Its well known that mortar needs a temperature above about 4-5 degrees C to set properly.
Various websites state that protection, covering, or other tricks may be used for lower temperatures, but they are very nonspecific - none of them seem to have a table that says "at X temperature, these precautions are sufficient". I need a more specific answer, on the lines of "this will be good enough to ensure the mortar sets properly".
I'm laying a small amount of structural masonry. The masonry is 2 courses of dense concrete block on foundations (the foundations have already cured), and is outdoors. The mortar is 1:3 sulphate resisting cement to sharp sand, with 1:10 of sika-1 waterproofer in the water (there's an adjacent overflowing drain, I can't fix it so I'm doing what I can to keep it from permeating!).
Eventually the blocks will support a 1 storey external wall of a building, but that part will be done by bricklayers. I need to get some of the base blocks in early to let me put a neighbour's fence back though :)
Here's a picture to give an idea:
I don't plan to use any other accelerants or additives, as they probably don't solve the basic problem and may provide false comfort, or not react well with the waterproofer. I'd rather rely on protection/warming only.
I have polythene sheet (DPM), hessian, and towels laying around. I also have some 3kW warm air blowers if needed, although that would mean setting up an enclosed shelter safe for electrical appliances around the block work, and a risk of over warming/drying, so I'd really prefer to avoid that.
Given temps around 0- 3 degrees (but not likely to be lower, maybe at worst -1 or -2 at night if very cold later on), what level of protection is appropriate to be sure the mortar sets nicely, and for how long should I use it?