Tag Archives: tenax

Glue for plastic models and buildings

I saw a question for the millionth time on a forum about what glues to use on plastic models and buildings. So I’ll cover the topic here, where it won’t get purged after 8 months.

Ask the question at a hobby shop, and the answer comes down roughly 50/50 whether to use some type of super glue (cyanoacrylate, often abbreviated CyA or CA), or some type of MEK-based plastic weld, such as Tenax 7R. Every once in a while, someone pipes up about the tube cement I used as a kid. You don’t want to use that stuff. If you’ve ever tried, you know why–it’s messy, dries slowly, and the bond isn’t as strong as it could be. Read on and I’ll give you the advantages and disadvantages of both alternatives, plus some secrets.

Continue reading Glue for plastic models and buildings

How to assemble a plastic model kit

Several months ago I bought a plastic model kit for the first time in probably 20 years. This past week I started to put it together.

I’m doing things differently this time.

Wash the parts. Plastic models have mold release on them, which makes it harder for paint and glue to adhere to the parts, making for a weaker model. The first step to building a proud model is washing the parts with dish detergent. Then avoid handling them with your bare hands as much as possible afterward.

Use better glue. The guys at the local hobby shop argue about the best glue to use, but they agree that the Testors stuff that comes in the tube isn’t it. It’s better to use either a plastic welder like Tenax-7R, or one of the many super glues on the market. Tenax welds the plastic together and actually makes one piece from it. The downside is its nasty fumes (wear a ventilator to save your lungs and your liver–really) and its permanence. Super glues work about as fast but make a chemical bond. The upside to super glue is that if you make a mistake, you can put the mistake in the freezer overnight, and then you’ll be able to pry it back apart and glue it again.

The downside to super glue is that it happily glues skin, so get a debonder from your hobby shop to bail you out if you glue your hand to your model or if you glue a couple of body parts together accidentally–putting your hand in the freezer overnight doesn’t work very well.

Both glues result in a stronger bond than the old tube glues we used to use.

Trim the flash. There’s always extra crud on the edges of your plastic pieces, due to the molding process. Trim that away with a hobby knife. Usually just slowly running the blade across the edge is all it takes.

Putty. When you glue your pieces together, there are always gaps in them. You can get plastic putties that chemically bond with the plastic and those are the best to use, but even a household putty like Durham’s Water Putty is better than gaps. Ideally you want the putty to be a different color than the plastic so you can see your work better.

Use primer. You should always paint your model, even the parts that are molded in the correct color, for reasons I’ll get to. But before you paint, you should prime the model. Use a good-quality primer like Krylon or Rustoleum Painter’s Touch. They are less expensive than hobby primers and they work extremely well.

Primer does several things. Paint sticks much better to primer than to plastic itself, so if you use primer, you can use thinner coats of paint, and you can also use paints like acrylics that normally won’t stick well to plastic. Second, primer can fill in minor flaws in the plastic, and make flaws that need to be puttied more visible. Third, primer makes the detail much more visible, which helps you paint better.

Spray on a very thin coat. It doesn’t have to cover completely.

Paint. Models should be painted for two reasons. The real thing is painted, so your model will look more realistic if it’s painted. Bare plastic looks more like a cheap toy. Second, decals don’t adhere well at all to bare plastic, because they are designed to adhere to paint.

The best paints to use is also a matter of religious debate. I like to use acrylics for the parts I have to brush paint, because acrylics have no fumes and clean up with water. They’re cheap and easy to work with. I can get craft acrylic paints for 60 cents a bottle if I shop around, and the bottles are big enough that they last forever. They’re cheaper than Testors enamels normally sold for models, and I don’t think they dry out in the bottle as quickly.

For the ultimate acrylic, visit a hobby shop that caters to wargamers and pick up some Vallejo paints. They’re thinner than the craft acrylics, so they’re less likely to obscure detail when detail counts. They also tend to be self-leveling, helping to conceal your brush strokes.

I prefer to spray rather than brush whenever I can, because then I don’t cover up as much detail, and I don’t get brush strokes. I can spray a light coat followed by a second light coat and get nice, even coverage. You can get sprays intended for plastic models at a hobby shop, but if you can find a suitable color from Krylon or another hardware store brand, you can use it.

An airbrush is nice, if you can afford its cost and can afford to invest the time required to learn how to use it and keep it clean.

So, should you paint before or after assembling the model? I find it easier to paint what I can before, and scrape the paint off the surfaces that need to be glued.

Masking. When you need to paint an assembled model and you need to keep the paint away from parts of it, use masking tape. Don’t use the cheap beige stuff, get some good blue or yellow painter’s tape, which is less likely to lift the paint that’s under it.

To keep paint from bleeding under the tape, you can either brush along the edge of the tape with the color that the tape is covering, or brush with some clear acrylic medium (look for it in the artist’s paint section of stores like Michael’s and Hobby Lobby) or, believe it or not, Future Floor Polish. This seals the edge, and if any of it bleeds under, it won’t be visible.

Decals. Dad and I could never get decals to stick right. What we didn’t know was that decals are nothing more than a clear lacquer sprayed on paper with something printed on it. They are supposed to bond permanently with paint underneath them.

So the first secret of applying decals is just to paint the surface beneath them. Decals stick better to glossy paint than flat, so if you don’t paint with glossy paint, apply a bit of acrylic gloss medium or Future Floor Polish (which is actually a clear gloss acrylic, not a wax), let that dry, and then apply the decal to that.

