As long as the Builder's Sharp sand is from river beds or quarries and not washed sea sand then yes you may use it instead of the Horticultural grade stuff. I do. Note that, Cornish silver sand is different though, that is much sharper (the particles are even more angular than sharp sand per se).

You do have to be careful, as some builders' sand retains salt, with disastrous effects on plants! :-(

We always use builders sharp/concreting sand.

Builder's sand (soft sand) is used in mortar for laying bricks. Sharp sand is a coarse sand used for concrete and often dredged from the sea so it will contain lime particles. Horticultural sand is coarse sand but lime free so can be used on ericaceous plants.

Well, I have been using Wickes Sharp sand for the last 16 years both as plunge and as an addition to potting compost without any sign of plants being damaged by its 'lime' content. Easy enough to tell, add a little vinegar to some sand and if it 'fizzes' then it contains lime.

You use so little its fine .

Depends on what you are growing though NP. My favourite potting compost for Alpines, is 1 part peat free compost, one part sterilised top soil and one part mixed grit and sharp sand (50/50). I also add a small amount of peat based stuff as this puts a moisture retaining material into what is a very free draining mix. So in many ways that is a fair percentage of sand in the mix.

Our basic potting compost is almost exactly the same as Owdboggy. Prefer leaf mould to the peat free compost but that is the fall back material.

I would prefer leaf mould too, but in the quantity of compost I make and use, I have not got any where near enough of it.

i agree like cacti youd use litteraly just pea gravel if you have them in the garden in a raised planter so they have total gravel but for basic every day plants its not a problem owdboggy.