"RTV101 release agent" Topic

I am experimenting with making a drop mould as it is something I haven't done before – I usually vulcanise my moulds and I have tried it using some things from Tiranti.

I embedded the figure in Chavant and then poured the first half of the mould. The rubber half is fine, but the chavant clay has stuck to everything including the rubber and the figure itself. I sprayed the clay with silicon release spray before embedding the figure and sprayed it again before pouring the rubber.

The mould isn't usable to make the second half because the clay is stuck to the rubber and will be a pain to clean off that and the figure itself.

Anyone got any better ideas for a release agent – would talc work better?

thanks

Mike

Must admit I usually spray and allow to dry several times before adding rubber. One possibility as well is that you tried to separate them too soon – the longer the cure, the less likely to 'stick'. Chavant also goes very hard when cold. Making sure it is at (suggesting only) 35-45 degrees C and you might find it 'peeling' easier.

I use a very fine coat of Vaseline. Careful though as it can clump which will show in the cast.

I think I've heard of the Vaseline being diluted but I'm not sure what with, maybe white spirit?

I bought some "liquid vaseline" the other day from the Range. I didn't have a use, but thought, that looks like it might be of use someday. Maybe it could be of use here…

link

I never use a release agent with silicone RTV unless I'm making a multi-part mould. Usually I pour a one part mould and then split it if I need to. It gives a much better parting line. You can cut the rubber to form its own key. I find that the silicone comes away from everything, except itself. I've never has any modelling clay stick to the rubber, though you should avoid ones that contain sulphur, as that can cause inhibition of the cure. I have found that un-evaporated solvent can also cause inhibition, so make sure it has all evaporated – a hair drier is handy if you're in a hurry.

I always make sure the master is sealed, so the rubber won't "soak" into the pores and to avoid any inhibition of the curing process. You also want to make sure the master has the surface texture you want the castings to have. If you leave is shiny, say after a couple of coats of PVA, then your castings will have a shiny surface as well!

If I'm doing two pour/two part mould I use the old fashioned method of Vaseline dissolved in white spirit – smelly and cheap but effective. You must allow all the white spirit to evaporate or it might effect the cure. Make sure the first layer of RTV is properly cured before you attempt to do the second.

i have used plasticine for embedding the original and some does stick a very small amount and is easily got rid of.
i now only make single piece moulds and cut them myself where i want the join, trickier to get the original out but less hassle with 2 part moulding and release agents ect.

Thanks for the replies. I left the rubber 24 hours to cure but do wonder if I had too little catalyst added which caused the problem. I am trying it again using talc as a release agent and rubber seems to be hardening faster than before.

If you make a single piece mould do you pour the rubber than drop in the figure, then pour more rubber?

Mike

Like the OtherOne suggests, the problem is likely to be the clay. In the local SPFX industry they only use 'KleenKlay' which does not effect either RTV or polyurethane molds.

I have seen problems with the clay used and molds failing to set up right. I was told that it is because of sulfur in the clay and that you should only use something like KleenKlay.

The clay I am using is non sulphur clay provided by Tiranti explicitly for use with Rtv101

Mike

To make a single piece mould fix the master firmly to a surface of the mould box and carefully fill with rubber until it disappears. I find it useful to mark a level on the mould box to fill up to. That helps ensure that the master is properly surrounded by rubber – it's better to avoid a "thin" wall. If you don't want one of the surfaces of the master to be at the side of the mould mount it on something that you can use as a pouring hole.

Leave to cure fully and then carefully cut the rubber until you have released the master. It helps to mark the edges of the box so you know how the master is orientated and can work out where you intended to cut. When you cut use a very sharp knife, cut into the rubber and then hold the two side apart so the knife doesn't get stuck and you can see when you reach the master. The several cuts into the rubber help form a key, but you can also accentuate this with zigzag cuts to give a better one. It helps to have three arms at this point, but you can get gadgets like rib spreaders to hold the sides apart.

It is always very important to measure the base and catalyst very accurately. It can be very sensitive to the correct proportions. I find domestic culinary digital scales with a 1 gram increment sufficient. Try and use the ones that you can zero yourself, but that don't self zero when you lift of the mass. I also find it better to measure everything into the one container rather than two and pour together, particularly with small quantities. Clear containers allow you to see if everything is properly scrapped from the sides and using a coloured rubber (usually white base and coloured catalyst) makes ensuring a complete mix easier. Soft cooking spatulas are also good as they get into all the corners.

I use Taranti RTV 101. I have not used a release spray until I am going to pour the second half of the mould. On the occassions when the clay sticks to the mould or figure I found white Spirit and a stiffish brush cleans it. But be careful not to disturb the figure. If all else fails ask Taranti they normally come up with the solutions (excuse the pun)to problems with their products.

I am not familiar with this chavant clay but if it is sulphur free like you say there shouldn't be any need for a release agent between the clay and the RTV at all. You can put a thin coating of regular Vaseline if you want. I used to use the thinner Vaseline Intensive Care but they've changed the formula and I haven't tried it yet. When I use clay as a base for the first part of an RTV mold I always put the entire assembly in the freezer after the RTV has cured. (About 15 minutes for a 3 x 4 mold frame is good). You don't want to leave it in there long enough to freeze; you just want to chill the clay enough to harden it. It will separate from the RTV much better. Work fast but firmly and gently as you don't want to pull the model out of the RTV. Another reason to work quickly is the clay is warming up under the hot lights you're probably working under. Some bits of clay will stick to the model and the RTV and I remove these with wooden toothpicks and popsicle sticks to avoid scratching the model.
Toby Barrett

Master caster and I have diferent takes on this – I peel the clay away from the RTV, he peels the RTV away from the clay!

Problem IU find with peeling the RTV away is with a 2 part mould – the master may stick in the clay, it can be difficult to get it back into the RTV. Spears, for example, 'spring' out and the rubber will get underneath it.

Garrison,
We have the same take if you read what wrote again. I try not to disturb the RTV at all that holds the master. I take the clay away from the RTV.
In my original I forgot to mention I use Vaseline as a parting agent between RTV sections too. In many years of mold making I have only used Vaseline to separate RTV and the finest talc powder to separate vulcanized rubber mold sections.