REVERSE MOSAIC TABLETOP

 Reverse Mosaic Tabletop  

This is a fun easy project that gives pleasing results and helps to give new life to discarded items. My neighbor gave me a triangular rebar stand he was going to throw out.  As he was handing it to me over the fence, I thought that it would make a great stand for a small garden table, but what to use for the decorative tabletop?  Answer:  A cast reverse mosaic slab of concrete!

 What You Need:

2-inch insulation foam 

Hand saw

3-inch box nails

marker

Assorted colored glass, shells, marbles…anything you want to use for your tabletop mosaic as long as it is reasonably flat.

Vegetable oil and a brush

Bag of sand topping concrete mix

Cement trowel and plastic mixing bowl

Urethane glue, if necessary

Natural colored sanded grout, if necessary

 

What You Do:

 

1.    To make a slab of any shape, make a mold using a sheet of pink or blue insulation foam from the home improvement store. It cuts easily with a hand saw and goes together with simple long nails.

 

2.    Decide what shape you would like for your tabletop; circle, square, free form, etc. Draw the shape on the sheet of insulation foam using the marker. Draw the same shape 2 inches larger all around.  Cut out the outside shape first using the hand saw and then cut out the inside shape, so you have a 2-inch-thick frame.  Use nails to attach to a base piece of foam.  This is the mold for your tabletop.  Brush it with vegetable oil as if you were oiling a cake pan. 

     

3.    This technique is called “reverse mosaic” because the mosaic elements are placed into the mold first and facedown, so you see the bottom sides. Cover the bottom surface of the mold with mosaic elements, staying at least ¼” from every edge. 

4.    Mix a manageable volume of sand mix with water to a consistency of thick frosting using the trowel and plastic mixing bowl.

 

5.    Be careful to add water sparingly, it is easy to add too much.

 

6.    Gently scoop mixed concrete over the surface of your mosaic pieces making certain to completely cover them.  Use the trowel to press the concrete over everything until the surface is smooth.   You can tap or bounce the mold to settle the concrete. 

7.     Mix up more concrete until the mold is completely full.  Smooth off the top with the trowel.

 

8.    Usually, you can wait for the mold to set overnight and take out the casting, BUT…don’t do that.  Because we want to be certain the mosaic pieces are firmly embedded in the surface of the tabletop, let the mold sit untouched for three days.  The cast concrete will be significantly stronger, and then you can easily remove the tabletop from the mol with less chance of losing pieces. Use gloved hands to smooth the edges.

 

9.    If some mosaic pieces come free, replace them using urethane glue.

             (Goop or E6000).  

 

10. If there are gaps around some of the mosaic pieces because the concrete did not make it around them, you can mix a small amount of sanded grout and fill the gaps.

 

11. Position whatever you are using for your base and then add your new tabletop!