Introduction: Recycled Glass Countertop

By Concrete Exchange

This bright blue recycled glass countertop was made as a shipping and packaging table in our Berkeley, CA warehouse.

The countertop contains 75 pounds of recycled blue glass and 50 pounds of Surecrete’s Terrazzo Mix. The color is CHENG’s SmartColor Indigo and the entire project is sealed with Surecrete’s PC-12 Concrete Sealer. The high amount of recycled content would qualify this countertop for LEED credits and only takes a few hours to form and cast.

Step 1: Supporting the Countertop

Before making a concrete countertop, consider how it will be supported. A typical countertop would be installed over kitchen or bath cabinetry and would not require any special supports or bracing.

This project will be installed on a steel frame with no cabinetry beneath to allow storage of large objects under the countertop. The top measures 24” x 91” x 1” thick and weighs about 125 pounds. This top is installed in the CHENG Warehouse and is used for packing and shipping.

Determine the type of countertop support:

  • The support must be flat, level, stable, securely anchored, and strong enough to support a heavy load.

Anchor the support:

  • We anchored our frame securely to the wall studs at the top, middle and bottom.

Step 2: Form Building

This is a basic 1" thick countertop slab that requires very little effort to form. Using our simple foam rail and adhesive forming system we were able to build this entire countertop mold in about an hour.

Tools and Supplies:

Lay out on melamine form base:

  • For this 24" x 91" recycled glass countertop we cut the 3/4" melamine form base to 28" x 95". This allows 2" on each side (4” total) to accommodate for the foam form walls.
  • Mark the form base with a pencil, laying out the 24" x 91" dimensions of the finished countertop.

Cut Form Walls to the Correct Height:

  • The CHENG Foam Form Walls and Liners are available in 2" and 2-1/2" heights. But for this project we need to cut them down to 1".
  • Use a ruler to mark the form walls at 1" high, along the length of foam.
  • Cut the excess foam off the top using a fine hand saw. If you have access to a table saw this can easily be accomplished with precision.
  • It is not necessary to cut the form walls to length before attaching them to the melamine base. They can overlap at the corners.

Attach Form Walls to Form Base:

  • Adhere double stick carpet tape to the bottom of the form walls.
  • Press the form walls onto the base board, making sure they stay straight and true to the penciled layout marks.

Cut Wall Liners:

  • Since the CHENG Pro-Form Wall Liners are more than 2” wide, we'll need to trim them down to 1" for use on this project.
  • Mark and cut them to 1" wide. Use a razor blade or knife to mark them. This will make an easily visible cut line to follow.
  • Trim the 1” form liners to length leaving them a hair short. Any gaps in the corners will be filled with silicone when sealing the mold.

Glue Wall Liners to Form Walls:

  • The wall liners are smooth and glossy on one side, matte on the other. Spray the glossy side of the form liners with spray adhesive. Wait a few minutes.
  • Attach the liners to the form walls, with the factory edge aligned with the top of the form wall. Later you will rely on that straight factory edge to ensure the bottom side of your recycled glass countertop section is uniform and straight.
  • After the form liners are glued in place run a bead of silicone sealant along the top of the form wall to prevent concrete from running between the foam wall sections and the wall liners.

Seal the Form:

  • Sealing the form with a bead of 100% Silicone will make it water tight, and fill any gaps at the corners or between the liner and the form base.
  • Tooling the bead of silicone with Corner and Seam Shaping Tools produces professional-quality rounded edges. Check out the Corner and Seam Shaping Tools Guide to learn more about how we seal the form and create perfect rounded edges.
  • After the form is sealed and the silicone has cured, remove dust and debris with a vacuum or compressed air.
  • Remove silicone residue with denatured alcohol.

Level Form:

  • Level the form before pouring to help maintain an even thickness throughout the casting.

Step 3: Mixing

Mix Supplies and Tools:

Safety:

  • Thick Rubber Gloves
  • Particle Mask

Combine Liquid Modifier and Pigment:

  • Wear a particulate mask and disposable gloves while mixing.
  • Shake the Liquid Modifier well before pouring it into the 15 gallon mixing bucket.
  • Add the entire bag of Indigo Pigment to the bucket of Liquid Modifier.
  • Blend with a paddle mixer to thoroughly blend pigment into modifier.

Add Terrazzo Mix:

  • Add 1/3 bag (16 lbs.) of Terrazzo Mix to pigment and modifier blend.
  • Vigorously mix until all the concrete mixture is thoroughly blended and free of lumps or unmixed material.
  • Occasionally scrape material from the sides of the bucket with a trowel, mixing thoroughly.
  • Continue adding Terrazzo Mix 1/3 bag at a time, repeating the above steps until 1 entire bag of mix has been added and fully blended.
  • As the terrazzo mix is blended into the modifier the mixture becomes thicker; hold the paddle mixer firmly to prevent kick-back.