To really blend the decal in with the paint, get a decal setting solution from a hobby shop.

Clearcoat. When you’re done, spray a clearcoat over the whole paint job. This gives a consistent and more realistic finish. A gloss coat is fine if you want your model to look factory new, but for a more typical real-world look, use a clearcoat with a dull finish. Testors Dullcote is the standard.

Before you experiment with Krylon or another hardware store clearcoat, take some scrap plastic, paint it with the same paints you used to paint the model, and then spray the clearcoat over it. Not all clearcoats are compatible with all paints. I once tried Dutch Boy clearcoat on a plastic model and it caused the paint to bubble, ruining it.

Following these tips won’t make award-winning models, but it will make your models look a lot nicer.

Fixing a Marx 490 O27 toy locomotive

Note: Please don’t do what I did in this post. Chances are you’ll make things worse in the long run.  If you’re looking for information on fixing a Marx train that won’t run, go here for instructions on how to do that.

I fixed my Marx 490 locomotive this weekend. I used the tips in The All Gauge Model Railroading Marx Trains guide. Scroll down to the heading titled, “The Marx motor.”

I was skeptical because these instructions call for WD-40, and it seems I’ve read a hundred other places never to use WD-40 on any model train. But my Marx 490 wasn’t running well, and it would cost more to have it professionally repaired than it’s worth.But before I continue, let me interject something. If you’re here from Google because you just found a box of old trains that say “Mar” on them, the company is Marx, not Mar. And the trains look a lot like Lionel, but they’re not Lionel. In a few rare instances, Marx trains are very valuable. But in most cases, a Marx isn’t worth as much as the box a Lionel came in. Which is why I said it would cost more to repair my Marx than it was worth. I just had two Lionels repaired for $25 each, plus parts. You can usually get a Marx 490 with some cars on eBay for $25.

But that’s not to say Marxes don’t have charm. They certainly do.

There. I feel better now. Back to the story. Where was I? Oh yeah. WD-40. I didn’t use WD-40 on my Marx. I used Gunk Liquid Wrench instead. Two reasons: The main purpose behind WD-40 and similar oils is to clean, rather than lubricate. They leave a little bit of lubricant behind, but not a lot. Gunk Liquid Wrench, like WD-40, is primarily a solvent. But it has synthetic oil in it, whereas WD-40 has kerosene in it. In my mind, this makes Liquid Wrench a better choice for this purpose because what little lubricant it leaves behind when the solvent evaporates will be of higher quality and last longer than WD-40’s lubricant.

But there was a second reason. Liquid Wrench was on sale, so it was cheaper. I also thought long and hard about Marvel Mystery Oil in a spray can–it works in cars and airplanes something wonderful–but opted for Liquid Wrench because the instructions called for a penetrating lubricant, and I didn’t know if the Marvel would exhibit the same kinds of properties. I’m a journalist-turned-computer tech by trade, not a chemist.

But first, I tried omitting the WD-40 step and just cleaned it with Goo Gone and TV tuner cleaner. Like I said, every time I turn around I read somewhere that you shouldn’t go near a model train with WD-40. Between the TV tuner cleaner and the Goo Gone, the train looked brand new very quickly. I was impressed. It ran very nicely too, but the next day it didn’t run at all. Figuring that now I had nothing to lose, I broke out the Liquid Wrench.

After a spraydown with Liquid Wrench, it ran too well–it flew off the track and fell 4 feet to my concrete floor. Ouch. That left a mark. One corner of the cab busted off, and it took me a good 15 minutes to find it. After I’d let the locomotive run 20 minutes–with a big load this time, to slow it down and keep it on the track–I re-glued the broken corner with some Tenax-7R plastic welder. Tenax is great stuff–apply a small amount of it, hold the pieces together for a minute, and they’ll stay. It’ll take 8 hours for the joint to completely dry and reach full strength, but after just a minute, the joint is as strong as it would be with every other glue I’ve ever tried on plastic.

Lesson learned: Keep your test track on the floor. Or surround it with pillows. Or use a Marx transformer that can send just a couple of volts on its lowest setting, so slow actually means slow.

The next day, I ran my 490 the opposite direction on my track–the first time I’d ever run a locomotive that direction on the track. And guess what? I found a bad spot on the track. It derailed–again–and the piece I’d glued fell off in spite of the cushions I’d placed all around my table.

Then I remembered that Tenax is amazing stuff if your two pieces fit snugly, because unlike some glues, Tenax doesn’t fill in the gaps at all. The break must not have been clean enough to give the Tenax adequate surface area to create a very strong bond. So I re-glued with epoxy, since epoxy will fill gaps. It held this time.

So now Marxie has a battle scar and he’s probably worth half what he was worth a week ago, but he runs very well. It’s short on ability but long on heart–it struggles pulling loads that won’t make a Lionel break a sweat. But it’ll pull them, and you can see it working hard doing it. And where a Lionel will just give up on a grade with a curve with a long load of cars, the Marx just keeps spinning its wheels, ever faster, until something manages to catch and it propels on its way.

I think that’s what I like about it. It never gives up.

There are a few other things to like about them too. Like I said before, you can buy a Marx locomotive for less than the price of the box a Lionel locomotive came in. Marxes are easy to take apart–mine’s held together by four joints, easily pried apart with a small slotted screwdriver. And the motor is simpler than a Lionel, so it’s easier to understand. If you want to learn how to fix toy trains, Marxes are easy to learn on, and if you mess up, you ruin a $15 locomotive rather than a $100-$1,000 locomotive.