I've always wondered about using aquarium sand when I was at one of the stores that also sold fish and fish tanks. I then read some where somebody suggested aquarium sand, so I finally picked some up. Might not work for ballast in HO because I think it's a bit to big, but for car loads I think it's ideal. A long time ago I used canary gravel. Odd name but it was used for the birds to eat and help with digesting food. It was the perfect color for limestone. Can't find it any more. I've looked and search the net.

They always say to look outside the box. That's what I'm doing. I think they call it cross pollination.

Bernd

Some success to report on the Hydrocal wall castings. I poured two last night and gave the molds a mist of dishwater rinse treatment per Bruce Hirst of Hirst Arts video #4. Below are pictures of the two castings. I still have a small bubble issue, but not as bad as before. I need to experiment more with the dishwater rinse. Also, I've come to the conclusion that I'm still stirring the mix to vigorously and stirring in bubbles. Technique, technique. I'll get it yet. The more you do the better you get at it, right? If not, I'm going to see if it'll stick to the wall when I throw it.



Actually for what I want to do after casting these walls those bubbles are insignificant. All I need is to cut out the individual stones to build the roundhouse wall master pattern. My whole purpose of posting all this info is to have it in one place on how not to do casting. What works and what doesn't. Plus, it's interesting to see all the solutions being brought forth by the members.

I've got to pour several of the smaller stone walls. Lets see how I do. I'll post results in a few.

Also I'm getting a little burned out on doing castings. I need to get back to my rock crusher project, since I've already started that layout portion. So, if you don't see my posting for a couple of days it's because I'm busy on both projects.

Later.

Bernd

Bernd, I wonder if you added a little detergent with the water while mixing the Hydrocal to break the surface tension. You know like we use wet water.

I'm going to have to try that. Thanks Frank.

Last night I did another two walls. Interesting thing that got my attention was when I added the Hydrocal to the water the amount of bubbles coming up out of the powder. I'm wondering if the powder traps the air and then releases it in the water. Anyway I let the mix soak up the water before stirring. This time though I didn't stir it as vigorously as I did before. I also placed the bowl on the vibrating table while stirring, which seemed to help out a lot. I sprayed the molds with the dishwasher rinse added to the water, shook out the access water and poured the pancake batter consistency in the mold while they sat on the vibrating table. A couple of hours later I pulled the molds. Here's the two molds. Note I have only one little area that has some bubbles.



Remember that I'm not using the full mold for a wall. I'm cutting out individual blocks to form a master pattern. So a couple of hard to see bubble holes don't matter. I'm just trying to get a technique down for the final casting of walls.

So this part of the experiment of casting technique and what material works best for what I want to accomplish comes to an end. I used three different casting materials to try, Durham's Water Putty, Plaster of Paris and Hydrocal. Hydrocal won out as being stronger and easy to cut with a wood blade in a fret saw. Plaster of Paris was to chalky in my opinion and the water putty was a bit to hard when it cured fully.

Up next I will be cutting out the blocks to build a master pattern. That will take some time. I'm going to take a break from the roundhouse project, but not from casting. The stone crusher project needs a support structure and it calls out for a cast concrete wall. Mmmmm........just got an idea.

Until the next post.

Bernd

Interesting experimentation, Bernd. I like learning from your mistakes rather than learning from mine.

George

Good job Bernd. We now have our answers for that sequence. Thank you very much.

I agree with George D, you saved your fellow modelers some raw materials from being thrown out.

I think I read letting the water sit on the powder for a while before stirring is called "slaking" and is recommended. But these days my memory isn't trustable...

dave

Changing only one variable at a time, shrewdly brought you slick results. :up: [:-thumbu

]Grandkids should learn this technique.

Jim

Bernd,

You are probably right about the powder trapping air while being introduced to the water. It might be interesting to try adding it though an old flour sifter just to ensure there is no clumping.

It appears very difficult to avoid bubbles when casting plaster, as the mixture is so thick and the cure time short. Nearly all of the hydrocal castings I have bought showed a few small bubbles here and there. Fortunately they are easily filled with a fresh mix and a toothpick though. Just make sure the casting is wet first, so it doesn't suck the moisture out of the filler.

Using some sort of a flow aid seems like a good idea, though I have never cast plaster in anything but rock molds. In such a case just a quick touch with a dental pick erases the flaw.

As you say though, it isn't an issue on this round. And your results are quite impressive.

Thayer

Well thanks guys. Much appreciate all those comments.

George said:

Well somebody had to do it. Glad you enjoyed the show.

Carl B said:

Thank you Carl. Much appreciated. It was a fun experiment. Now all I need to do is clean up all the dust and little pieces laying all around. Wanna' help clean up?

Dave said:

Yes Dave I've heard that term used. I think you are right on. I think I'll need to do a little more "slacking off" ....er Slacking next time.
Jim said:

Sometimes it's the only way to find a solution. I surprised myself for being able to stick through the whole experiment without losing interest halfway through. I guess posting what you're going to do is a good incentive to keep going and keep you from looking like a fool if you don't try.

thayer said:

I like that idea of using a sieve. Going to have to buy one. I don't think the wife would let me use one of hers.

