Dissolved styrene as a filler/sealer? Make fins smooth as plastic with plastic?

[Marc_G]

Hi folks,

I get lots of ideas. Many of them are dumb, some just don't work.

I'm always looking for better ways to seal/fill/strengthen my balsa (occasionally basswood) fins. My current go-to methods are papering followed by CA flooding, or occasionally just saturating with CA, or for simplicity just repeated coats of filler primer (fills, doesn't strengthen).

I had one method a few years ago where I mixed auto body spot putty with Minwax wood hardener. It worked, but took a while to set up. I moved on. Eventually landed relying on CA-based methods most of the time.

A couple weeks ago we were at a Halloween event at a local park, and there was a "mad scientist" who offered an invigorating tonic to a volunteer. "Just pour it in that styrafoam cup first" ... and the cup melted instantly. This was outside , but I nonetheless caught a whiff. Lacquer thinner, or something like it.

Now, there's no surprise to me that styrene melts in LT. But nonetheless it got me thinking... What if I made a mixture of LT and styrene, thin enough to soak into balsa, thick enough to build up...

Today I was working on an old project ... a Renegade-D (single stage version) from 4.5 years ago. It was a project I started with my older son, he lost interest, and I saved it for when he would be interested again.... that never happened, so I decided to finish it. You have to glue these pods based on plastic nose cones to balsa fins. It's a plastic-to-balsa bond you need. YEah, I know most people would use epoxy, but my epoxy takes a long time to set up, and the positioning of this bond is very finicky and pretty much has to held in place until it sets... I almost tacked it on with CA followed by epoxy fillets (and I would recommend that for anyone reading), but I decided to use plastic glue, which I've found sticks pretty well to balsa as long is it is thin and runny.

But all my plastic glue was dried up to a thick consistency. No use.

I decided to melt some styrafoam in LT and make my own plastic glue. So I took a polypropylene cup, put a splash of LT in it, and dumped a chunk of styrafoam in. FST! it melted and formed a blob at the bottom of the LT. A few more chunks of styrafoam went in. FSST! FST! Interestingly, the melted plastic didn't really seem to dissolve in the LT, it stayed as molten plastic with s specific consistency no matter how much I stirred. OK, still useful.

I got some on a Q-tip and used it as glue... it soaked into the balsa reasonably well, and bonded nicely to the nosecone plastic of the pod, and pretty soon I was all set. I only had to hold each piece for a minute or two.

I ran out of time but plan to come back to using this mixture, or a similar one with a different solvent blend, to fill some scrap balsa and see how it goes. Maybe acetone would work better than LT for this?

Has anyone tried this kind of thing, and if so do you have any experiences? I'm trying to combine ease of finishing to a smooth surface with a good penetrating capability. Yeah, probably I should just stick with CA, but as long as I'm using stinky things I might as well experiment with plastics.

Very interested to hear any experiences in this line of application.

Marc

 

[Screaminhelo]

Acetone can be used for bonding styrene, so the plastic may actually dissolve into it. MEK will also dissolve styrene quite nicely but it evaporates very fast and may not give you much working time. During my last deployment, I ran out of Ambroid Pro Weld for the kits that I had and got some acetone and some MEK from the hangar and found that about a 50/50 mix worked well for models. I don't know if the MEK substitute they sell these days will be any good or not.

 

[Marc_G]

Thanks. Next weekend maybe I'll do some experimenting with Acetone and other things...

 

[grapetang]

Some thoughts though I haven't tried any of this:

There's also the ready-made plastic modelling putty (like Squadron green or white: https://www.squadron.com/Squadron-Tools-Green-Putty-SQ9050-p/sq9050.htm). It's essentially what you are making. This putty (thinned w/lacquer thinner), automotive glazing putty, or thinned bondo will work but it might be a little on the heavy side.

It's probably best to use after gluing fins to the tube as white & wood glues would be useless after fins are finished with either, unless epoxy is used. There's also the question of the glue/epoxy bond strength if the glues bond to potentially weak filler rather than soaking into the balsa.

Interesting idea. Don't forget about the fumes & safety precautions!

 

[Rex R]

if you don't insist on styrene, might I suggest plastic pipe cement? it is largely plastic pipe dissolved in a solvent(depends on which type of cement you buy). I have used ABS cement as a filler on an ABS rc boat hull(did have to use small quantities to keep from melting the hull).
Rex

 

[Marc_G]

I tried pipe cement once a few years ago, with poor results. The stuff dried kind of soft. Not really hard sandable. I'm not sure which type it was, although almost certainly it was PVC pipe cement since that's the kind of pipe I have in my house for drain pipes and the like. I could get some ABS version of the cement next time I'm at the hardware store and give it a shot.

 

[Rex R]

the 'primer'(clear or purple) is cement minus dissolved plastic, it might work to dissolve styrene.
Rex

 

[Charles_McG]

This has come up in the last couple of years. I have this blog post stashed in my 'ideas's collection.

https://fdsailor.blogspot.com/2011/08/how-to-make-sanding-sealer.html

 

[Marc_G]

@Charles_McG

Thanks for the post. That's basically exactly what I'm thinking of. I was sure my idea wasn't original. Right now I don't have a good container to store the mix so I'm on hold.

I did happen to be at a hardware store yesterday, and bought a can of the pipe cement for ABS (actually, it lists as working with PVC, CPVC, or ABS) and the results were the same as with the PVC pipe cement... it sealed sure but didn't add any stiffness, and I don't think it would be good for sanding. Bzzt.

Hmmm.. Maybe I should dump the pipe cement, rinse and reuse the can and that swab thingie...

Marc

 

[Rex R]

hmm a mason jar in pint or jelly size would work...
Rex

 

[Marc_G]

True I have several of those. Won't solvent kilobyte lid inner lining which probably wasn't intended to hold up to MEK or LT?

 

[Rex R]

not sure, acetone hasn't done in the lid on the pint jar yet(2 months) that I have been storing some in.
Rex

 

[Micromeister]

Marc:
As a filler material Poly-Styrene, ABS or Acrylic shavings in either Acetone or MEK, can work OK. Lacquer Thinner is not a good choice at all, as it is the weakest of the solvents. Just be aware after reducing these plastics to a Liquid they lose most of their structural strength. As the materal hardened is also become very brittle.

For Decades in the Sign Industry we have Liquified these and other plastic types with a much hotter solvent MC (Methylene Chloride) This solvent renders Acrylics into a water clear liquid that can be as thin as water or as thick as heavy syrup. Drys fairly quickly but Does NOT have any structural strength PERIOD.

As mentioned with white or clear Polystyrene it might make a interesting filler but the weight addition should be considered a problem. Oh almost forgot any of these liquified plastics will be very hard to sand.

I'd suggest skipping such things and going back to the basic Grey Auto Primer/Filler for a "Looks Like Plastic" finish with out the hassle.