Concrete Lamp




this is a lamp in concrete, glass, and steel.

this is a project for futurecraft (blog here)

Step 1: Stuff You'll Need

You will need:

concrete (rockite works best). something to mix it in/with
something to make formwork. Plywood or melamine work well. Foam Core can also be used.
16" of 1 1/2" X 1/4" steel bar stock
3 pieces of glass: 1/4" thick: 12" X 4"; 1/8" thick: 12" X 3 1/2"; 1/16" thick: 12" X 3 1/2"
(you can cut these yourself, or easier yet have a glass store cut them. they need to be fairly precise.)
screws, drill, drill bits, driver
glue gun
ceramic lamp socket
4" threaded lamp post
light bulb (bright)
lamp cord
lamp switch
screw driver
space to make a mess
free time.

Step 2: Making the Outer Formwork

first, you need to make the formwork. this will make or break (literally) this project. the more precise you can make it, the better.

The inside volume needs to be exactly 4" square. You can use melamine, which will give a smooth surface. You can also use lumber or plywood, with can give the concrete texture.

If you use 3/4" material, you'll need 2 pieces 4" X 14", and 2 at 5 1/2" X 14". And 1 bottom (which is actually the top) at 5 1/2" square.

Again, make this as precise as possible. If you don't have access to a shop, you can use 1/2" foamcore, and a knife and ruler. Use a glue gun to glue it all together. If you coat the inside surface of the foamcore with clear packing tape, the concrete won't stick, and you'll get a smooth, glassy surface on the concrete. The foamcore method is probably easier and less forgiving, and works pretty much in the same way. Just make sure to seal the joints really well, with the glue gun or packing tape. Otherwise, it will leak. everywhere. The concrete will be very liquidy. Like heavy cream. Don't underestimate it's ability to find cracks and leak out of them.

Step 3: Make the Lamp Base

You can do this many different ways. I used steel, infilled with rockite (concrete). This requires welding and grinding equipment. You can also just cast a hunk of concrete. Or, a block of wood. Just remember that you need to get the cord in there somehow.

I used 1/4" thick steel bar stock at 1 1/2" wide. To make a 4" square, you need 2 at 4" and 2 at 3 1/2." Weld these together, grind the welds. (pictures 1-4) Then, because i'm going to pour concrete into the volume, i welded two little pieces of 1/4" bar to keep the hunk of concrete from slipping out someday... (picture 5).

Then drill a 1/4" hole as far to the bottom as possible on one of the sides. This is for the cord.

We won't fill the bottom all the way with concrete so that the cord can come out of the post and out our little hole. So put in a piece of foamcore to the top level of the hole we just drilled. Seal the edges with the glue gun. We'll pour the concrete from the top.

Then glue with the glue gun the threaded rod post onto the foamcore. Make sure it's not off at an angle.

Ok the last two photos are what it looks like when it's dry, top and bottom. Get the idea?

I think the next time I do this, I'll probably forget about floating it above the base. I think a hunk of wood could look nice. This took too long.

Now for our first pour. This will be good practice for the big one. I recommend getting rockite. It's available at a lot of smaller hardware stores. The stuff is awesome. It's like plaster, just a lot stronger. and it has a beautiful smooth finish. Mix it as per instruction so that it's like heavy cream. Or melted ice cream. Not too runny! The more water, the weaker. It's easy to add too much water. Add it slowly.

Pour it in just short of the top of the steel base.

Now, this is the annoying part. I don't think i would do this again this way, but here goes. I wanted the thing to "float" off the base a bit. So i decided to cast in some 1/4" steel bar legs. I welded these little bits of wire on to the legs so that it would adhere well to the concrete. I won't get into the details, because I think it's a bit of a cockamamied way to do this. But you need to make sure the wire won't interfere with the glass for the main pour.

For this step, I'm just setting them into the base about 1/4 inch, so that the shade will seat securely into the base. These will be easy to remove once it's hard, and then I'll cast the legs into the shade. I know, ridiculous.

The trick is you have to somehow hold these little guys in position while the concrete dries. This can be accomplished with small clamps. Or maybe duct tape But have a game plan before you pour. I didn't have one, so this is my improvised half-assed on-the-spot effort. It worked

Rockite dries fast. It's pretty amazing stuff. It will start to set up in about 15 minutes. After an hour you can carve it with a blade. In 24 hours it's wicked hard but you can sand it and shape it a bit. After a week it's rock solid.

Step 4: Preparing the Mold

Ok, you'll need to build some formwork for the void in the middle. I used foamcore and melomine. I think it would be better to use all foamcore, or a solid piece of ridgid insulation foam (usually pink or blue, available at home depot.) The reason for this is because you have to get it out once the concrete dries. I thought the foamcore would be squishable enough. But it was a pain to get it out. So, use foam, and you can coat it in packing tape for a better finish and easier release.

