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Construction Site Play Set

This is a post about a play set I made for my (then) 3 year old son. He loves construction trucks and playing in the sand and dirt. I looked around for construction-site themed play sets but I really couldn't find anything available. There are lots of figures and truck sets but nothing that consisted of an entire play set. So I figured I am a crafty guy...perhaps I could make one?
The idea came when my wife would typically set out a baking pan full of rice, flour, peas, noodles or other food items for my son to "run his trucks through". Obviously this proved to be quite a mess. So I thought why not make something contained, movable and at the appropriate height for him to use in a more permanent way. And as an added bonus, keep the house clean!
So I'll begin making some posts describing my journey (over the coarse of a year!) to make this play set. But for now, here is a photo of the finished project.It was a lot of fun to make. If your interested I'll be making additional posts about how I put this crazy thing together.
Play Set Construction 
Over a year ago or so (actually I think around October'07) I had the idea that I wanted to make some kind of rugged construction site related play set. Having constructed a Model Railroad before I knew how to do the terrain and scenery it would require but it would be way too fragile for the abuse it would receive by a 3-year old. So something much more rugged and 'child-proof' was needed. What I needed was some kind of play set (probably plastic) which he could run trucks and cars through. The terrain should have lots of outcroppings and rock faces. I looked around but just couldn't find anything quite like that.
So one time while I was at the iHobby Expo show in Rosemont I visited the Alumilite Booth and they had a new product which would fit my needs perfectly (but we'll get to that later). Anyway with that I was finally able to realize what I had in mind. So I began to construct the play set.
Making the Play Set Box
The first step required making a box. The play set portion (or insert as I call it) consists of a box filled with pink insulating foam and covered with a urethane resin creating a hard outer shell.
Here's how I went about creating the play set insert. First thing was to create a simple box. The box itself is 2' x 3' x 5" high. I used 1/8" Masonite cut into 5" wide strips for the sides and reinforced in the corners with 2" x 2" lumber like shown on the right. The box could be made out of anything but these are the materials I had on hand.
Next I filled the box with a few layers of 1-1/2" thick pink insulating foam and laid out the basic scene. After that I cut out sections making different levels to resemble the sides of a quarry or strip mine. Just anything which might look like a construction area site was fine. I also filled in some of the edges with a paper mache product called Mu-Cla. It takes a while to harden but is very easy to "mush" into place and soften some of the edges. Mu-Cla is a product used frequently to form rock surfaces and terrain. I wanted to experiment with this product for a while so I decided this might be a good time to use it. So I tried it out. I worked out pretty good. The picture on the left looks like a mess but with enough imagination you can kind of see where this is going.
So this is all fine and good, but it's still foam and paper mache in a box. Big deal. Any kid would tear it apart in 5 seconds flat. Plus it doesn't look very good. So this is where the Polyurethane Resin comes in.
Making the Terrain and Rocks
As mentioned earlier the Alumilite Corporation make a very cool (well, actually very HOT) 2-part resin called "Skin Coat - Rigid". You simply mix Part A and B equally and you have about a minute or so to spread it on. Its probably not the best thing to do, but I just wore latex gloves and just smeared it on everywhere. Be careful though. The stuff gets pretty hot due to the exothermic reaction caused by the two parts combining. But it was kind of fun to just make a mess of it all.
You'll also notice from the photo's a bunch of rock castings. To make the castings I once again used another Alumilite product call "2-part Liquid Plastic". This stuff is what you'll find in most hobby stores. The rock molds I used are from Woodland Scenics. I just mixed and poured in the 2-part Liquid Casting Plastic into the molds and waited. A few minutes later I had perfect rock castings. This liquid plastic stuff is excellent for making reproductions of just about anything.
