Guide for Beginners: Seam Fixing
Seam lines are the second most problematic fix on most kits – right after nub marks. Whether painted or not, a seam line running down the middle of a part completely ruins the sense of scale and immersion. Fixing these things is a royal pain so I've come up with a sledgehammer method to make sure it gets done the first time.
More modern kits are often engineered in such a way that part joints are covered by other parts or assembled in such a way as to make the joint look like a natural part of the model. That said, they’re still present on many cheaper kits – especially SDs, HGs, and NGs. Your loving design team at Bandai spent their budget on RGs, MGs and PGs. As such, seam line removal is a skill that will always be useful in modeling.
You may be asking, why would I even do this?
The answer is that seam fixing is one of the cornerstones of competitive model building. In competitions that use a derivative of the IPMS standard you will lose a point for each unfixed line. This adds up very quickly.
Another good reason as I stated above is realism. A giant war machine is never going to have a cavernous gap running down what is meant to be its strongest armor plates.
Before we jump into the modding process, we should take a moment to plan the work. Inspect the parts and think ahead. Can you reassemble them after gluing or do they require some extra mods? It's very easy to get ahead of yourself and close seams, only to realize you can’t put the part back on the kit.
Sometimes you will run into a double seam, or a part that needs to be fixed inside another assembly that needs to be fixed. In this case you have to make a choice. You can either fix and paint the first part, then mask it off completely or fix both at the same time and paint it like a garage kit with multiple masking layers. Neither is easier, the choice is yours.
My process is quite a bit simpler, or at least more cut and dry than some of the information you'll find out there. First you use cement, then you putty over the line. Then, finally you sand, clean, and re-scribe if necessary.
Let's take a look:
Plastic cement will fuse two halves into a single part. This is also the only method which physically removes the seam line.
Step 1 – Apply Cement
Snap the part together so it is 95% fitted, then tap the cement onto the line. Thin cement will run along the entire line by capillary action just like a panel wash.
For bigger surfaces, consider using thicker, slower drying cement (Tamiya normal type). It gives you much more working time, so you can apply it over the entire area before it starts to dry.
Don't worry about damaging polycaps as the material they are made of (polyvinyl) does not react with plastic cement.
Now squeeze both halves together hard. Don’t worry about excess plastic running out of the seam line. This plastic lip is something we want, as it shows the parts have joined properly. It is important to let this dry and "set" before sanding it. If you start off right away you can damage the surface with plastic that is still in it's semi liquid state.
You can use clamps to hold the part together until the cement dries.
Step 2 - Remove the excess material and apply putty
Next you will use a sharp knife or sanding stick to remove the raised line of plastic.
You may think you are done here and indeed that is what many people do but I like to go one step further for safety. Apply a thin layer of putty over the fixed line to fill any micro defects.
Allow the putty 4 hours to cure then sand it down and buff it to 800 grit for surfacing. There you are, a perfectly seam fixed part!
This process is my least favorite part of building so I fully understand if this sounds boring and tedious to you.
A healthy dose of Seneca may be of help:
A gem cannot be polished without friction, nor a man without trials.
The extra step of adding putty to every part may seem like a longer process at first but when done assembly line style, the time it saves having to come back later after finding errors in your primed parts is significant.
If you do NOT want to paint your kit you can instead use what I call Sprue Goo. It's a thick paste of dissolved runners in cement. This is the only way to match the color 100% but luckily its very easy to use and make!
Once the parts have been sanded up to 1000 grit it really is an invisible fix.
Step 3 – Fixes
The combination of cementing and puttying the lines should guarantee that the line has been removed. If any micro defects remain simply reapply putty and sand down until they are gone.
If you accidentally fill panel line details while seam fixing you can use a razor saw or a panel scriber to redefine the detail.
Panel Scribing tutorial: Here
All the products used in this article can be found: Here
I earn a small commission for each purchase made through this link. I thank you in advance for supporting Zeonic Corps and myself by shopping from my store.
Thanks for requesting this tutorial and for taking the time to read it. I hope my process works for you as well as it does for me.
