I'm a plasterer in Germany.  I had a few things to say.  First, I wanted to help anyone doing this.  With experience you can guess the amount of water to use by eye.  I suggest measuring it though.  This guarantees that you always have enough material and you don't waste too much.  You can make the measurement in 3 minutes, write it on your mold, and never need to calculate again.  

First, measure the surface of your mold in cm.  Height times width and approximate.  If it's mostly a square, keep that measurement.  A triangle cut in half, or a trapezoid.  This can be approximated.   Multiply this by 100cm and you'll have the volume. ( This equation will give you the water for 1 meter because it's an easy number to work with). The volume is in cm^3. Divide this by 1000 to give you dm^3 which is equal to Liters.  The liter amount should be multiplied by your expected loss/waste. I usually calculate with 15% waste, so multiply your liter amount by 1.15.  multiply it one more time by 0.7 to change your fresh mortar amount into water amount.  This number is now how much water you need.  


I'll give an example just to make sure.  Let's say the mold is a 5cm by 5cm square.  The surface is 25cm^2. The length is 100cm so the volume of this mold would be 2500cm^3 per meter.  This is 2.5dm^3 which is also 2.5 liters.  2.5 liters is multiplied by your expected loss (if unsure always add just a bit more water.  Nothing's worse than not having enough to finish a 95% finished mold that is now useless). I'll use 15%, so 2.5 × 1.15 = 2.875.  this is multiplied by the water/plaster value of 0.7.    2.875× 0.7 = 2.0125 is the amount of water you need.  It doesn't have to be precise.  2 liters is an adequate estimate.  Now you know that this particular mold requires 2 liters of water per meter.  It's super easy and you have this information in just a few seconds.  If it's a one-time thing it's not that important, but if you're pulling 800 meters of this mold for a client, and waste 1-2 kg of plaster every run, it adds up pretty quickly and will cost you unnecessary money and wasted material that you have to dispose of.  
Secondly, if possible use the same bucket of plaster for the whole piece.  Measure your water, sprinkle the powder on top until small islands form.  After letting it sit for 2-3 minutes until all the dry powder absorbs water, (it should look like the top of a desert which small cracks running through it) mix the upper 1/3 of the plaster with a whisk, not a machine.  The more you move plaster, it becomes more soft for a short time then it's hardening process accelerates drastically afterwards.  Mixing it by hand is highly recommended.  Let the material become a little more still before putting it on the table.  You can't build up layers if it's water.  The most common mistake is not waiting long enough to start working the plaster.  Build up the plaster on the table until it's about the same size as your mold.  The first run through should by 80% filled already.  Move the mold slowly using your hands to pinch and work the material.  Material that starts spreading to the side can be scraped towards the top again go fill more holes.  The first few runs can be done slowly and calming filling in most of the mold.  Later the material is hard enough that you're pressing it into the mold instead of working/pinching it.  One of they key points is only mixing the top 1/3 by hand.  This means the top material which goes on the table first, hardens first and allows the softer fresher material in the bottom of the bucket to go on top and do a better job of flowing more easily into any gaps and allowing for a good surface.    My previous recommendation about using one bucket is because plaster binds in a crystal structure.  If you put new plaster on old plaster it might adhere for a while, but it's not a chemical connection.  The likelihood  of chipping, flaking, etc. Becomes much higher later down the road.

Thank you for not adding music and just letting the sound of work and artistry shine.

You doing well sweeping, the plaster. I’m an ornamental plaster& architectural sculptor for nearly 40 years. Feel free to shoot me a message if you ever want to talk technique or anything else associated with the trade? I wouldn’t mind sharing some secrets with you as I’ve gotten older and retiring from it.. I’m glad to see some are still keeping the craft alive.

I'm glad you don't put videos out too often because I would never get anything done, I could sit and watch you work for hours. Absolutely beautiful craftsmanship. ❤

I am pretty much speechless.  This was so beautiful to watch.  I think the only thing better than watching a master craftsman, would be being one.

