While We’re Talking About Fillers

During episode #42 of The Plastic Scale Modeling Hour I mentioned that I preferred using styrene as a filler media. When I do use putties or glazing compounds it is to address minor cosmetic issues that still exist after using styrene as a filler. About the only time I use CA or Super Glue it is for areas not necessarily visible and that don’t have any risk of damaging surface detail when sanding and shaping. CA makes a good first stage filler for those areas which DO NOT incur any stress from torsion. CA has a high static tinsel strength but a very low shear resistance. You can hang from a beam all day long from a cable glued to it, but if someone comes along and taps the glued joint sideways…you’ll drop.

Take a look at this Airfix 1:48 BAC Lightning F1/2 shows a very disappointing revelation in the wing to fuselage fit. A sizable gap which is the result of the two mating surfaces not being of the same shape. The fuselage side of the joint is contoured inward, but the wing does contour to match.

Unfortunately I didn’t catch this before prepainting the parts and mating of the wing to the fuselage. The fit along the rest of the joint is acceptable and this imperfection can be fixed using filler material. Here is an example of a joint that styrene is IMO the best option. Why? Well the joint bears a load of the weight of the assembled model when sitting on its gear. It is also a very small surface area as the wings are thin in profile.

To fill this area I will use various thicknesses of styrene. Either from pre-cut strips or by cutting my own from larger sheets of card stock.

Gauge the styrene to the width of the gap. Use as thick a piece as you can to minimize the number of pieces necessary to fill the area. I will place the strips vertically inside the gap and liberally apply a suitable solvent to weld the gap closed. A hot solvent such as Weld-On #3 is my go to solvent, but you can use others.

I have mentioned before about FREE styrene resources. I am using a bookmark that came in some junk mail. Its of suitable thickness, so using a metal ruler as a straightedge I score a line using my hobby knife to cut off a strip as tall as I need double the thickness of the upper wing half. You do want it to stick up above the joint surface!

The upper wing joint had a rather big gap, fortunately the under side didn’t have as pronounced of one. A single thin strip was sufficient. A RULE OF THUMB: Fill as much of the length of the gap with styrene as possible. If you have the patience keep inserting ever thinner and thinner shims of the styrene strip along the seam as you can to fill the void. I recommend that you at least fill 75% of the length of the joint needing filler with styrene. Once it has been set in place and a liberal application of solvent has been applied, use your knife blade to press it into the gap…GENTLY! Then let it sit somewhere to cure for several hours. Evaluate the results and add more styrene strip if needed and repeat.

This will assure enough contact between the parts to maintain a strong weld which will hold the torsion load of the model sitting on its gear. While this sits and cures here is another example I used styrene strips as filler.

We all agree that the true measure of a quality kit is in the fit tolerances of its parts. Some kits have crisp detailing, but often have poor fit between assemblies. The green house to this helicopter is a good example. It becomes a choice of sanding and fitting, sanding and fitting until you are satisfied with the overall fit. Many times doing this with canopy parts can have serious consequences…such as a misshaped part induced by the modeler through sanding.

I’ve seen so many modelers do everything else well, only to find the fumbled the project when they affixed the canopy, windows, windshield or other clear parts with haste. They tend to be afraid of using solvents and fillers with clear pieces. Here the green house required a mix of sanding and filler strips. Once could not cement the glass to the strips, so that the green house could be removed to allow shaping and painting of the filler strips first before attaching the canopy. Since there is a good sized opening in the center I can still access the inside of the canopy to fuselage joint to touch up the seam with paint so I cemented it into place. Again liberal amounts of solvent to weld both sides of the joint.

Note: the mating surfaces are free of paint, exposing bare plastic to ensure good bonding/welding.  I’ll let both these sit and return with the next steps in another post to show you how I finish fixing the gaps. Have a great weekend!



  1. This is great information Hawkeye. I’ve never heard of this method before and it’s one I will certainly have to give a try.

    How careful do you need to be to insure that you don’t damage the plastic model while applying the solvent? Do you finish off the gap with a typical putty filler? Or does the styrene spread out enough to completely do the job?

    Keep the shows coming Hawkeye. Always getting something new out of every episode!


    David Rowe

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