More modern kits are often engineered in such a way that part joints are covered by other parts or assembled in such a way as to make the joint look like a natural part of the model. That said, they’re still present on many cheaper kits – especially SDs, HGs, and NGs. Your loving design team at Bandai spent their budget on RGs, MGs and PGs. As such, seam line removal is a skill that will always be useful in modeling.
You may be asking, why would I even do this?
The answer is that seam fixing is one of the cornerstones of competitive model building. In competitions that use a derivative of the IPMS standard you will lose a point for each unfixed line. This adds up very quickly.
Another good reason as I stated above is realism. A giant war machine is never going to have a cavernous gap running down what is meant to be its strongest armor plates.
Before we jump into the modding process, we should take a moment to plan the work. Inspect the parts and think ahead. Can you reassemble them after gluing or do they require some extra mods? It's very easy to get ahead of yourself and close seams, only to realize you can’t put the part back on the kit.
Sometimes you will run into a double seam, or a part that needs to be fixed inside another assembly that needs to be fixed. In this case you have to make a choice. You can either fix and paint the first part, then mask it off completely or fix both at the same time and paint it like a garage kit with multiple masking layers. Neither is easier, the choice is yours.
My process is quite a bit simpler, or at least more cut and dry than some of the information you'll find out there. First you use cement, then you putty over the line. Then, finally you sand, clean, and re-scribe if necessary.
Let's take a look:
 |
| Cements. Thin, Normal, and Homemade Sprue Goo |
Plastic cement will fuse two halves into a single part. This is also the only method which physically removes the seam line.
Step 1 – Apply Cement
Snap the part together so it is 95% fitted, then tap the cement onto the line. Thin cement will run along the entire line by capillary action just like a panel wash.
For bigger surfaces, consider using thicker, slower drying cement (Tamiya normal type). It gives you much more working time, so you can apply it over the entire area before it starts to dry.
Don't worry about damaging polycaps as the material they are made of (polyvinyl) does not react with plastic cement.
 |
| Gloves are always a good idea. |
Now squeeze both halves together hard. Don’t worry about excess plastic running out of the seam line. This plastic lip is something we want, as it shows the parts have joined properly. It is important to let this dry and "set" before sanding it. If you start off right away you can damage the surface with plastic that is still in it's semi liquid state.
You can use clamps to hold the part together until the cement dries.
Step 2 - Remove the excess material and apply putty
 |
| Pretty good but not perfect. |
Next you will use a sharp knife or sanding stick to remove the raised line of plastic.
 |
| A small amount is plenty. I apply putty with a toothpick. |
You may think you are done here and indeed that is what many people do but I like to go one step further for safety. Apply a thin layer of putty over the fixed line to fill any micro defects.
Allow the putty 4 hours to cure then sand it down and buff it to 800 grit for surfacing. There you are, a perfectly seam fixed part!
This process is my least favorite part of building so I fully understand if this sounds boring and tedious to you.
A healthy dose of Seneca may be of help:
A gem cannot be polished without friction, nor a man without trials.
The extra step of adding putty to every part may seem like a longer process at first but when done assembly line style, the time it saves having to come back later after finding errors in your primed parts is significant.
If you do NOT want to paint your kit you can instead use what I call Sprue Goo. It's a thick paste of dissolved runners in cement. This is the only way to match the color 100% but luckily its very easy to use and make!
Once the parts have been sanded up to 1000 grit it really is an invisible fix.
Step 3 – Fixes
The combination of cementing and puttying the lines should guarantee that the line has been removed. If any micro defects remain simply reapply putty and sand down until they are gone.
If you accidentally fill panel line details while seam fixing you can use a razor saw or a panel scriber to redefine the detail.
Panel Scribing tutorial: Here
All the products used in this article can be found: Here
I earn a small commission for each purchase made through this link. I thank you in advance for supporting Zeonic Corps and myself by shopping from my store.
Thanks for requesting this tutorial and for taking the time to read it. I hope my process works for you as well as it does for me.
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