Starship Modeler - The complete information source for modelers who build sci-fi, fantasy and real space subjects

Filling Seams 1: Baking Soda and CA

By John Lester
video & text © 2007 Starship Modeler

This is a short how-to on filling seams with baking soda and CA (superglue). Please also see the notes below.

Many thanks to Robb "SteadyCam" Merrill for his help with this video.

Image: The results, after sanding and a coat of paint. As you can see, the seam at the rear of the wing virtually disappeared, though there is one spot that needs another application of filler. In the front, the CA puddled up against the tape mask, neccessitating some further file work.

Synopsis & Notes

This technique is most useful on smaller gaps/thinner seams, where epoxy putty is overkill but you need more strength than you would get with a spot or glazing putty such as Bondo or Squadron Green. You will need some ordinary baking soda (or talc) and some water-thin CA (superglue). Pack the baking soda in the gap, brush off any excess, and carefully drop the CA onto the baking soda.


  • Strong gap filler with reasonably smooth surface
  • Quick
  • Inexpensive

Disadvantages: Baking soda + CA results in heat (so either use talc instead, or use in small amounts) Sets up rock hard very quickly (so you must do any sanding within 10-15 minutes after application) Can be hard to see the joint after application (so tint the baking soda/talc before use)

Baking soda and CA react quickly, and this reaction give off noticeable heat. In modest amounts, this will not damage your model (though the vapors released will fog clear parts). Superglue and talc (i.e. "Baby Powder" - but make sure to read the ingredients, as a lot of products labelled "baby powder" use cornstarch instead of talc) do not react so "hotly"; about the only difference in results is that the talc/CA mix takes somewhat longer to set up.

Water-thin CA can be a pain to apply, as it tends to flow everywhere, including places it is not wanted. Mask off the seam to help prevent this. You might also try one of the long, thin Teflon applicators made especially for CA.

Whether you use talc or baking soda, the mixture will rapidly set to a rock hard consistency. Any sanding should be done within the first 15 minutes after application of the CA. If you wait longer, you will need to use metal files, and you'll have to be more carefull not to damage surrounding, softer detail (the kit resin or plastic parts being easier to sand than the CA).

This mixture cures clear, and so it can be difficult to see what needs to be sanded or where further applications are necessary. Because it cures so hard, so fast, painting the seam isn't always the best option. One way around this is to tint the baking soda/talk with food coloring or inkjet printer inks. Ward Shrake is the resident expert here; he has a great many tips and details in this thread on the SSM forums.

Go back up | Tech Library Main Page | Starship Modeler Home | Site Map | Feedback

This page copyright © 2007 Starship Modeler™. First posted on 29 October 2007.