What do we need to consider?. well of course the first thing on our mind is the toughness of the casts we are making, however that's only part of the problem. We need to consider Expansion, working times, drying times and of course our very worst enemy - Bubbles. as well as all of that we need to consider using more than one single product, for example if we are casting a large roof sheet we may need strength as well as low expansion to avoid warping, whereas if we are casting a really delicate fine part we really need the high strength. and in all cases we want to eliminate trapped air.
Also I forgot to mention that all important element of cost. there is not much point using your most expensive product just to cast a simple tower roof or a small footpath when it will work just as well in a cheaper but still adequate product
What to Use
With many products on the market you will have plenty of choice, also depending where in the world you live there are many different brands, some of the best and hardest products are what is termed "Alpha plasters" however there are a number of these, so where do we start?
Herculite 2 is a good all rounder, not too expensive, fairly hard, easy to mix and you have about 10 minutes to pour and level it. I have used this many times and got really good results. for the most part you will be very happy with the results. there is always a draw back though so here it is, the expansion is about 0.60% which is fine except if your using larger moulds and especially thin larger sheet moulds they may bow slightly due to the expansion, also if you are building a large model I think its not as precise as some of the high end products, however its a fine starting point.
You can buy Herculite 2 from many places including places like ebay, all I will say is be carful you are getting the right product and its not a cheaper version like plaster of Paris, which is not up to the job.
TuffCast is the material we sell, it is essentially a blend of a number of casting powders designed to give a higher strength than Herculite 2 and less expansion which makes it a good product for both small moulds as it provides strength and for large sheet moulds as its expansion is extremely low.
There is a lot to be said on the art of mixing, first we need to consider that the more water content the weaker the cast will be, on the other hand the less water we use the more likely we are to trap air bubbles, so what we are looking for is a balance. Every product is slight different but the same principles apply so lets get started.
here I will start with Tuffcast, however the same applies except the setting times and strengths will vary from one plaster type to another.
Mix at 40:100 ratio of Water / Powder
So lets make life reallgy easy, get yourself some of those cheap plastic cups, put one on a weighing scale and measure 100g of powder, then place a mark on the cup where the powder level comes too, Now with another fresh cup do the same with the water except this time it is going to weigh 40g and again mark the cup level. Now we can save these as masters, I suggest you write the name of the powder on the cup as different powders have different weights, so you will need a new cup marked up for each product you may use.
the next part is easy, put the water in to a fresh cup or mixing utensil, the start adding the powder and mix as you go, when you have a nice consistency let it settle for a minute, that will let some of the air bubbles escape, tap the cup on a work surface *See the videos" and this get rid of more bubbles, the your ready to pour. In most cases it works better if you pour from the centre of the mould part "See Video"
I will not explain the rest of the pouring as you will see how it is done in the videos and we are covering mixing here.
So when you have extracted your casts you may think you want to add more or less water. its now easy to just mix up another batch and make marks on your water cup to suit what you feel is comfortable.
All the videos shown below are also on our Linkaonline YouTube channel but you can watch them right here, New videos are currently being created and will be placed here covering all gauges of moulds