Great article Roy, I enjoyed reading it. One question though. What are dryer sheets? Or can you suggest an alternative for us in Australia.

Ken

I should have read through the earlier comments and seen that my question has been answered already. Still a great article Roy I shall try it out some time.

Ken

Dryer sheets, sometimes called "bounce" after one of the name brands, are small sheets of synthetic fabric coated with some chemicals that help clothes dry in a drier without wrinkles or static build up.  They are often purported, in advertisements, to give clothes a 'fresh' smell.  I don't know how 'fresh' that smell really is - my orchard owning neighbors tie them to new trees since the deer hate the smell which gives the trees a fighting chance for survival when they're small and are targets for young bucks to rub the fuzz off their new antlers...

Charlie

Love this article, going to try this out with my next rock castings. Wonder if this could also be used for more deatailed castings like pieces of buildings and such.

Ok I followed all your instructions to a"T" and on Dec 6th I made a silicone mold 4-1/2 inches wide and 7-1/4 long. I applied wet water in fact I poured wet water in a plastic 4 inch deep Rubbermaid container with 2 gallons of water and three table spoons of Ivory dish soap and mixed it well. 

I have used this same mixture of wet water for years for mold making and usually set the area I plan to copy and cover with latex face down into the wet water mix then turn upright on to a plastic covered table top.

I then applied the 1/8 inch layer of "GE" 100% Silicone II Clear". I used my finger soaked in wet water to spread the silicone into a thin constant layer in the area. Once that was done I covered the silicone with a single layer of surgical gauze.(I have a dozen 12 inch wide rolls) I then put a small amount along the outside edge of the mold to tack the edges and gave it 4 days to dry.

On Nov 11th I applied a second 1/8 inch layer of Silicone and covered it with more Gauze and left it alone until yesterday evening Nov 16,2012 when I remembered I had the mold drying on the train table and went in the room and started to pull off the mold.

As I pulled the edges were completely dry and came up with no trouble. Then about 3/4 inch in the silicone was gooey and sticky and hadn't cured I thought this was strange. I continued to pull off the mold leaving behind chunks of gooey silicone which only about 50% cured.

The only thing I could think of was I used the wrong silicone so My question is now.

? What was or is the exact name and manufacturer of the silicone you used to make your molds?

I used "GE Silicone II Clear 100% pure silicone, Premium Waterproof. Window/Door/Attic/Basement 3hr Rain Ready completely dry in 24hours @ 3/16 inch thick and I made mine 2/16 inch thick.

I really think it's the silicone and not your method!

also The batch use date said use by Feb 2012 and I bought it on the 6th of November the same afternoon I started the project.

Thanks and please give me the names of the product.

Dan

I made vibration pads for the wife's washing machine by filling 4) 2-1/2" automotive rubber expandable freeze plugs (with the washer and stud removed) with GE Silicone II Black caulk. Onto the wet silicone I placed conventional drive in steel expansion plugs upright for the legs of the washer to rest on. Filling 4 rubber freeze plugs required a tube and a half of silicone to give you and idea of how much silicone was in each freeze plug. I set them aside to dry.

Much to my surprise and as Dan has experienced the caulk was gooey inside after a week. You could easily feel it by pressing on the surface. It took over a month for the entire freeze plug to firm up to the point I felt it would not squish out under the weight of the washer. More than a month!

My lesson learned... thick applications of silicone caulk dry very slowly. The story has a happy ending. The vibration dampers work exactly as intended. If the noisy old Maytag was a bit less noisy you would never know the washer is running and it hasn't moved a drop in 6 years.

Yikes, Dan, I'm so sorry that didn't work. Your product is the same type of stuff that I use, maybe a different brand, but still 100% pure silicone. I buy mine at Home Hardware, which I don't think you have in your area. The only thing I can think of is that the silicone was to thick and still hadn't cured. To be honest I can't tell you why.

One trick I learned the hard way, having an almost identical experience as you when I first started using this system, is to gently push on the mold prior to lifting it off. If it feels spongy anywhere you know that the silicone hasn't fully cured. The mold must feel firm and have no give. My molds are even thinner now than when I wrote the article, but I also have disasters periodically. Most of these are caused by not placing enough pressure on the silicone when patting it into place with the result that I end up having bead lines or voids in the mold. Still, even when I wrote the article, I was making castings in the evening with molds that I'd first formed in the morning. I guess temperature or humidity could have a bearing, but you mentioned that the mold was in the train room, so that shouldn't be the problem. You've got me stumped. Myabe one of our members more knowledgeable in chemistry might have an answer.

Give it another whirl with a smaller mold and let me know how you make out. I think I did about three or four before I started becoming comfortable with the method.

Roy

Here is something I found on another site that seems like it could be pertinent.  Apprently high humidity actually speeds curing of the silicone...who knew?