Add Recycled Bottle Glass Aggregate:

  • Add 25 lbs. of recycled blue glass aggregate into the terrazzo mixture and blend with paddle mixer until all glass is evenly distributed.
  • Always wear a particle mask when working near glass powder or dust.
  • Add another 25 lbs. of the glass aggregate and blend.
  • Add final 25 lbs. of recycled glass aggregate and mix until all glass is evenly distributed throughout the terrazzo concrete mix.

Adjust Mix Consistency:

  • Add 2-3 cups water as necessary to maintain a semi-pourable consistency.

Step 4: Casting

Casting a recycled glass terrazzo mix is very similar to casting ordinary concrete with one notable exception – the aggregate is really sharp. The crushed glass will tear through thin latex gloves so for this casting we’ll use heavy duty rubber gloves for protection.

Materials and Supplies:

Attach Vibrator to Casting Table:

  • The casting table should be protected from weather and direct sunlight, preferably indoors. This is where your countertop will cure overnight.
  • For this project we used two table vibrators, one at each end of the casting table.
  • Attach the Table Vibrators and Variable Speed Controller to the casting surface with long screws. Plug the controller into a wall outlet and the vibrators into the controller. Test to make sure they are working before you start mixing.

Pour Concrete:

  • Your casting table should be indoors so your countertop can cure away from direct sunlight.
  • Turn vibrator on to a relatively high speed to help the recycled glass terrazzo mix flow.
  • Using a bucket, transfer the terrazzo concrete mixture from tub to form, bucket by bucket, until all the mix is in the form.
  • Spread the mix and push it into the corners with gloved hands or a trowel.
  • The form should be filled completely and evenly.

Vibrate and Trowel:

  • If you've over filled the form, screed the excess concrete off the casting with a clean, straight edge of wood or steel. Work the board diagonally across the surface of the concrete in a sawing motion being careful not to disturb the foam walls or wall liners.
  • Once the terrazzo mixture is level with the top of the form and no more concrete is required to fill the form, turn the vibrator to a low setting.
  • Allow the vibrators to run for roughly 8 minutes while all trapped air is driven from the terrazzo mixture. This will help reduce the number of air bubbles in the recycled glass countertop section.
  • Pat down the edges with a trowel so they are flush with the form.

Cover and Cure:

  • Tent the form with a thin covering of plastic to create a humid environment. Do not cure in the sun.
  • Cure for up to 24 hours.
  • After curing, you are ready to grind the bottom flat.

Step 5: Grinding

Before removing the concrete from the form, we use a grinder to flatten any areas of concrete that might be too high or that have run over the edges of our form.

This is also an ideal opportunity to grind the front, bottom edge, making it straight and consistent. It is much easier to shape the underside of the recycled glass countertop before demolding.

Tools:

Safety:

  • Particle Mask
  • Rubber Gloves
  • Safety Glasses

Grind Bottom of Countertop:

  • Always wear adequate breathing and eye protection when grinding concrete. For this project we used an Alpha WDP-120 polisher attached to a HEPA vacuum cleaner, which helps minimize dust.
  • The form wall liner is your grinding guide. You will be grinding until the casting material is just flush with the form wall liner. This will ensure a consistent countertop thickness.
  • Using a grinder and disc (or segmented grinding cup if the surface is very rough), grind the bottom of the slab around the perimeter of the casting.
  • Continue grinding around the perimeter until the material is ground flush with the form wall liner.

Mark Location of Supports:

  • The metal frame that the countertop will sit on has two support bars in the middle. Mark their locations on the slab and grind the concrete flat in those areas.
  • Grind wherever the countertop supports will touch the bottom of the countertop.
  • If your countertop support is a flat surface (not a metal frame like ours) you will need to grind the entire bottom surface.

Step 6: Demolding

Don't be deceived by how straightforward demolding this recycled glass countertop is. The majority of all cracking or breaking will occur at this step if proper precautions are not taken to protect the countertop from damage.

Once the countertop is removed from the mold, it must always be supported every 12 inches to make sure it doesn't crack.

Remove Form Walls:

  • Peel away the form walls and set aside. We'll use them when we roll the countertop over.
  • Before flipping the top over, knock down any ragged edges on the concrete with diamond hand pads. This will minimize spalling and create a smooth surface when you run your hand along the underside of the countertop section.
  • Gather the foam wall scraps and position them 12 inches apart as shown.

Roll Over:

  • Have 2 or 3 people on hand for this step. Roll the top on edge, and then completely turn it over onto the foam scraps. Lift evenly and without prying on the corners.
  • The melamine form base may stick to the slab. Remove it after the slab is settled on the foam scraps.
  • At this stage, before polishing, the finish is consistent, with only a few specks of recycled glass showing through.
  • The silicone that was applied and tooled when sealing the form has created smooth edges that don't need finishing.

Step 7: Polishing

Polishing your recycled glass countertop will take a considerable amount of time and patience. The glass aggregate is very hard and a lot of material has to be removed to expose the glass and create a homogenous appearance.

