Have started to lay a laminate floor but have found that where there was once a fireplace there is now just a large rectangle of uneven concrete.
Have chipped away most of the concrete so that now is is lower than the level of the floorboards.
I need to fill the space with something to make it the same level as the floorboards but what is the best product to use?
Can I use ready mixed mortar? The depth is up to 15mm - 20mm max in some places.