Fix for a sinking fireplace hearth

Why this job requires more than house jacks

By Inman News Feed
Add Comment Add Comment | Comments: 0 | Posted Nov. 7, 2012

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Why this job requires more than house jacks

Bill and Kevin Burnett
Inman News®

Q: I live in a Craftsman cottage in Davis, Calif. Like many Craftsman homes, it has a fireplace in the living room with a handsome mantel, a tile surround around the firebox, and a tiled hearth. All appear to be original. My problem: The hearth is sinking.

Currently the hearth sits about 1/2 inch below the hardwood floor. I've been under the house to take a look from that angle. The tile appears to be laid on a cement slab, which is supported by 4-by-4-inch posts resting on a couple of concrete piers. I'm not quite sure how to get the hearth back to level with the hardwood floor. I don't want to break any of the tiles.

What is the best way to elevate the slab to be level with the floor and have the least chance of cracking any of the tiles?

A: We think you may be able to gently ease the hearth back into place using house jacks and two 5-foot lengths of 2-by-12 framing lumber. Then you'll need to pour new concrete footings and add new posts.

We caution you that this is not a job for the casual do-it-yourselfer. It requires B or B-plus carpenter skills. Also, this type of structural work often requires a building permit and inspections so make sure to check with the city before you get started.

Your first job is to lift the hearth back into place.

House jacks are large screw-type jacks used by house movers to raise houses in order to place large beams under a house for transport via truck and trailer. You'll need to rent two or three of these. Place one of the 2-by-12s on the ground near the existing piers. The wood base will prevent the jacks from sinking into the ground when lifting the slab.

Next, place one jack at each end of the board and use the jacks to snug the second 2-by-12 against the concrete substrate of the hearth. Make sure the jacks and the 2-by-12s overlap the slab. The upper 2-by-12 will distribute the load evenly across the substrate, lessening the chance of cracked tiles.

Gently turn the screws on the jacks about a quarter turn at a time, alternating jacks in the same order to lift the slab evenly. If the lift is uneven, a third jack should be used to ensure the slab rises evenly. If a third jack is needed, make sure to support it top and bottom with wooden blocks. (A second pair of 2-by-12s isn't necessary.)

This is a delicate, two-person job -- one turning the jacks, the other in the living room monitoring the progress of the lift. If all goes well the substrate will move into level with the floor.

Once the substrate is in place and supported by the jacks, remove the old posts and piers and replace them with new ones. Use the old excavations, but widen and deepen them so they measure 12 by 12 inches square and 12 inches deep. Pour fresh concrete to fill the holes and set new precast piers in the wet concrete, making sure to level the piers side to side and front to back. Let the concrete dry for a couple of days.

Then place a 4-by-4 beam against the slab and support it at each end with 4-by-4 pressure-treated posts nailed to the wooden blocks on the top of each pier with four 16d nails. The finished product will look like an upside-down "U." Make sure this structure fits tight to the slab by using shims between the slab and the beam.

An alternative to precast piers is to imbed metal anchors into the concrete to accept pressure-treated posts. Pressure-treated material is required for this application because the wood is too close to the ground and is more susceptible to termite or carpenter ant infestation.

Let the new concrete cure for a week. Remove the jacks and the hearth should be level once again for a long time.

A final word: No matter how careful you are, there's no guarantee that you won't crack a tile or two, and it's possible that you'll end up searching the salvage yards for pieces that match your fine old hearth. Good luck.

                                     

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