tl;dr

I created a coffee table from a toolbox chest of drawers, castors, wood, steel and concrete.

Background

Like many others, I picked up a Ikea Lack table for my living room. It held up admirably for a year or more, but it eventually started to fall apart. It needed to be replaced.

So I drew up some coffee table requirements:

Drawers, ideally without having to make them

Castors, move it out of the way

Solid countertop, easy to clean and durable

Appropriate height, similar to the Ikea Lack table

Nothing crazy, pretty typical for a coffee table.

Discovery

One of the first decisions I made was that I would like to use a toolbox chest of drawers as the base.

I knew that some big box home improvement stores carried toolbox chests that were the ‘middle’ of a stack; not the bottom of the stack on wheels, but also not the top of the stack with a compartment that lifts up.

The toolbox that I chose was from Home Depot:

HUSKY 27 In 3-Drw Intermediate Chest

Model # HTA-103B

Store SKU # 1000831248

Price $120

https://www.homedepot.ca/en/home/p.27-in-3-drw-intermediate-chest.1000831248.html

That specific model doesn’t seem to be available any more, but I found a similar chest on Amazon: https://www.amazon.com/Waterloo-Professional-3-Drawer-Intermediate-Internal/dp/B00OI4ZS74

Next, castors had be strong enough to carry the toolbox and countertop, from Amazon:

Meccion 2 inch Swivel Caster Wheels Rubber Base & Double Bearing Heavy Duty with Brake Set of 4

Price $32.99

https://www.amazon.ca/gp/product/B074P6XCNY/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

I was also planning on creating a spacer to place between the toolbox and countertop, to bring the countertop to the desired height. The plan was to make it out of wood and glue galvanized steel to the exterior.

My first choice for the countertop of the coffee table was Corian. I am pretty sure this was the material that our office countertop was made from. It is lightweight, wears well and had interesting colour options.

When I inquired at Home Depot I was told that there was a minimum order of $800 for Corian. So unless I wanted to make 5 or more coffee tables, Corian was out.

(It maybe that there wasn’t a minimum order and that the representative I talked to just wasn’t interested. Either way, I didn’t pursue it.)

So finally using my Civil Engineering degree, I decided on casting a concrete countertop.

Concrete Countertop Background

Casting concrete is not hard, but making it look nice and sealing it can be a challenge. I have a book by Cheng on casting concrete:

https://www.amazon.ca/Concrete-Countertops-Design-Finishes-Kitchen/dp/1561586803

I have also watched several Youtube videos on casting countertops:







I considered using glass fibre reinforce concrete (GFRC), the advantages are that the casting can be thinner and lighter. However, I have never used it before and it requires a compessor and sprayer, so I decided against GFRC.

Concrete Countertop Approach

The general approach is to create a mold out of melamine, sealing the corners and joints and casting the countertop upside down. When the form is removed, the concrete has the smooth finish from the melamine.

A concrete a metal mesh is placed in the middle of slab halfway through the pour to provide strength.

For this countertop I used a prepared high strength countertop concrete mix, so I did not add any extra additives, nor did I add any dyes to change the colour.

Once cured, the concrete will then be wet sanded, polished and sealed.

Plans and Materials List

The following is a list of materials to create the concrete countertop:

Melamine 3/4 in 30 in x 60 in, for mold link Black silicone sealant For corners of mold link Masking tape Tape off where the sealant shouldn’t go Wood screws To join the mold Concrete mix QUIKRETE 80-lb Gray High Strength Countertop Concrete Mix link Galvanized metal lath Used as reinforcing mesh link Tarp or plastic sheeting Cover the concrete during curing Spray bottle Used to keep concrete damp link Sandpaper and sponges 400, 600, 1000, 1500 grit, finish surface link

link

link

link Cheng Concrete sealer Seal and protect the concrete link Mirco fiber cloth To apply sealer link Drop sheet or somewhere you can make a mess sealing link Bucket or container to mix sealer link

The spacer between the toolbox and countertop was made of SPF Dimension Lumber with galvanized sheet metal glued on for aesthetics. The following is a list of materials for the spacer:

SPF Dimension Lumber Square Edge Lumber, 2 in x 4 in x 8 ft link Wood screws 8×2/1/2 Flat Head Wood Screw link Sheet metal 36X24 Sheet Metal 26G Galvanized link Glue Adhere the sheet metal to the wood link Paint thinner To remove the oil on sheet metal so the glue with adhere link Corners 3d printed PLA

The four castors where bolted to the toolbox, 4 holes each:

Bolt x16

Washer x16

Lock washer x16

Nut x16

The following but are needed, but you may already have:

Drill

Metal drill bit to make bolt holes for castors in toolbox

Screw driver and bits

Saw suitable to cut the melamine, or get home improvement store to do it for you

Concrete mixer, wheel barrow or suitable contaner and shovel

Measuring cup and bucket for water

Cutters to cut reinforcing mesh and sheet metal

Sander block

Caulking gun

You will need somewhere to mix and cast; somewhere to wet sand, and somewhere to seal.