I'm still out on the flow aid. I'm not 100% convinced that it works. Perhaps do to the viscosity of the mix since it is thicker than water sheathing of a glass in the dishwasher. Sounds like a few more experiments are in order on the next castings.

Thanks for the kind words. Much appreciated.

Well I'm going to start back on the rock crusher building. I have two new casting projects for that. One is going to be a real "twist" on casting.

Until then.

Bernd

Here’s what a professional (C C Crow) wrote in a November 2000 article:





Looks like variants of the steps you’re taking. I like the sabre saw idea.

Mike

Hi Mike,

Thanks for the info. Okay, looks like something else to try. I should have tried the water into the mix method. I did that all the time when I did the brick work on the house. I will definitely give that a try. I'll have to try out the saber saw trick also. At times I didn't think I got enough of a vibration out of the motor. C.C. Crow is definitely the master. Much appreciate that info.

Bernd

Bernd, How about contacting Russ at NE Brownstone for some tips? They make really high quality plaster castings.

Hi Bill,

Thanks for the tip. I just looked at his web site. Very interesting products.

Bernd

Okay, in the last four days I went down the per-verbal casting rabbit hole. I’ll start off with Mike and Bill’s website suggestions.

I surfed over to C.C. Crows site. Although the material he posted is a little dated I did pick up some pointers on casting Hydrocal. Also he doesn’t get into any great detail of how he makes the rock faces. He points out that Jack Work penned an article on producing individual “fractured rocks”. Of course that set me off on a rabbit hunt. No rabbit at the end of that hunt.

I have spent many hours on the “Modelers Forum” following John Siekirk’s build of his layout. What fascinated me most was his roundhouse build and locomotive machine shop build. The block work on both of those buildings is what I wanted to duplicate on my roundhouse build. This lead to following the “The Official F&SM Layout Thread” since that’s where I saw more pictures of a version of John Allen’s block roundhouse. Found out later that George gave John a couple of the original castings to make his castings for the roundhouse. I later discovered the South River Model Works was where it all originated.

All that surfing the net and websites and reading the posts gave me no answer as to how one makes fractured rock faces on Hydrocal castings. I did learn that George Selios made his walls from individual rocks/stones to make wall castings for his models. A member on this forum and The Modelers Forum was also interested in how George made his individual rocks and was looking to get an answer. I never found out if he got that answer.

So anyway, I figured I find out how they did this in the 1:1 world. Many videos later I came across this guy’s videos. Very informative on how it was done. In his #4 video he mentions how the railroad’s built there bridges and so forth using what he calls rockfacing and shaping rock. Now all I need are miniature tools for HO scale rockfacing. I always wondered if those thick walls were all rock or were they just a facade. He gives very good info on such questions and how they were constructed.

Here’s his first video. https://www.youtube.com/watch?v=IkzB...eHaduckMasonry

The rabbit hunt is not over yet.

I did work on the master pattern and also did some casting.

This is for the roundhouse section. I made a jig to do up one wall. I used my Sherline to make the arched windows spacers to build the rock-work around. I used the double sided adhesive paper to fasten the Plexiglas to the paper pattern. Blocks were then cut from the cast Hydrocal walls and the individual blocks were filed/sanded to size and then glued to the jig with white glue.







I also had an urge to see what kind of coloring would look good on the walls. I used some neutral gray acrylic paint thinned to a wash and tried it out on one for the Hydrocal wall castings.



After being a bit frustrated with the outcome of the master wall, that’s another story in its self, I cast the pattern that will be used to hold up the crushed rock bins. I’ll describe that project in another post later. Here’s the sequence of pictures leading up to the mold for the concrete base of the rock bins.

A refresher of the parts I’m talking about being milled on the CNC Sherline.







Here’s the mold box and the mold.







Remember I mentioned that one will be a real twist on casting. Here it is.



Yup, that’s an 18” long by 3/4” diameter concrete drill. Do I plan on drilling holes in Hydrocal walls? Nope. I do need more augurs for the animated rock crusher. I did make an augur in the lathe, but that was very strenuous on the lathe drive system because it was actually cutting a very course thread. Something like four threads per inch. So I had this idea of using one of this concrete drills. I was never able to find one long enough for what I wanted to do until that one day at Lowes when I was just browsing the tool section. A bit steep on price at $38 but I might use it to drill a hole in concrete one day. The plan is to make a two part mold and then us resin to make the augur. Since I ran out of RTV, this part of the project I will have to wait till I need more RTV for another casting session.

When I poured the mold for the three wall sections I had a little bit of RTV left. In my search for rock faces I came across a video that showed how concrete blocks were split to give a rough face. I came up with the idea of using a section of 50 grit sandpaper used on a hand held belt sander and just dumping it on of what was left of RTV. I trimmed it square and the next time I pour some Hydrocal I’ll just pour some on the mold and see what kind of texture it gives to the Hydrocal.





That just about brings it up to date for now.

Tonight I got bachelor’s quarters. The wife is having her second knee replaced. That means I can have more than two beers.

Until next time.

Bernd