Building a Custom Mailbox

Gonzo’s Rock Mailbox


Note that when I built my mailbox, I could not find a lot of helpful information with material lists, so I had to wing much of it. I hope someone can use my information to help them build something as nice. I used graph paper to draw mine out completely for a list of materials I still made changes.

 ~$600 plus rock covering. Use native rock if you have it and cut the backs off flat to adhere.


·        Home Depot Extra Large Architectural Mailbox Model #950020B-10 - $69.97

·    Order a number plate beforehand. There are people who make these custom on Etsy. We ordered ours here from Jim Grady at 
12-16 cinderblocks depending on curb height
Grout bag               Tube of RTV sealant
       Home Depot ArchitecturalMailbox
·    18, 80lb Bags of Maximizer concrete
             2 Bags Type-N mortar            
      2 Bags Sand
·    Sheet of 15/32ths plywood
       10ft crown molding

        Box of 1.5” Deck screws

·     Brad Nailer –for tacking on support strips of scrap wood 
       24 2x8x16 cinder pavers  

     Angle grinder with a segmented diamond-blade cutting wheel on it Water available           Trowel          Shovel    Wheelbarrow to mix in       Reciprocating saw      Level

      Disclaimer: That may or may not be an all inclusive list… Use safety gear like gloves and goggles when grinding, etc


Mailbox opening should be 41-46” high, consider if you are building in residential with a curb that provides additional lift from the street level. Measure from the street. Add or omit one level of cinderblocks to drop 8-inches.

Building an Architectural Base

Using an architectural base as I am calling it (due to the taper edge look), you can eliminate a row of cinderblocks. Is it cost effective? No, but man it sure looks nice. My base took 17 bags of concrete at a weight of 1360 lbs. With a heavy base, the addition of blocks, concrete, rock and a top won’t tend to tilt the box over time.

      1)     Cut two 34” x 20” and two 30” x 20” pieces of plywood. Use a heavier plywood that will standup against the weight of concrete.

       2)     Pre drill three holes down each 20” edge of the 30” pieces, top, bottom and center. Align with edge of 34” pieces and predrill in the edges, this will prevent splitting the wood.

       3)     Using wood screws, secure the pieces into a box shape.

       4)     Cut  crown molding to fit around the top edge of your box. There are lots of you-tube videos that show the best way to cut molding, I like flipping it upside-down and just making a 45* cut.

       5)     Tack the molding around the top edge with your brad-nailer. Your box should now resemble the image shown below.

       6)     Using scrap wood, brad nail pieces across the corners to reinforce and align the molding.

       7)     Smear RTV sealant to seal the corners and along the bottom edges of the molding. 

Dig a Hole and Cement the Base

1)     Your Architectural Base will sit 8” above ground and 12” below. Dig a hole 12” deep in the size of the outside dimensions of your box.

2)     Measure the box above ground to get a feel for how far down you’ve dug. Once deep enough, set the box inside the hole squared with the street direction. Use a level to make sure the box is level front to back and side to side and diagonally. Pack dirt along the inside edge to keep concrete from seeping underneath.

3)     Pack dirt back around the form to keep it in place and stop the plywood from bowing.

4)     Start mixing your maximizer concrete in the wheel barrow. Make it a bit wetter so it will be easier to get air pockets out of it. Be ready to mix and shovel and mix and shovel until this form is filled to the top edge of the crown molding. As you fill each layer, use a reciprocating saw with out a blade installed up against the edges of the box to vibrate the air pockets up. Once full, screed the concrete across the top of the moulding using a short 2x4 until it is level. Keep working the air pockets out. Let set at least a day.

5)     Rinse your tools and wheel barrow out.

6)     Dig the form out and undo the screws you can reach. I worked the loose form up using a shovel.  To be honest, I didn’t use the reciprocating saw method but wish I knew about it when I built this. My neighbor told me about it after the unveiling of the base. But it looks cool none-the-less. I smeared it with mortar and used a piece of crown molding to reshape the bubbled damage.

Building of the Tower

Your base is finished, neighbors are watching and intrigued, lets give em something to talk about. Determine first how many levels you will need to get the bottom of the mailbox to around 40”. I have no curb, used the 8” rise of the base and 4 levels of cinderblocks (12 blocks).

