Real Dirt and Magnetic Particles

[Gary S]

We always hear that we shouldn't use any dirt that has magnetic particles in it. But is this just anecdotal, or have folks actually come to grief because of it?

Reason I ask is that I found an easy source for some fine powdery dirt from an old dirt road, but there is definitely some magnetic particles in it.

I'm not talking about using it for ballast, but for general ground cover underneath the ground foam and static grass.

Seems to me that if the material is properly glued down - similar to how ballast is done - thoroughly soaked by white glue - that there won't be any way for the magnetic stuff to come loose and get in the loco motors.

I am considering winding me a big electromagnet and uisng that to suck out all the magnetic stuff, but is that really necessary for material that won't be closer than about 2 inches from the track?

[faraway]

It should be ok as I do keep anything magnetic at least 2" away from the tracks. Ok, that "should" be. In fact did the CF-7 with RTR motor collected little metallic pieces under the motor and causes shorts for some weeks. The engines did find each other day another small magnetic pieces. I discovered never the way the pieces toke from milling on one side of the room into the south yard on the other side of the room.
It should work but you may get a surprise....

[nachoman]

Gary, a place like Harbor Freight or Northern Tool should sell large permanent magnets relatively cheap. Look near the welding supplies. I wouldn't worry about it too much. I usually use real dirt for scenery, and never see magnetic particles stuck to my motors.

[tetters]

Do you normally have to bake the dirt at low heat before you use it? Just kill off any critters, spores or mold bacteria that might be hiding in it? :?

[Gary S]

Tetter's, what little I've used, I haven't worried about baking the sand and dirt All of the dirt I use is inorganic for the most part. Our actual soil here in Houston is typically black gumbo clay which isn't good for using on the layout. It becomes a gooey-gummy mess when wet. So I don't bother with that.

The soils I use are more like finely crushed rock or shell from "gravel" roads and road shoulders. Southeast Texas dirt roads aren't really dirt if they are to withstand traffic after a rain. They are typically built up with crushed concrete, shell, or crushed caliche, and that is the stuff I use.

Here's a photo of a test strip I did with various stuff I collected over the past couple of years.

   

1 - Sifted from a pile of broken up asphalt road surface. This stuff has quite a bit of magnetic material in it.

2, 3, 4 - sifted from various "caliche" type road surfaces. These can get really powdery and dusty after a dry spell.

5 - A lighter colored version of the above. I can't remember where I got this one, wish I could because I need more.

6 - Similar to 2, 3, 4.

7 - Sifted from crushed concrete off of an abandoned road. It is more gray than in the picture.

8 - Sifted crushed concrete from a new access road at a residential construction site.

[Gary S]

Kevin, the thing about a permanent magnet is that it is difficult to get the little magnetic bits off the magnet when you want to clean it up. And then the bits tend to get knocked off back into the dirt when trying to suck them out of the mix. A big electromagnet would be perfect.

[e-paw]

Gary you got it right , the Electromagnet is the way to go, cleanup is so much easier. I need to acquire a new one my self. I generally cook up the sifted dirt in the toaster oven to kill off the unwanted stuff and run said magnet over it just in case.

[Gary S]

But the real question is how necessary is it to get those metal particles out before using the stuff on the layout.

[Charlie B]

Gary, here are my thoughts....Keep it 2 inches from the track, glue it good and don't worry. After it has set hard, then run you magnet around. Anything that comes lose will be what you pick up. You will probably run a vacuum over it once it sets too, to remove the loose stuff, and probably have to clean every so often that what little is there shouldn't be a problem. Now, if you get some dirt from around the scrap yard, then I would worry.
Charlie

[faraway]

But the real question is how necessary is it to get those metal particles out before using the stuff on the layout.

Gary, how much and what size of magnetic material do you expect? I wrote about the turning that resulted from milling locomotive frames etc. They are a problem you should avoid but what kind of particles do you expect and how do you get them in the dirt on the streets of Houston?

[nachoman]

But the real question is how necessary is it to get those metal particles out before using the stuff on the layout.

Gary, how much and what size of magnetic material do you expect? I wrote about the turning that resulted from milling locomotive frames etc. They are a problem you should avoid but what kind of particles do you expect and how do you get them in the dirt on the streets of Houston?

Only a few naturally occurring mineral are magnetic - primarily one called magnetite. I'm not exactly sure if there are secondary reactions that form or concentrate these minerals within the soil, but within whole rocks magnetic minerals are pretty rare in most places. I suspect in roadside "dirt" the magnetic particles are primarily from cars and trucks wearing out (probably mostly brake and clutch dust). Sifted railroad ballast would be the same way. Any water running from the roadway would carry these particles into nearby streams, and from there could travel quite a long way. That would be an interesting study if someone used magnetic particles as an "indicator" of sorts. Lead compounds from years of burning leaded gasoline can be found in most soil, especially along highways, and I've seen that used as an indicator. Certain radioactive isotopes are also present in modern soil as a result of nuclear testing. When scientists report a radiocarbon date it is always reported as years prior to 1950, because nuclear weapons testing disrupted the natural carbon ratio in the atmosphere. If one is trying to determine the age of a sedimentary deposit, presence of materials like lead and radioactive isotopes help pinpoint the age.

EDIT: It seems that people are already using magnetic particles as pollution tracers:
<!-- m --><a class="postlink" href="http://books.google.com/books?id=bitQZH6YG_IC&pg=PA314&lpg=PA314&dq=roadside+magnetic+particles&source=bl&ots=40C01mjHwS&sig=uNbopgfma_st452UK9iOxMJ95eo&hl=en&ei=lEX-TJ3NMpOCsQP_p9CvCw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCgQ6AEwADgK#v=onepage&q=roadside%20magnetic%20particles&f=false">http://books.google.com/books?id=bitQZH ... es&f=false</a><!-- m -->

[Gary S]

Charlie B, I was thinking what you were thinking, go ahead and use the stuff, then run a magnet over it after the glue has dried, and vacuum it too.

Reinhard, I am thinking what Kevin said, the magnetic stuff comes from vehicles, probably brake wear.

I'll take some photos of a magnet with the dirt.

[doctorwayne]

Kevin, the thing about a permanent magnet is that it is difficult to get the little magnetic bits off the magnet when you want to clean it up. And then the bits tend to get knocked off back into the dirt when trying to suck them out of the mix. A big electromagnet would be perfect.

If you use a permanent magnet, put it in an oversize clear plastic bag, then, after you've passed it over the area to be cleaned, evert the bag to encapsulate the particles.

Wayne

[P5se Camelback]

... If you use a permanent magnet, put it in an oversize clear plastic bag, then, after you've passed it over the area to be cleaned, evert the bag to encapsulate the particles. Wayne

Whoa! doctorwayne! Good one ... and it shall be chosen as our designated "Vocabulary Word of the Day!"

It's a good word, People! It is a transitive verb and it means to "turn a body part outward" or "to turn something inside out."

Now, as the Vocabulary Word of the Day, you are each challenged to use the word "evert" three times in conversation today.

Have fun!

[Gary S]

Excellent idea DocWayne, and so simply obvious that "why didn't I think of that?"

Here's a photo of my magnet with some particles. The tiny magnetic particles are a dark color, but they tend to trap the tiny lighter colored dirt on the magnet.