I'm 73. Growing up, my dad and 3 of his brothers never called anyone unrelated to build or repair anything in any trade. As a kid, I thought they could do it all. I grew up to become a millwright. I just got a masterclass in something that has fascinated me for most of my life as I have always loved old houses. Thank you

I rarely take the time to comment, but this is honestly some of the most impressive work I've seen on YouTube. The coving and arches were impressive, but that corner bead...wow. I never knew plaster of paris was so adaptable. You, sir, are an artisan!

Is there nothing that this man cannot do? Where on earth did he acquire such a amazing range of skills and expertise? I am truly in awe.

This felt so much more like watching a sculptor work as opposed to watching a home renovation. Very impressive!

Just the other day I was thinking to myself I wonder how Russ is getting on with his house and his crazy CNC... 'very well' seems to have been the answer.

Man, very very beautiful. Most people wouldn't put the time and effort into making this so. Also the patience you do this with. Applause, you are a real artist.

Humbling that our ancestors took so much care and pride in their work even for a narrow hallway like this, compared to the low-effort but huge houses we see built today. Kudos on restoring it with the same care and pride as the original builders.

Worked at the trade most of my life. When I was a kid, the old timers would tell me how it was done. I'm 72 now, and you sir have shown me how it is done. You have all my respect, you are extremely talented.

Breathtaking - especially for those who have tried something similar before. I've learned a lot in the last three quarters of an hour - it was worth every minute. Thanks a lot for this! Georg (from Germany)

It is heartwarming to see that a guy your age has become a Master of these skills. In an age where we are subjected to a lot horrible Modern architecture ( there is some great stuff as well, but much of it is just soul suckingly bad), it is great to see a true artisan who is able to repair and preserve classical architectural touches.
Thank you for your dedication to art.

When I say your work is phenomenal, it’s an understatement. It’s like a masterclass in whatever you’re working on.

Heavens above that was satisfying. It's a very forgiving medium plaster of Paris. Watching you brush in the butt joints it really was working with you. That's not to say your skill and control wasn't a major factor of course! The arch went so much better than I was anticipating, you basically used the techniques those artisans did 100+ years ago. Such a fabulous series. I assume we're all invited round for a toast when it's all done, yes?

Suggestion, rather than removing the moulding you could have made a thin cut across and inserted a stiff piece of cardboard or ?, scribed the profile and you would have been done, as the template is made of thin material you would be fine
Thought myself how to do this 30 years ago, most difficult tool to find was a Mitre Rod
You can use rigid foam insulation as a backer to help strengthen and lighten the moulding, your mix seemed to either be too stiff or too loose in the beginning
A note to watchers, never leave the horse/template in the moulding as, as the plaster cures it expands and it will lock the horse within the profile and you will need to cut or break the moulding to get the horse out
Traditionally mouldings, corbels and ceiling medallions were attached with a thin mix of plaster, as the wall or ceiling plaster is relatively dry, when you press the moulding to the wall the drier plaster will suck the moisture out of the thin wet plaster within 20-30 seconds and the bond is complete, this works for overhead medallions, the nice thing about this is that if you need to remove an old original one, that all you need to do is build a padded platform to catch it, take a broad drywall knife and dead blow mallet, put the knife edge at the intersection of the medallion and ceiling and give it a hard blow, it will break the bond at the intersection and you will save the medallion

I sat here absolutely fascinated, what a fantastic commitment to perfection. Loved every minute, thanks for inviting us along. I’m sure your mrs forgave you for all the dust for that end result.❤️❤️

Absolutely brilliant!  I'm not personally much of a fan of the high Victorian style like this, but when it's done to such exacting standards, so beautifully filmed and so precisely documented it's impossible not to just sit and watch in awe.  Oh, and the scene of the artist materialising out of the dust is genius.