Question: We wish to build up the bottom of the fire box and hearth approx. 3 - 4 inches. Reason being that our fireplace seems to have poor draft. We have to be careful how we positions logs in the fireplace so as not to get a room full of smoke. Last year we purchased a brass/glass door front insert and that seems to help - but due to the size of the fireplace opening (37 1/2" w x 33" h & 19"d) the top of the insert falls about 1/4" shy of the top of the fireplace opening. Adding another layer of brick or pulling the existing fire brick out and laying a few inches on concrete/mortar and placing the fire brick on top of the new foundation would solve that problem. We would also like to increase the height of the hearth off the floor the same number of inches. Presently, the hearth is made of mortar inlaid with random shapes of ceramic tile (very ugly). The hearth's present thickness is 3/4" and it lays atop solid oak flooring. The dimensions of the hearth are 19" x 60". Was thinking about building up this area with concrete and then laying ceramic tile on top. Any help you could give us would surely be appreciated. We are particularly interested in what materials we can safely use for this project. Can I simply pull the existing firebrick out (the mortar is weak and they would come out with little effort), pore a few inches of common concrete and then replace the brick, or is there specialized concrete for this type of work? Answer: You are thinking along the correct lines. Either concrete or thin (4" or so) cinder blocks are fine for building these surfaces up..as long as they are topped with full thick (2 1/2") firebricks. You might consider leaving the old ones in and simply laying a bed of mortar on top of them and them setting more firebrick. If you need to raise the hearth a small amount, you can simply use one or two thicknesses of wonderboard or dura-rock which are cement tile underlayment panels. You can get them at Home Depot or tile supply stores. Cement, concrete or cinder block is also fine for raising the hearth. Use thinset (cement) tile adhesive to set the tile (do not use mastic, etc).