DIY Manufactured Flagstone

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Introduction: DIY Manufactured Flagstone

About: I've come to make stuff and chew bubble gum...and I'm all out of bubble-oh wait. I found another piece.

During the concept phase of remodeling my backyard I came up with the idea of bordering a stream i was building with flagstones to make a more appealing transition from river rock to gravel. Sort of like a carpet to tile transition in a home. Flagstone is pretty expensive, so if you've looked through any of my other 'ibles you'll know I'm too cheap for that. Since my remodel was going to be over the course of a year or so I figured I would have time to work on faux flagstones and spread the cost out.

Supplies

Tools:

Drill and various drill bits

Saw

Bucket(s)

Shovel/Trowel for mixing concrete

Latex/Rubber Gloves

Materials:

2x3

Plywood

Screws

Clingwrap

Craft Foam

Cardboard

Portland Cement

Medium Sand

Concrete Colorant

Step 1: Mold Construction

The molds are pretty straight forward. I started out with only one to prove my concept. I had some plywood and MDF scraps from other projects and used this as the base of the mold which would eventually be the "top" of the flagstones. Next I cut up random lengths of 2x3 for the mold walls and predrilled some screw holes for securing them to the wood base.

While arranging the mold walls I wanted to come out with a flagstone that was elongated to maximize the length without using too much concrete but also make it look natural and aesthetically pleasing. After my first "rock" was complete I made three different molds. I have a total of 5 different shapes at the end by changing the position of the 2x3 on two of the molds after I had made several of the original.

Step 2: Adding Depth and Detail

I didn't want stones that looked flat or slick like curated slate. Some fancy flagstone for sale looks almost like tile because they take extra care while separating the layers so they get a smooth surface. I didn't want this look. Instead I wanted the surface to look more like a stone you would find naturally with grooves, pits, and a coarse surface. The first attempt was done by layering random cutouts of 1/8" craft foam. This came out really well but still looked a little flat, so for later attempts I started adding random cut outs of cardboard from whatever spare boxes I had laying around. The cardboard mixed with the foam added another level of depth.

The last detail was lining the molds with clingwrap. This served two functions. First, I wanted to reuse the molds possibly dozens of times so I needed to protect them from the moisture of the concrete mix. Second, the tiny folds and wrinkles of the layered clingwrap added more character to the final surface.

Step 3: Mixing the Concrete

So for the concrete mix I went basic with Portland cement, medium sand, water, and colorant. I did this so I could play with the mixtures and give the rocks more sandy textures. They aren't going to be supporting any weight other than the occasional person stepping on them. Since the final strength wasn't as important as the look then I was free to get loose with the ratios until I got something that looked good. My rocks ae supposed to be imitating desert sandstone so I tried various mixtures of colorant. In the end I found that the terra cotta color with a little bit of red gave a good result but it varied depending on the sand/cement mix. Generally I went with 3 parts sand to 2 parts cement with a little more water than needed. This resulted in a pretty grainy mixture.

Step 4: The Artsy Part

After putting the cardboard and foam down I lined the mold with the clingwrap leaving enough extra to fold over the concrete once it was poured. This will help keep the moisture in while curing. The very first rock I made i just began pouring the concrete on top of the clingwrap which worked fine but the result was way too smooth almost to the point of being glossy. The next time I experimented with putting a thin layer of sand down first. This gave the finished product a sandy texture. The rocks were poured in layers to give it a striated look from the sides. I mixed small batches of concrete in a 5 gallon bucket so the variations in color between batches made the different layers stand out but subtly. One thing I also tried was putting a layer of sand between pouring layers of concrete in the hopes that if I wanted to break the rocks they would break in a layers but that didn't really work out. While pouring each layer I also built little sand dams along the sides to give the edges of the rocks more depth instead of just being flat from the forms. The rocks vary in thickness from 1.5" to 2.5". After pouring all the concrete I let them sit without covering for a few hours while the excess moisture puddles evaporate off the top. When they were just barely damp still I folded the extra clingwrap over to help keep them damp while curing.

Step 5: The Reveal

After about a day I was able to demold the rocks. They were cured enough to be solid but still damp enough to work with a little more. After taking them out I unwrapped them and laid them face up. I then put a glove on and rubbed the sand off the top. I did this pretty rough so that I would disturb some of the soft concrete with it. Because the concrete mix was sandy this made the final surface very course. I saved the sand and concrete dust that came off while doing this to use as the top layer for the next casting. Because the loose sand absorbed some of the concrete color it added more color variations to the next rocks. Some of the rocks cured dark, some cured light. I think I got a good mix.

