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How to Make a Pre-Thickened Silicone Brush-On Mould
June 26th, 2010 | 
Author: There are times when it is essential to use a pre-thickened type of rubber using a brush-on application to make a mould of an object. An example of this would be to reproduce architectural ornamentation attached to a wall that could not be removed. Another would be the duplication of large pieces of sculpture. It would be difficult to apply the regular type of silicone or polyurethane used to make moulds by pouring, to do this type of vertical application without them sagging, so a pre-thickened type of silicone such as Gelsil is used.
1. Making Good the Model Surface: Before commencing the mould making, make good the surface of the original by repairing any cracks or damaged portions and allow the repairs to dry.
2. Some Models Must Be Sealed: The next step is to seal the surface of all porous articles, such as plaster, concrete, wood or stone. One or two coats of fast drying shellac may be sprayed on using the aerosol form of shellac available at most art or hardware stores, as this does not interfere with the surface detail. Spraying the sealer has the advantage that the coverage of rough detail and undercuts is easy. If sealing is not done the silicone will penetrate into the interstices of the porous surface and would be difficult or impossible to remove.
Sculptors please note, shellac is also suitable for sealing modelling clays that contain sulphur such as Roma Plastelina and clays containing moisture. It is not necessary to seal objects made of glass, glazed ceramic, sulphur free clays and hard plastics such as acrylic and PVC.
In all cases the sealing agent must be allowed to dry thoroughly before continuing on to the next step.
3. Application of the Release Agent: The release agent should now be applied. The aerosol Stoner 234 is recommended for silicones and should be lightly sprayed across all surfaces that will be in contact with the rubber and allowed to dry. Another release agent that can be used is a 10% solution of Vaseline or petroleum jelly dissolved in naptha or white spirit. When using most silicones this step is often not essential but until you have tested the surface it is better to be sure than sorry. For all polyurethane rubber, followed by a light spray, as polyurethane sticks to anything.
Before starting any major project, the effectiveness of the sealer/release combination should be tested using similar surfaces, on a small scale before starting the main work.
4. Measuring and Mixing: This will require two plastic containers as they must be weighed. Gelsil requires 10 parts by weight of the catalyst to 100 parts of the silicone. The pot life is 20 minutes and the model can be de-moulded in 6 to 12 hours. We usually leave overnight. It is Thixotropic by nature and is ideal for brush on application. It has a shore hardness of 25 and is capable of picking up very small detail. It has a low linear shrinkage of 0.40% and high tear strength. It is very suitable for reproducing models with pronounced undercuts.
Mixing tools should be of metal, glass or plastic. The Gelsil catalyst is coloured to ensure complete mixing. After weighing out the required quantities of silicone and catalyst pour the catalyst into the silicone container and mix thoroughly for 3 minutes making sure you scrape the sides and bottom of the mixing container several times. Use a flat paddle action rather than a brisk beating action to reduce the amount of air you beat into the mixture. You will know when you have achieved a good mix when you have a good even colour.
5. Rubber Application: The silicone must be applied in layers. The number of layers of rubber required is between 4 to 6 dictated by the size and shape of the model. Use one of the cheap Chinese white pigs bristle brushes sold in most art shops for brushing on the silicone. The fist coat is important as this will pick up all the fine detail of the model. Apply this “detail coat” in a thin layer taking particular care to cover the entire surface. Use a dabbing action rather than a painting action especially around undercuts to reduce the amount of entrapped air and to pick up all detail. Let this first coat dry till it becomes tacky before adding the next coat.
Repeat adding layers of silicone in thin layers especially for the first 3 or 4 coats till the necessary thickness is achieved. Later layers can be applied thicker providing the silicone is not applied so thickly it drips off the model. To prevent the possibility of de-lamination do not allow any of the layers to fully cure but apply each new coat when the previous coat has become “tacky”. When working in difficult or dark conditions, a mould maker’s trick is to add colour to each layer to ensure complete coverage has been achieved, but this is not essential in normal working conditions.
