Concrete release agent

[Quickstep192]

I’ve got a little art project where I 3D printed a mold and I’m planning to use that mold to cast a design in concrete. Countertop concrete to be exact…

Once the casting has cured, I plan to age it using muriatic acid.

So, in addition to making the concrete release from the mold, the release agent can’t be something that gets absorbed into the concrete or must be something I can wash out, or something that won’t stop the muriatic acid from affecting the concrete.

Oh by the way, the casting is a block with a design in it. The overall size is 7” x 7” x 2” thick.

Any ideas?

 

[PlanB]

Try canola oil. If it does adhere, you'll probably be able to wash it off with soap and water

 

[cmandp]

Ive always heard to use Pam cooking spray which had Canola oil.

 

[PCustoms]

One off I'd maybe try oil

I was doing a bunch of stuff and bought this

https://a.co/d/9GrdEgH

 

[PopcornSutton]

Your form (mold) material has a big effect on releasing. A rough sawn wood form compared to a smooth metal form. Like most things that stick, wax, plastic, etc. does not allow adhesion.
Commercially, form oil varies, but many do have a waxy substance. A pump up sprayer is used a lot to apply, and in time they get gummed bad. But others use anything, like used motor oil.

 

[Quickstep192]

My mold is 3D printed of PLA which seems pretty non-stick, but the shape has some complexities. A Plaster of Paris prototype didn’t release easily.

Here’s a picture of my mold. I’ve made the sides come off to facilitate removal of the casting.

 

[PCustoms]

My mold is 3D printed of PLA which seems pretty non-stick, but the shape has some complexities. A Plaster of Paris prototype didn’t release easily.

Here’s a picture of my mold. I’ve made the sides come off to facilitate removal of the casting.

No pic...

 

[Quickstep192]

No pic...

Dang it! Attached now.

 

[545_days]

That shape may be challenging. Casting a mold in something flexible like silicone may help.

 

[Quickstep192]

I’ve ordered rubbery 3D printing filament if this doesn’t work out.

The sides come off and I’ve got a decent amount of draft in the mold so…

 

[imagineer]

Like cmandp commented, I've also used Pam spray for a release agent and it's worked well. I've cast a few countertops and a bench seat using countertop mix and have had good results. For forms, I used Melamine coated particle board.

I'd suggest trying to smooth out your mold a bit. Those small printing edges will "key" onto the concrete. Wet sanding works well but you can also try smoothing it using flame or acetone vapor.

 

[Viper98912]

For wood, I've used some simple vegetable or canola oil from the kitchen, but I wasn't looking for a nice finish.

With the 3D print filament, there is a good chance that the concrete may "embed" into the nooks and crannies of the print lines, so oil may not necessarily help.

But since your design has bolted-together sides, I'd recommend unbolting the sides to get the block out, but getting the center piece out may not work. You may need to consider adding a draft angle to the sides (chamfer) of 2 or 3 degrees to help it "slide" out.

At the end of the day, I foresee you potentially needing to grab a small flathead screwdriver and pick out lines of filament from the concrete.

 

[Quickstep192]

All the shapes on the mold have a 6° draft angle and filleted edges.

Ironically perhaps, it’s the draft angle that creates the ridges. If the sides were straight, they’d be smooth.

 

[WildBill]

I have used Pam but not sure if that will effect any further coatings. Didn't seem to on the concrete counter tops I've made.

 

[Viper98912]

All the shapes on the mold have a 6° draft angle and filleted edges.

Ironically perhaps, it’s the draft angle that creates the ridges. If the sides were straight, they’d be smooth.

The draft angle definitely adds more "ridges" in a second axis, so yes that ironically can make it worse too.

Have you considered reducing the draft angle to 2 or 3 degrees, or perhaps taking a light blow torch to flame-smooth the surfaces a little?

 

[Quickstep192]

I sanded the areas with the ridges smooth.

Then, I used a small brush to coat the inside of the form with Vaseline. Then I warmed it with a heat gun to smooth out the brush strokes.

I had seen a video where a guy used Vaseline to coat tubing that was buried in a foot of concrete. The tubes slid out easily after the concrete cured. Also, liquids tended to pool in the bottom of the form, but Vaseline stayed put.

I just filled the mold with 6lbs of countertop concrete.

Look for a follow up in a few days!

 

[Quickstep192]

Update:

The sides came off easily. I used plastic wedges to pry the form away from the front. It messed up the form, so no re-use, but that’s OK.

If you zoom in, you’ll see some pick marks where tiny air bubbles got trapped despite my best effort. How can I avoid that on my next attempt?

 

[PCustoms]

Update:

The sides came off easily. I used plastic wedges to pry the form away from the front. It messed up the form, so no re-use, but that’s OK.

If you zoom in, you’ll see some pick marks where tiny air bubbles got trapped despite my best effort. How can I avoid that on my next attempt?

No pics...

 

[no704]

Update:

The sides came off easily. I used plastic wedges to pry the form away from the front. It messed up the form, so no re-use, but that’s OK.

