Melted Sprue for Filler

[balls47]

I'm building the DML, 1/144 scale F-16 Thunderbird that is molded in white sprue. This is gonna be an in-flight, so I needed some filler. Here is what I did. I chopped up some sprue and and put it in a glass Paasche jar. I covered the sprue with (too much) MEK. The next morning, there was a white liquid in the jar that was about the consistency of coffee with cream. I took the lid off and let it sit outside on the deck. After a couple of hours, the goo was about the consistency of thick Elmer's Glue. I used a toothpick and put some on a piece of sheet styrene. It dried back to the hardness of the original sprue and melted right into the sheet. It sands out just like plastic. When you get to the thickness you want, just put a tight lid on the jar and it will stay at that thickness. I did this four days ago, and the goo is still the same thickness. I have melted sprue before with all kinds of "stuff," but MEK works the best by far. There are two downsides. The first is the fact that it is MEK. It's very flammable and hard on the body if you don't take proper precautions to protect yourself. The second is that it will create "spider webs" just like the old tube glue did. To prevent this, just be careful, and don't pull the application tool off of the model too quick. Simply take your time, and you will figure out how to avoid "spider webs." The good thing is that if you do get "spider webs," they will be dried by the time they fall onto the model. No damage, just annoying. I used the goo on the 1/144 F-16, and it worked great. Give it a try. Good Luck!!!

Edited July 20, 2013 by balls47

[dmk0210]

I do this all the time. It is the same hardness as the surrounding plastic so sanding/shaping/carving is easier. It is the same color as the surrounding plastic. It also has the same strength as the surrounding plastic, where putty may crack in some places that may see some flex.

The drawbacks are fumes, cure time can be 24-48 hours. I have also seen bubbles appear in the surface and they need to be filled. Thin CA works best for that, putty doesn't get down in the tiny cavities.

It's not a cure all. I still use putty and CA. The melted sprue is just one more option in the toolbox and a good solution for specific situations.

[balls47]

I do this all the time. It is the same hardness as the surrounding plastic so sanding/shaping/carving is easier. It is the same color as the surrounding plastic. It also has the same strength as the surrounding plastic, where putty may crack in some places that may see some flex.

The drawbacks are fumes, cure time can be 24-48 hours. I have also seen bubbles appear in the surface and they need to be filled. Thin CA works best for that, putty doesn't get down in the tiny cavities.

It's not a cure all. I still use putty and CA. The melted sprue is just one more option in the toolbox and a good solution for specific situations.

Yessir, What do you use as your melting agent for the sprue? I've tried lots of stuff, but MEK is the winner by far. Like most things, I came up with this by screwing up (adding too much MEK). It turned into a very thin liquid, and I had to let it evaporate (outside of course) to get to the right consistency. I also used to have trouble with bubbles. I think that came from shaking or stirring too vigorously. This last time, with the MEK, I had NO bubbles. Like I stated, the only glitch I had were the "spider webs," but they dried so fast that they weren't an issue. I simply brushed them off with a brush. And, Dave, you're absolutely right. This is just another tool in the toolbox. Like you,I still use CA, putty, spot primer & filler, and the list goes on. Thanks for the reply.

Edited July 20, 2013 by balls47

[dmk0210]

I use Weld On #3.

It looks like you avoided the bubbles because you made the mixture so thin. It let the bubbles float to the top and disperse.

Edited July 21, 2013 by dmk0210

[jimmy07]

Brilliant idea! Definately using that one!

Jim

[MarkusN]

Just remember that this, being a rather solvent heavy dissolved plastic, will have considerable shrinkage. You will need to overfill and then sand down.

The high solvent content is also what causes the bubbling. Just like the old tube glue; if the temerature is high enough to rise the vapor pressure of the solvent enough so it can "crack open" the internal strength of the still liquid putty, a bubble will form.

[Mike C]

One stupid question: What is MEK???

[SBARC]

There's an article in the Tools and Tips section on the ARC site about this sort fo filler. I used lacquer thinner in my article.....lacquer thinner is easier to buy in any city.

Filling with Plastic

[jimmy07]

One stupid question: What is MEK???

Methyl ethyl ketone. Similar-ish-ly to acetone and REALLY strong smelling stuff!!

[Mike C]

Methyl ethyl ketone. Similar-ish-ly to acetone and REALLY strong smelling stuff!!

Where would I find this thing? Hardware store? Can I use acetone as substitute?

[balls47]

Where would I find this thing? Hardware store? Can I use acetone as substitute?

Just this week, I saw MEK at Lowes. I have also used lacquer thinner, but the MEK works much better. Just be

careful, because it can be nasty if you get a good lung full of the stuff.

[galileo1]

I've tried this before unsuccessfully and I think it was due to the melting agent (Tamiya Extra Thin cement) not being strong enough. I'll give a shot again with MEK and see how it goes. Thanks for the tip balls!

Rob

[balls47]

I've tried this before unsuccessfully and I think it was due to the melting agent (Tamiya Extra Thin cement) not being strong enough. I'll give a shot again with MEK and see how it goes. Thanks for the tip balls!

Rob

Hey Rob, It's also a lot cheaper than using the Tamiya cement.

Tim

[galileo1]

You're certainly right, Tim. I almost used and entire jar of the stuff without success.

Thanks again!

Rob