Reinforced Cement Housewares and Decorations With 3D Printed Molds

Hello all,

This is my first instructable! Please forgive the older photographs, it wasn't originally made with instructable in mind :)

This will be a brief guide in making your own household objects out of sturdy reinforced Portland cement. This ash tray was made as a gift, and is super durable with sister samples surviving multiple serious hammer blows! Aside from its incredible strength, the reinforced cement has a wonderful look and almost soft smooth feel.

Supplies

CAD modeling software of your choice

3D printer + Software

Portland Cement

Shredded fiberglass (E or S glass will due just fine, as will scissor chopped matt)

Water

Mixing cups and sticks

Gram scale

Gloves

Heat Gun or Oven

Step 1: Design Your Item

Decide what you want to make!

I wanted to gift an ash tray, so that's what we'll be following here.

I made a 3D model of the exact object I wanted. This is important to know how much material you'll need later, and for designing your mold.

Tip: Keep your first design simple, as there are geometric limitations that you'll learn with experience.

Step 2: Mold Design

Once you have your 3D model ready, you can start designing a 3D printable inverse of it.

Think about where you're gonna pour cement from, for me this was the bottom of the ash tray, which became the top of the mold.

Tip: Once you have the internal shape of the mold set, try to thin out the walls of the mold as much as possible to ease the later removal of plastic.

Step 3: Print

Print that baby out. I recommend going for the finest surface finish you can get, that means low layer heights and ironing steps for a smooth finish.

PRINT IN PLA

Also, this step will be a sobering moment when you realize your 3D printing skills can use some work... you may have to re-design the mold once or twice to get the detail and smoothness that you want.

Step 4: Dangerfluff Cement

Shredded fiberglass... My friends and I started calling this stuff dangerfluff from an abundance of caution. But it's really not that bad and used all over the place with composites.

You'll need to figure out how much cement you'll need by volume to fill your mold (plus some spare) then figure out how much mass that is, then just 2% of that mass will be substituted with our dangerfluff:

Measuring:

Ex: If you need 100 ml to fill your mold (Check your CAD model!!!)

And that comes out to say 160 grams of Portland cement

You'll need 3.2 grams of danger fluff.

Mixing:

Add the DRY cement to the dangerfluff

Mix well while still dry (sturdy stick recommended)

Slowly add some water, mix, repeat.

Once all the water is in, glove up and start breaking up the fiber clumps by hand.

Note: I usually add the water by feel, starting just under the manufacturer's recommendation and working up from there until I'm happy with the slurry.

Tip: Some companies sell this stuff as shredded fiberglass, but for our project chopping up some woven or mat fiberglass will suffice.

Step 5: Mold Packing

By now you'll have finished the pleasure of mixing the hairy mess of the fiberglass reinforced cement.

Once all or most of your fiber clumps are out, begin pouring/packing your mold. Usually with some vibration, the slurry can be coaxed to flow out of the mixing up and into the container. Try and pour the cement down one of the container walls to minimize air entrapment.

Pour:

Pour about 1/10 of your slurry down a wall

Tap the mold on the table

Nudge cement into places it needs to go with finger or stick

Repeat until full.

May require massaging as pictured to level out the cement.

Wait a full day for the cement to cure.

Note: I didn't use any mold release on this project so I can not comment as to its utility.

Tip: Use a round dowel to roll out the top, sheering with a flat surface drags the cement on top.

Step 6: Burnout

After the cement is cured, use a heat gun or oven to significantly soften the plastic mold, and begin cutting it off. Snips, dowels, dental picks, and X-acto knives come in handy.

Go slowly, don't force anything. Use a lot of heat and a gentle touch with the tools to peel away only very soft plastic.

Sorry pictures of this step were lost or not taken.