Regardless, it need to be 3" square, exactly, and the same length as the outer mold, PLUS the amount you want it to "float" above the base, if you want to do that. I used 3/4". This way, the base can rest on this while we cast the feet into the shade, and it'll keep the right spacing (see photos).

Ok the glass. You can glue the glass directly to the inner formwork, as shown. This way, the glass will be exposed on the inside of the shade. This glue will come off easily when you release it. The thick piece of glass overhangs 1/2" on either side of the inner formwork. The other 2 pieces butt into it and overhang 1/2" on their respective sides. Obviously, you can modify this layout. There should be at least 3/4 on the top and bottom. This is critical so that the concrete has some structure, since we're cutting it all up with the glass.

Now slide it into the outer formwork. This might require loosening some screws. This is not an easy step. You'll have to futz with it. If your measurements were good, it will be easier. It's critical that the glass butts into the outer formwork so that the edge will be exposed, and that it is securely glued to the inner formwork, so it will be exposed in the inside, so the light can get out. This will take patience. Trial, error, adjust.

The last step, once the formwork is adjusted, tight, and SEALED (you can use the glue gun like caulk if need be), invert base over the top so that you can cast the legs into the shade. Make sure they're reasonably straight, and that everything looks good. Take it out. Next step: pour.

Step 5: The Big Pour

Mix up enough rockite. I'll leave this up to you to figure out. Pour it slowly into the mold, until it comes flush with the top edge. you can overfill it a bit and then scrape it flush after about 10 minutes. Invert the base over it to cast in the legs (you can glue these temporarily into the base with a glue gun, or use duct tape or something. You don't want to lose them to the concrete abyss.

Once it all looks good. put it away for at least 12 hours.

Step 6: Break the Mold

Time to break the mold. Take off the base, but leave the sides attached. It's tempting to look, but it'll be easier and safer to ream out the middle if you leave the sides attached. If you used solid foam, get a big, fat, long drill bit and ream it out as much as possible Stick screwdrivers in there, putty knives, whatever you need to do to get that foam out. Foamcore is the same deal. Needlenose plyers and yanking might help.

This step is a pain in the ass. Take your time and be gentle. It's possible to break this thing.

After you get the center pretty well cleaned out, you can take the outer mold off. Make sure it didn't crack anywhere (if it did, you can fix cracks with superglue). You might need to excavate a bit the glass edges so they are exposed. Be gentle. you can use a flat edge screwdriver to do this. You might also need to do this on the inside, if some of the rockite got in between the formwork and the glass. It should chip off. Be gentle.

Finally you can sand lightly the sharp corners, and rinse the whole thing off in the sink. Make sure all the glass is exposed cleanly inside and out.

If it came out first try, nice work. If not, hopefully you can re-use the glass and re-pour.

Step 7: Assemble Lamp

Put the lamp together. Thread the cord up through the base holes, screw the thing on top. You can put a switch on the cord too, if you want. I'm not getting into wiring here. If you don't know what you're doing, ask someone who does.

Use a bright bulb. I found this fluorescent (incandescents will get the thing really hot - better to use compact fluorescents (and less energy!). This bulb is a 150 watt equivalent, which uses 32 watts. The shade will block a lot of the light.

Notice that you can see through the shade on the thick piece of glass (even when switched off!)

Ok, you're done. Please, if anyone is crazy enough to try this, let me know how it goes.



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    79 Discussions


    2 years ago

    C'mon. Let's focus on the design, the effort and the processes.

    Personally the design is great, the effort - obviously intense and the processes - effective.

    I think the end product is a testament to all of these elements working together. Cement/concrete/mortar/whatever and who really cares.

    Great job hands_on!

    double thumbs small.jpg

    3 years ago

    Cement is the part of concrete that goes through the crystallizing/hardening. The rest is sand, rock, and water.


    10 years ago on Introduction

    Looks great and very clever! Just to prove I have no life, I'll throw in the following: It's cement when it's in the bag, and also when it's in a liquid (or semi-liquid) state. It's only concrete after it's hardened. "Hardened" because cement does not "dry" by evaporating water. It hardens--into concrete--by a chemical reaction. OK, sorry to be such a stickler, back to the lamp. Lamp's cool!

    11 replies

    Umm...not to be a jerk, but, that's not what I have been told. I was told that it's cement when it's dry, concrete when it's mixed with the other ingredients that make it concrete, and... My stepfather was a General Contractor, and I have other family that is in construction also... they've always said that you have to wait for concrete to "dry" and that is why it isn't good to lay concrete in wet or cold conditions. Hmm...

