I'm looking at using STS TG4 cement boards in our bathroom. My local stockist is out of stock of sealant (they offer Illsbruck SP540 rather than STS's own stuff so there must be loads of alternatives? I'm not looking to cut corners, just a suitable alternative - STS only sell theirs in boxes of 12 AFAICT and I need 5 I reckon. I don't have a sausage gun, so limited to 300ml-ish cartridges. Any recommendations? Many thanks