How to Remove Nubmark (Sprue-Mark) Tutorial | Gundam Building 101

How to remove or clean nubmarks (a.k.a sprue marks) properly has been a problem that has bugged everyone who has (and ever will) build a Gundam kit. How do you get rid of those ugly nubs on your Gundam’s armor?  Your friendly neighborhood Spiderbeef is here again, this time to share with you some nubmark removal tricks that I’ve learned over eight months of Gunpla building.

NUB MARK alert!  Below is a nub mark! (Of course you know what that is right?)

Nub Mark Removal by Progressive Sanding (15)

There are 3 ways to do this, depending on the tools available to you so we could remove those pesky nub marks like the one above.  Grrrr!


1.  Cleaning the nub using side cutters.

Use this method if you only have side cutters around.  It happens… many of us do not have the luxury or access to tools.  If you really do not have a side cutter, then your alternatives may be nail clippers and nippers, scissors and even diagonal cutters.

Just a side note:

I started out with the Bandai side cutters (the one that comes with a pair of tweezers, small metal file and parts separator in a set), but it quickly got worn out and rusty.  I now use the one I bought from Alexan; it’s chrome-plated so it’s virtually rust-proof.  For this technique, I found that you can minimize damage to your Gunpla if you cut the nub off gradually, instead of cutting it off in one fell swoop.  Always keep your cutters sharp.

Anyway, moving along…  Here’s a part of MG Char’s Gelgoog’s inner frame with a big, nasty nub on its side.  The idea is to cut the part bit by bit (slowly but surely) as if you are biting on the nubs.  Do it carefully, so you don’t damage the surrounding area, until you manage to level the nub nicely.

Nub Mark Removal by Progressive Sanding (18)

And here’s how it looked like after cutting.  I cleaned it afterwards with a piece of cloth so it wasn’t very noticeable.  See, it still has a little white mark left, but most of the time you will hardly notice the nub mark.

Nub Mark Removal by Progressive Sanding (19)


We get this question a lot, too: what’s the difference between side cutters and diagonal cutters?  The cutting edges of the side cutter are straight and level with one side (I guess that’s why they’re called side cutters), while the diagonal’s cutting edges are sloped inward.

Step 1 Conclusion

Pros: fast and easy

Cons: still leaves visible marks, especially with the bigger nub marks that will almost surely have a rough and whitish surface; may damage the area surrounding the nub when you apply too much pressure


2.  Shave off the nub with a hobby knife.

Do this when you have side cutters and a sharp hobby knife.  I heard some use blade cutters, scalpels and knives as an alternative.  My say, do as you wish, anyway the general idea is like this.

Remove the piece from the runners with the side cutters cutting as near as you can leaving some nub in the process.  Then shave it off little by little with the knife.  If done properly, it’s good enough to hide nub marks even on armor pieces.  The key here is patience…

Big nub mark

Nub Mark Removal by Progressive Sanding (15)

Nub mark being shaved

Nub Mark Removal by Progressive Sanding (16)

Voila!  Almost no nub mark!

Nub Mark Removal by Progressive Sanding (17)

Step 2 Conclusion

Pros: much cleaner compared to approach number 1’s results

Cons: the constant threat of slicing off your finger with the hobby knife


3.  Progressive sanding.

Do this when you have side cutters, sanding sponges (or regular sand paper) and hobby knives (optional).

I just recently tried this out, and I really liked the results.  It is almost the same as number two, but this time we use sand paper in place of the hobby knife.  You can still use the hobby knife if you want.  The basic concept is to sand the nub off progressively, so as not to damage the surrounding area.  Start with a rough grit like 600, then use finer grits to give it a smoother surface.

Here’s an armor piece from Gelgoog again.  After trimming down the nub with my trusty hobby knife, I sanded it off and along the edge of the armor piece with a 600 grit sanding sponge.  Yep, I got to use my cheap sanding sponges!

Sanded with 600 grit:  Sand it until you level the nub. Beware! – 600 grit can really do some damage if you over-sand the part.

Nub Mark Removal by Progressive Sanding (7)

Sanded with 800 grit:

Nub Mark Removal by Progressive Sanding (9)

Sanded with 1200 grit:

Nub Mark Removal by Progressive Sanding (10)

Sanded with 2000 grit:

Nub Mark Removal by Progressive Sanding (12)

And finally, I cleaned it up with a piece of cloth:

Nub Mark Removal by Progressive Sanding (13)

Not bad, huh?  This technique even fooled me – I sanded the leg armor part below for this blog post, threw it onto the pile of other Gelgoog parts and promptly forgot all about it.  When I went back to removing the nubs from the rest of the parts, I happened to pick up this certain piece again… and went, “WTF??  Where are the nubs??  How come this one doesn’t have any nubs??”