Now back to the terrain. As you can see from the photos, you just mix the 2-part Urethane and spread it everywhere you can until the entire thing is covered. I had to do this in about 4-5 passes since I couldn't spread as much as I could make in one batch. But that's not a problem. It sets up pretty quick. I think I used two bottles of the stuff all together. While I was spreading the Urethane I also embedded the rock castings randomly wherever they seemed to fit. I just kind of took the castings I had an pressed them into the Urethane where ever I could.
I also tried embedding some truck tracks into the Polyurethane before it had a chance to set. This gave a permanent impression of big construction truck crawler tracks which looked cool. I also occasionally sprinkled small amounts of play-sand into the 'wet' Polyurethane before it set. This gave the terrain a rough, gravel type texture. This is similar to what Model Railroad folks do to make terrain textures. A common technique is to sprinkle ground foam onto wet paint for the same effect.
Finally to kind of smooth the transitions between the rock castings and the terrain I filled in the gaps with Tile Grout. Probably overkill but it was easy to work with and left a real gritty texture on the surface so I think it worked out pretty well. Again I just simply scooped out the Tile Grout and applied in around the rock castings making a point to cover any gaps. Wearing latex gloves I just smoothed and pushed the ground all around the edges as shown in the photo on the right. After the group was applied and obviously the Urethane too, I noticed a lot of brittle sharp edges throughout the landscape. These obviously would cause problems with a small child's fingers getting caught on them and possibly cutting themselves. So I took my Dremel tool with a right angle attachment and small sanding drum and went around the entire play set and ground down those edges. This further helped to blend in the rocks and base together.
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Tile grout used to fill in gaps between rock outcroppings and the terrain.
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Rocks shown here with tile grout applied and blended with terrain.
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A Dremel tool was used to grind down and smooth sharp edges.
Finishing and Weathering The Play Set
OK, now with everything covered with urethane, rocks added, gaps filled with tile grout and everything filed down smooth it was ready to paint. I wanted to first give the entire play set a base of tan or brown to represent the color one might see at a typical construction site. So I first washed the play set very well with warm water and soap. Then I spray painted the entire play set with automobile primer. After the primer I painted the play set with Rustoleum American Accents Satin Soft Wheat spray paint. Once the final coat of spray paint was applied the play set was really starting to look very realistic.  
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American Accents Satin 'Soft Wheat' spray paint.
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Primed and ready for painting.
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Completely top coated with spray paint.
Once the entire set of painted I felt it looked pretty good, but it could use some accents or highlights to emphasize the rocks and some weathering one might see. The mono-tone color of the play set just didn't seem to make the terrain stick out very much. So I borrow some techniques from doing Model Railroad scenery and began highlighting the rocks. I painted a light grey color on the surface of all exposed rock outcroppings. I also added some burnt umber and some subtle shades of various brown, tan and red acrylic pains I had lying around. I really didn't have much rhyme or reason to what I was doing. Just kind of used a thick brush, dabbed it in what ever color looked good and stippled it onto the play set surface. Kind of half dry brush technique and stippling. Once that was dry I then high lighted (dry-brushed) the rock surfaces with a white paint. This gave the rock's raised surfaces some depth and helped them stand out from the rest of the surface. Finally I dabbed a small foam brush in a diluted India Ink wash (combination of India Ink and Isopropyl Alcohol) and just coated the whole thing in the stuff. I allowed the wash to run down groves as rest in the valleys. This create a muted effect allowing the colors to blend better and look a bit weathered. It was nice how the wash also settled into the crawler track impressions I made earlier really making the entire play set look dirty, grimy and grungy. Just like it should! Below is a photo of the final result.
The completed play set; painted and weathered.
Wheeled Cart Construction 
The play set insert itself was certainly the most difficult and complex part of the project. However with that done, it was clear I now needed something to put the play set in. Just having the play set box lying on the floor was OK, but something like a table or platform it could sit on or in would be much better. It would need to be an appropriate height for a 3 year old however and also be kind of fun.
