I recently redid my living room ceiling from basic drywall to a coffered ceiling. And I love it! But the plan from the beginning was to add more detail. So I’m using molds to create plaster decorative details. I thought I’d show you how to make a DIY Plaster ceiling. But you could use these decorative onlays on furniture, a fireplace, or even on the wall!

before

Going in, my pink ceiling was so cute! But I’m not letting that stop me from making it even more special.

Here’s the before- it’s a really nice ceiling. Just wait to see what it can become!

diy plaster ceiling

Let’s start by making a plan! When I visited the historical home Vizcaya in Miami, I took a picture of the ceiling and always knew I wanted that to be the inspiration for the living room. Step one was the coffered ceiling and this DIY plaster ceiling is step two. I sketched out the ceiling to figure out how many pieces of each decorative molding onlay I’d need to create the plan.

SUPPLIES

Putty Mold Making Kit
Scale
Plaster of Paris– I ended up using 32 lbs. Buying in larger buckets will save you money!
Disposable cup and knife
Latex paint in your color of choice (I’m using Beloved Pink)
Onlays to make a mold from- Large Rosette, Small Rosette, Leaf, Shell, and Oval
Construction Adhesive (make sure to get Instant Grab!)

step 1- make the molds

To begin, let’s make some molds! This part is really fun because you’re going to take the store bought onlays and be able to duplicate them as many times as you want!

Start by following the manufacturer’s instructions for mixing the silicone rubber compound. For the Silicone Mold Making Kit I bought, it has a 1:1 ratio- so you mix equal parts A (blue) and B (white) by hand. Use a scale to weigh each part so they’re exactly the same.

Thorough mixing is crucial to ensure the silicone cures properly. I fold the putty between my hands and press it back together to mix it nicely. At first you’ll be able to see the blue and white marbled together, but by the end of mixing the putty should be a solid lighter blue color. Note, only mix a little bit at a time because it hardens up very fast.

Place the putty on the surface of the onlay and make sure it’s covering the sides as well. Press the putty firmly onto the surface of the onlay especially where there are details in order to push out any air bubbles. It’s important to take your time making sure the mold is pressed firmly onto the onlay or all of your casts will have issues.

These are the onlays that worked best for me for this project- Large Rosette, Small Rosette, Leaf, Shell, and Oval. Objects that are round or oval in shape with no negative space. Making the mold worked for each onlay I chose, but these made the best plaster replicas.

Follow the manufacturer’s recommended curing time for the silicone (usually this takes 20-30 minutes).

Finally, de-mold each of the silicone molds. Once the silicone has fully cured, carefully remove the mold from the onlay. It’s exciting to see all the imprints and details from the onlay captured in the mold!

If you have a piece you want to make lots of castings of, I’d recommend making at least two molds of that piece. I knew I needed many leaves (48 pieces) so I made three molds so I could cast two pieces with each batch of plaster I mixed up.

step 2- create the plaster pieces

Next, mix up some Plaster of Paris and put it in the molds to create the pieces for the plaster ceiling.

To mix the plaster, I like to use a plastic disposable cup and plastic knife. I’ve used a nice cup from my cupboard and when the plaster dried, it was almost impossible to get it out. A plastic cup will have some give so the sides can be wiggled and the excess plaster can be removed and thrown away. One plastic cup will work over and over for the plaster mixing.

Use cold water and pour into the cup. Then pour some Plaster of Paris into the cup. Try for a 1:1 ratio of plaster to water- this looks like runny pancake batter. If you want it to cure faster and the plaster to be stronger, add more plaster for a thicker mixture. You will use a lot of plaster for this so keep that in mind when you figure out your preferred ratios.

*Note- make SURE to put the water in the cup and then add the plaster. If you put the plaster in first and then add the water, I’ve found the mixture gets a lot of water bubbles and then the when it dries it’s brittle and breaks. It’s a small instruction, but an important one. And it’ll help you waste less plaster.

Once the plaster is mixed, pour it into the molds until they’re full. Wiggle the molds or vibrate them to release any air bubbles. Let the plaster dry for 20 minutes. The thicker the mixture was, the faster it’ll dry. If it was a really wet mixture of plaster, it might take longer to dry- up to 30 minutes.

