Learn me permanently sealing an unused exterior door

I volunteered to help fix a couple things at my wife's church. I'm out of my league on one task: how do I make sure this permanently closed exterior door NEVER leaks?

It's ~10' up, often bears the brunt of heavy rain. The facade is sandstone over standard brick/mortar. The wooden door framing appears to be intact, for now.

My idea was to create a hardie board plug sized to the stone opening (not the door), push the board in flush with the door frame, apply [insert the most durable sealant you kind strangers recommend here] to the edges of the door frame, screw the board to the frame, and seal the edges with [more durable sealant].

Or something else entirely?

I'll take a stab...  your idea would probably work.   I would one-up it.   I would build a 2x4 frame attached to the inside of the existing door frame so that  i would have something beefier to screw the hardi to.  Doing that would also allow me to have a brace in the middle to fight potential fleing/bowing of the hardi panel.   Then I would caulk the edges like there was no tomorrow.

I would...

• Strip all the wood out.
• Clean up the stone, fix any loose mortar joints
• Build a pictureframe of treated 2x4s or 2x6s lagged into the stone, set it nice and square and shim it up.  Maybe add some flashing or a drip rail to the top.
• Build a plug like you would build any other wall, screw it into the pictureframe.  Depending on how you want to finish the interior, build it with a plan of taking out the adjacent drywall and refinishing the whole mess.  Sheet the exterior with tyvek and OSB
• Install your preferred exterior board/covering on the exterior just like any other exterior wall.  

why not make it a big glass block window?

AngryCorvair (Forum Supporter) said:

why not make it a big glass block window?

This!

Use NP-1 sealant.  It'll outlast the building.

Is it wrong to suggest actual masonry like it should have been done?

SV reX said:

Is it wrong to suggest actual masonry like it should have been done?

I was wondering why the correct answer had not been mentioned yet. Last I checked the Masons had not checked out of business.

I also like the idea of a window. What is on the other side of the door?

Also consider a bit of flashing at the bottom to divert water from the sill.

Thanks for the responses. 

The framed-plug route sounds simplest.

There isn't budget to hire a mason. (Also, the sandstone facade is a PITA to deal with [requires periodic sealant] and may be difficult to obtain matching stone?? I have no idea, but it's 100+ years old.)

BTW, this is literally an old backdoor to the church, not a priority to make perfect. 

Glass blocks would be cool, but... on the other side of the door is a hallway with an ADA ramp that is several feet above the bottom of the door.

The inside of the door has a piece of 1/2" plywood screwed to it, then drywall. Whoever closed it in didn't  match the rest of the wall in the hallway - it bumps out ~1 foot to the door. In other words, you can't tell there's a door there, from inside. 

Plug it.  Seal it.  Put a faux-doorknob on it and maintain the look of a door that is inexplicably ten feet in the air.

It's a church... use your imagination for an appropriate (or inappropriate) sign to put on that door.   

Why is matching the stone important?  ANY masonry would look better that a crappy piece of plywood and some caulk. 
 

A forum where there's nothing we won't DIY (except circumcision), and folks are skeered of a little masonry?  It's a trade that's 10,000 years old!