With that in mind I decided to build a movable wheeled car in the basic shape of a construction truck. Inside the truck then would be the play set. My vision was to have it look something like a wooden railway train table or how some of the novelty kids beds look (something like those race car beds we see for kids). So the idea developed into a simple construction vehicle with enough room inside to place the play set at a typical child's "play level".
The construction of the cart was done in two parts. One part was the bottom frame which would hold the axles for wheels and provide the basis for a strong sturdy frame to build around. This part was mainly painted in black. The second part was the upper vehicle shell which was mainly in place to contain the play set and give the cosmetic appearance of a typical construction vehicle. This part is mainly painted in yellow. So all together the entire construction site play set consists of 3 major parts; The bottom frame (black), sandwiched on top by the top vehicle shell (yellow) and of coarse the play set insert which would see all the action.
Constructing the Bottom Frame
So starting with the bottom frame, the construction was pretty basic. Since the vehicle shell would be the support for the play-set (inside it) as well as contain the bottom frame underneath it, the outside dimensions of the bottom frame needed to be the same as the play set itself. So I constructed a 3/4" plywood frame which was 24" x 36" using ripped plywood strips which were 6" wide. I simply butt jointed the frame together and reinforced the corners with 2" x 2" x 6" long posts. I used wood screws and glue to fasten it all together. The 6" 2x2 posts helped keep things square, but I verified corner to corner the frame was square.
Next I added 1x4 reinforcements across the 24" width for support in the middle of the frame. These were spaced out inside the frame to actually serve as the axle mounts which would come next. Note it was important to recess the cross supports underneath the frame to eventually accommodate the 2x4 axles. Once the basic frame was put together it was primed with regular latex primer.
Wheels and Axles
The cart obviously needed wheels. I searched around for suitable "truck" wheels which would look realistic but searching for them proved to be quite a challenge. Finally I found a huge lot of 10" diameter tires with hubs and bearings at Harbor Freight. The hubs were white, so I removed the tires and separately spray painted the hubs an obnoxious bright yellow. When they dried I reassembled them and re-inflated the tires.
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Tires found at Harbor Freight for $5ea!
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Hubs disassembled and painted yellow.
The bearing hole in the hub was 5/8" in diameter so I purchased a length of 5/8" CRS rod from the local hardware store and cut those axles to length and ground down the edges. I decided to just have each axle run the width of the cart. It seemed a bit easier to construct this way and would also prove to be more sturdy in design even though it turned out to be quite expensive. To hold the axles in place, I cut two 2 x 4's and dadoed a 5/8" grove down the center of them to snugly hold the axles in place. I used mending plates (2 on each axle) to hold the axle in place after they were inserted. I also carefully drilled a hole at the end of each axle to accommodate a cotter pin which would hold the wheel itself onto the axle.
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Good ole hardware store 5/8" cold rolled steel cut to length for axles.
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Axle mounts cut from 2x4s with a 5/8" dado to accommodate the axle rods. Primed.
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Axle rods installed into painted axle mounts. Axle rods held in place by common steel mending plates.
It's hard to see from the pictures above but I cut a lap joint into each of the 2x4 axle mounts to allow it to be set inside the bottom frame against the cross supports for mounting. This joint really helped the axle mount to fit snugly in the frame and not allow any twisting or unnecessary stress. After priming and painting the frame and axles I bolted them together using 1/4" x 20 bolts. The entire bottom frame was painted with plain old high-gloss black paint.
Constructing The Vehicle Top
Up next was the top part of the vehicle. This would be constructed like a cap that would be placed over the bottom frame. The bottom frame was intended to sit inside the underside of the top piece. The top consisted of yet another frame the thickness of the plywood larger than the play set perimeter. This added a nominal 1-1/2" to both sides but to make sure I could insert and remove the play set easily I added another 1/8" for wiggle room. So the entire outside perimeter of the top is 37-1/2" x 25-1/2".
