A large section of my new railroad is built on a slope. The track work is installed on a PVC ladder system and its time to start building up earth and rock around it. I plan on using plenty of rock since it should create some dramatic scenes. It can accommodate a number of formations ranging from small, maybe no more than 8-12” high, some in the 24” range, and at least one opportunity for a really large formation possibly as high as 7 feet. I’ve seen some spectacular rock work on these forums (Ray Dunakin’s RR comes to mind) and I would like to pose a few questions to you guys that have “been there and done that” with rock. In no particular order:
When is it advisable to mortar in the rocks verses dry stacking? Is it a question of height, drainage, slope, or aesthetics? If mortaring, how thick do you apply it to the backside of the formation? Do you reinforce it with chicken screen? When working with real rock in various sizes, will it act as a retaining wall or do you install a retaining wall and veneer the rock to it? On taller formations, due you install a sub-base such as crushed 3/4"granite and sand before you begin?
Thanks for your suggestions.
Joe
SoCalJoe When is it advisable to mortar in the rocks verses dry stacking? Is it a question of height, drainage, slope, or aesthetics?
I'll try to answer your questions as best I can. However, I'm not really an "expert" per se. I'm just going on my own experience...
Height: This can be a factor, especially if you're building something tall. I know I feel safer standing beside a large cliff that has been cemented together with mortar.
Slope: The degree of slope is definitely a factor; the steeper you go, the more likely it is that you will need mortar. On steep slopes, and especially "cliffs", mortar will usually be necessary.
Drainage: As I found out recently, even when you can dry-stack rocks in a stable manner, the gaps between them can allow runoff to erode the soil behind the rocks. Of course, my layout has very few live plants, and no ground cover plants, so there's nothing to hold the soil even on a mild slope. Almost everything on my layout is mortared, but if you have a lot of plants to hold the soil in place you would have less need for mortar.
Aesthetics: Dry-stacking leaves a lot of gaps that can be unsightly, especially if you're trying to simulate the look of a natural, sheer cliff. The most carefully stacked rocks will look more like a full size stone wall, than a miniature cliff, if the gaps aren't filled in.
SoCalJoe If mortaring, how thick do you apply it to the backside of the formation? Do you reinforce it with chicken screen?
If mortaring, how thick do you apply it to the backside of the formation? Do you reinforce it with chicken screen?
I mostly apply it between the rocks. But I add concrete coloring pigments to the mortar, to help blend it into the rocks. Getting the exact color to match isn't critical, just get closer but go a shade or two darker. Then, rinse off the excess with a fine spray of water, to minimize how much of the mortar shows.
I do use some behind the rocks, but the quantity varies. In my case, most of the rocks are built onto the existing slope, and are either mortared directly against the (very hard) soil, or against a base of concrete blocks.
Never use chicken wire to reinforce mortar or concrete. It's not strong enough. A better choice is hardware cloth. I don't generally use it when building my mountains, though.
SoCalJoeWhen working with real rock in various sizes, will it act as a retaining wall or do you install a retaining wall and veneer the rock to it?
Depends on the soil. Mine is extremely hard sandy material, formerly a seabed. In some places it is almost as hard as sandstone. It doesn't erode easily and doesn't slump when wet, so it doesn't need much "retaining".
Anyplace where my mountains are built on fill, or where the soil is not quite so hard and stable, I have installed some form of concrete retaining wall and added the rocks over it. Usually I use the special retaining wall blocks that are designed to fit together securely without mortar between them. On the lower end of the layout, where the blocks are only stacked 2-3 feet high, that's how I did it. In other places, I actually put mortar between the blocks for extra strength. When mortaring the blocks together, sometimes I didn't even stack them as designed, but fit them together in a more compact fashion.
SoCalJoeOn taller formations, due you install a sub-base such as crushed 3/4"granite and sand before you begin?
I used smaller gravel, where needed. If I remember correctly, the stuff I used was labeled 3/8" but the larger stuff would probably work too.
Hope this helps. You can check out my construction pages, and the cliff-rebuilding pages, to see some pics of how I did things.
Ray:
Thanks so much for the info! I appreciate you taking the time to answer my questions. I'll try to post some pictiures as I progress. My soil is heavy clay. Although it doesn't erode much, it will swell a bit with moisture and then dry out and crack. I expect the base of my formations will be anchored in the clay so I'll probably use a gravel sub-base as you suggest. Then I'll have quite a bit of fill dirt behind. I'll probably use a variety of techniques, but mortaring has a lot of appeal given the site. Thanks for the tips.
Just FYI about obtaining rocks. Since rocks are not readily obtainable here in my area, I will be purchasing it from a local sand and rock supply retailer. They have several choices which can be purchased in varying sizes (cobble, mini-boulders, and larger rock). I can pick through their inventory and mix sizes so I should get a good variety.
Next up is to finish stripping the ground cover (Red Apple) off the site and scheduling deliveries of rock and fill dirt.
I love this stuff!
Howdy Joe; As Ray stated, I use 27 lbs retaining wall blocks 12”x 8” x 4” that more-less lock together. I’ve had good luck planting Wooly Thyme etc. between the blocks on the top row and letting it trail down the walls. A note of caution, some jurisdictions require walls over certain heights, 4’ in my area, to be engineered. This can also be over come by terracing your 7’ wall into two 3.5’ walls for example.
Good luck, Rob
Thanks Ray. Those are good points to keep in mind. I think my 7' wall will wind up being two terraces with the 1-11/2 feet being rock facade, but not structurally part of the hill.
I ordered 2.5 tons of rock yesterday. It will be delivered next week along with about 5 cubic yards of dirt. My son is home from college so he can help me wheel barrow the dirt into place. I'm looking forward to experimenting with the rock.
I too am a SoCal resident, and if this is an outdoor track then you need to keep wildlife in mind too. Cats, raccoons, coyote's, etc. are or can be a major factor in whether a peak stays up or not. You may find driving some rebar into the soil and through/into the basic mountain will help give you some stability. We also have earthquakes to deal with so making your setup stable can save you all kinds of headaches.
I would echo Ray's comments, with one minor exception. Some times I will use a contrasting color for the mortar and make that psrt a bit thicker than most. After the mortar has set up for about 2 houes I wire brush it to add striations. This gives the look of a different rock strata. Most times I like the look, on those occasions I don't like it, I rip it out and do it over.
Tom Trigg
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