1. Mixing of the additive

BLUESIL ADD PA THIXO can be added to each of the two parts of the RTV-2 system separately before mixing, or to the mixture of the two parts after they have been blended together for catalysis.
When using fast curing BLUESIL RTV products, it is suggested to add BLUESIL ADD PA THIXO before catalysis. In that case, it is recommended to add BLUESIL ADD PA THIXO to both parts in an equal amount to avoid significant viscosity differences that would complicate mixing.

a) Catalysis of the RTV-2 silicone

For a polyaddition RTV-2 silicone, mix together part A and part B of the BLUESIL RTV product according to the correct weight ratio (usually 1:1 or 10:1) indicated in the product datasheet.
In case of a polycondensation curing RTV-2 silicone, BLUESIL ADD PA THIXO can be used too, but we recommend the use of BLUESIL ADD PC THIXO, that is far more efficient with such products group (please refer to the product own Technical Data Sheet).


To 100 parts of the catalysed BLUESIL RTV A+B mixed (according to §a)), add 0.05 to 0.50 parts by weight of BLUESIL ADD PA THIXO. The additive should be well incorporated into the RTV by hand or with a mechanical mixer. Mix until perfect dispersion of the additive into the silicone.
Once the BLUESIL ADD PA THIXO is added to polyaddition parts containing the Pt catalyst, it is advisable to use that part within the 24 h after addition.
The correct amount of BLUESIL ADD PA THIXO is given by the needed  thixotropic behavior case by case: the higher the added amount is the more thixotropic the product becomes, until a non-flow condition is reached.
Exceeding the suggested maximum amount of BLUESIL ADD PA THIXO, of 0.50 parts by weight, could lead to a deterioration of other intrinsic silicone properties.

2. Degassing

The degassing of a RTV-2 silicone just before casting is recommended to eliminate the entrapped air introduced when mixing the two parts. Nevertheless, when using BLUESIL ADD PA THIXO in a BLUESIL RTV, the product becomes so viscous that the degassing is often non efficient in eliminating all entrapped air bubbles. Moreover, since the BLUESIL ADD PA THIXO is needed when a RTV product has to be applied by brush or spatula, during this kind of application additional air is introduced anyway into the silicone.
The below procedure is needed for a correct degassing:
The catalysed product is degassed under a 30 to 50 mbar vacuum. When the vacuum is applied the product expands 3-4 times its initial volume and bubbles form on the surface. Once bubbles disappear, the mixture collapses back to its initial volume. To complete degassing simply wait few minutes before releasing the vacuum, then the product will be ready to use.
Remark: pull and release the vacuum several times improves the degassing. For easier degassing only fill a recipient to one 1/3 of its height.

3. How to use

Apply the so obtained thixotropic BLUESIL RTV product directly on the model by brush or spatula, trying to avoid bubbles and voids. When the added level of BLUESIL ADD PA THIXO is very low (e.g. < 0.05%), the viscosity increase is limited, thus offering the possibility to apply the product by casting.
Models can be made of several materials (stones, concrete, metal, etc). Even though silicone is naturally non-adhering to most materials it is always recommendable to prepare the model to avoid any risk of the silicone sticking and so damaging the model. Remove dust and apply a pore filler like soapy water, waxes diluted in xylene etc.

4. Notes

BLUESIL ADD PA THIXO does not work with the polycondensation range of the series BLUESIL 32xx and 33xx SPU, and not for the polyaddition series BLUESIL RTV 313x.

BLUESIL ADDITIVE PA THIXO may be stored at temperatures between -20°C / -4°F and 50°C / 122°F for up to 36 months from its date of manufacturing.Please consult the Safety Data Sheet of this product.


BLUESIL ADD PA THIXO (Thixotropic Additive) is a rheology modifier for RTV-2 silicones that imparts a thixotropic behavior to the silicone. Its high efficiency allows to reach the non-flow condition with a limited added amount .


Functional Fluid


  • Easy and fast processing
  • High efficiency
  • Excellent compatibility with both polycondensation and polyaddition RTV-2 silicones.


Typical target of BLUESIL ADD PA THIXO are the cases where a RTV-2 silicone must be applied by brush or spatula, e.g. on vertical surfaces.

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ColorTranslucent / YellowMonocomp
AppearanceViscous LiquidMonocomp