# A porous deck for the DC&M



## dawgnabbit (Jan 2, 2008)

Hello, All Since the prefabricated plywood ladder modules are made from exterior plywood, there is some risk of delamination if water gets between the plies and freezes. Filling all open voids and careful painting help reduce that risk. The modules on the DC&M are then topped with a porous deck that facilitates drainage and rapid drying after a rain.
To make the deck, I staple half-inch mesh wire fabric to the ladder, folding it over the sides:









This is topped with spun-bonded polyester landscape fabric, which is stronger and more permeable than the usual kind:









Painted wooden trim strips cover the folded-over fabric, and “rain caps” provide a clean edge. The deck will be topped with a “loose fill,” which drains well and simulates natural ground. However, loose materials generally make a scurvy track base, so sealed wooden “riser blocks,” nailed to the underlying ladder structure every eight inches, provide firm support for the track on the DC&M. Here's a section that's ready for loose fill:









It's time consuming to work the rain caps around corners; they have to be kerfed to bend, and the kerfs have to be filled and repainted. I'm not sure the improvement in appearance is worth the effort. I will probably dispense with rain caps in the future and just use a taller trim strip to retain the fill. 
Now, for loose fill I've tried a number of materials, and discarded most. I can tell you that loam soil from my garden looks highly realistic, but doesn't drain well at all. Neither do crusher fines or plain sand, surprisingly. Crushed rock (no fines) drains much better and dries quicker, but looks like, well, like crushed rock. The jury is still out on this issue, so if you have suggestions, I'd love to hear them.
In the meantime, I'm really much more concerned about drainage than appearance on _most_ of the right-of-way, except at a few “detailed” places. So the DC&M uses a ¾-inch thick layer of washed, 3/8 inch mesh “rainbow rock” for loose fill. This is just natural (not crushed) pea gravel with a fancier name, a little more color when wet, and a higher price tag. It drains as quickly as you can pour water on it, and is dry and warm again a half hour after the rain stops. Realistic, it doesn't look. This section is ready for track:









Attaching track is just a matter of tacking it down to a riser block every so often. So far, track on the DC&M hasn't squirmed or buckled in spite of air temperature variations of 100 F or more (-20 F last winter, 98 F two weeks ago). I do leave small expansion gaps between rail sections, of course.

Once again, if you can suggest another material that might make a better loose fill, I'll give it a try on my test section. I'm anxious to hear your ideas on this.
Thank you for looking.
Steve Seitel


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## Greg Elmassian (Jan 3, 2008)

The smooth rocks will indeed not make a good base for the track. You need crushed stone with sharp edges that interlocks, like the real railroads. I think what you have is fine, although I suspect that your track will eventually roll up and down because of the wood supports. 

Many people use crushed granite, also marble chips. Anything that is sharp edged, really the opposite of the type of rock you are using. I believe then you would be fine without the wood riser blocks, one less thing to rot in the outdoors. 

Regards, Greg


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## wchasr (Jan 2, 2008)

Greg, 
I "think" that with the support being on the wood which is screwed to the plywood frame work at intervals that the track will really rely on the wood supports and not on the rocks and substructure. The rocks in essence in this case are likely only for looks. MY fear would be that the trackwork would sag where there was no support. I think on the POC that Ricjard has used a ladder style track support with dirt, rocks, ballast, etc. around it on a similar mesh and landscaping fabric? Steve please let us know how the track has held up or holds up? Whether it dips in between the wood blocks or not? Stee, the Ballast I'm using is cr-1a crushed limetsone from the local asphalt plant trucked in ad I picke dit up less than 2 miles from my house and hauled it home on my utility trailer. It is about 3/8 to 1/4 crushed pieces with some fines but not a lot. Still out of scale for actual ballast but it does seem to drain well. Considering I've got it mounded up at close to a foot tall around my loop of ladder roadbed so far it's held up well. OF course your definition & qualification for drainage may be different than mine right now?My plan in the future is to continue to use this size up and onto the decks I plan on building eventually. 

Chas


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## NTCGRR (Jan 2, 2008)

What will your min Radius be on the main line?


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## armorsmith (Jun 1, 2008)

Steve, 

Consider this option to obtain the best of both worlds. If I assume the the blocks you screwed to the support structure are wider than the tie strips then 'C' clamp some 1/8 x 1 1x2 lattice strips to the outside of the blocks. Spread the larger stone on the outside of the lattice strips and use the Crusher Fines / Crushed Granite / Crushed Marble, whatever your choice is on the inside of the lattice. Allow the fine material to settle some, then remove the lattice strips. 

My tuppence worth. 

Bob C.


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## dawgnabbit (Jan 2, 2008)

Hi, All

Glad you're interested. Your suggestions are most helpful, especially since this is really my first rodeo.

Greg - The crushed "pea gravel" available locally might have been a wiser choice for track support, for sure. But that had a lot of smaller stuff in it, not well-screened, and I'm paranoid about good drainage. Fortunately, it's easy to scoop out the loose fill and replace it with something else if I decide to later. I am planning on ballasting the track with something sharp edged (but no "fines") to help prevent it from washing away in the rain.

