DIY Vintage Doorknob Back Plate

To build my mold box I used some scrap pieces of furniture backing. You don’t have to use furniture backing but it needs to be something with a slick surface so the mold rubber won’t stick to it. To create a sturdy reusable mold the box needs to be a ½” bigger than the antique back plate all the way around. As well as, the highest point of the back plate which is the doorknob hole.

Since furniture backing is only 1/8″ thick I attached a 3/4″ piece of scrap wood to the bottom to create a sturdier base for my mold. This will make more sense in a minute.

I filled the cavity behind the backplate with Play Dough. This prevented the mold material from spilling into the keyhole and doorknob hole. Which would have entrapped my backplate inside of the mold. Then I turned it over and pressed out as much of the excess Play Dough out as I could.

My backplate was a little bent so to straighten it out and hold it in place I used 4 x ¾” cabinet screws to attach it to the bottom piece of my mold box.

Using a Xacto knife I cut away the excess play dough that squeezed out. Then I cut out the keyhole and doorknob hole so that they would be included in the mold.

To finish making the mold box I used a hot glue gun to attach the sides. I made sure all the seams were sealed so the mold rubber wouldn’t ooze out everywhere.

To make the mold I ended up using Smooth-On OOMOO 30 Liquid mold rubber. I avoided buying this stuff at first because it is pricey but in the end, it was worth every penny. I attempted several other cheap DIY mold making strategies and they all failed. My liquid rubber mold has so much detail you cannot tell the difference between the original backplate and my replicas. Since I am using this mold to make backplates for all my doors it was easier to justify the cost of the more expensive mold material. You get what you pay for right?

The liquid rubber was so easy to use. I mixed up equal parts of A and B then stirred until it turned purple and there were no more streaks. Then I poured it into the mold box starting at the lowest point and let it flow over the backplate. The directions said that this prevents air bubbles. I continued to fill the mold box until it cleared the doorknob hole by 1/2″.

I followed the directions and let the mold set up for 6 hours. After it was cured I removed the sides of the mold box and very carefully pulled the mold off of the antique back plate.

I was amazed at the detail; it looked exactly like the original backplate. I started getting excited at this point. After so many failed attempts things were finally starting to turn out.

I did a test run with Plaster of Paris. There was some gunk left behind from the antique backplate so the plaster pulled all of that out as well.

Now it was time for the real deal. The mold is supposed to be warm to help the resin cure so I threw it in the microwave for 1 minute. Then I used Alumilite Amazing Casting Resin to make my back plates. It was so easy to use and it set up super fast I was really impressed. You can make 10 backplates per box.

So just like the mold material I mixed equal parts of A and B and stirred until it turned clear.

Then I poured it into the lowest spot and let it flow into the rest of the mold. This prevents air from being trapped and leaving holes in your finished piece.

The box says it cures in 10 minutes but it took like 3 minutes for the resin to cure. This part was fun to watch, it starts spiraling white from the bottom until it completely turns white.

For the best paint adhesion, the directions suggest painting right after de-molding. So I sprayed them with Rust-Oleum Espresso right after I pulled them from the mold.

When that coat was dry I sprayed them with a light coat of Rust-Oleum multi-colored brown textured spray paint.

To add a rusty metal effect I sprinkled them with a little bit of cinnamon. After that, I sprayed another light coat of the textured paint and they were done.

 I used a 9/64 drill bit to re-drill the four holes that I used to attach the back plate to the mold box. Then I painted eight 4 x ½” Flat Antique Copper Finish screws with the same textured paint and attached my back plates to the door.