A basking platform is the most essential part of an aquatic turtle's aquarium, yet there are very few basking platforms specifically made for turtles. The platforms on the market are mostly floating platforms which work for small to medium sized turtles, yet the largest ones made are ugly, expensive, and hardly work for large turtles.To tackle this I created a large turtle dock for my own yellow bellied slider.The main design is similar to creating a 3d aquarium background, but it is free standing. This dock is sturdy and since it is covered in hydraulic cement, it will last forever and yet still float if you use densely packed foam as the base. The turtle dock made in this instructable is intended for large aquariums as it is 4 feet wide and 18 inches wide, but you can adjust the measurements and the 3d model to make a larger or smaller one.

Supplies

High density foam sheet(s) (insulation panels work great and are dirt cheap. I had to use two 4ft by 8ft panels
Quirkette Hydraulic Cement IT MUST BE QUIERKETTE brand hydraulic cement, as it has been used by many aquarists and deemed safe. I used almost three 10 lb buckets, so if your making something bigger, buy the 40 lb bucket.
Measuring tape and/or ruler
Wooden skewers
Toothpicks
Serrated knife/ laser cutter if you have access to one
Cheap disposable paintbrushes ( they will get ruined after this)
Marking pen
Wire cutters
Cement pigment ( I used quirkette brown pigment)
Half pallet/ table (it may get stained be careful! )
Dropcloths/ old cardboard
Sanding sponge (use a very course grit like 36)
Water cups (disposable kind)
Disposable medicine measuring cup ( or anything to measure the amount of pigment)
Fusion 360 (free 3d modeling software)
Slicer for Fusion 360 (also free)
Respirator
2 Disposable buckets (one for mixing, another for water)
Wooden paint stick/ piece of wood for mixing cement
Nitrilite gloves
Protective eyewear

Step 1: Creating Your 3d Model

To properly sculpt the design you want, it's a good idea to find a 3d model or even create one. I will post a link to 3d model I designed, but feel free to browse sites like Thingaverse.com to look for other models. You can even create your own model for free at tinkercad.com.

Once you find a model you like, download the model as a .STL file.

3d Model:

turtle dock 3d model

Step 2: Slicer for Fusion 360

After creating your 3d model, you have to download a free 3d model software called Fusion 360. Don't worry, this software has a free trial . After creating a autodesk account and installing fusion 360, you will also have to download slicer for fusion 360. Fusion 360 is a more advanced version of tinkercad, and the application slicer will essentially cut your model into layers that you can follow and stack up to create the dock.

How to use Slicer

Open slicer up and import your model ( you model must be an STL. file in order to do this).
Rotate the model to its proper positon if needed.
Make sure that your 3d model is in the proper unit you measured when using slicer.
Use foam for manufacutured settings.

Select stacked slices and make sure dowels is selected.
You can type in the desired length, width and height, but slicer will automatically adjust it for the 3d model. To counter this, use tools like shrink wrap.
Make sure that your 3d model is in the proper unit you measured when using slicer.
View the slices by clicking on assembly steps. If you are cutting by hand use the assembly steps to guide you;slicer automatically generates a mini animation on how to stack each layer if you click on the timeline at the bottom.
If you are lucky enough to use a laser cutter, click on get plan and save the file as dxf. Then use your laser cutter to cut out the slices.
Save the plan itself by moving the mouse over the slicer logo and click save.

download Fusion 360

download Slicer for Fusion 360

Step 3: Stacking and Stabbing

Once all of the layers have been cut out, open up the plan again in slicer and use the assembly steps as a guide on to how to stack them. Slicer automatically generates a mini animation on how to stack each layer if you click on the timeline at the bottom.
If you used a laser cutter, it should have etched some guidelines to help assemble the layers, just match the edge of the upper layer to the engraving on the bottom layer.
Use wooden skewers to nail the layers together. If you selected the dowels option in slicer, then the laser cutter should have left a few holes to put some dowels in.
Use toothpicks for smaller pieces.
You may have to use a mallet to nail the skewers in, depending on the thickness of the layers and the size of the project. Carefully tap the skewers in to prevent the foam from cracking.
If you used a laser cutter, it should have etched some guidelines to help assemble the layers, just match the edge of the upper layer to the engraving on the bottom layer.

Step 4: Sculpting and Sanding With Concrete

Now this is the part you have been waiting for, the concrete. The hydraulic cement acts as sealant and provides a more porous surface for your turtle to climb on. Always follow the preparation labels and make sure to wear proper attire when mixing the cement.

You must wear protective eye wear, a respirator and nitrilite gloves. Work in a well ventilated area/ outdoors
Please note that the warmer it is outside, the faster the hydraulic cement will harden. I made the terrible mistake of working with this stuff in 90 degree weather and it was hardening before I could even properly shape it.
When mixing the cement, use a stirring stick to prevent the gloves from tearing, and wear clothes that you are not fond of.

Place disposable cloths/ some king of lining underneath the area you are working on. Trust me this stuff gets everywhere! Then place your pallet ( a half pallet works perfect as well) on top.
Carefully open the cement mix and pour some into a mixing bucket, then use a cup to pour cool water into the mixing bucket. For quirkette, mix 4 parts concrete mix to 1 part water to get a putty like consistency. Use this measurement when you need to sculpt ramps and to make a smooth ramp/ side. Then for the rest of the areas add a little more water to create a thinner layer to paint the concrete on.
Mix a small amount of cement at a time so that the cement does not cure in the bucket while your working on your turtle dock.
Use a small foam piece to practice putting concrete on. save this piece for the next step.
For the first layer, you do not have to add any pigment, just make sure to cover every nook and cranny. wait a few hours to ensure that the cement has cured and then flip the dock over to cover the other side.
Use any spare cement to add pigment to and apply on the test piece, start with a little bit of pigment and create a line with it, try different concentrations to find the color you like and write down the concentrations below the test lines.
Next wait another few hours ( or overnight) and then sand any rough areas and pick away any weak/ cracked areas if they appeared. Be careful not to sand too much, or else you will have to cover that area again.

Step 5: Painting With Concrete

After adding your base layer, you can now paint the dock with cement pigment. Remember to wear gloves, protective eye wear and a respirator when painting.

Create a thin layer of cement by using a the regular measurement and slowly add more water while stirring until you get a thick paint like consistency. Then use the test piece to find the concentration of pigment you need to make for the color you like. I used 10 ml of quirkette's brown pigment to create that red/brown color.
Use disposable brushes to paint. I recommend using some cheap chip paintbrushes as these brushes will get ruined in the end.
You may have to go over a spot multiple times while changing the direction of the brushstroke to fully cover the area.
Use any stiffer pieces of cement to plug any stubborn holes that the paint can't get into of to smooth an area.
If the concrete is getting too thick or stiff add a little more cold water and mix until it gets thin again.
Wait a few hours before fliping the dock over to paint the other side to ensure the paint has fully dried.

Step 6: Soaking It All In

The final steps are to rinse and soak the dock after it has cured overnight. Rinsing insures that any leftover pigment or dust will not leech into your aquarium. You can either by a pH testing kit or bring a water sample to a pet store like petsmart and they can test the water for you.

Rinse the fully cured turtle dock with water.
Soak the turtle dock for 24 hours.
Test the pH of the water. At first the concrete may change the pH to basic; if this occurs dump out the water and bath the turtle dock for another 24 hours.
Test the pH again. If the pH is zero then feel free to put the turtle dock into the aquarium. If the pH is still too basic then repeat step 3 until the pH reaches zero.