I have an interior stonework fireplace made of horizontally stacked pieces of slate with mortar in between. The mortar is flaking and dusting and the stone is somewhat stained from previous water intrusions. I'd like to seal the stone and the mortar so that it looks good and doesn't dust. I don't want a shiny effect and would like to avoid brushing it on since a brush will raise fine dust from the mortar.

Any ideas about a sealer and whether I could spray it on?

Thanks!