Curing time of GE Silicone I & II molds

Interesting read, Blue. That could explain why my molds seem to cure reasonably fast, seeing as I live on Vancouver Island. Though our humidity isn't oppresive like back east in the summer months, it is always here. The point about the vinagery smell struck home with me. The stuff I use has a strong smell.

Roy

I did a web search and found GE products like their SIlicone II dry in 24 hours in a 3/16 inch Bead and cure 100% in 25-40 days. So Ill just recote it and try to remove the mold again just about Christmas time or maybe News Years Day.

Also Thanks Kevin (Blue comes through again) for the web pages on the acid and moister This will speed things up I hope.

Dan

I wonder if there was a reaction between the Silicone and the Ivory soap?

If the silicone likes humidity for fast curing maybe making molds in the shower area would be a good idea (vbg)

Charlie

I wonder if there was a reaction between the Silicone and the Ivory soap?

Charlie

I wondered that myself.  I did see one reference to using scent free, antibacterial free, dish soap, so perhaps that has some merit?

I found, (Google is my friend) a couple of very interesting tutorials on making silicone molds.  Water is indeed the catalyst in curing silicone.  I read that one fellow made a thick mold that took nearly two months to cure fully.  Once the surface had cured and no more humidity was able to get to the remaining uncured silicone inside, curing went very slowly.

One mold maker uses acrylic paint mixed into the silicone.  He claims that the resulting mix will cure amazingly fast, like you won't believe it, fast!

Another actually cuts the end of the tube off and expels the silicone into a pail of soapy water, where he manipulates it with his hands and then pulls out a big ball of silicone and spreads it on his mold master.  As long as your hands are wet with the soapy water the silicone will not stick to you, so he claims.  I do know a wet finger tip smooths a bead of caulk nicely, but it must be kept wet!

All in all a very interesting article and subject for further discussion here at MRH.  Thanks Roy for bringing this to us!

Here are the links to the two tutorials I found.

Making a Simple Rock Mold with Silicone Caulk

Silicone Caulk Mold Tutorial

A modelling friend found another link that also confirms the moisture and silicone type reference.

http://www.myheap.com/book/chapter-07/siliconecaulkmolds.php

It looks like they are discussing the use of silicone for large molds, but I guess the information is still applicable to the system I use for small molds. Even though I did a Google search when starting out on this project, I obviously didn't use the right terminology in doing my search.

I have used Mono brand silicone and the house brand from Home Hardware, a Canadian company. From the link above and those that Blue posted moisture and thickness are the key to curing. I cringe at the thought of using chemicals referenced in the above links, but it might be necessary for what the individuals are trying to achieve with their molds.

I haven't added anything to my silicone to hasten the curing process, nor have I used anything other than "wet" water as a release agent. The soap I use is a cheap no name brand dish soap. I use plaster-of-paris to make my castings and a modeling friend uses a commercial plaster that is much harder. So far some of the molds have made thirty + castings and are still being used.

Thanks Dan for bringing this discussion to the fore. I sure hope the process works out for you and everyone else. Blue, thanks for the links, they were a very interesting read.

Roy

Roy,

Thanks for that link too, it's in my bookmarks. Some very interesting information there and it seems to confirm the use of acrylic paint and who knew, Glycerine, as additives.

Very interesting article and discussion!

Just finished setting up two molds in the garage. The temperature is in single digit Celcius or low 40's Farenheit at present. Humidity is reasonably high outside with low overcast clouds and a light rain. I only used soapy water and Home Hardware brand RTV silicone. I'll give and update as the molds cure.

Roy

Is this surgical gauze the sort of gauze used in making wound dressings or is it the stuff for making casts?  If it contains any plaster, the plaster will suck the moisture out of anything it touches, and may hinder the curing of the silicone.  I also think you need to do a thin layer of silicone bead, and then let it cure before adding additional beads of silicone.  Let each layer cure before adding more layers.  If you build it up too fast, the middle of the mold won't cure very well.

I thought that this bit from Blue's link was interesting: "add a little saw dust or wood flour, thin with a little VPM Naphtha and you can actually paint the rubber on." Aside from confirming that water speeds the cure, the thinned caulk could be used the way latex rubber is in making molds, if one wanted to stick to "the way we've always done it."

~Ken

Brilliant idea. Even works !!  There had to be a 'better mouse trap'. I have made 3 moulds, and I'm impressed with the results. Thanks.

On30 in New Zealand.

I'm glad it's working, Classic. Will look forward to pictures if you get a chance.

Reading about Dan's difficulties and the additional links that were posted prompted me to rethink the whole process. With the weather cool and damp here I went out to the garage and made two more molds yesterday using the exact same process I described. I left them sit for 24 hours simply because of other commitments. Both separated from the master easily and are now sitting on the workbench with their edges curing. I both cases, the maximum thickness if the silicone is no greater than 1/8th inch. Again, I used spent dryer sheet as the bonding membrane between both layers of silicone.

