OSB Supporting Hearth and Hearth Extension

[eduritsch]

I recently moved into a 30 yr old 2 story brick home with what I thought was a nice fireplace with a large stone hearth extension and surround. A previous owner had converted to gas logs so I planned to convert back to wood. Diving in deeper I find that the gas pipe was run thru a finished basement into the ash pit and up thru the ash clean-out door. I had no issues removing the gas line back to where they tee'd it off at the water heater. The ash pit clean-out door is behind drywall but appears to be closed. This is where it gets bad. I want to patch the hole in the ash pit wall where the gas pipe entered so I cut a hole in the drywall ceiling next to the fireplace. What I find is a 2' x 2' piece of plywood glued to the block wall with a slot cut into it for the pipe to enter. Upon removing the plywood, I see a 16" x 16" opening where 2 concrete blocks were removed. Looking up at the hearth from below, the plywood that was used to support and form the bottom of the hearth and extension is still in place. The rear section against the back of the chimney brick is supported by 2 vertical 2x4's under a horizontal 2x4. I know it is against code to construct a fireplace this way and it must not have been inspected originally. I know I need to remove the wood but I'm not sure how best to support the hearth from inside. I don't care about deleting the ash pit as I would never use it anyway. I already purchased the firebrick to match for filling in the door. I have found very little on this subject online with the exception of a few home inspector forums basically saying that it's a fire hazard and needs to be fixed. I'm thinking I could maybe build a block wall inside the ash pit from the poured foundation up to support the hearth, after removing the wood of course. Will the poured concrete grip the outer brick enough to hold up the hearth when I remove the wood framing below? Thoughts?

 

[eduritsch]

2 Supporting images. Sorry It was a little dark in there.

 

[bholler]

This is very common we see it all the time more often than not actually. It is not right and the wood should be removed for sure. Generally it is just the bottom of the form and is no longer supporting anything so it can just be removed. But i cant say that for sure without being there.

 

[eduritsch]

Thanks for the reply. I’m afraid to remove the 2x4 support holding up the back of the plywood in fear that the hearth will drop although it seems like it would be anchored somewhat to the outside brick. There is no other support structure beneath that side of the hearth. I may be able to lay block inside to support it before removing the wood and then remove the wood in sections. Sounds like fun I didn’t want to have.

 

[eduritsch]

Another photo. This one shows the form sagging under the weight of the pour. It is unsupported on the sides.

 

[bholler]

Thanks for the reply. I’m afraid to remove the 2x4 support holding up the back of the plywood in fear that the hearth will drop although it seems like it would be anchored somewhat to the outside brick. There is no other support structure beneath that side of the hearth. I may be able to lay block inside to support it before removing the wood and then remove the wood in sections. Sounds like fun I didn’t want to have.

I have never seen one that was not tied in somehow but like i said i am not there to see yours so i cant tell for sure