6. Curing: Allow the mould to cure at least, overnight before making the back-up mould. In cold conditions leave for at least 16 hours to ensure complete curing. After the back-up mould is made and the silicone mould is removed post curing of the mould for 4 to 6 hours at 60 degrees celsius is an advantage and will increase the physical properties a great deal.
7. Applying a Back-Up Mould: To ensure subsequent castings are accurate the silicone mould must be held in the correct shape by a support or back-up mould. This can be made of either plaster or fibreglass. For the plaster back-up use an oil soap release agent applied to the exterior of the silicone mould. For the fibreglass use PVA release agent.
It is essential to locate any undercuts on the silicone mould that would prevent its easy removal and fill them in with Plastelina Clay or alternatively make a two piece back-up mould.
8. Using the Silicone Mould: If the mould is to be used for concrete use a vegetable oil thinly applied as a release agent. For plaster use an oil soap release. This should be applied to the mould before each casting and any excess accumulating in undercuts or detail should be removed with a cloth to remove pooling of the release agent.
9. Mould Life and Storage: When fully cured these moulds are tough and have a high tear strength if properly used and stored. The life depends on how you use it. Abrasive materials such as concrete will eventually cause mould detail to deteriorate while non abrasive material will not affect detail. After use wash moulds with warm soap and water and let dry. Moulds should be stored on a level surface in a dry non sunny, cool environment.
Stan Alderson.
Copyright. 2010 Aldax Enterprises Pty Ltd
Important: The Material Safety Data Sheets (MSDS) should be read prior to using any Industrial moulding making product and are available upon request from Aldax or may be viewed on their website. Directions should be read and followed carefully to ensure safety.
The information contained in this article is considered accurate. However, no warranty is expressed or implied regarding the accuracy of the data, the results to be obtained from the use thereof, or that any such use will not infringe upon a patent. User shall determine the suitability of the product for the intended application and assume all risk and liability whatsoever in connection therewith.
For Technical help:
Tel. 02/9533 9555
Fax 02/9533 9955
Website: www.aldax.com.au
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HOW TO MAKE FAKE ROCK
Many methods can be used to make fake rock and boulders and all achieve realistic results.The method you choose to make fake rock is often determined on the price of the filler material and availability. Very realistic faux rocks or boulders can be made using any of the following filler materials.
Building Materials and Methods
- Building rubble such as second hand bricks or crushed concrete.
- Recycled real rocks
- Polystyrene
Alternate methods to make fake rock involve using some way of giving an approximate shape to the finished rock before the application of the mortar.
- Chicken wire bent to shape is widely used for the smaller rocks
- The general shape can be formed with carboard boxes cut to size.
- Rebar and expanded metal.
If the same design of rock needs to be repeated many times the use of moulds will greatly assist.
- Casting from a mold
The material and method you use to make fake rock will be the one that you consider to be the fastest and cheapest to give you the best finished result. The level of detail in the rock usually determines the amount of time needed to complete the job.
Garden boulders and other larger rocks usually look best with a smoother and less detailed finish compared to smaller decorative rocks and require less work and material.
A garden landscaping job will often require the use of several of these different finishes to give the required natural look. The more methods and techniques you know how to use to make fake rock the better the final result will be.
Solid Fill Method
Due to readily available building material on site this is one of the most widely used methods but it is also slow and expensive. Not being of hollow construction it also gives the closest sound and feel to natural rock.
Materials which are required for this method include:
Rubble from demolished buildings.
This material can usually be obtain free of charge as it is most likely destined for disposal. It is essential to hose it down before use to ensure proper bonding.
Concrete blocks and recycled bricks
It is still cheaper to use these materials rather than concrete even if you have to purchase them. Difficult shapes such as waterfalls are also easier to construct due to the regularity of their shape.
Polystyrene
As a by-product from packaging this material can usually be found free of charge. The nature of the product allows it to be easily shaped and produces quite a light weight finished faux rock. It holds the shape of the rock and does not slump with the weight of the mortar, unlike some of the other filler materials.
Recycled rock and other natural materials
These are often on site and easy to use giving very natural shapes. Wash before use.