So to build the top, I started with planks of 1 x 12" pine boards. I cut 2 of them a length of 25-1/2" and another 2 of them 37-1/2" to form the sides. I mitered all the edges 45-degrees so I could assemble it with glued edge joints making the construction more difficult but I think it looks much better since there was no board edges to sand and finish this way. After each of the boards (side panels) were cut to length I then cut a dado 3/4" wide all around the bottom perimeter. This was done to accommodate an inner frame made of 1x4 pine to serve as a kind of inner-shelf or plate for the top to sit on the bottom frame, as well as the play set to sit on top of. Essentially this left the inner shelf sandwiched between the play set insert and the bottom frame. This allowed the three individually constructed pieces to come together very easily.
Before assembling the side panels, I also cut what might be wheel wells into the longer side panels. The wheel wells are the sort of trapezoidal patterns cut in the panel (2 on each side). I also cut a similar pattern on the two shorter panels just to make the shape of the top a little more interesting. Kind of loosely modeling the lines of a construction vehicle. Lastly I also drilled 1/4" holes with 1/2" countersinks to accommodate some black anodized 1/4" x 20 bolts and washers which would be used to fasten the top to the bottom frame. It also served as a nice embellishment from the outside giving it kind of a tough look having some black bold heads visible around the bottom of the side panels.
Lastly, before I put the side panels together I built a inner-frame or shelf which would fit into the dado cut around the perimeter of the side panels. This inner frame was made of 1x4's and constructed using simple butt joints with dowel rods into the ends of each piece. This frame consisted of 8 dowels (2 on each side) requiring 16 holes. My dowel drilling jig came in handy here. Once the glue on the inner frame dried, it was easy to lay it flat and begin gluing and assembling each of the side panels. The inner frame helped keep the side panels in line. I clamped up the whole thing and let it dry. Once everything was dry I had an unpainted vehicle top shell. I checked it for fit by placing it over the bottom frame and everything came out OK. Whew! Measure 8 times, cut once...or at least sand a lot.
Painting and Finishing the Wheeled Cart
With basically all the construction completed, it was time to prime, paint and finish the vehicle. I primed both the bottom frame (as seen above) if basic latex primer. To make this thing really look like a construction vehicle I figured I had two choices; orange & black or yellow & black. The orange just seemed a bit odd and wasn't what I liked. So I decided to go with yellow and black. The bottom frame was painted gloss-black and the top was painted yellow-back. It was as simple as that.
Now I also figured the top part at least would see a lot of wear and tear from kids leaning on, grabbing, ramming cars and what not. So I figured even though the gloss-yellow paint was pretty tough, a few coats of Acrylic might be in order. I used a water based Acrylic finish to cover the entire vehicle top. This gave it a nice shiny and very hard outer coat which hopefully will avoid future paint wear. I later attached the wheels to the axles and inserted a cotter pin to hold them on. The top and bottom were now complete.
Assembling and Decorating the Vehicle
Finally! The fun part. Adding the final touches and decorations to the vehicle top. As I mentioned earlier the black anodized bolts along the bottom edge kind of gave it a sort of "tough" look so I though those looked pretty good. I also added some "grab irons" to the sides. These were actually just simple black painted steel cupboard handles (the "rectangle type") available at Menards (a big box store). I attached shorter ones to the front and the longer ones to the back. I also added two white round reflectors to the front of the vehicle and 2 round red reflectors to the rear of the vehicle. This made it look like there were head lights and tail lights. Lastly I had drawn up and made a vinyl decal for the front grill and applied it. Lastly I had two vinyl lettering signs made up using this Army font I found. I sized it appropriately so that "Sam's Construction Company" could be displayed on each side. After the decals were applied it was ready to go.
My son has spent many hours playing with his "construction site" and always seems to be a popular hit whenever his friends come over to play. You may have also noticed a sand-like substance inside the play set. This is actually Moon Sand which is an awesome product. It clumps and allows kids to make things with it and never dries out. There is a 1 lb bag of the stuff in the play set you see here. A perfect touch for any construction site.