I’ve been away for a while but busy with modelling projects. A problem that I have yet to solve: How do you use gap filling putty? I know it sounds easy but my technique has not yet resulted in satisfactory results. I am using Squadron Putty, I squeeze a small amount on some scrap masking tape and then poke small amounts into the gap [with a tooth pick] and then push it in with my finger. I am usually trying to either repare or compensate for a poory fitting model kit. I let it dry and then use 600 grit sand paper to smooth it out. I always seem to get a “crumby” uneven looking result - even when painted - not smooth and flush with the gap surrounds. It’s as if the putty has not consolidated consistently into the gap. I would very much appreciate any wisdom out there as to how to achieve good results with gap-filling putty products. Is there a solvent that you could use [sparingly on your finger] to make the putty “flow” better?
In my experience, the secret to gap filling putty is to get it warm. It is sufficient to work it between your fingers or in the palm of your hand. Your body heat will make it more pliable and less prone to crumble. What I do is to sort of massage the putty with my fingers, kind of like when your wife kneads pie dough or bread dough. Give that a try. You will get better results.
How old is your tube of putty? If it is a few years old, the solvent may have evaporated out of it and make it crumbly.
For small areas, I generally use a screwdriver blade to push ot into the area at be filled, leaving some excess on top. Then let it dry overnight. First sand with 200 grit sandpaper to get most of the excess off, then 400 or 600 grit to finish.
I’ve use a lot of Squadron putty, and the only time I’ve seen it get “crumbly” is with old putty that dried too much in the tube, in which case I avoid using it on a model. The surface of the putty dries quickly, so squeezing some onto a work area results in a fair amount of waste since using the dried crust isn’t going to produce good results. The only portion that works is whatever is still wet. Discard everything else as you go.
I treat putty a lot like drywall mud, applying it with something like a dull X-Acto chisel blade or a scrap of styrene in place of a taping knife. When first applied, the putty extends beyond the spot I’m working on just like mud typically ends up occupying a larger area at first than when it’s finished. I start sanding with fairly coarse 150 or 220 grit, and work down to finer grits only once most of the putty has been smoothed. Using a sanding block helps to keep the sandpaper aligned with the surface area surrounding the putty so everything ends up flush.
Most putty’s have a shelf life of around 6 months or so after it’s opened. After that then ya, it’s usually still good but it starts to degrades to the point where it is unuseable.
I use 3M Glazing and Spot Putty which is intended for autobody work. To apply it I use an artist’s spatula which has a very thin flexible blade about 3/8" wide with a round end. Here is the one I use. I got it at Micheal’s:
I take the putty directly from the tube by pressing on the tube until there is a small amount protruding from the tip which I then take off with the spatula. That reduces the time that the putty is exposed to the air and thus the putty still retains most of the solvents when it is applied to the model. The spatula makes it easy to push the putty into the desired area and much of the excess putty can be scraped off with the same tool.
When the putty has set I use a very fine sandpaper to smooth it out - garnet 320 grit, and for finishing I will use used sandpaper (almost worn out) so the abrasion is very gentle.
One word of caution with the auto glazing puttys - they have to be applied to styrene in thin layers. Otherwise the solvent can affect the styrene. If you are working with very thin styrene (i.e. .010 - .015") then don’t try the auto putty - it will melt the plastic.
Perhaps a better question might be: can you revive Squadron putty with a few drops of some solution? The stuff that is at the neck of the tube usually retards the drying out of the rest of the material below (acting as a moisture barrier to some extent); however, if there is a way to squeeze some out, then remoisten it and mix in with a toothpick, etc, that might be better than using stronger substitutes which might degrade styrene. Can anyone help out on this angle! Cedarwoodron
Thanks to everyone for the suggestions - I have some things to try. On the question of the solvent for Squadron Putty, I see from the tube that it contains toluene. I have a small can of this [get it at Home Depot] so I can take a small amount and see if I can reconstitute the putty or perhaps put a small amount on the finger when pushing it into the gap. Can use nitrile gloves. Toluene is of course not a nice chemical but in small amounts it’s OK. I was a chemistry student in university many years ago and got exposed to much worse than this!
