What is Shore A Hardness?
Essentially this is an international adopted scale which defines the hardness of a product be it plastic or rubber and many other things too! As a general rule the higher the number the harder the RTV Silicone will be.

It will be more durable it is and its tear strength will usually increase. There are of course downsides to increasing Shore A which include reducing elongation to break (stretchiness in Layman speak).

How safe are Condensation Cure RTV Silicone Systems?
In a single word, "Very". The RTV SIlicone Base is nigh harmless and non hazardous, don't get it in your eyes or on your clothes though. Only the catalyst of our systems is hazardous and is flammable due to alcohol content.

The catalyst, either fast or slow, contains Tin, an accumulative poison like lead. So wear gloves and definitely dont drink it (however nice it may smell!). keep it out of reach of minors.

So I have a former with deep undercuts, which Silicone?
Deep undercuts present issues during demould. Putting it simply they will hang on to your cast like trying to pull a triangle through a round hole! Its just not going to happen!So a more flexible RTV Silicone will allow easier withdrawal of a deeply undercut piece.

However with a benefit there always a drawback. The softer the RTV Silicone the more likely it will sag or slump, deforming your cast! So there is a fine balance to judge and mainly experience will tell you what you may get away with.

Latex demoulds from the deepest of undercuts but isnt compatible with all casting medias. Therefore sometimes you just have to make a sectional or split mould to prevent slump but give easier release.

What are Addition Cure RTV Silicones?
These are two part systems where part A looks like rubber and so does part B usually. There is no "catalyst" just 2 parts to be mixed together often in 1:1 by weight. These addition cures are usually skin safe as the catalyst part is Platinum and not Tin which is inert to the human body.

There are two types of these, which we will stock shortly. Regular addition cure for mouldmaking and Food Safe which can be used in baking and making sugar candies, chocolates, muffins and more.

Never use a Condensation RTV (Tin Cure) for life casting, or to make food shapes, the Tin is very harmful and should be respected. Ask yourself, would you serve dinner on a Lead Plate?

I have a simple shape, no undercuts, now which one?
Hard will give good durability but dont be in a hurry to go with hard. If you rough handle it may well split and then the mould is destined for the refuse

Consider trying the medium grade and move onto hard if you find durability an issue. Some media like polyesters and polyurethanes are aggressive on RTV's

Whats the best all rounder?
Our Medium grade is used by 9/10 of our customers, has good durability and releases well from undercuts. Its popular in sectional or split moulds too and it definitely a good place to start. Its also our suppliers biggest seller which must tell you something!

If you are new to RTV Silicone and really dont know where to start, go for the medium grade and make some smaller moulds and build knowledge and confidence!

OK I Picked my RTV Silicone Hardness - Which Catalyst: Fast or Slow!
Fast is the choice for smaller moulds or the seasoned pro. Its fine in the winter but in the summer can catch out even the most experienced, with potlife (useable time) dropping to as little as 5 minutes! You can demould and cast same day, though if using polyesters and PU's we recommend a post cure of 48 hours.

Slow is good in warmer temperatures and for the novice. It does produce a better RTV Silicone Mould allowing the rubber to cure slower it will give better durability. However its an overnight curing system, but as we said be patient!

Thanks for taking the time to read this section on our RTV Silicone Systems. We appreciate your custom and look forward to not only receiving you first order but any subsequent orders you place. You will get the same level of service whether you are making a one off purchase or become a regular customer! All information is supplied in good faith and for guidance purposes. No responsibility or liability for loss or personal injury can be accepted. The products are supplied as fit for the purpose intended.

We are customer focussed and seek to maintain a 100% feedback score. Visit our website for more information on mould making with our products and watch out for the new casting, filler use, troubleshooting and public forum sections coming soon!

TOMPS Online Management Team
www.tomps.com