    It is true that the concrete "cures" and doesn't just dry out. Also are you sure you heard them correctly? In northern Australia (where I am from), it is often too hot for the concrete to set evenly (causing cracks etc.). To combat this, most "pours" are done late in the afternoon when it is cooler, and then once the concrete has begun to set, its given a good spray with the garden hose. I honestly think (though i'm no expert) that being wet and cold are ideal conditions for curing concrete.
    Oh and i'm not sure but I remember seeing a documentary on the construction of a huge dam somewhere (maybe in the U.S. or China? pfft) where they actually had to chill the concrete to prevent it from curing too rapidly. 
    And I think they actually added ice to the mix when building the Burj Dubai. But that was to stop the mix from seizing under the pressure when being pumped up so high...


    Reply 7 years ago on Introduction

    It can but is more likey to spall.
    Thats when concrete freezes, or cures too hot, and after curing the top smooth surfaces slake off in chunks, exposing the rough rocky interior, making surface look like broken concrete.


    Reply 7 years ago on Introduction

    interesting.... might be a design element to take use of. that is if the concrete wouldnt just fall apart or something.

    If it's really cold it can be important to keep the pour warm while it cures, because clearly there would be trouble if the water in the mix was to freeze.

    Large pours have to be watered, often for several days after being laid, because the curing reaction is exothermic. Setting concrete actually produces some heat, so a large amount of concrete setting can cause enough heat to be problematic.

    I've never bothered with the semantics of concrete vs cement, and I figure nobody will be confused by using set, cure, and dry interchangeably.

    I am a division of the state architects structural inspector, and was a general/electrical contractor for 30 years. Cement is a dry powdery ingredient, in concrete When it is mixed with sand, and aggregate (rock) it becomes concrete mix. When you add water, it becomes concrete Cement is made by heating limestone (calcium carbonate) with small quantities of other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which is then blended with the other materials that have been included in the mix. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'Ordinary Portland Cement', the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient of concrete, mortar and most non-speciality grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white. After pouring concrete, it is important to keep the concrete hydrated and above freezing temps. Hot weather will cause the outside of the concrete to begin curing faster then the inside, causing shrinkage cracks, As concrete cures, it produces heat as a chemical reaction. When looking for a smooth outer surface, use a vibrator to remove bubbles and consolidate the concrete. Keep it cool, and if possible cover it with plastic after the surface has cured long enough, so it will not leave plastic fold marks on the concrete. If you are making a lot of concrete objects, a fairly inexpensive cordless drill mounted vibrator that has a phallic shape can be dipped into the concrete to consolidate and remove exterior bubbles or what is referred to as rock pockets. Once you remove the forms, keep it covered for as long as you can to prevent cracking. Vibrators can be rented cheaply at tool supply centers Humidity is concretes friend, when curing. To add a nice touch, quartz, turquoise, minerals and fossils can be imbedded into the mold when pouring, then polished with a hand grinder when finished. The colors really stand out, after grinding, and coating it with a clear concrete sealer, to give that wet river rock look. Hope this info helped. Canoeman

    I live in England and when I worked for a leisure company installing patios and conservatories I regularly used to have to lay concrete in the wet or cold conditions; It does set, but it just takes longer, it sets through a reaction withthe lime in its mix.

    and to help with the Concrete/ cememnt argument , the English Oxford dcitionary defines the following:

    " Cement/ noun/ : a powdery substance made by calcining lime and clay, mixed with water to form mortar or mixed with sand, gravel, and water to make concrete. "

    I'm not sure if you said this or not (I couldn't understand what you said exactly), but cement is an ingredient for concrete. Concrete is made up of sand, rocks, cement, etc.


    10 years ago on Introduction

    Waaaay cool. I'd like to know what the weight difference is between that RockStuff and standard cement. Guess I'll find out soon enuff. Great work!!

    1 reply

    Reply 7 years ago on Introduction

    This could also be done with concrete backer board, and then troweled with grout, to eliminate mixing concrete. Then sanding grinding the outside smooth, to expose the glass.
    I have built a few pony walls like that.

    (pony wall = A short partition wall about 3 to 4 feet high.)


    I wonder if you could add the same materials to the concrete/cement mix that is used in making the lightweight "concrete" planters and such? Or, would make it not as heat/fire-proof, I wonder? Although, if the light source was a lower wattage, would that matter?

    broken glass added to the mix maybe. if you left glass in a cement mixer with just the sand and let it run for a while it would take the sharp edges of the glass and give sand blasted effect to the glass. i dont know if adding water would help.
    This is kind of a new technique used on concrete floors and some wall covering
    where nails, screws, glass, and bits of well anything really is added, then ground flat to remove sharp bits using Carborundum Stones. mosaic of bits of crap