Chas - Yes, primary support comes from the sealed redwood track risers and the structure beneath them. I did some experiments first. With code 332 prefab track, supported on 8 inch centers and no rock beneath, there was virtually no deflection with a point load of ~ 25 lbs on the rails, centered between supports. I measured no more than 1/32" sag. The rainbow rock and the mesh beneath adds a surprising amount of additional support. I don't think it will be a problem even with the heaviest mainline locos (mine are all narrow gauge, anyway). I chose this support method after I saw that Rick Marty was supporting his track about every 8 inches in some sections, and hadn't noticed any problems with flex.


Marty - Turnback Curve, at 16 ft radius, is the tightest on the railroad. Next tightest is 28 ft radius. Switches are Train-Li R7's so far. I'll use tighter curves on industrial spurs and in yards, of course.

Bob - Great idea. The blocks are the same width as the ties, but I can slip a temporary thin retainer in alongside them to hold the ballast while it settles. Or even leave it in to inhibit wash-outs if it's not too conspicuous. I'll try it.

Please, if you have more ideas, spit 'em out. I learn a lot that way. Thank you all.


Steve Seitel


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## bnsfconductor (Jan 3, 2008)

For a scale ballast I use something called "bridge topping" which is a crushed rock that is 1/8th or smaller with no fines. I got mine from Manufacturer Minerals a local company in Renton, Wa. I'm 'think' it's used in hot asphalt mixes or in concrete mixes. Call a mineral supplier company and see what they call stuff smaller then 1/8". Most of what I see in Garden railways is 1/4" or bigger and sees over sized to me. 

Craig


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## NTCGRR (Jan 2, 2008)

Craig 
I'd use scale, more scale ballast if posible, but around here the birds steal it so fast.


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## bnsfconductor (Jan 3, 2008)

Why do they steal it Marty? That seems like a weird thing for them to take.


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## Greg Elmassian (Jan 3, 2008)

Birds often "eat" grit to help them digest their food... that's why it's called "chicken grit".. 

Greg


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## Greg Elmassian (Jan 3, 2008)

Birds often "eat" grit to help them digest their food... that's why it's called "chicken grit".. 

Greg


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## jake3404 (Dec 3, 2010)

First, I really like your idea Steve. It seems like it is a little more work, but I think your deck will last much longer then most. 

So, let me give you an engineering explanation of what you have discovered. First your rock, you experimented with finer materials and discovered that they dont drain as well and that is true because of the smaller voids between the particles. A smaller void restricts the flow of water. Any material that has "dust" or as we term fines, will restrict water flow. That is why it is desired for a base under concrete or asphalt. 

Greg was right with the shape of your rock. A rounder edged rock, such as what you have, will more freely move because there are no edges to restrict the movement. An angular rock, such as something that has been through a crusher, will "lock-in" because the flat sides will rest against each other and prevent movement.

Another made a suggestion to make a separation and put finer material in the center and the more coarse stuff on the outer is a pretty good idea. After a while the small material will flow into the coarser stuff but I dont think that will be a problem. You could also just spread a small layer of finer material on the top of the coarse stuff also. You will still get good drainage. It will be a little slower, but the water will not be an issue. You will have to replentish the finer stuff on top sometimes as it flows into the coarser stuff.

Finally lets talk about the optimum rock diameter size. Keep in mind, this is from my experience of crushing rock for the DM&E for their roadbed. This is consistant to what the UP and BNSF use on their lines around this area also. Also, railroads will spend what they want on ballast. If they can find a cheap alternative then they will use it. Why do you think for many years and probably some still do, used ash from the ash pit for the ballast. This means the size can vary based on the importance of the line and the area where the line is constructed. What I crushed was 3" clean rock. This meant that the maximum rock size was 3" and the majority of the rock was in the 3" size. However, there was some smaller rock in the mix as well. But, there were very little fines. The standard is less than 2% total fines in the material. So that meant this stuff was pretty clean. 

To transfer 3" diameter rock into our scales

1:20.3 = 0.148" or 37/250" which no one makes so we have to use - 1/4" rock. You might luck out and find a quarry that makes a rock called "-4 +6 fines" this is a rock that has a range smaller than a 4 sieve ( approx 3/16") and larger than a 6 sieve ( approx 1/8"). This material is used in special asphalt mixes so you might see it in a quarry that supplies material for asphalt mixes such as what my quarry did. It is probably the closest your going to come to actual "scale" ballast. 

For other scales the material would be even smaller, quarrys do not make smaller material on a production basis. You would have to make custom stuff on your own. Which would require buying a appropriate sized sieve to "screen" the proper size. Here is a list of the sieve sizes available. Sieve Table (Sorry for the music, its theirs but this is the best table I could find that was easy to understand).

There is one glaring problem with using material this small, we are outside. And just as you were concerned about drainage, the small material will be difficult to keep in place. My suggestion is go with a little oversized 1/4" and live with the oversized look. 

Sorry for the length of the post but I couldn't explain it in lesser terms.


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