concrete lamp

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.

Comments

[charonme]

Stick tinfoil on the outside of the glass (between the glass and concrete) so that a bit less light is absorbed by the inside concrete walls. This might make the overall light output a tiny bit brighter and reduce heat buildup a little.

[SugargirlDesigns]

Or, what about using Copper-Foil Tape, as is used in Stained Glass Constructions? Just a thought. It might be a little less work and a little neater. If anybody else already suggested this, sorry, I haven't read the whole thread yet, and I am new here.

[i.am.flink]

Pam works rather well. It's easier to apply and doesn't have the risk of leaving a "shadow" in the finished concrete the way Vaseline can do.

[StickyC]

Could you coat the inside of the glass with vaseline or similar to make it easier to remove concrete spillage?