One of my molds really curled up when full with plaster. I want the plaster appliqués to lay flat. So after pouring the mold, I’d wait 2 minutes for it to harden up a bit. Then I’d flip it upside down onto of a cookie sheet. After the 20 minutes were up, I’d use a scraper to get the plaster appliqué off the cookie sheet. Then I’d de-mold it as usually. This made for a super flat filigree!

The plaster should be set after sitting in the mold after 20-30 minutes. If it is, pull the mold away from the plaster on the edges, then put it upside down on your hand and pull the mold away to remove the decorative piece. If there’s excess plaster around the edges, gently break it off. Be careful when removing the mold so that the piece doesn’t break.

Repeat this step for as many plaster pieces as you want. When I’m ready to mix more plaster, I dump out any dried plaster in the cup by squishing the sides so it falls off. I throw those dried pieces away. Then I repeat with mixing more plaster of Paris.

figuring out the layout

In my head, figuring out the layout was really simple. That ended up not being true. Why? Each beam in our living room is a different length. Ranging from 45-62″. To deal with that, we came up with 3 different layouts for the different lengths of beams.

Each was symmetrical with a small rosette in the middle clad by two leaves. They each have an oval on each end. Then each side differs based on how much space is needed to be filled. Because they have equal spacing between each piece, the eye doesn’t really notice that there’e a change in the pattern. It reads as very uniform.

Here’s how many pieces we ended up making

A total of 307 filigree pieces!

Tip- figure out the layout before making the pieces so you know from the beginning how many need to be created.

Plaster clean up tips

After step of mixing the plaster, make sure to clean up properly. My recommendation is to pour any excess mixed plaster in the trash. Then let the rest of the plaster that you can’t scrape out dry in the cup.

When the plaster is dry, push on the sides of the cup. Since disposable cups are flexible, the plaster will break off and you can throw it away. Use the disposable knife to scrape off any excess plaster off the cup and throw it away.

Never wash mixed or dry plaster down the drain. It will harden even underwater and then cause problems with the pipes.

If plaster has spilled, let the plaster fully dry and scrape it off. I like using a Cricut scraper for this step. I keep a dust pan and broom handy for cleaning up the plaster off the table. Then vacuum up any dust or pieces that have fallen on the floor. Plaster is a messy project, make sure to keep a wet rag hand ready so you can get any plaster off your hands as you work.

where did Plaster of Paris get it’s name?

Did you know that Plaster of Paris got its name because it was historically made from heated gypsum found naturally in Montmartre (in the hills of Paris, France)?!

My son asked me so I looked it up. I love learning new things! In the 17th century, wooden buildings in Paris were covered with plaster to prevent fires. So all of the beautiful plaster work you see in Paris is so it wouldn’t go up in flames (London had a huge fire in 1666 that prompted the King to mandate the plaster work- it was a law he created).

These days, the gypsum to make plaster no longer comes from Paris. It is still produced by heating powdered gypsum to about 300 °F. When mixed with water, this forms a paste that will harden within minutes, producing an exothermic reaction, which means it warms up.

onlays that didn’t work

I tried two onlays that I couldn’t get to work. First, I tried a bird onlay that was super cool looking! But the mold was so thick and complex, I couldn’t get it to come out of the mold without breaking the plaster in a million pieces

Next, I tried a simpler bow onlay. I tried that one four times, but still I couldn’t get the plaster to come out without breaking. I tried covering the mold in Dawn soap to help the release. You might think adding yarn and wire to the plaster would help- it didn’t. And I also tried keeping it on a flat surface, making the mixture thicker, and using ice cold water.

It broke time after time so I went a simpler route. It seems like pieces that are a round or oval shape without negative space work best for plaster casting in a mold.