- If the material being used is in small pieces it can be placed in plastic bags and stacked for ease of assembly.
- Cut open the plastic bags to expose the filler material inside.
- You will then need to apply two coats of acrylic polymer stabilizer. This should be thrown on using a brush and is designed to ensure the structure is rigid before applying the finishing mortar mix.
- Now apply two coats of the mortar, with each coat being 40mm thick.
- Complete the process as described with the other techniques.
This type of faux rock is relatively easy to make. It also uses plain concrete and a basic mortar mix for the final shaping to further save any complications. You first need to build up a base for the rock in concrete, then build up the shape a bit with some rubble, add more concrete, more rubble again and so on until you have achieved the finished shape.
To make fake rock with this method it is a good idea to be doing several rocks at the same time. As the concrete sets on one piece of rock you can be creating another piece. Application of mortar can commence once you have completed the rough shape and it has set.
The mortar generally adheres better when it is applied in a throwing on action rather than trowelling. It also provides a rougher surface for successive layers or mortar to be applied to. Start from the top and work downwards with the finishing coats. If you are working on rocks which are side by side take care to ensure join lines are emphasised. Definition is very important with these seams to give the rocks a natural appearance.
Construction methods for hollow rock
Chicken Wire
This method is suitable for making hollow rocks of a smaller size.
- Cut and wrap the chicken wire to the rough shape of the finished rock.
- Bend all sharp edges of wire inwards using pliers.
- Now cover the wire with some newspaper soaked in 50/50 diluted white woodworking glue and allow to dry.
- Cover the wire with several layers of plaster of paris bandage which has been briefly soaked in water and allow to dry.
- Using diluted acrylic paint mixed 50/50 with sand decorate the final rock to create a realistic stone representation.
Re-bar and Expanded Metal Construction
If you need to make fake rock which is hollow this is a very common method. Using this method rocks can be shaped to cover taps, pool pumps and other equipment. This method can produce waterfalls to garden arches due to its ability to be easily shaped.
The expanded metal can be attached once the re-bar has been set up. Tie it to the re-bar every 100 to 150mm. Ensure that it is firm. Coat the structure with two 3 to 4cm coats of mortar mix leaving a minimum of an hour or overnight between coats, depending on the temperature of the day. Add texture to the project using similar methods to the solid fill method.
Cardboard
Large and small cardboard boxes cut to shape can be built up to form a strong structure resembling the desired rock shape. Making faux rocks of all shapes and sizes is easy using boxes that are readily available free from your local stores.
- Make the structure rigid by stapling, wiring, screwing or gluing the cut box shapes together to form the rough outline of the desired rock shape.
- Using a throwing action with the brush, apply two coats of polymer stabilizer mix straight onto the boxes. If too much is applied at once there is a danger that the cardboard will be soaked and collapse. Between coats allow the cardboard to full dry allowing it to attain the required strength to support the final mortar mix.
- Two coats of mortar mix can now be applied in 8-mm thicknesses.
- Now you can texture the structure followed by staining and sealing.
Casting from a Mould.
Using a mould can produce the most accurate representation from natural stone of all the methods. They are perfect reproductions of stones in nature. The same design of stone can be reproduced endless times. Moulds can be made using latex or silicone usually with a plaster back up mould to retain the original shape.
The process which involves the use of texture moulds will be the subject of a forthcoming article.
Copyright © 2010 Stan Alderson
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How to Make 100% Profit Selling Plaster Painting Paint
This is one time the $2.00 shops are not the best way to go. Although they sell packed acrylic paint at a very low price you can do very much better by repacking your own. Plastic vials are less popular than glass ones with screw on lids among the successful plaster painting studios as they have found they have a tendency to leak.
We have been searching and testing many plastic containers with push on lids which are around the size of a 50c coin. We have found these to be quite easily filled and are usually larger than the glass vials. Previous versions did leak, however the latest version shows no sign of leaking and are very reasonable in price.
