Adding a concrete overlay can add new life to a tile floor that may be worn or out of date, design wise. This can be done at a cost that is lower than it would be to remove and replace the tile.
Step 1 -- Decide Overlay Thickness and Design
You first need to consider how thick your concrete overlay will be. This will determine what will go into your cement mixture. Portland cement and sand mixed with water will suffice for an overlay that will be less than one inch. You need to add gravel if you are doing a thicker overlay. Also, plan out your design that you will be stamping into your concrete forms.
Step 2 -- Mix Concrete
For thin overlays, the rule of thumb for mixing is 2 1/2 parts sand to every 1 part Portland cement. For thick overlays, mix 1 part sand, 2 parts gravel, and 2 part cement. Always add water in gradual amounts. It is better to have too little water than too much. Your finished cement mixture should be about the thickness and consistency of oatmeal. You will also need to mix a thinner bonding slurry of 1 part fine sand and 1 part cement. Combine the 2 dry ingredients first, and then add water in increments. Remember, only mix enough concrete to use within an hour; each batch mixed at different times will also have different curing times.
Step 3 -- Pour in Sections
Use your 4x4 pieces of plywood to create a form block; this is simply a box that will hold the shape of your concrete until it hardens. It works by securing each side together with clamps so that it can be easily taken apart. If you are working with smaller areas, adjust the size of the plywood accordingly. The edges of the form block should be lined up to give clean borders for your concrete overlay. Pour concrete sections one at a time that are approximately 1/10 of the total area of the tile you are working with. It is helpful to measure and calculate this ahead of time.
Step 4 -- Blend Concrete
If you are doing a thick overlay, you need to lay an additional layer to apply over the top of the first layer you just poured. Mix a batch of concrete that contains only fine sand and cement, and then smooth this over the top with your trowel. The underlying concrete should ideally still be as wet as possible for smooth blending, so it is important to mix and pour your overlay quickly. Make sure the surface of your overlay is wet enough, then quickly apply a layer of your cement slurry. Level off the final surface with your 2x4 board, by dragging it evenly across the surface. Allow your finished concrete to cure for 30 minutes.
Step 5 -- Apply Optional Stamped Design
If you are including concrete stamped designs, press them into your concrete after it has set for 30 minutes. This is long enough for it to harden, while still staying damp enough for the stamps to leave a clean impression. Be sure to apply firm pressure when using concrete stamps. Allow the finished concrete to cure and harden for three to four days before walking on it.