Although 3C GP is generally targeted at the internal mastic joint sealant market, it's also been tested for use externally and works fairly well outside as a gap filler/air sealing sealant when pitted up against extended UV and other weather extremities so if you're after a an all-rounder silicone sealant for various small jobs then GP is for you, however, as mentioned previously, we never oversell our individual products just for sales sakes, so if purchasing a product that you know will specifically be used for exterior applications such as the perimeter of frames etc. then we'd suggest that a far better suited product would be 3C LOW MOD
All sealant products are categorized and thus, in general there's a crossover with many of the materials in as much as that they can be used for multiple applications, but, one area of joint sealant application that requires specialist material is natural stone. 3C GP has a cure system that utilises acetic acids and will most likely bleed or leech into the surface of the stone causing unsightly staining. When sealing joints in natural stone, either internally or externally, a specialist stone sealant should be used such as, either a dedicated natural stone silicone, or a hybrid polymer (or Modified Silane such as 3C Multi-Use).
For general purpose use, such as around shower trays and bath tops etc. the width of joints that silicone sealants are applied is anywhere from 3mm-20mm. This is either a butted joint or a fillet joint application but occasionally, there's a requirement for a larger joint to be used. With this in mind, most products are thoroughly tested to determine whether they'd succeed at greater depths and widths and thus we can tell you that, as long as the surfaces are clean, dry and absent of dust & debris etc. and the depth is backed out as required (read our blog regarding joint backing here) then 3C GP can be used up to a maximum of 30mm wide. Any wider than that is at your peril!
Ok, so maybe this is not a frequently asked question directly, but when people ask us 'why it's so cheap?' and 'whats the catch?' etc. there's a simple answer..... GP Silicone is just what it says it is, a general purpose silicone sealant! We sell better quality products as internal premium sealants (such as 3C HM) specifically intended for use in bathrooms & kitchens etc. and we also sell better quality products as external premium sealants (such as 3C LOW MOD) intended for use outside in expansion joints or frames etc. So we won't oversell 3C GP but rather sell this decent quality product out at a very decent price! However, customers are usually surprised with just how good this product really is! Give it a try and make your own mind up!