Another option I could have tried is casting with resin. I think that would’ve easily worked. However, I really wanted that plaster look and I was worried how resin would take paint. Plus I’m always trying to use less plastic/chemicals in my crafting. So I didn’t try it. But if you aren’t opposed to resin, that’s another option.

step 3- paint

And now, paint each decorative piece. I’m using the color Beloved Pink which will match my ceiling. I figure I’d rather paint the pieces on a table than when they’re over my head. I just use a paint brush and cover each piece with paint. Some are a pain to get in every crack and on the sides. But it’s exciting to see them coming together!

Make sure to completely cover each piece with paint. I did two coats of paint on all of the pieces for the DIY plaster ceiling.

If the backs of the plaster pieces aren’t flat, give them a light sanding. This will help so they’ll lay flat on the ceiling when they’re glued on. Have a brush handy to remove the plaster dust off the back of the appliqué and off the sander.

We used some loose sanding paper to remove any excess plaster on the side of the pieces.

step 4- glue onto the ceiling

Finally, take the plaster pieces and glue them onto the ceiling. This is the exciting step because you get to officially see how they’re looking installed!

For this step, my husband used a hardware jig and drilled a hole for where center is on the beams.

Then he pushed it against each beam and drew a center line with a pencil on the ceiling. He also marked center of each beam and the spot where each beam intersected.

Next, I applied construction adhesive to the back of the plaster pieces and then placed them on the ceiling. We started with the center piece (the small rosette). The large rosette went where the beams intersected. Then the middle pieces were filled in based on the length of the beam. Smaller beams have less appliqués and larger beams have more.

Make sure to use adhesive that is “instant grab” so it’ll hold right away. Or else it’ll fall off. Also be careful to not put too much adhesive on the onlays- it’ll create a mess that’s annoying to clean up.

After putting everything up, touch up the paint. I also painted over any pencil lines that were showing.

after

I am so happy with how the ceiling turned out! The detail now on the ceiling is beautiful and I love how it draws the eye up!

My vision was for this room to look more like a castle or a historic home- with lots of plaster details. And I think that was achieved!

Lots of people like to tell me that my house is “too much,” but being a maximalist, I like having a lot to look at! So this is very fun for me.

The onlays feel expensive and high end. With this being our most formal room in the house, it’s exactly the vibe I wanted.

price breakdown

As I was making this, I was spending money on the molds and the plaster and it was adding up. So I began wondering if I was really saving money making my own DIY Plaster Ceiling? I thought I’d add it up to see.

Here’s what I paid to buy one of each onlay and the supplies to make the molds.

$6 small rosette onlay
$4 leaf onlay
$10 large rosette
$44 mold kit (I needed 2 kits)
$73 plaster of Paris
$22 Loctite instant grab

Total Price I spent on the DIY plaster ceiling- $159

If I would’ve bought all the onlays

Small Rosette Onlay $6×60= $360
Leaf Onlay $4×119= $476
Large Rosette Onlay $10×16 = $160
Shell Onlay $5 x 64 = $320
Oval Onlay $9 x 48 = $432
$22 Loctite instant grab

Total price to buy the pieces instead of making them myself- $1770

So yes- it was much cheaper to make my own even though it took me days longer than if I’d bought all the pieces. So saving over $1600+ means more work, but for me I couldn’t have done this project if it cost close to $1000 so I was happy to put in the hours for this DIY plaster ceiling.

Time Breakdown

Mold making: 8 minutes hands on, 20-30 minutes dry time per round
Casting pieces: 30 hours/ over 7 days (of hands on time- 4 hours of dry time)
Painting: 4 hours
Installation: 6 hours

Total- 40 hours. This is a time intensive project- especially the casting part. I’ve been putting off this project because I knew it’d take a lot of time and I was right.

Overall, I am SO glad I took the time to do this project myself. It definitely required more patience than just buying the onlays, but being able to customize everything and save so much money made it completely worth it.

I love how much character these plaster details added to the room- this is exactly the kind of charm I picture when I think of an old home filled with history. And the best part is, once you know how to make the molds, you can use this technique anywhere- furniture, walls, even other rooms in your house.

If you’ve been wanting to add architectural detail to your home on a budget, this is such a fun way to do it. It’s a little messy, a little time-consuming, but the end result feels so custom and high-end. And for me, that’s always worth it.

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