      1)     Set 3 cinderblocks on the base. Two side-by side (16” wide total) and one across the back (24” deep total). With the width of the new 14-inch wide mailbox, we will need to add two inches to build up around the metal box. (16 - 14 = 2” to split around the box). Stack a 2 x 8 x 16 on its side against the conderblock. Now you can measure and center your tower on the base. 

      2)     Chalk a mark around this stack, remove the 2 x 8 x 16 and chalk the side of the cinderblock you couldn’t get to. This is to help mark where to set the mortar and blocks back.

      3)     Ready to stack? Mix the Type-N mortar and sand (2 parts sand, one part Mortar) to a workable consistency. Working up a little at a time will help keep it from drying up on you. I continually add water to keep it pliable until I am finished.

      4)     Using a trowel, plop mortar inside the edge around your chalk mark and across the center if your cinderblock has a center ridge. Tap the cinderblock down into the mortar using the trowel handle or a light mallet. Mud the side of the next cinderblock that will rest against the first and tamp it down to the base and against the first block. Scrape away excess mortar as you go.

      5)     Repeat step 4 for the rear block across the back of the front two side-by-side blocks.

      6)     Move to the next level reversing the pattern. Side-by-sides in the back and cross ways across the front.

      7)     Once you have reached your top level, start working the pavers up the side. Consider the following patterns for different heights, with or without the base 8”, or curb. Note that you will need to cut blocks in half for 3 or 5 level stacks.

Mounting the Mailbox

      1)     First, remove the flag from the mailbox. It cannot be used in this position. On most brick mailboxes, postmen will check for outgoing mail in them if there is no flag. But I will cover an ingenious (if I do say so myself) way to attach the flag later.

      2)     Center the mailbox onto the cinderblock and pull it out over the front edge. You will need to leave enough room for the door and hinges to swing open and not have the rock impede its progress. About 2” should do depending on the thickness of your rock. See where the box can line up in the cinderblock edges. Drill a couple holes in the bottom of the mailbox here and mark the cinderblocks for drilling.

      3)     Using a masonry bit, drill out the two holes in the cinderblock to align with the mailbox hole. Plop some mud under the box and set it in place and screw it down using 3/16ths masonry screws.

       4)     With the mailbox mounted, use the 2 x 8 pavers to built up around the mailbox. Three upright or two laying down and one upright as illustrated. Mud and stack em.


There will be two pavers across the back and one side paver that will need to be cut down to make the corners meet.


       6)     There is the gap above the mailbox in front. Use a pencil to trace the shape of the mailbox onto a paver that will fit into this space. Using the grinder, cut the arch on both sides and cut slits up the center for reliefs to break away at the excess pieces. Mud and put into place

       7)     The next three pavers are put across the top to cover the box. Before I did this I plopped some mud between the mailbox and the pavers to firm it up. The paver caps will straddle the uprights about an inch on each side. Note the short gap in pictures above.

       8)     Let this sit a day so the neighbors will balk at such an eyesore. Perhaps, if yours was as bad as my previous mailbox, it might be an improvement. Mine had been hit with a bat a few times and now help in place using duct tape. Your mailbox is now usable. Congrats. Have some rock to attach to it? Lets continue.

Rocking the Mailbox

So you wanna be a box rocker…. Lets do it. I had excess faux Austin stone from my last house. Now living in Arkansas, the Austin stone is kind of out of place, but looks so good. I watch people slow down to drink in its beauty as they pass by. Attaching rock is an artsy kind of project. The only thing to watch for is:

·        Keeping a small gap between the pieces if you are going top grout it

·        Get that first row straight and level

·        Avoid running a seam all the way up if you can. Changing sizes and patterns help break the seams up. I didn’t have any corner pieces so I do have corner seams

·        Keep the mud workable. It should be moist enough to suck and hold the rock onto the cinderblock, but not too wet it wont hold.

       1)     Mix mortar (Type-N again with sand). Start at the bottom and work your way up, changing sizes and patterns to best mix up the seams. Use the grinder to cut pieces to fit. Apply mud to stone and press into place. Hold it for several seconds and slowly release.


