Effect of calcium carbonate

[Kastally80]

Hi all,
Does the addition of calcium carbonate to polyester resin reduces shrinkage ?
It's for boat mold making.
thank you

[LyndonJ]

excerpt from
http://users.lmi.net/~drewid/resin_faq.html


calcium carbonate and talc are often used to fill resin to give the casting the look of porcelain or marble ............................

Fillers cause two problems of their own. First, they carry air with them into the mixed material. Second, in the amounts that will eliminate the shrinkage and heat concerns, they turn a liquid resin into a viscous porridge, in some cases too thick to vacuum. Both cause or exacerbate air-bubble problems in the casting.

_________end quote_______________________________________

So it looks like ir does reduce shrinkage but it might be weak and very hard to get it into a layup.

[conceptia]

Is there any alternative material you'd suggest for calcium carbonate?

You must not fear shrinkage if you take it into account in your mould design!

Next point is, that you usually work with thin layers at a time, so shrinkage is low.

And if it is still a problem, almost every solid additive / filler will reduce it. Chopped glass fibre, the mentioned c c, or other minerals are all quite helpful.

The entrapped air is´nt a severe problem when you work on one layer at a time, you usually work it out when applying the resin to the glass.

Regards
Richard

[Kastally80]

Can we obtain the same results as working with special tooling resins like RM2000 from Nord Composites or Optimold from Cray Valley by just adding 40% of calcium carbonate to polyester resin ?

[ondarvr]

Originally Posted by Kastally80

Can we obtain the same results as working with special tooling resins like RM2000 from Nord Composites or Optimold from Cray Valley by just adding 40% of calcium carbonate to polyester resin ?

No, the chemistry is very different and the additive that makes them zero or low shrink isn't something you would be able to get and add easily.

The technology can also create water resistance issues.

What is you want to use it for?

[hoytedow]

How much water resistance does it need if it is only for the mold?

[ondarvr]

Originally Posted by hoytedow

How much water resistance does it need if it is only for the mold?

Not everyone wants to use low or zero shrink products for making molds, they can be used in many different applications, although only one of the products is easy to use and can be infused.

I've seen some very large tools that were stored outside and had large areas blister, these were as large as a dinner plate. This was a filled zero shrink system.

[Kastally80]

It's for mold construction

Just forget about the shrinkage. Do´nt play with unknown parameters.
Give leave for the specified shrinkage with the resin of your choice and fix your design accordingly, thats it!

Regards
Richard

[Kastally80]

I found this very interisting document.

[conceptia]

thank you..

[Herman]

I have seen many boat moulds being made with RM2000, RM3000 and more recently with RM5000 (infusable) which turn out very OK.

It is however, import to follow the guidelines as indicated by Nord Composites, and another very important factor is no direct light on the mould during construction.

The fillers in the resin (ATH and others) make for less water resistance. If you ever plan to park the mould outside, please do coat the outer surface of the mould with some topcoat (any colour and quality will do. Great way to get rid of some old stuff, or ask your supplier for outdated stuff)

Another option is to go very conservative with your layups, doing one layer at the time, let cure, then do the next layer. This is the way quality conscious mould makers did it in the past, and there is no reason not to do it that way, except when you are in a hurry.