Hi,

Yes, that's exactly why it won't work; the product Thixotropic Additive for Addition Cure Silicone is only intended for use with addition cure silicones. Their chemistry is quite different and the additive has no effect on a condensation cure silicones unfortunately. I am sorry for any frustration this has caused.

I understand your point about a warning if one product is purchased with an incompatible product but in reality this might be quite difficult to implement. Certainly if you ordered over the phone and asked for both of these products then our staff would advise you that they do not work together but in terms of automating this process for an online purchase I'm sure you can guess that we have literally thousands of product combinations that don't work together and that coding this sort of incompatibility checker could be very complicated. I'm not trying to make excuses but we did name the product as best as we could to try to make clear that it's for addition cure silicones only

Learning from your post though I have added a bit if extra information to the product page to highlight the incompatibility with condensation cure silicone.

For condensation cure silicone, you could try adding fumed silica. This does have a thixotropic effect on the silicone although it's not as impressive as the effect of the thixo additive on addition cure silicone.

Describing the shade of grey is rather subjective (I would probably describe the correct shade as mid grey!) but needless to say, it should be the same shade regardless of quantity so at least one of those mixes is wrong but I have no way of saying with certainty which one!