Welcome back to the Trick or Trivia Blog. In this installment, I am going to lightly document the process I used to build the faux tombstone that will be used to hold the Raspberry Pi 7-inch touchscreen. My original plan was to buy a 5-foot tall Frankenstein statue, or some other tall halloween figure. Unfortunately I was unable to find anything locally that fit within my budget of $100 for this segment. After talking to a few friends, and watching several videos on YouTube, I decided to just build my tombstone from 1-inch thick construction foam insulation.


During the planning of this project, I realized I needed to make the tombstone thicker than 1-inch as the foam is quite weak. This led me to search for 2-inch thick foam, and while it exist, it seems to not be sold anywhere in South Carolina. In the end, I wish I would have been able to find the 2-inch thick foam as gluing the sheets together proved to take a lot longer than I anticipated. However, the end result was still quite amazing, and I find myself still wondering how I managed to pull off such a realistic looking tombstone.



The Hardware and Tools Needed




Below you will see a list of the hardware and tools used to build the tombstone that we will use to hold our 7-inch touchscreen. All of these tools and materials can be purchased at your local home improvement store, and most can even be found online. The only thing that is brand specific is the Glidden Gripper primer that is used as a glue. This primer / sealer is what many foam tombstone builders use to glue their models together as it is cheap, dries without exposure to air, and it carves easily.


    • Glidden Gripper Primer / Sealer (Used as glue to glue the foam together.
    • Stone Grey Latex Paint
    • Black Latex Paint
    • 2oz acrylic craft paint White
    • 2oz acrylic craft paint OD Green
    • 2oz acrylic craft paint  Desert Tan
    • Acrylic Caulking
    • Great Stuff Foam In A Can
    • 1-inch Closed Cell Insulation Foam sheet. 4’x8’
    • Xacto  / Hobby Knife
    • Jigsaw with 2” 32TPI blade or 32TPI Hacksaw blade
    • 2x 2-inch Chip Brushes
    • Old Soldering Iron or Wood Burning Iron Kit
    • Popsicle Sticks or Wooden BBQ Skewers
    • 5-inch Prop Skull
    • 1-meter straight-edge
    • Curve Ruler
    • Compass / Circle Ruler
    • Fine Point Sharpie
    • Acetone / Acetone-based fingernail polish remover
    • Hot Glue Gun
    • Stanley Sureform Foam Shaping Rasp



The Design




I chose to go with a mix between a traditional tombstone, and something you might find in a classic B-grade horror flick. After quickly scratching out a general outline on a piece of paper, I sat down in Sketchup and modeled what the tombstone would look like. As you can see, it borrows from traditional, gothic, and horror-movie tombstone designs. The overall height is about 5.5-feet, and places the touchscreen at a height that most children can easily access it.




This design fits entirely from one 4’x8’x1” sheet of pink / green / blue insulation foam from any big-box home improvement store. I do suggest gluing the two main tombstone pieces together before hand and cutting them out once they are dry.




You can download the Sketchup design file for this project which includes 3D models of the finished tombstone, layouts with dimensions, etc, from here. Use this file to get the dimensions you will need for each piece. I simply printed out each design on a normal sheet of paper, and used them to layout each part onto the foam.



The Build





I like to start all of my projects by laying out any tools, components and materials neatly so that I can quickly and easily access them when needed.




With all of the tools and materials laid out, I decided that the easiest thing to do would be to cut the large foam sheet into halves, and then half one of the halves again. This would give me two 2-foot by 4-foot pieces which I could then glue together and set aside while the glue dries.




I do not have a photo of the actual glue application process as it was fairly warm outside, and the Glidden Gripper was drying almost instantly. The basic method I used is exactly the same as you would use when painting a wall. Use a small roller brush to apply a very liberal coat of the Gripper onto one side of one of the sheets of foam. Then place the other sheet on top of the freshly “painted” surface. Align things so that at least two edges align at a right angle.




I knew I would need a way to index the two sheets of foam together, and after searching for toothpicks for about half an hour, I found some craft sticks that would work just fine if I cut a point onto them with my hobby knife. Place one of these sticks in each corner of the foam sheets, and push down until you are sure that both layers have been penetrated.


Now set the laminated foam sheets to the side, placing heavy objects on top of them. This will help apply enough pressure so that the sheets get a good bond when the Glidden Gripper dries. I used two drink coolers filled with water, which applied about 200lbs of pressure.