Nub Mark Removal by Progressive Sanding (14)

You can have your choice of grits, obviously; some people use up to 2500 or 3000 grit to ensure a smooth finish.  I’m just too lazy to hunt those sandpapers down 🙂  Some also prefer to start with 800 grit, but I think 600 is safe enough for Gunpla.  Be careful not to inhale the plastic dust, so wear a mask to be safe.

Step 3 Conclusion

Pros: leaves almost no trace of nub marks

Cons: takes a LOT of time and patience

That is all!  Hope you enjoyed this post, fellow Gunpla builders.  Till next time!


31 thoughts on “How to Remove Nubmark (Sprue-Mark) Tutorial | Gundam Building 101”

  1. Nice…., My first time to assemble a kit.. I used a big nail cutter and a cutter. It’s more cheaper than hobby knives, you got to be careful though as spiderbeef mentioned above. Up to now I use the nail cutter, I suggest you buy TRIM brand. Then the sand paper will do the rest.


      1. hahaha!! Maybe the young ones…they use to twist it to remove the parts from the runners….my 7 year old nephew did that, when his mother bought him a SD gundam. ….poor kit 😦


      2. I did with my first gundam. After buying the next one i cleaned up my first gundam using sidecutter and sand paper. There’s always a first time. 🙂


  2. Nice one. I’ve used my own hands plus a pair of scissors to remove the parts from the runners. Then I’ve read here how alexan side cutters were good so I bought one immediately and it was awesome.


      1. At one point I was using just fingernail clippers! Now I use an amalgamation of wire cutters, nail clippers, exacto knives, and hopefully on my next build your sanding technique. thank you very much 😀


  3. Interesting tips! I’m using the 3rd tech – progressive sanding. 
    I’m also interested in Alexan side cutters..can you compare it to Tamiya side cutter in terms of quality and price? Thanks! 


    1. I’d love to do that… only I don’t have the Tamiya side cutters LOL.  I still have my rusty Bandai cutters though 😀

      I can do a quick comparison based on the Tamiya’s appearance: I think you can use it for hard-to-reach places and make more precise cuts, because the Alexan cutters are quite thick.  It was intended for electronics, after all, not plastic model kits.  I exercise caution whenever the part I’m cutting is a bit too close to the runner.  The Alexan cutters work for me since I do progressive sanding anyway, so there’s no need for a lot of cutting, and the little thing cost only Php110.00.  Yeah, I’m cheap :))  And like I said in the post, it’s virtually rust-proof, so it probably will be quite some time before I buy another pair 🙂  I want the Hasegawa one for my next, but it’s quite expensive 😦

      I have a question about the Tamiya side cutters myself: I hear the one with the black handles is better than the one with gray, is that really true?


      1. I can share my experience here since I own em both. And I love the Tamiya(black) side cutter. As the blade is ultra sharp and when cutting plastics it is effortless. I was at awe when i first use this because I started with Alexan cutter.  Today, I still use them depending on the thickness of the plastics. I use Alexan for the thick ones. And for precise cut and hard to reach places I use Tamiya. 

        Spiderbeef, give us feedback when you have the Hasegawa side cutter. I’m curious as well. ^_^


      1. Opo, wala lng po pagkakataon ngaun kasi magboboard exam XD previously, nipperl ng gamit ko panlinis..recently started using topcoat..pag-aaralan ko padin pano magpost ng pics dito so kpg ngwa ko na po..babalitaan ko po kau ^_^


  4. some question regarding the sandling technique, after i level the nub using a 600 sandpaper. do i have to sand the area near the nub or just the nub with a higher number of sandpaper?? it is my first time building a gunpla and i dont want to damage my precious 00

    tnx 😀


    1. Probably a bit late, but still:
      If you want a cleaner result, polish the whole area near the nub that you affected with the coarser sandpaper. You’ll notice that even with the 600 you left a bit of “scratching” after leveling the nub, probably nothing serious but noticeable; so you use a higher grit over the hit area to polish it up – By the time you’re done, once you fully brush away the sanded area you shouldn’t even be able to tell it was hit by sandpaper.

      The higher grit will do much less damage, so it’ll mostly even out the scratched area.


    1. if you use 2k grit immediately, it will take a loooong time for the mark to dissapear. use lower grits first and when its gone then use the high grit to smooth it


  5. I think I should add it in here. Step #3 Progressive sanding is mostly done for vanilla kits, kits that will not be painted. But if you plan to top coat a kit then do the #2 since the paint will hide most imperfections.


  6. i had around 7 HGs growing up and I only used my hands. When I got into it again like (15 years later) I disassembled everything to smoothen them up and repaint them.


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