The children can now use either glass or plastic type containers. You may be wondering what the best type of paint to use on plaster is. The obvious answer is an acrylic paint. Acrylic paint is water based which makes it really easy to clean up if you are quick. If you let it dry however it can be a different story. This type of paint when dry can prove very difficult to remove from clothing. Supplying a basic apron to your regular clients is recommended.
After much searching we have sourced a quality acrylic paint from one of our suppliers in Melbourne packed in 2 litre containers that can be set up to pump fill your containers without spilling a drop. These paints come in the primary colours and can be mixed to produce a full palette of colour. With the attractive price of $11.95 per bottle including GST you can get the price down even lower by purchasing a set of six colours which will reduce the price as low as $9.95 per bottle. If you sell about 100 to 200 vails of paint to your clients for about a dollar each you will only be spending 10c for the paint it conains. And that is worth getting up for in the morning! You can purchase paints here.
To make life easier it is worth getting the pumps that fit on each 2 litre container. A simple push on the pump and paint is drawn out of the bottle and into the container. The only remaining thought I can give along the road to making some money out of plaster painting is to check out the brushes.
Many have told me the $2.00 shops have cheap brushes but they only come in assorted sizes, most of which you don’t want. We have found the Chinese white pigs bristle size 6 to be the best brush for a plaster painting setup. Any smaller and it will take too long to paint and become tedious. Any larger and you will lose detail and waste too much paint.
As a result we carry bulk stocks of this very size at a reasonable price. Remember to wash the brushes out after the students leave to keep them in good condition and they will last for years.
Click here to purchase paints and supplies
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Posted in Aldax Custom Work and Info | 
Tags: acrylic paint, plaster painting, plaster painting paint | 
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Question on Coin Moulds
Question:
I really need some help here folks, LOL
I made a mould of a coin it’s one sided.
I then tried my first go at melting the pewter on my BBQ. It melted fine. Quite easy. It was liquid and runny. As soon as I poured it into the mould it looked like this on demould.
HELP!!!!!!!! It was windy and I have a little ladle I am using. Iv’e tried 3 coins. I haven’t got any talcum or graphite powder. It also looks like my mould is showing pinholes bin a couple of places but overall it is good. It was windy and I was outside doing it at night. Can you help me please?
Answer:
Hi, It is a lttle hard to see if the mould has reproduced the detail etc without air bubbles but assuming that is OK pre warm the mould by casting a few coins and discarding them. Then dust the mould with graphite powder and pour the pewter at as low a melting point as possible. Do not overheat. All the best Stan Alderson
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Question on Making Aquarium Ornaments
Question from a customer:
Hello,
I have found your website very helpful & it’s given me hope my ideas may come to life, though I have a few questions.
I am looking at making aquarium ornaments. I have already made some rough caves from a mix of concrete & sand, in a sand mould, that are holding up well, but wish to expand my designs & materials. Some ideas will need me to use cement, though many new ideas I’d like to use recycled plastics with more intricate designs.
If I understand your articles correct, latex would be the best to make moulds for both mediums. Is this correct? Could a latex mould be used for both plastic & cement? I understand that any mould I use cement in cant be too detailed, unless of course you have a suggested recipe that will pour easy but not crumble in the water.
Any ideas, hints, suggestions you have will be greatly appreciated.
Answer:
Hi,
You can make the mould latex as it is the cheapest to use and cast in lightweight concrete or resin filled with cheap fillers such as marble dust. Both are used widely in the industry.
All the best Stan Alderson
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Model Railway Wagon
Question:
Dear Sirs,
I have just finished viewing your web site. It is most informative and gave me a good idea of what is required to make models. So that you know that I am serious, I am in my seventies and coming back to railway modeling which I did many years ago. In those days I bought all my rolling stock complete or as metal kits. Now, I would prefer to build from kits. It not only keeps me occupied but ready-built rolling stock is more expensive that I can afford, at around $40-$50 a piece.
The attached image is a HO scale railway wagon in white metal. This is a very old kit and is no longer available. I would like to make a mould to cast it in polyurethane? Or what ever material you recommend.