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    28 Comments

    0
    milosrajkoovic
    milosrajkoovic

    5 days ago

    These are really amazing. I love it.

    0
    Angie Denyer
    Angie Denyer

    16 days ago

    These are SENSATIONAL! We have a large property and multiple projects and I have been looking at moulds for paving but even though you can get a set of 5 they still look too perfect and fake. I will definitely be trying these. Thank you for the comprehensive instructions - including things that didn't quite work!

    0
    Nick70587
    Nick70587

    Reply 15 days ago

    The things that don't quite work are the best part, to me. It helps make the next project better. One thing i didn't show was I had made an attempt to further rough up the stones with an angle grinder and a stiff wire wheel after they had completely cured. This was a mistake, as it scarred the concrete with dark marks and didn't look good. Roughing it up by hand when the concrete is still damp after unwrapping it worked much better.

    0
    TD56
    TD56

    Question 17 days ago on Introduction

    If I wanted to make a path to be walked onto how thick would these flagstones have to be and what would you put under them please?

    0
    Nick70587
    Nick70587

    Answer 16 days ago

    Walking path pavers don't have to be very thick if they are supported properly. You could go with 1 3/4" to 2". The ground underneath should be level and compacted. If you plan on putting them on top of gravel I would level and compact the underlying dirt first and then lightly compact the gravel on top of that. Just so there is no wiggle when you put your walking path down.

    0
    TD56
    TD56

    Reply 16 days ago

    OK thank you for your quick reply, I appreciate it. Keep up the great work.

    0
    Billnparker
    Billnparker

    17 days ago on Introduction

    Those look great… I’ve been waiting for someone to show me how. I’ve now got all winter to make a bunch of these. From your pictures, looks great. Tha

    0
    Nick70587
    Nick70587

    Reply 16 days ago

    Thank you. Good luck with yours.

    For years I've used sheet foam and inch or 2 in thick And it cuts really easily with a foam hot knife. I'm an artist and sculptor and I've made a number of sculptures with this method, And they have been on exhibit in different towns in Colorado over the last 10 years or so.

    dancers concrete sculpture.jpg12 Sellers koi pink tree.jpg
    0
    TD56
    TD56

    Reply 17 days ago

    Very nice sculptures.

    0
    Nick70587
    Nick70587

    Reply 17 days ago

    Wow, those are very pretty. Is that foam covered with concrete or plaster, or do you mean you create the shapes with foam as a mold for concrete?

    0
    0194164
    0194164

    17 days ago on Introduction

    My personal favorite project of the whole year! I need classy natural looking pavers baaaaad. Thank you.

    0
    lifewithmykids
    lifewithmykids

    17 days ago

    Amazing job!
    I love rocks and will be trying this in the summer. Thanks for the great details

    0
    Nick70587
    Nick70587

    Reply 17 days ago

    Thank you, and good luck.

    0
    VikkiGreen
    VikkiGreen

    17 days ago

    I am totally sold! As an artist, I see you are also! Thank you for posting this and this is my Spring project for sure! We rent in AZ and have spent a ton of money on landscaping the rental property. I would rather make the rock than spend more money. We live on a Granite shelf and everything here is decomposed granite so it will look great with your flagstone recipe and I have all of the supplies already! Thank you again for sharing your project! GREAT JOB!!!!! You are truly an artist! (Question: Are those 2x3" or 1x3"? The look smaller than 2x3"..I know photos are often deceiving...just checking!)

    0
    Nick70587
    Nick70587

    Reply 17 days ago

    Thank you. They are 2x3.

    0
    johnfredbarry
    johnfredbarry

    17 days ago

    Thanks you your awesome narrative. Describing the evolution of your technique is Clicks for me. Great work

    0
    Nick70587
    Nick70587

    Reply 17 days ago

    Thank you.

    0
    jeanniel1
    jeanniel1

    17 days ago

    Perfect timing - I was about to buy some flagstone and hiccuped at the cost! And I have plenty of cement and time.

    0
    dchall8
    dchall8

    Question 4 weeks ago

    Nick, DUDE! I've seen a lot of faux rocks, and these are beautiful! You solved the edge problem, the surface 3-d problem, and you solved the surface roughness problem. Great job!
    I saw you poured small batches, and you made your own sand and cement batches, but about how much cement did you use per stone? A bag? Less? I'm thinking of going with 18x24-inch rectangular stones, and really like the cardboard and foam effects.