itself. I marked those in red on the second picture.

If you want to use the eye sticker, hold off until final assembly. Repeated test fits will tear it off.

This head needs some work before seam removal.Parts marked in red need to be removed.
No need to be fancy about it – just cut off excess plastic with your nippers and sand the leftovers flat. Quick and easy. Cutting off extra bits.
Here you can see all the parts I trimmed. I also had to shorten the face mask a bit. Trimmed head parts.
Once modded, the face easily slides in from the bottom.

Don’t worry if it’s loose, you can always glue it in during the final assembly.

Face slides right in.

Upper Arms

Another tricky mod I encountered were upper arms on RX-79[GS].

As you can see, the armor pieces sandwich over the elbow joint, with each half connecting at two points. Best way to go about it would be for the finished piece to slide in from above. Those round pegs at the elbow make it impossible though. We need to do something about them.

Upper arm pieces sandwich over the elbow joint.
Sanding them down would be one way to deal with it, but I decided to do something more interesting.

Using the Madworks zero chisel, I cut the round details from the main armor piece. Since the cut was a bit rough, I had to use some epoxy putty to make them fully round again.

They fit right into the elbow pegs and can be mounted independently.  It also creates a slight gap between them and the armor, making it look consistent with the knee joints.

Cutting off round details.
Next up, I had to mod the inner pieces – simply trimming the top edge so it looks like a cross rather than a square. This created space for the armor pegs, allowing the glued piece to slide in. Modding the inner piece.
And this is the final result, once painted and panel lined. Finished arm.

Thought I had some more examples, but I guess this is it for my HGGT Ground Type-S. I’ll try to expand this section in the future, with mods from other kits.

For now, I hope you found this guide helpful.

2 Responses

  1. Harriet says:

    I found this tutorial as I was looking for a solution to the same issue I am facing with removing the seam lines on the head unit. Unfortunately I am working on a SD gundam which does’t have a t-bar and is completely integrated. I might have a go at paiting the face first and then putting masking tape over it when I spray the head unit.

  2. KageToTora says:

    Really appreciate all the info. This site is amazing.

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