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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  4:11:31 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
As I said this gets a little messy. Have plenty of paper towels around to wipe your hands and utensils with. Especially if youíre taking pictures. You donít want a sticky camera.
Trying out using a dipper for the Part A. This is heavier than the Part B. The measuring cup has a line at 2 Ĺ cups, thatís the goal.





Pouring Part B straight from the container. Works better and is less messy.



The numbers are very hard to see on the measuring cups. A quick side by side shows I need to take a bit out of the Part B measuring cup.



Into the 5 cup mixing bowl.



Hereís where the fun part begins. Iím pouring in Part B while using the mixer with one beater to stir (beat) the two parts together.



Once itís all poured in a good mixing ensues.



The two parts are mixing very good here. I have the mixer on its lowest speed.



Looks like I added to much yeast. <BG> I figured Iíd have bubbles, but this many?



Before I started pouring the rubber I let it sit for a few minuets before pouring over the master. Pouring from about 1 to 1.5 feet up helps eliminate many of the bubbles. Also just pouring a thin layer over the master and letting the bubbles surface helps.



And after 5 cups of RTV the mold is not quite filled up. In 24 hours Iíll de-mold it and weíll see what we have.



Until then, enjoy.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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deemery
Fireman

USA
8836 Posts

Posted - 11/27/2020 :  5:15:58 PM  Show Profile  Reply with Quote
When I saw the mixer, I worried about introducing too many bubbles. Looks like the careful pour of the initial coat helps! Looking forward to seeing the result.

I wonder if you should look into an improvised partial vacuum chamber... https://www.instructables.com/How-to-Make-a-Vacuum-Chamber/

dave

Modeling 1890s (because the voices in my head told me to)

Edited by - deemery on 11/27/2020 5:17:14 PM
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Bernd
Fireman

USA
3947 Posts

Posted - 11/27/2020 :  8:42:45 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by deemery

When I saw the mixer, I worried about introducing too many bubbles. Looks like the careful pour of the initial coat helps! Looking forward to seeing the result.

I wonder if you should look into an improvised partial vacuum chamber... https://www.instructables.com/How-to-Make-a-Vacuum-Chamber/

dave



As you saw it did introduce bubbles. If you let it set for 5 to 10 minuets there are less bubbles. Also pouring it the way I did by putting a thin layer over the master helped with bubbles. We'll see tomorrow when I de-mold it.

I made a vacuum chamber a couple of years ago when I first started casting resin and RTV. I used a refrigerator compressor. Worked great. I'll have to post some pictures of that someday.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/28/2020 :  09:27:25 AM  Show Profile  Visit Bernd's Homepage  Reply with Quote
With yesterdays pour there was concern of the bubble created when I use a mixer to blend the two part RTV. It did create lots of bubbles as can be seen in the previous picture. After letting the RTV set for a few minutes it released any of the larger bubbles. Then pouring it from a height of about 12 inches making sure that a very thin layer covered the master the rest of the bubbles escaped. Also letting the thin layer of RTV set for a couple of minutes helped. Pot life of the mix is 30 minutes, so there is plenty of time for the bubbles to escape.

So this morning I pulled the mold.



A quick close up shows no bubbles in sight.



Hereís the impression. I canít find a bubble anywhere, can you? The sides need to be trimmed a bit.



I did destroy one of the sides. No problem. Iíll just make a new one the next time I need this mold. Hopefully itíll be a long time.



Cleaning out the bowl is quite easy the next day. Just pull the remaining material from the plastic bowl.




So I have four more molds to do. Iím going to do three today and am saving one to do Monday. A model railroad friend of mine is stopping by to see how itís done. He wants some firsthand experience.

Once all the molds are done Iíll start with casting the plaster walls. Question: should I use casting plaster or Hydrocal? If Hydrocal, where can it be purchased? I havenít seen anything local.

Thanks for stopping by as the adventure of building a block wall roundhouse continues. I think itís time to get back to the rock crusher building and finish that.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Frank Palmer
Fireman

USA
6129 Posts

Posted - 11/28/2020 :  09:47:53 AM  Show Profile  Visit Frank Palmer's Homepage  Reply with Quote

Nice molds. Where do you get your RTV from?

Frank
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deemery
Fireman

USA
8836 Posts

Posted - 11/28/2020 :  12:49:12 PM  Show Profile  Reply with Quote
Glad to see all your bubbles escaped!!

dave

Modeling 1890s (because the voices in my head told me to)
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Bernd
Fireman

USA
3947 Posts

Posted - 11/28/2020 :  12:56:19 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Frank Palmer


Nice molds. Where do you get your RTV from?



I get it directly from Smooth-On. Not cheap. That quantity cost me $163.74 + shipping/handling + tax for a total of $208.98 But at the quantity I use I don't think its bad, plus it's the best stuff I've used so far. It can take a bit of miss-match when mixing part A & B and still come out okay. I guess if I was in the business of making molds I look for something cheaper.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/28/2020 :  1:00:57 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by deemery

Glad to see all your bubbles escaped!!

dave



Not all the bubbles escaped. The RTV poured onto the master with a thin layer has no bubbles. I attribute that to letting it set for a few minutes before adding the rest of RTV. I did some trim work on the larger one and found there were bubbles entrapped. So, if you have bubbles in the liquid RTV, pour a thin layer over your master. Let it set to release the bubbles and then pour the rest of the RTV on top and you have a bubble free surface to pour your plaster or resin into.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Pennman
Fireman

USA
4694 Posts

Posted - 11/28/2020 :  1:44:57 PM  Show Profile  Reply with Quote
Bernd,

So glad you chose this particular topic, as I have yet to do the same soon. Your molds turned out very good and your method of execution is at least near-perfect. Sometimes the Gods are with us !!

