An old geezer out our back makes these blocks as well to burn in his grate, he made a frame from some discared old but not broken double glazing panels in his garden to act like a solar kiln to dry his fire blocks out on, clever old bugger.
Treat them like firewood. i.e. make them now, dry them out over the summer, ready for use next season.
DeJaVue thread.
The effort required to process the ingredients, make the brickquettes, the drying time and the cumulative handling time makes these an inefficient heat return for the labour expended. A much greater heat return per unit of labour would be returned from sourcing decent wood.