Rebuilding garage entry door sill

[mandelbrot]

Happy for any thoughts here, pardon the long intro ...

A previous owner of my home had converted our small 2-car garage into a second living area. He did it so poorly and the space was so awkward, that we went ahead and converted it back to a garage, and have been much happier being able to park our cars indoors for the last few months :-D

In this thread I need some help with the space directly under the new pre-hung interior/exterior door that we installed as part of the garage un-conversion. This would be the door that runs from the garage into our house. From here on I will just call this "the door".

The garage, as it was originally built, had a concrete tire stop built into it, as many garages do. Sometime later, a new divider wall was built right in front of the tire stop. For some reason the owner (at that time) chose to lay down treated 4x4 posts as the base for the new wall -- to bring it up in line with the rest of the house, I suppose. So this 4x4 base now defines the plane of division between the house and the garage. Our new door (THE door) is set into this wall.

It's a bit of a longer story involving some removal of extra homeowner-added concrete pads, but what we have NOW is a situation where the prehung door is anchored strongly into the studs on either side of it, but is not really resting on anything below. The reason things turned out this way is not important -- misunderstanding between myself and the contractor. But the point is, there is a "break" in the 4x4 post, right underneath this door. It is empty space in there, and the edges of this empty space are pretty ragged due to some concrete debris, a little decay on the edges of the 4x4s, and so on.

So the situation, basically, is that the aluminum threshold for new door has nothing under it. For the time being I have shoved in a couple of 2x6s under the threshold, and shimmed it suitably enough so that the threshold has temporary structural support.

There is also a small (~1/4") air gap between the bottom of the aluminum threshold, and the top of our in-house flooring, which drops off to the garage concrete floor, about an inch inside the threshold.

To fix this, I need to fill in this "gap" under the threshold with something strong that can be (preferably) cleanly finished. I haven't done anything like this kind of work before, so I would love some suggestions. It is an irregularly-shaped space to fill, as I mentioned. My initial thought was concrete of course. But the only way to pour in concrete will be from the garage side. And the garage side will need to be closed off as part of the form work ... so I don't see that as an option.

Any other ideas would be appreciated! Thanks.

[mandelbrot]

This was pretty raggedy to describe, so pictures help ...

https://goo.gl/photos/x2iRJhXAaQahF4jVA

I have shown the threshold from a couple of vantage points -- from inside the house and from inside the garage, of course. Under the threshold is the short stack of 2x6s that I mentioned earlier, with shims and a 1x board on top.

Meanwhile on either side of that short stack, you can see how ragged the underneath is. On the left side the end of the 4x4 is clearly visible -- the front is somewhat decayed or gunked up with residue from what used to be a homeowner-added concrete pad. On the right side it's a little less clear what exactly is going on. Definitely some residual concrete from that same concrete pad we removed ... also maybe seeing the front edge of that hidden tire stop.

In any case this should clarify what exactly I'm dealing with.

[worms]

Interesting problem and I will be interested to see what the expert solution is from the forum members.

My house is an old Scottish cottage built with the rubble stones that would have been in the ground around the site.  When I have problems like you have, I part fill the space with mortar then hammer home suitable sized stones from the yard, with old pieces of slate immediately under any timber for damp-proofing.  Not sure how you do that with modern construction, though!

[Greg]

I would use polyurethane glue to affix some more treated wood into the hole.  Once there's a base of treated wood (one should pretty much always use treated wood against concrete) you can shim above it sort of like you have to make it solid and level.

On the finished floor side, that floating floor needs a 1/4" gap minimum between the ends of the flooring and the door sill, if it's in the same plane.  If the sill is above the flooring disregard as long as you have that gap.  Because that's a floating floor, you can't just caulk the joint, it needs that slip space.  I'd seal it well with foam and caulk on the garage side.

[mandelbrot]

Thanks Greg, I was hoping someone would recommend something other than just detaching the whole door assembly, pouring a concrete sill, and re-hanging it. That sounds like it's roughly along the lines of what I was hoping to do.

That said, I am a n00b on this particular class of DIY things ... is there any potential long-term downside to putting in a 'constructed' sill made of (mostly) treated wood, as opposed to using a 'proper' concrete sill?

I can't think of any, but I'm trying to be fully informed here.

Thanks to all.

[Greg]

Functionally and structurally it will make little difference, except that normally the wood against the concrete (mudsill) is bolted to the concrete via anchor bolts embedded in the concrete edge (stemwall). 

In your case, glue should be good enough, if you're worried about it make sure the side facing the garage is flush with the stemwall and use straps and wedge bolt anchors to tie the build-up sill to the concrete on teach side.  You'll to borrow/rent a rotohammer for this, and the installation varies a bit from fastener to fastener.  But really just filling the void should be fine.  Maybe paint it gray. :)

[mandelbrot]

Makes perfect sense Greg, thanks! I think using straps to anchor to the existing stem wall -- or to the 4x4 post, as it were -- will probably be unnecessary, as you implied. But the gray paint? That will be quite necessary.

Thanks again.

[Fishindude]

a. Take up the sill and remove that wood blocking.
b. Build some forms and pour that area in with bag mix concrete, replacing the area of curb that is missing and wide enough to provide a bearing surface for the entire aluminum threshold.
c. Re-set the threshold in place.  Shim threshold to fit nice to door bottom and anchor it down with pan head "Tapcon" concrete anchors.
d. Caulk threshold perimeters.