Jump to content

Your tools and techniques on seams

Recommended Posts

A good technique to learn first is using liquid adhesive like Tenex (no longer available) or Pro Weld or Plast-i-Weld. Learning the capillary technique allows you to make the joins with no steps in them. You can find many videos on line that will help explain the steps.

Link to post
Share on other sites

Well, I haven't finished anything in a few decades. Shift work and family can dampen your mojo quite a bit. Since retirement, I have only started Airfix;s new 1/72 Hawker Hurricane. Now this kit fits together quite nicely and the seams were small with few gaps. About all I've used so far is Mr. Surfacer 1000, a bit of Superglue, some 600 grit sandpaper and a Tamiya Fine Sanding stick.










Edited by dogsbody
Link to post
Share on other sites

I really like Tamiya Extra Thin. In eliminating seams the most important step is minimizing them to begin with. Careful dry fitting and making adjustments so that the parts line up properly goes a long way. Once the parts are lined up as best as possible, I use Tamiya Extra Thin glue and let it wick into the seam one small section at a time and hold the parts together till a small bead of plastic forms. Use clamps or tape to hold parts together if necessary. Once the whole thing is glued, wait until the cement has set completely. If you start sanding too soon the plastic will still be soft from the cement and you will have a mess.

There are frequently spots that just won't mate completely. What I use to fill them depends on their size. Small gaps I use thick super glue. Apply the glue, hit it with a little accelerator and then sand smooth after a few seconds. You must start your sanding relatively quickly, before the glue completely sets and becomes too hard. If that happens, it will be very difficult to  sand the glue down without taking out too much surrounding plastic too. I also use Tamiya White putty. It is a regular modeling putty like Squadron Green or White but finer and shrinks very little.

Very small gaps I use Mr Surfacer 500 or Mr Dissolved Putty. They work great for filling in those pesky little seam lines that keep showing up.

For larger gaps, I use AVES Apoxie Scupt. Its a two part epoxy putty that thins out and smooths down with water. It has a long working time and once dry sands to a smooth edge. Makes very strong joins.

Finally, for some gaps, especially long ones at wing joins, I will use strips of plastic inserted into the gaps and sanded down. Then some super glue or Tamiya White putty to finish it off.

Hope this helps.

Edited by Mstor
Link to post
Share on other sites

First and foremost is to get the 2 mating surfaces to meet without any gaps. Sometimes, like the Minicraft 1/48 XF5F-1 I am currently building, you'll have out-of-box. Other models, like every Amodel 1/144 kit I've built, will need help to get to that state. If you need to do work, you need rigid abrasive tools to ensure you don't introduce additional gaps or part mismatches. For larger parts, from nacelles, tail surface, wings, and fuselage, a  sheet of glass provides a fairly good planar surface for a sheet of 600 grit paper. Lay full sheet of abrasive paper grit side up, and slide the part along the abrasive. For smaller parts or parts with only local issues, a file can work quite well. You may have to decide if you want to keep locating pins/lugs intact. If so, you may need to use smaller, but still rigid, tools to work around said pins/lugs. During this process, I might decide that shims are needed to address larger gaps or mis-alignment due to warpage or some other issue that filing alone won't address. My usual shim is Evergreen plastic strips laid along appropriate seam edge. Glue it in with Tamiya Extra Thin, wait for that to cure, perhaps 30m to 1h, and then file as needed to mimic the part it's glued to and then mate properly with the other part. Don't stop working on this until you've got the best possible alignment and mating.


Once you have a gap-less, or best possible,  joint, you need to very carefully align the to parts. For smaller parts with simple joins, I will just hold them together and then get them fully aligned. For larger parts, more complex joins, or less stable joins, I will hold the parts in partial alignment, clamp or tape them together, and then get them fully aligned. Regardless of the clamping method, checking very carefully for full or best alignment is important. Ideally, the clamped parts are well aligned and there are no steps or overlaps between the 2 parts. If you have steps or overlaps due to size differences between the parts, try to figure out how to best align the parts. For example, I will prefer to align the fuselage top and repair the bottom seam if the parts don't fully match despite my earlier alignment process.