For this project we chose to use a single head wet/dry polisher but if this project were any bigger we'd have used a triple-head planetary polisher for quicker results.

Tools:

Polish:

  • Start with a coarse 50 or 60 grit pad to remove as much material from the surface as quickly as possible. This is commonly referred to as the "cut" because you are cutting into the surface of the countertop to expose the aggregate cast into the concrete.
  • For this countertop we started with a 60 Grit Wet / Dry Polishing Pad on the Wet/Dry Variable Speed Polisher.
  • As you polish, periodically stop and check the surface to ensure that you are polishing the entire surface evenly.
  • Next, polish with the 150 grit pad. Each successive grit removes the cut marks created by the coarser pads.
  • After the aggregate is uniformly exposed, the densifying process can begin.

Step 8: Fine Polish and Densify

Use the lithium densifier while polishing to create a slurry to fill in air pockets as you go. This method creates a slurry that closely resembles the base mix, but if you prefer using conventional acrylic slurry that option is always available.

Tools:

Create Slurry:

  • In a spray bottle, mix 1 part LD1800 Densifying Agent with 1 part water (50/50 ratio).
  • Mist the surface with the LD1800 dilution while dry polishing with a 300 grit pad on the variable speed polisher.
  • This will create a slurry which will fill any air pockets on the surface. The densifying agent will cure to a glass-like consistency.
  • Continue polishing and misting the surface with the LD1800 dilution until the entire countertop has been polished and all the air pockets are filled.

Continue Polishing:

  • Continue dry-polishing with higher grit pads to achieve a desired appearance. Since we are going to seal this project with a sealer that forms a topical membrane we won't need to use pads greater than 500 grit.
  • Don't touch the unsealed surface with your bare hands - the natural oil on your hands will stain the concrete.

Before / After:

  • Using the Lithium Densifier while polishing created a slurry that filled in most of the small air holes in the surface.
  • The slurry is seen here as a white / grey powder. Because we want a more uniform look, the surface will be sealed with Surecrete XS-PC12, a color-enhancing sealer, which will make the white slurry much less obvious.
  • If we were using a non-color enhancing sealer we would have used the Pro-Formula Acrylic Slurry instead of the lithium densifier.

Step 9: Sealing

To achieve the boldest color possible we are going to seal this recycled glass countertop section with a high-gloss color enhancing sealer. We'll apply two coats of Surecrete PC12 Sealer which will provide adequate protection and performance.

If this were a kitchen or bath project we'd likely sand and seal an additional two coats to create a higher quality finish.

Tools:

  • Surecrete XS-PC12 Sealer
  • 6" Paint Roller
  • 6" Foam Roller Cover
  • Graduated Mixing Container
  • Quart Stir Stick
  • Orbital Sander 320 Grit Sand Paper

Safety:

  • Rubber Gloves
  • Particle Mask

Mix and Stir Sealer:

  • For the first coat, you will need 6 ounces of sealer.
  • Mix 4.5 ounces of Part A with 1.5 ounce of Part B (3:1 ratio).
  • Stir the sealer for 3 minutes.

Apply Sealer:

  • Pour a liberal amount of sealer on the countertop.
  • Spread the sealer with a high density foam roller, working the sealer into the surface, covering the entire countertop in a uniform layer.
  • Using the roller, push excess sealer off the edges.

Back Roll:

  • For an even finish, back roll the sealer with minimal pressure to knock down air bubbles.

Roll Edges:

  • Using the roller vertically, apply sealer to all 4 edges.

Let Sealer Cure:

  • Let the first coat of sealer cure for 24 hours before sanding and applying the second coat.

Sand Sealer:

  • After curing, lightly roughen the surface with 320 grit sand paper.
  • Using an orbital sander makes this go quickly, but be careful not to sand too much – just enough to flatten any high spots and create a rough texture for the second coat to bond to.

  • Sand as evenly as possible, including the 3/4” edges.

Apply Second Coat of Sealer:

  • After wiping the countertop down, apply the second coat of sealer following the same steps as the first coat.
  • Mix 6 ounces of sealer using 4.5 ounces of Part A and 1.5 ounce of Part B (3:1 ratio).
  • Stir the sealer for 3 minutes.
  • Apply the sealer to the entire top and edges with the roller.
  • Back roll the sealer to smooth out the finish coat.

Cure and Final Polish:

  • After 24 hours the second coat of sealer is ready for light-duty service.
  • The sealer takes 48 hours to fully cure.
  • If any impurities or debris are present in the final coat, they can be sanded down and the sealer can be progressively polished up to a 2000 grit wet-sand.

Step 10: Finished Countertop

This countertop has been in use for a few months, and most of the product that ships out of our office in Berkeley passes across this surface. Because of the heavy use, the sealer has lost its original glossiness and has a few deep scratches, but is still holding up fine.

Be sure to enter the Concrete and Casting Contest before it closes on 28 July!