Hell all!
I am about to begin modeling the urban part of my layout and wanted to know what is the best way to create the sidewalks in N Scale. If I use sheets of Styerene how thick should it be? If I use plaster, what can I use to get the right height for the side walks.
Thanks,
Sherman
[:)]
Ordinarily, a 6" curb height is prescribed, but this can vary depending on how new the sidewalk is. When a street is first laid, the curb might be 7" to 8" tall, to allow for future repaving. Over time, the street will be paved anew with more and more asphalt, building up to the point that the curb becomes almost level with the street. This would be particularly true on a street that was originally cobbles or come other paving (even concrete slabs); asphalt would have been poured directly over it.
In N scale, 6" is not very tall, and as I’ve just explained it is not critical to get it exactly 6" above the road surface. Half a millimeter, or about 1/32" (0.030" +/-) would be right. Remember to scribe in control joints at regular intervals (every 3’ to 4’); these are force the concrete to crack in the right places, so it doesn’t look unsightly. A sidewalk might still crack, though, if the ground beneath it is disturbed somehow, such as by a tree root that lifts the walk out of the ground. Plus, portions of a walk might be re-cast when they are repaired, or when they are taken up in order to access a water main, and end up being a different color or texture. Be sure to include some details like these, for variety.
You don’t mention what era you are modeling, which would be helpful to know. As mentioned above a 6" thickness is now standard. In the past sidewalks as thin as 2" of concrete were common. In the relatively ‘tiny’ scale you are using I’d suggest you trust your eye for suitability. If you decide on styrene thicker would likely result in less warping due to shrinkage in the substrate and heat deformation.
Avondale’s ideas on heaving and crackage were very insightful…I intend to make use of them. Scribing the prototype 3 to 4 foot crackage lines may look a bit too close. As always in scale perspective work “If it looks right it is right”.
Randy
As a highway designer, sidewalks (at least here in the MIlwaukee area) are generally 5 inches thick. The typical walk width is 5 feet, with a joint troweled in the new walk every 5 feet. A contraction joint is generally placed every 100 feet. The difference is that the trowelled joint is about an inch deep, and the construction joint is all the way through and there is a 1" thick felt material placed here. This is to allow for the concrete to expand and contract with the temperature. Yes, concrete and steel expand just like any other material. The reason for the five foot joints is as explained by other readers, that is to control cracking. The darn stuff cracks wherever it wants to, and we try to "encourage " the locations. This sometinmes doesn’t work, and it cracks where you least expect it (usually a foot away from a joint). The walk is then sawd out and replaced. The replacement is never the exact color as the original, so you may want to vary the color of a few pieces. Roots and frost will over time crack a few more, so these are replaced as needed.
You can scribe the joints as noted by others, with every 20th (100’ spacing) painted black to represent the felt. Also, if your walk is abutting the curb, felt is placed here also, so a thin black line between the back of the curb and the walk would be prototypical. As mentioned by others, the 1/32 thickness is about right, although since you will be viewing this from above, you could cheat with thicker material, as there is a concern about scribing right through the thin plastic. Hope this helps, have fun modeling!
Thanks everyone for the help.
Construction will now begin. I will post pics. if any one wants to see them. I will supply the site later.