Once I have aligned parts, I run the Tamiya Extra Thin brush along the joint, making sure it wicks into the joint. You can apply a little extra clamping pressure to push a little bit of plastic out of the joint to provide an ideal joint seam, but don't get carried away with this lest you risk deforming the parts or forcing them out of alignment. I'll then let it sit for a couple minutes if the joined parts had no warpage fighting the alignment, longer if they did.


With the glue cured, you can remove any clamps or tape and inspect the joints. In the ideal case, you get that little bulge of plastic at the joint; next best is no apparent joint. In any event, I will now use files or abrasive blocks/sticks to clean up the entire joint line all the way around the parts.


Any gaps are now filled. You don't want attempt to fill any "air gaps" or joints without plastic-to-plastic mating with filler--it will only crack at some point. If you didn't shim parts before gluing or you find larger gaps, use plastic to fill the joint. Lay the plastic in the joint and apply Tamiya Extra Thin. You can sometimes force the plastic into the joint with a putty spatula or side of a knife blade a minute or 2 after the glue has evaporated, but be careful lest you damage the kit parts when their soft from the solvent.


Vallejo putty in the tube is great for getting into tight spots, like wing, tailplane, or nacelle joints to the fuselage. Apply the putty as if you're caulking a joint and then smooth it with your wet finger after a minute or so. With a little skill, you're now done. If you don't like the joint, clean it up with a wet rag or cotton bud and try again.


Tamiya White and Mr Surfacer 500 are good for other situations. I haven't tried Mr Dissolved Putty due to availability, but it's probably good too. You may want to first apply tape around a joint you're going to putty to protect surrounding detail. I like to apply the putty with a small putty spatula, trying to get nearly final coverage. Once the putty is firm, I'll use a cotton bud dipped into Mr Thinner to wipe away excess putty. You need to be careful on a flat or convex joint so you don't remove putty below the surface or future surface. Leave the putty slightly proud of the surface in these cases. When the putty has fully cured, I'll use files or abrasive blocks/sticks to fair the putty in. I like to finish with a #6 file or a nail buffer block/stick for the smoothest possible joint.


Medium CA is my choice for very thin to hairline cracks. Also for filling in engraved panel lines. I'll apply it with an application tool, wait 15m to 30m until the CA has cured, and then file the seam line, first with a #4 file then a #6 file. DO NOT wait too long, like multiple hours or overnight, before you file CA. If you wait too long, you just fused a ROCK into the plastic and you'll be very very unhappy. I use a grazing light and my fingers to inspect the seam as I'm filing.


In all of this, keep working at the seam until you can't feel it or see discontinuities in grazing light. With fully plastic-plastic joints, you should not be able to see the joint. With putty or CA, you will see the joint due to color variations, but the grazing light will accent issues.


The final test is a primer coat. I use thinned Mr Surfacer 1200 as my goto primer. It will fill in slight surface scratches, but doesn't obscure detail.

Edited by dnl42
Some wordsmithing...
Link to post
Share on other sites

Like one post says, minimize the gaps to begin with. What I do is get a large piece of wet sand paper, and lay it on a flat surface. Hold the fuselage or wings over the sanding surface and start sanding lightly. Be sure to put down uniform but not too much pressure so that you create an even surface throughout. Do that to the other side also; note you may have to cut off the locating pins. Now you have even mating sides with roughed up surfaces that'll make a real strong joint once you hit it with Tamiya extra thin cement. 

Link to post
Share on other sites

A tool I find useful is a touch and flow applicator.  It is basically a pipette that holds your favorite solvent and allows it to flow into seams. 

Link: https://www.flex-i-file.com/adhesives.php

My favorite solvent is methyl-ethyl ketone or MEK.  It is available anywhere paint is sold.  Evaporates very quickly. 

Trial fitting and getting a good mating surface is important too, as others have said. 


Geoff M

Link to post
Share on other sites
  • 1 month later...
  • 2 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...