How to deal with shrinkage problems of silicone mold?

Generally, all silicone mold would have shrinkage problems, the difference would be how much it would shrink. 
 

For example, the shrinkage of the addition cure silicone rubber would be lower than that of the condensation cure silicone rubber. 
 

And also, the larger the product is, the more the shrinkage would be. 
 

Then what to do with it? Here are some suggestions. 
 

1. Choose the right hardness to make the mold.

Normally, different silicone should be choosed according to different product's features, for example:

For products within 20cm: with intricate designs, soft silicone is suitable, such as 10-20 shore A.
For products of 20cm-80cm: with intricate designs, 20-25 shore A is suitable; with simple designs, 25-30 shore A is suitable.
For products of 80cm-150cm with intricate designs, 30 shore A is suitable; with simple designs, 30-35 shore A is suitable.
For products more than 150cm, with intricate designs, 30-35 shore a A is suitable; with simple designs, 35-40 shore A is suitable.

When using soft silicone to make a large mould, saying 100cm, then the shrinkage must be larger than the moulds made by a harder one. 
 

2. control the addition of catalyst if you are using the condensation cure silicone rubber

Usually, more catalyst would be added if we want to cured fast, but more catalyst would make the silicone mould shrinkage more.

3. add the fibreglass into the silicone to make the mold if possible.

In fact, we suggest all the large silicone mould shoule have the fibreglass in it for shaping up, and also, increase the tear&tensile strength of the silicone would. The ageing-resistant performance and the duplication times would increase at the same time. 
 

4. make the outer mold for the silicone mould

This may have the same function of the fibreglass. And making the ourter mold for the silicone mould that made by brushing way would be suggested strongly.

Outer mold can be made by the plaster, resin, ect. 
 

5. Do not remould so fast.

Please  let the silicone mold cured completely, which would take about 24 hours, then remould.

And some other exprienced craftsman would put the mould for another 24hours to start the production.
You know, the chemical needs enough time to act. Enough reaction would make the mould stronger. 
 

6. when you produce the products, please put the mold flatly, then pour the plater or other materials into it smoothly. When you do not usually the mold, you should store it flatly, not fold it,and you also can pour the plaster into it and not remould the fisinished plaster products, leaving it in the mold to keep the mold in original shape.
 

7. enlarge the mother mould

If possible, enlarge the mother mould by 3~5‰. After cured the silicone mould may shrink, then you can make the products.
This is a way that not so practical, but still it is way. 

2019-05-23