The links that were posted were very interesting. My take on using the various chemicals as curing agents is that they are used when trying to make block molds rather than skin molds. There is no doubt that they work. I have in the past purchased liquid silicone in one liter/quart size containers that is available in hardware stores and is painted onto the intended surface. I don't know how this type of product would work using the process I described. I do know it was more expensive than the cheap tub RTV silicone.

As the posted links indicate, moisture and thickness is the key to curing. Thanks to everyone participating in this discussion.

Roy

The Gauze is Basic Sterile single layer that is used to make all types of medical bandages and is thinner than a single layer of Cheese cloth. I got it cheap from a medical supply company where my friend works.

The gauze wasn't the problem but it was the extremely dry basement and Silicone II. After removing all the $6.50 a tube silicone II and redoing the mold with cheep stinky $2.00 a tube clear silicone from Wal-Mart the molds are coming out GREAT! OH YEAH!!

I've made a few really nice molds now, and in less than 2 hours to cure each layer. so the cheaper the silicone the better the mold comes out. Go Figure.

I think the Silicone II would work if I waited 4 to 6 weeks for it to cure but who wants to wait that long. beside the cheap stuff makes the molds cost less than 1/3rd the price for each one. win win cheap and fast perfect.

Dan

Congrats, Dan.

To be honest you had me baffled. I didn't even know there was silicone II. Looking forward to pictures when you get a chance.

Roy

Thanks for a great article.  I am going to give the process a try.  But first, what do you mean by "wet" water?

Roy Simpkins

Raleigh, NC

Some people may use other "additives" like alcohol.  The problem is that water has a surface tension that needs to be broken to get it to disolve.  As an example, if you try to ballast your track with some water soluable medium and water only, the water will tend to sit on top of the ballast and not soak in.  If you put a drop or two if soap in the water first, the surface tension is broken and the water soaks right into the ballast without disturbing your carefully contoured edge profile.  It doesn't take very much soap to water to break the surface tension, just a few drops in a spray bottle

Great answer, Russ. Thanks.

Roy

Earlier in this thread silicone curing time was brought up. Well, as things go, the dryer went on the kaputz over the holidays so we got a new one. While the space was empty I took a photo of the silicone vibration dampers I made. For reference the damper is 2-1/4" diameter by 1" deep. If you use a similar amount of silicone expect a month long cure time. For what it is worth the dampers work great. The silicone has just the right amount of "wiggle" to it to dampen the sound yet not get squished by the weight of the appliance.

Loved this article. Fast simple and it works. Great Photos too. Keep 'em coming.

I also had to give this a try and they did make molds but I had one problem.  I got seems in my molds that showed in the casting I made.  The seams are between the bead of calk and no matter how hard I pressed the silicon on the rock I was molding I would get seems.  After about 4 or 5 molds I purchased some "Mold Builder" Latex to make some molds and had no problems with it at all.  The cost is a little more but I still use the cry sheets between layers just like the silicon version.

Hi Railbuilder.

Seams can be a problem and I do get them sometimes. I've found that I have to manipulate the silicone sideways a bit as well as press down. Latex is very expensive where I live, so if I want variety silicone is my only option. Thanks for trying the process and good luck with the latex.

Roy

I wanted to share my experience using Roy's article.  Which, by the way is 5 Star!  However, in regard to the saying "your milage may vary" I offer my ideas/experiences as a way to reduce the learning curve that I went through!  I did follow all the steps per Roy's instruction, however, adhesives and I do not see eye to eye.  You recognize us folks with glue/acc/silicone/elmers all over ourselves and the two items it was intended for on the floor. So, as you well may know by now, half of my first tube of silicone (high end stuff too) ended up in the trash.  With that vision in your head I offer my lessons/experience with Roy's method.

1. I soaked the my master rock in wet water.  Why? I did not want to brush it on, and I had the bucket with wet water for my fingers anyway....so in went the rock.  How long?  Long enough to get it wet.

2. I did not smooth/press the first layer of silicone with my fingers (ON THE 2d ATTEMPT!). I soaked the dryer sheet ( or whatever you folks Down Under use) then firmly pressed it into the silicone. And presto, no silicone adhering to my wetted fingers! I then added the 2d layer of sealant. This layer I pressed into place with a soaked paper towel. And I got Roy's result.  So, if you are "GLUE Challenged", try that method.

3. I used both high end and low cost silicone....I got the same results from both.

4. Patience is a virtue while letting the silicone cure. My time line is eight hours.

5. I used plaster of paris.

6. Acrylic paint thinned with alcohol and water was used.  I also rubbed dark shades of chalk across the rock then rubbed it with a damp paper towel.

The finished product which is two seperate molds one just leaned against the other.

John

Merrill, WI

Great suggestions, John. The rocks look really good. I'll be giving your idea a try. It's amazing how different rocks can be and only over a short distance. On my way home from a train show in Nanaimo today I watched how different the rocks were along the roadside. Colours, types and orientation varied drastically in the cuts over short distances. Variety, the spice of life and fun.

Roy