With the two large pieces drying, let’s move onto cutting out the base of the tombstone. We will need to glue it together as well. As I mentioned earlier, I printed out the design files for each element of this build, and I used a yardstick to transfer the dimensions over.




It is important to remember to pull your measurements from one of the factory-square edges. This will ensure that everything aligns nice and square in the end.




Here you can see one of the major issues with construction insulation foam. It’s built on a tongue and groove design that greatly speeds up installation, and improves its efficiency. This groove is problematic if you plan on using the full 4-foot dimensions of the sheet though. I simply chose to place this piece facing the back so that it is not seen.




With all of the pieces cut out, I dry-stacked them to test for proper fit. As you can see, the foam warped a little, but since this is supposed to be a 100+ year old tombstone, I am ok with the less-than-perfect look. Before I glue things up though, I need to rough the edges up a little so that they look like they have been exposed to the elements for the last century.




To rough the edges I used the Stanely Shureform Foam Rasp. I practiced on a scrap piece of foam and found a stroke that would not rip the foam, but shave it. After about 10-minutes I was quite pleased with the results.




Now it’s time to glue the base layers together. Again using a liberal coating of Glidden Gripper, I  coated each layer, then stacked them together using sharpened popsicle sticks to hold the alignment. Just like the two larger pieces, place this to the side and stack something heavy on top to ensure a proper bond while the glue dries.




With the base out of the way, it’s time to get to work on the cross that will adorn the top of the tombstone. I began transferring the design over, and used a curve ruler to get the clean lines the base of the cross calls for.




As you can see, I goofed my layout a little, but caught the mistake before cutting anything out. Remember to measure once, and cut twice! I used the blue ruler off to the right to draw the circle. I bought it on amazon years ago, and this was the first time I ever used it. I like it because it allows you to quickly draw a circle of any size up to 12” diameter.




I used a hacksaw blade and hobby knife to cut the cross out. In hindsight I should have used my jigsaw as it would have turned this 25-minute task into a three-minute job. Here you can see that I have already roughed the edges with the rasp, and shaped the cross a little. Now it’s time to add some faux cracks and surface blemishes.




Using a wood-burning tool, and the rasp, I added several cracks and surface blemishes to the cross. This was actually pretty fun, and I was able to really add some fine detail with the conical tip on the wood-burning tool. The surface blemishes were created by pressing the rasp into the surface and twisting it from side to side while pushing up or down at the same time.




I started painting the cross with the stone grey paint. The surface blemishes along with the cracks proved to make this process a little more difficult as the paint had to be “pushed” into the small crevices. I found that the best method was to sort of stab the paintbrush into the cracks, and “wiggle” it on the surface blemishes.




With the cross painted, I sat it aside and let it dry for about 12 hours before applying a second coat. One thing to be aware of is that latex paint will not dry if the humidity is too high, and if any dew falls on the paint before it dries, the paint will stay wet.


I let the cross, the base, and the main tombstone body dry overnight, and well into the next day. I would estimate that things dried for about 14 hours, and unfortunately the Glidden Gripper had not fully dried by the time I got around to laying out the tombstone body. In hindsight, I would much prefer using something like a non-solvent based contact cement to glue the two sheets together. Glidden Gripper is pretty common for gluing foam together, but in general, you should wait about 48-72 hours before it is fully cured.


I was highly frustrated at this point and I forgot to take photos of the tombstone’s layout on the uncut laminated foam sheet. I used the same method to lay it out as I did everything else. I also cut it out using a jigsaw this time as two sheets proved to be a little too difficult to cut with a hacksaw blade by hand.




I then lined the edges with blue painters tape, masking off between 1.5 and 2-inches. This was part of a failed experiment to use acetone to melt a significant portion of the surface which would create a relief cut look. As I later found out, new insulation foam like this is coated in a solvent-resistive film that prevents things like construction adhesives, spray-paint and other solvent laced things from eating it away. The big blank spot at the top is where the LCD will mount.




Again being frustrated, I failed to take photos of the next process. I decided to use my plunge router to remove the first ¼-inch of the surface where I wanted the acetone to etch away. Unfortunately, even pure acetone had a hard time etching the majority of the surface, but I did notice that large puddles would eat away portions of the foam, leaving these cool craters behind. So with this new found knowledge I dripped puddles of acetone onto the surface and used the rasp to speed up the chemical reaction by etching where I wanted the craters. As you can see, it gave the tombstone a really cool, aged look. I did make sure to hose the tombstone down to help nullify any remaining acetone residue that might have been hiding.




