Cascamite or any other similar trade name has always been marketed as a gap filler, not sure they meant gaps quite as wide though
From a H&S perspective you have to take more care handling it than other glues, it is a Urea Formaldehyde glue and can cause a skin reaction. Also as it comes in powder form you need to be careful not to get the particles airborne and breath them in. As Steve said it is brittle when dry so be careful turning it as some of the waste comes off like shards of glass.
In use let it sit before using it or you may find airbubbles forming (although that could be interesting in itself?) The mixing ratios are fairly important so not sure how mixing with pigments, either powdered or liquid qill affect the strength but then using it as filler it won't matter will it?