Andre Laas
Sealiner
I have also been playing with silicon moulds for a while and have had the same problems with MM30. Some time ago the guy at our local AMT sold me a high temp silicone (the brand name was wacker) that I guess is similar to MM60. It worked quite well, but as far as I know they do not sell the wacker silicones anymore.
To form my mould boxes, I purchased a Lego building pad and some Lego blocks, and it works like a charm as you can change the dimensions and depth of your mould to your heart’s content. I modified some blocks by grinding and sanding off the little buttons on top so that you get a smooth surface. I first build a little starter box of a single layer of smooth blocks (depending of the size of the object), and then over-fill this box with toolmakers clay (also from AMT). From here I use a flat blade to cut off the excess clay (this is where the smoothed blocks helps a lot) so that you end up with a smooth block of clay into which you can imbed the object. After imbedding the object, I again cut off all clay that has been displaced by the volume of the object. Now it is a case of replacing the smooth blocks with regular blocks and then building up the box to the desired height. Now you can pour and cure your first half, and then basically build a new box around the first half to make your second pour.
Something that made quite a bit of a difference to the quality of my castings was to vibrate the silicon in the mixing container before pouring, and then vibrating the mould after pouring. For this I used a handheld massager that I purchased from the SPCA shop. This helps removing air bubbles or at least move them away from the casting surface. (Vibrating Plaster of Paris castings also helps quite a bit)
I have read somewhere that it helps reduce bubbles if you pour your silicon slooooowly from pretty high above your mould and in one corner so that you get a thin stream of silicone that spreads out over the object as the mould cavity fills up. I have been doing it this way, and it seems to help a bit.
I am not sure of it is necessary for lead and tin casting, but after curing my mould for a day at room temperature, I post- cure it in a little oven at about 50-60deg Celsius for 3-5 hours. This is usually done to make sure all volatiles that could interfere with some resins are removed (…that’s what I read on the data sheet)
Finally, I dust my moulds with baby powder (talcum) before every cast, and I have found that it makes a difference in the longevity of my moulds.
To form my mould boxes, I purchased a Lego building pad and some Lego blocks, and it works like a charm as you can change the dimensions and depth of your mould to your heart’s content. I modified some blocks by grinding and sanding off the little buttons on top so that you get a smooth surface. I first build a little starter box of a single layer of smooth blocks (depending of the size of the object), and then over-fill this box with toolmakers clay (also from AMT). From here I use a flat blade to cut off the excess clay (this is where the smoothed blocks helps a lot) so that you end up with a smooth block of clay into which you can imbed the object. After imbedding the object, I again cut off all clay that has been displaced by the volume of the object. Now it is a case of replacing the smooth blocks with regular blocks and then building up the box to the desired height. Now you can pour and cure your first half, and then basically build a new box around the first half to make your second pour.
Something that made quite a bit of a difference to the quality of my castings was to vibrate the silicon in the mixing container before pouring, and then vibrating the mould after pouring. For this I used a handheld massager that I purchased from the SPCA shop. This helps removing air bubbles or at least move them away from the casting surface. (Vibrating Plaster of Paris castings also helps quite a bit)
I have read somewhere that it helps reduce bubbles if you pour your silicon slooooowly from pretty high above your mould and in one corner so that you get a thin stream of silicone that spreads out over the object as the mould cavity fills up. I have been doing it this way, and it seems to help a bit.
I am not sure of it is necessary for lead and tin casting, but after curing my mould for a day at room temperature, I post- cure it in a little oven at about 50-60deg Celsius for 3-5 hours. This is usually done to make sure all volatiles that could interfere with some resins are removed (…that’s what I read on the data sheet)
Finally, I dust my moulds with baby powder (talcum) before every cast, and I have found that it makes a difference in the longevity of my moulds.