The next morning I set up the wood burning tool again and began creating more faux cracks into the surface of the tombstone. I also took the tool and used it to define the line between the letters, edges, and LCD mounting spot. This made the inside portion really stand out. While it’s not pictured here, I also used the rasp to create more surface blemishes to tie in the tombstone body to the cross.


Before I get to the next part, I want to show you how I prepped the small 5-inch prop skull to be mounted onto the tombstone.




The skull was purchased at Target for about $3, and was the perfect size for a tombstone of this size. I wanted a foam skull, but unfortunately almost every skull you find in the USA is blow-molded.




Since I needed a way to firmly attach the skull to the tombstone, I decided to fill it with Great Stuff foam in a can. To allow the foam to expand (it expands by 3-4 times the volume used) I cut the back of the skull off, and then created a 1.5” dam with masking tape. This would ensure that the foam rose high enough above the cut line that I could get a good flat cut later on.




Since the skulls jaw is moveable, I taped it shut in the event that the great stuff foam glued it into place.




I then taped the skull to the railing on my homes back deck. This allowed me to use both hands when filling it with foam. In hindsight I should have wrapped this rail in plastic from a trash bag or something. I got lucky and no foam dripped off, but it could have turned into a disaster. Great Stuff literally sticks to anything and everything, and is almost impossible to remove.




Here you can see the foam expanded. I only filled the skull about half way with the wet foam, and once dry, it was significantly larger in volume. I mistakenly thought that it was fully cured here, and cut the top off at the tape line.




What I did not know was that the foam inside that had not been exposed to air was still liquid. After I took this photo I laid the skull in a box and to my surprise it had expanded more overnight and the foam had squirted out of any crack it could find. This process repeated itself three times. I later found out that I could have layered in wet paper towel strips every inch or so of foam. this would allow moisture to wick in and help cure the foam faster.




With the foam skull finally cured, I traced its outline onto the tombstone, and used my router to “hog out” the material by about ¾-inch deep.




Then I used a low-temp hot glue gun to secure the skull to the tombstone. I used this method because when I tried a few other glues, they did not seem to stick well to the Great Stuff foam as it was very porous. Hot glue worked great, and dried almost instantly.




With the skull recessed about ¾-inch into the surface of the tombstone, I used a latex / silicone blend caulking to seal the edges and give it a nice transition to make it appear as if it is part of the stone.




With the skull in place, I could finally begin painting the whole tombstone. Just like the cross, painting in the cracks and surface blemishes proved to be a tough task. I spent two hours making sure that everything was properly coated, and that no pink from the foam was showing.




I apologize for not getting any good shots of the painting process, but it was getting late and I was in a hurry to beat the fast-setting sun. The image above was taken after two coats had been applied, and let dry for about 24 hours.




Now it’s time to paint the base. Much like the tombstone and cross, getting paint into this rough surface was challenging, but after about an hour and two coats later, I managed to get everything covered.




One important thing to mention is that when painting rough surfaces like this, it is paramount that you rotate the piece and check it from every angle. Even after two coats, I still found a few tiny pink spots that I missed.




Once again, I do not have any photos of the finishing process. I took about 30 photos of the dry and wet brushing techniques my Girlfriend and myself used to detail the tombstone, but for some reason I lost all 30 of them and four videos I had recorded as well. There are dozens of videos on YouTube and thousands of tutorials on the web that detail these techniques though, so if you are interested in these processes, search for “dry brush technique” and “wet brushing” or “paint washing technique” on YouTube.


Building this tombstone took way more time than I thought it would. All in all, I think I have about 14 hours into its design and construction, and about $140 in materials, tools, and other things I bought for it. While my budget was only $100, I feel that $140 is a fair number since I got some tools, and enough paint to do another 1-2 of these. The biggest thing is the time it took be to build it. Including the waiting times for things like glue and paint to dry, the project took about 4.5 days to complete, which put me way behind on its posting schedule.


That is going to wrap this installment of Project: Trick or Trivia. Check back in a few days for the next installment, where we finally mate the screen to the tombstone, and permanently mount the candy dispenser mechanism. Until then, remember to Hack The World, and Make Awesome!


Win this Kit and Build-A-Long


  1. Project Introduction

  2. Building The Trivia Interface

  3. Interfacing Ambient and Triggered Audio Events
  4. Building The Candy Dispenser & Servo Coding
  5. Carve Foam Tombstone
  6. October 24th -  Assembly and Testing
  7. October 28th - Project Wrap-up