2) You will again need to cut an arch around the mailbox inevitably. I used a large piece here but it may have been easier and more pleasing to the eye to use smaller pieces around the mailbox.

Now your neighbors see what you were seeing in your head when you started this fiasco on their street and may be getting envious. But there’s more to do. This mailbox needs, nay begs for a custom mailbox cap. Get your saw and plywood back out because we need to make a new form.

Build a Mailbox Cap Form

       1)     Cut four strips of 2.5” plywood, a table saw is your friend here. Two pieces need to be 23” long and two pieces need to be 29” long.

       2)     Using your deck screws and drill bits, predrill the edges of the 23” boards into the 29” boards to form your rectangle box and screw them together.

       3)     Bevel cut two triangle pieces 29” long at the bottom edge with an 8* bevel. Side cuts should be 18.45” also with an 8* bevel.

       4)     Bevel cut two triangle pieces 22” long at the bottom edge with an 8* bevel. Side cuts should be 18.45” also with an 8* bevel.

       5)     Wedge all four pieces into your form upside down, slide down to the edge and drill/screw into place.

       6)     RTV seams. I also used duct tape on the outside to ensure no spills. Allow to dry 8 hours.

Mailbox Flag Install

      1)     Using the flag off the mailbox, drill out the studs using a larger drill bit but don’t drill all the way through, just enough to remove the studs and leave a beveled hole to inset the countersunk screws and allow the flag to pass over without interference.

      2)     Use two wall anchors and two 2” wood screws to set the bracket on the edge of the cap form. 
      3)   Drill trough the form and install the screws from the outside, with the anchors on the inside about ¼” in from the wood edge. This will ensure that the anchor is well cemented in place.

         3)     Set up the form on a level surface, raising it using 2 x 4s to clear the peak.

       4)     Mix maximizer concrete and shovel into form, using reciprocating saw without a blade to vibrate the air pockets out. My estimates are 150 lbs of concrete used. Screed the top using a 2 x 4.

       5)     Let is sit 24 hours.

       6)     Unscrew the 2” screws from the anchors.

       7)     Unscrew the form and remove it from your new cap. Don’t worry if its not perfect. It just adds to the rugged good looks of it all. Rub or sand any excess RTV off.

      8)     Check the level on the top of your tower before beginning. If its visually off, you can give it the appearance of level by placing stones under the cap corners to make the cap sit level.

      9)     Mix more Type-N and sand and plop on top of the tower.

      10)  Get help to lift and set the cap onto the tower after mud applied to top of tower. Ensure that your flag corner is facing the street before setting it in place!! Guess what, I get to drill two more holes for my flag in the proper location. Well, these two molded screw holes will be used to mount a solar panel that will run rope lights under the cap!
      10) Use two 1.5" countersunk screws to attach the flag to the cap.

I Am Grout

      1)     Mix up Type-N and Sand into a wet mixture.

      2)     Fill a grout bag and start squirting that mess into all the seams, jockeying it in and out as you go. You will most likely need to cut the opening up a bit from how it comes from the store. It is hand tiring work. Wear gloves so your hands don’t dry out from all the concrete mess. This is where you take care of any visual discrepancies. It all comes together at this point. Wipe away any spills and pack as mush grout in as you can. You will clean it up later and make it look nice. It needs to set up 20 minutes or so depending on wetness and heat outside. 

      3)     With all the blobby looking cement setting up, you can use a wire brush to sand away and shape it. I waited a day and it was too hard at that point, but the angle grinder and rock cutter wheel on it made short work of shaping the mortar.

      4)     Finale’. I adorned mine with bronze stars my wife picked up. Drilled 3/16ths holes through the rock and cinderblock to put concrete screws in. then I mixed some JB Weld and filled in the screws so a screwdriver cant be used to remove them.  We just love this new mailbox.

Night Lights

I ordered a solar charged string light from Amazon for $9 and did one wrap around the box just under the cap. I clipped off the extra lights not needed. First night I got up and these were still bright at 5 in the morning.

Amazon Fairy Lights

Here is the Mailbox lit up for all to see.

Flippin Gonzo's Blog Page


  1. So much detail anyone should be able to follow this and make their own! Great job! That mailbox looks SOOOO good!!!


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