After reading the notes on your website, I tend to lean towards silicone for the mould. What would you recommend as a casting agent? The heavier the better but I would not be disappointed if it wasn’t heavy. I also need release agents. Do I need it for the silicone? Do I need it for the release of the two-part mould? What else do I need? As you would have gathered I am new to this and will be guided by your advice. I would also appreciate it if you could tell me where I could find instructions (book/video) that would tell me how to construct the basic mould box so that the casting medium flows correctly and also allows air to escape.
Some of my old rolling stock still exists in reasonably good condition. With a little care I could disassemble these and maybe have 5 or six different models. So I have a requirement for say 10 different moulds with anything from 20 to 50 castings from each.
If it is possible, could you please construct a shopping list for me to cater for the above? I will then purchase these items from your firm. If the book/video is available I will also purchase that from you. I hope I am not wasting your time.
Thanking you in anticipation.
Valued Costumer
Answer:
Hi,
Thank you for getting in touch with us. I am also a model railway enthusiast and have played around with making moulds of my existing model kits. I would certainly recommend silicone for the manufacture of the moulds.
I have experimented with the use of metal powders in my casting resin to increase the weight and the results were quite good. I used CraftCast 75 for the casting resin and mixed in up to 50% iron powder to the mixture, making sure I mix the metal powder in before mixing the two parts A + B of the resin together. The reason you add the metal before is because once the resin is mixed, you will only have 2 – 3 minutes to get the resin mixture into the mould before it starts to set.
You don’t need a release agent when casting polyurethane resin into a silicone mould.
We are currently in the process of developing a mould box kit for sale but this is a few months off. Until then we recommend using small pieces of timber or lego to construct a wall around the original piece and to ensure it is water tight, apply non-drying clay such as our plastelina to the corners and edges of the wall.
A shopping list would be something like:
Aldax CraftSil 750 Silicone (to make the mould)
Aldax CraftCast 75 Resin (to cast into the mould)
Iron Powder
Aldax Plastelina (non-hardening clay)
Unfortunately we don’t have a video on this process yet, except for the online videos on our website which goes into some mould making with silicones.
I hope this helps. Please get back to me if you have any more questions.
Kind regards,
Joseph
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Question on Resin Mould
Question:
Hi. Do you have any picture frame moulds that would be suitable for resin?
Cheers
Valued Costumer
Answer:
Hi,
The only picture frame moulds that we have at the moment are plastics. These can only be cast with resin if you use a good release agent and one of our slow setting resins. The quick setting resins often generate too much heat for the plastic and cause damage to the mould. You could however cast a plaster into one of our plastic moulds and then make yourself a silicone mould.
If you do have problems in making a silicone mould though, you can click here for an article on our website on how to make one.
Kind regards
Aldax Moulds
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Posted in Casting and Casting Materials |
Tags: plastic moulds, release agents, resin mould |
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Question on Casting on Plastic
Question:
Hi. I was wondering if you can help. I would like to make a plaster reproduction of plastic lunchbox. I intended making a negative mould using latex or silicone. Can you advise me which products I should use to achieve the following?
- No damage at all to the plastic lunchbox. This item is nearly irreplaceable (plastic is black, glossy, scratched. circa; 1969)
My preference would be to use latex, but not sure if it will cure on plastic.
Thank you.
Valued Costumer
Answer:
Hi,
Yes, latex will cure on plastic. Have you had any experience in making latex moulds? You need to apply it on in layers and is quite time consuming.
Silicone will also leave the surface undamaged. Both silicone and latex do not require release agents on plastic so both will not do damage to the original item. The only risk you may have if using silicone is if something goes wrong with mixing, for example wrong mixing ratio, not mixed well enough etc. In this case you will have slimy, unset silicone covering your original which can prove difficult to clean. Latex is an air drying product so there is less of a risk of this happening.
Our latex is called Kwik Mold #70
We hope this helps.
Kind regards
Aldax Moulds
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Posted in Casting and Casting Materials |
Tags: latex moulds, plastic casting, silicone moulds |
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