Construction and Assembly

The toolbox will determine the size of the cast countertop. The toolbox dimensions were 66 cm by 45 cm and I wanted a slight overhang all around of about 2 cm (about 3/4 in). Typical countertop slab thickness should about 3.8 cm or 1.5 in.

Cast countertop dimensions:

Length: 45 cm + 2 cm + 2 cm = 49 cm (19.3 in)

Width: 66 cm + 2 cm + 2 cm = 70 cm (27.5 in)

Depth: 3.8 cm (1.5 in)

Based on these target dimensions, the form was planned. The form that I made had the edge supports screwed into the base of what would become the top of the form. This configuration required including the thickness of the top form in the cuts.

Melamine form cut plan pdf

The form was then assembled and screwed together with wood screws, I would recommend drilling pilot holes for the screws to make sure there is no splitting.

Once assembled, I taped near the joints, so that when the sealant was applied it would be easy to isolate to the corners and remove any excess. Using black sealant on white melamine also helps identify and remove excess.

With the mold ready, measure and cut the re-enforcing mesh, leaving about 1 inch space from the edge of the mesh to the edge of the mold. Flatten the mesh as best you can.

At this point I would recommend setting aside about half a cup of dry concrete mix, removing most of the large aggregate. This will be used later to fill any small voids or bug holes.

Mix the concrete according to the instructions on the bag. I used a wheel barrow and it was hard work. I also ended up adding more water to get a consistency that flowed nicely. This is one of those things you will learn from experience. Once you have added all the recommended water and mixed throughly, if it is still too ‘stiff’, slowly add water about half a cup at a time until it flows nicely.

If in doubt about how much water too add, watch Youtube videos to see how the concrete moves when it has enough water.

Finally, shovel some concrete into the mold and pack by hand the corners and edges, trying to remove any voids. Keep adding until it is about half way full, tapping and vibrating the form as you go.

When the mold is about halfway full, place the re-enforcing mesh. Pack it in so that it is worked into the concrete, but not jammed to the bottom of the mold (which will become the top when flipped over).

Finish adding the remaining concrete, tapping and vibrating as you go. Once the mold is full, level off the top with a board, using the spray bottle, spray water and cover with plastic.

Leave the mold for about a week, everyday lifting the cover and spray water, keeping the surface damp.

After a week, the concrete is strong enough to be taken out of the mold. Unscrew the sides and being careful of the corners and edges, pry the form open. This is the moment of truth!

Be really careful of prying around the corners and edges, being too rough can chip the concrete.

At this point you will likely see some small voids or bug holes in the countertop. Using the half cup of concrete mix you set aside, mix up a small amount of very wet mix, into a slurry and work it into the voids. Don’t be afraid to over apply to the whole surface.

I did not leave any concrete mix aside, so used portland cement and water, which had a much different colour. Fortunately, most of this sanded and polished off, but you can see the colour difference.

For my finish, I did not want to expose the aggregate, so I only lightly wet sanded and wet polished the surface. The result was a incredibly smooth texture.

Concrete will stain when exposed to water, tomato juice, lemon juice and other common household materials. So it is recommend to seal the surface.

I used Cheng Concrete Sealer and had some issues. First, the instructions on the bottle and the instructions on the Cheng Youtube video are not consistant.

I diluted the sealer, got the countertop wet and applied about 7 thin coats waiting about 10 min in between. After that I started to reduce the dilution until I was full strength. Do not leave any drips or spots.

The sealer finish was okay and has prevented stains so far, but I expect sometime in the future I will polish off the sealer and re-seal.

Finally, the spacer was created by determining the desired height of the countertop and buying the appropriate wood. The wood was then cut to length, screwed together and galvanized steel was cut and glued to each side of the wood.

I then printed corner angle pieces and glued them to cover the corners.

Results

What Would I Do Differently?

First, save some of mix to fill bug holes. This would match more closely the cast concrete and avoid the discolouration as a result of using portland cement mix.

Second, I would do the sanding and polishing outside. I did this in an apartment bathtub, would not recommend. 😀

Finally, the sealer used was okay, instructions were inconsistent and I am not 100% happy with the results. I expect to have to reseal the concrete in the future.

Tagged 3D Printing, howto | Posted on Monday, September 10th, 2018 | Comments Off on Concrete Countertop Coffee Table