If you zoom in, you’ll see some pick marks where tiny air bubbles got trapped despite my best effort. How can I avoid that on my next attempt?

Can’t see anything. Not sure about concrete. But when casting plaster moulds i add a very small amount of Ajax lemon dish soap as a surfactant and viberate with a palm sander. For some unknown reason only the Ajax works and actually cures faster. Others inhibit the curing.

 

[Quickstep192]

When you say a very small amount….

My mix is 8lbs of concrete mix in 10 ounces of water. How much dishwashing liquid would you add. And, will it not make the mix foam?

 

[Kurt4440]

Update:

The sides came off easily. I used plastic wedges to pry the form away from the front. It messed up the formhole , so no re-use, but that’s OK.

If you zoom in, you’ll see some pick marks where tiny air bubbles got trapped despite my best effort. How can I avoid that on my next attempt?

That looks very good. The voids can be reduced by using a palm sander to vibrate the concrete, they could also be filled in with a little slurry after the piece is removed.
If you cast another piece, adding 5-6 psi of air pressure to the hole in your form will help to separate the piece from the form.
Keep up the good work.

 

[whateg01]

My mold is 3D printed of PLA which seems pretty non-stick, but the shape has some complexities. A Plaster of Paris prototype didn’t release easily.

Here’s a picture of my mold. I’ve made the sides come off to facilitate removal of the casting.

I 3d printed corners for a slab I poured and then used 2x4 for the straight sections. Mine was obviously less complex of a shape but the corners pretty much fell right off. It looks like you might have benefitted from some draft in the design. That might have prevented destroying the mold. Don't know if the design would be ok with the draft though.

 

[PCustoms]

I believe they had 6° of draft, which is a lot.

-use a plasticizer in the concrete
-use a good release
-can the mold be sealed? Look into using a flexible mold
-vibrate the form after filling
- use temp differential to shrink/expand mold after a proper cure

 

[CV428]

The surface texture will work against you. Pam spray is good- believe it or not, that used to be an FDA-approved mold release in the medical mfg world. Lots of concrete guys use WD40. I know this sounds crazy, but you might consider bacon grease to smear over the surfaces to make them slick and smooth. I'm not kidding either.

 

[whateg01]

The biggest issue with this is the fact that it's 3d printed and has areas where the concrete (plaster is worse) can get caught under the layer lines. I've combatted that by taking drywall compound (sands very easily) and smoothed the vertical surfaces. As I recall, I sprayed a clear coat to seal the compound then sprayed that surface with cooking spray. The parts pretty much fell out of the mold when we turned it over. I did that once for a Christmas tree base for the porch and several times with another mold for a base for one of those name signs that people stand up next to the front door.

 

[Viper98912]

Update:

The sides came off easily. I used plastic wedges to pry the form away from the front. It messed up the form, so no re-use, but that’s OK.

If you zoom in, you’ll see some pick marks where tiny air bubbles got trapped despite my best effort. How can I avoid that on my next attempt?

Have you considered trying to finish this with a fine non-sanded grout?

 

[Quickstep192]

Have you considered trying to finish this with a fine non-sanded grout?

I have considered grout, mostly for the color choices. Do you think grout will be strong enough?

 

[PCustoms]

I have considered grout, mostly for the color choices. Do you think grout will be strong enough?

For an art project?

Absolutely. People walk on grout daily.



Or are you talking for the whole thing?

 

[Viper98912]

I have considered grout, mostly for the color choices. Do you think grout will be strong enough?

Depends on what you're banging on it

 

[Quickstep192]

Thanks for all the thoughtful replies.

It’s ironic to me that it’s the draft that causes the layer lines…

But, I did sand out the layer lines.

I do really like the idea of grout, but I’ve always thought of grout in applications of relatively small thickness confined on both sides. This thing is 1-3/4 thick.

 

[whateg01]

Thanks for all the thoughtful replies.

It’s ironic to me that it’s the draft that causes the layer lines…

But, I did sand out the layer lines.

I do really like the idea of grout, but I’ve always thought of grout in applications of relatively small thickness confined on both sides. This thing is 1-3/4 thick.

I don't think the draft is causing a problem. The layer lines are there regardless. Draft can make them more visible but the undercut should be no worse.

 

[Viper98912]

Thanks for all the thoughtful replies.

It’s ironic to me that it’s the draft that causes the layer lines…

But, I did sand out the layer lines.

I do really like the idea of grout, but I’ve always thought of grout in applications of relatively small thickness confined on both sides. This thing is 1-3/4 thick.

For clarification, when I said grout, it was only to fill in the pinholes, not to coat the whole surface

 

[Quickstep192]

For clarification, when I said grout, it was only to fill in the pinholes, not to coat the whole surface

Aah… Thanks.

I’m thinking about aging it with Muriatic acid which should make the pock holes less noticeable.

 

[Quickstep192]

Here’s a picture of my second attempt.

I used a more flexible material for the mold and used compressed air to urge the casting to leave the mold.

I made the mix a little loose and vibrated the mold using a palm sander as I poured to get bubbles out.