You asked a Question: "should I use casting plaster or Hydrocal? If Hydrocal, where can it be purchased? I havenít seen anything local."

You can buy hydrocal online at Ebay, but plan on a high shipping fee. I bought a six pound container of Ultracal 30 and shipping was $17.00+ The Ultracal 30 is IMO, the best used to bring out fine details.
Amazon also has it in 10 or 25lb. bags, just search for: 10 Lbs ULTRACAL 30 Gypsum Cement - Plaster - for Moldmaking and Casting, Ideal for Latex Molds! Takes Excellent Detail -- $21.50 or ULTRACAL 30 Gypsum Cement - Plaster - for Mold Making and Casting, Ideal for Latex Molds! Takes Excellent Detail (25 lb) -- $49.99
I like to purchase from amazon, as shipping costs are eliminated if you have prime.

Hope this helps.

Rich

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Pennman
Fireman

USA
4694 Posts

Posted - 11/28/2020 :  2:11:56 PM  Show Profile  Reply with Quote
quote:
Originally posted by Frank Palmer


Nice molds. Where do you get your RTV from?



Frank,
I have yet to make a rubber mold using something like RTV rubber. So, last year I stumbled upon John Siekirk's Stone Roundhouse build, (like Bernd referenced), and sent John a message. He recommended me to purchase: Ten-To-One / High Tear Strength Mold Rubber, 28 Fl. Oz. - Item #: 82663, from Micro-Mark.
You can find that here:

https://www.micromark.com/Ten-to-One-High-Tear-Strength-Mold-Rubber-28-fl-oz-_2

My reason for buying this brand was the fact that I didn't have too many molds to make, just a few walls. Hopefully it will work for me, and if there isn't enough product, I can buy more. I'm not a fan of overbuying a huge amount especially if it goes bad after opening, if not totally used up.

With Bernd's thread, hopefully I can get over the nervousness and make one of my own! We shall see how far my product goes.

Hope this is another option for you in case you are interested in making a purchase.

Rich
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Bernd
Fireman

USA
3947 Posts

Posted - 11/28/2020 :  4:45:26 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
Thanks Rich for the Hydrocal info.

I see Micro Mark also sells Smooth-On RTV and their Smooth-On resin. Must be something new. I started with the smaller kit from Smooth-On. They make two verities OO-M-OO 25 and OO-M-OO 30. The first has a 15 minute pot life, the second has a 30 minute pot life. The smaller version amount, or what they call trial version, is 2.8lbs. That's a perfect size for making one medium size RTV mold. Price is $27.25 for the RTV. If interested for more info go here: https://www.smooth-on.com/category/tin-silicone/ and click on the OOMOO Series. They also have some videos on making molds and casting techniques.

Now on to the casting medium. I'm going to start with a casting plaster to see how it works and if it will break easy for what I'm going to do. I'll look into getting some Hydrocal to try also. One thing I'd like to try is Dental casting plaster. I have two kits that have walls made from dental plaster and it seems quite hard material and picks up detail well also.

This is one of the kits. Notice it states "dental stone" castings.



And here's a close up of the brick wall detail. Very clean.



I found a vendor on E-bay that sells all kinds of dental plaster. Price seems to be comparable to Hydrocal.

https://www.ebay.com/sch/plasterguys/m.html?ssPageName=STRK%3AMEFSXS%3AMESOI&_trksid=p2053788.m1543.l2654

That's for now.

Note: Just discovered that the guy selling dental plaster also sells hydrocal. Maybe I'll order one of each for a test.

Bernd


New York, Vermont & Northern Rwy. - Route of the Black Diamonds

Edited by - Bernd on 11/28/2020 4:47:45 PM
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Pennman
Fireman

USA
4694 Posts

Posted - 11/28/2020 :  5:38:48 PM  Show Profile  Reply with Quote
Bernd,

You can buy a 25 lb bag of plaster at any good lumber yard or hardware store. IMO it's not as good as hydrocal or the dental stone. Castings I have made from plaster seemed too brittle even after they cured, (several days).

My next choice would be dental stone, then hydrocal last. It's up to you to try what you think is best. If you google both, the internet is full of resources for both products with articles and reviews.

Rich
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Carl B
Fireman

USA
4147 Posts

Posted - 11/28/2020 :  5:53:24 PM  Show Profile  Reply with Quote
I've read good things about the "plaster guys".

Haven't used them myself, but given your upcoming experiment Bernd, perhaps you can enlighten us then....

I may want to try these "stone" type plasters so I can see how strong they really are...
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Bernd
Fireman

USA
3947 Posts

Posted - 11/28/2020 :  6:32:39 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Pennman

Bernd,

You can buy a 25 lb bag of plaster at any good lumber yard or hardware store. IMO it's not as good as hydrocal or the dental stone. Castings I have made from plaster seemed too brittle even after they cured, (several days).

My next choice would be dental stone, then hydrocal last. It's up to you to try what you think is best. If you google both, the internet is full of resources for both products with articles and reviews.

Rich



I just ordered three types of casting material from the "Plasterguy" on E-bay. Time for a little testing.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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Bernd
Fireman

USA
3947 Posts

Posted - 11/28/2020 :  6:34:42 PM  Show Profile  Visit Bernd's Homepage  Reply with Quote
quote:
Originally posted by Carl B

I've read good things about the "plaster guys".

Haven't used them myself, but given your upcoming experiment Bernd, perhaps you can enlighten us then....

I may want to try these "stone" type plasters so I can see how strong they really are...



Carl,

I'm sure you saw my answer to Rich. Should be able to test starting next week hopefully. I'll give a full report.

Bernd

New York, Vermont & Northern Rwy. - Route of the Black Diamonds
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