I see people mentioning solvent, but surprizingly I don’t see the most common modeler’s choice - liquid plastic cement (e.g. Testors) - it is well know among modelers (do a simple web search), generally it is close at hand when you are assembling plastic kits (although some people buy bulk cans of MEK, most use the bottles of liquid cement), and it does work well to soften the putty for application and molding.
ETA: since it’s rude not to leave a cite, check this Fine Scale Modeler link to a thread discussing this very issue - not just liquide cement is mentioned as a solvent, but its there.
Just thought of a simpler solution perhaps: how about taking small bits of styrene, as from parts trees in kits, using an exacto blade to shave them off, and on a durable non-plastic surface, or just wax paper, mixing regular styrene cement and making a home-brewed small amount of styrene putty that could be quickly applied, then after drying, be sanded to suit? Remembered that was some old timers suggestion in an old MR column. Cedarwoodron
Just thought of a simpler solution perhaps: how about taking small bits of styrene, as from parts trees in kits, using an exacto blade to shave them off, and on a durable non-plastic surface, or just wax paper, mixing regular styrene cement and making a home-brewed small amount of styrene putty that could be quickly applied, then after drying, be sanded to suit? Remembered that was some old timers suggestion in an old MR column. Cedarwoodron
Alan, how old is that tube of Squadron Putty? The consensus seems to be that the age of an opened tube of the putty can affect the performance of the putty and quite possibly cause the crumbling you are experiencing.
It does sometimetimes take more than one application of putty/drying/sanding to get the desired results. Putty should be applied in thin layers, even if it takes a few putty/drying/sanding cycles. For larger gaps, I often use plumber’s epoxy putty or JB Weld’s JB Quik. When hard enough, (about 30-60 mins), it can be carved, drilled and sanded like styrene. Any small imperfections can then be filled with putty. I put a little putty on some scrap plastic and add a drop or two of liquid plastic cement and mix for a thinner mix for small seams, scratches etc. I always squeeze out the first 1/2 to 1 inch of putty to get to the “fresh” part of the tube. I also use 3M Spot Putty (from an auto parts store). You get 3 times as much for about the same price as Squadron and you don’t have to find a hobby shop. The JB stuff is usually avaiable in the same place.
Throw the stuff away. It’s not as good as the various body putties as described by Dave, above. I’m using Acryl-Blue Glazing Putty by 3M. It’s cheap, and a tube will last years. No, decades. I lost my old one in a move, so I bought this one several years ago. It’s still fine.
And, when applied, it doesn’t get all crumbly like the stuff you’re using. It’s a treat to work with! It does shrink, though; so you’ll probably have to use several applications.
Many thanks to everyone who responded - there have been many excellent suggestions that I will be following up on. I should say that my main concern with using putty has been with fillling gaps when building model aircraft - I do this as a diversion from railways stuff - so there are curved surfaces and fine surface detail to deal with. Most higher end models come together quite well - but not always!
I actually build model aircraft too and gap filling is, in many ways, the most challenging part of the hobby. Squadron putty isn’t really all that useful. A 2-part modeling clay works a lot better for gap filling since it won’t shrink and you can use a wet finger to smooth it out prior to drying. A lot of people also advocate super glue but this requires a lot of sanding since you will inevitably overfill the gap and have to sand it down, which often means you lose some of the surrounding detail. However, if you really want a gap to disappear these two methods are much likelier to succeed than putty.
One more tip is to use a product like Mr, Surfacer or Tamiya putty as a topcoast after filling the gap. These products can be painted on and dry hard and they are a way to smooth over a filled in gap. Doing this plus some sanding followed by primer should make the gap disappear…
On smooth surfaces I don’t use putty but I do use very thin superglue with an accelerator to fill small gaps and then sand down the surface level again with increasingly fine grits of sandpaper or crocus cloth.Makes an invisible permanent repair.