Planning the layout –
Measure the length, width and height of your liner, and then arrange into one or two flat areas as in the diagram. Remember, silicone is expensive, measure twice and pour/cut once!
Determining the amount of silicone for your mould – I would suggest a liner thickness of 3mm for the most cost effective use of your silicone as well as not taking up too much space in your mould, while retaining adequate strength. After you have determined the surface area you will need to cover with silicone (the internal surface area), ensure the measurements are in cm, and determine the total surface area in cm squared. If you want a 0.3cm thick mould (3mm), multiply the surface area by the thickness of the liner to get the volume of silicone in cm cubed, or cc’s, or ml’s. This volume is equivalent to the material in weight (as 1cc/ml of silicone is approximately 1g of silicone), so for measurement purposes convert the volume to weight.
Here is an example to illustrate:
Liner surface area (as contained in the frame) is 39x32cm = 1,248cm2 1,248cm2 x 0.3cm(thick) = 374.4ml (or cc’s) = 375g silicone. With the average cost of silicone at $0.05/g = $18.75 As you can see increasing the thickness will greatly increase the price of the liner:
1,248cm2 x 0.5cm(thick) = 624ml (or cc’s) = 624g silicone. = $31.20 1,248cm2 x 1cm(thick) = 1,248ml (or cc’s) = 1,248g silicone. = $62.40 Materials:
· Long wooden battens or strips of cardboard or any other straight objects to make frames.
· Stirring stick/spatula, plastic tub, and gloves.
· RTV Silicone (I would suggest starting with about 1kg for cost effectiveness and for just enough volume without huge investment. If you plan to make many liners or if you have large liners, 5kg packages are the most economical and cost effective of the smaller packages, ranging from $200 to $250AUD)
Desirable properties (guide only):
Low to medium viscosity (45,000 cps or less) for smooth pouring, medium cure time (min about 6 hours to full cure and 30min pot life to allow working time, real cure time is usually half of advertised cure time), and Shore A hardness of 25 or greater – the firmer the silicone (Shore A of 35-50) the thinner the liner can be while retaining the same strength and support (as long as the other qualities are still present).
Australian Resources and Suggestions:
Adelaide Moulding and Casting
Suggestions: (made by Barnes Silicone)
Maximould, M4503, Ultrasil.
Barnes Silicone (http://www.barnes.com.au/) Suggestions: Use caution if you choose to use Pinky Silicone, as this silicone must be molded in about 6minutes, which may not be enough time to pour/spread your liner, otherwise it’s the best silicone so may be worth a try! Tufsil 25, Maximould, M4503, Ultrasil.
Suggestions (Tin Catalysed): Solid Mould 500, Polytek TinSil 70-30.
Check your local Fiberglass and Mould Making Supplies Store; many carry RTV silicone and the Barnes range of products (their website lists stores that supply their silicone). Just look up “fiberglass” or “molding and casting” in the yellow pages.
1. Layout the batons into the surface area rectangles required for your size liner, to contain/mould the silicone. Be sure to use a right angle tool or the corner of a sheet of paper to square your frame.
2. Tape around the edges of your walls to prevent any silicone leaking out.
Tips: You can use the side of the silicone that is touching the surface as the inner or outer part of your liner depending on which you prefer. Sometimes it is better to pour your liner onto a slightly textured surface like paper or MDF and use the side that contacts the MDF or paper as the outer side of your liner, because it will not grip onto your outer wooden mould when inserting.
4. Mix your silicone as per the manufactures guidelines (search for pouring silicone and the “bombs away” method on the internet for some really good videos. Tap Plastics makes great instructional videos). Pour into your frame using the “bombs away” method to reduce air bubbles. The bombs away method is essentially pouring a very thin stream from a height to stretch and pop any bubbles that were trapped in the silicone during mixing. Using a plastic spatula spread the silicone into the corners and even-out thin or thick areas.
6. Cover your frame with a board or other stiff cover if you are worried about lint or pets/kids getting into it while it hardens. Allow curing for the recommended time, heat generally speeds up the cure (as the reaction is endothermic), so a blast with a hair drier, heater or keeping it in a warn room will quicken the process. Do not use a heat gun or flame on the silicone, as this is TOO hot. To clean up your mix pot and spoon, just let the silicone cure and peal off, it’s really easy to clean! Or you can put the silicone pot with the extra silicone on the sides in the freezer to prevent it from curing for about 1-2 days, and use it later to join/weld your liner sides.
7. When dry, peal off the frame and surface. Trim/slice the silicone sides to fit into your mould.