Moisture Protection for a Wood Door in a Stone Threshold

A church door replacement job raises questions of protecting wood from moisture in contact with stone.September 25, 2014

Question (WOODWEB Member) :
I just put in a bid to build a few doors for a historic church. One set of the side doors is currently an old wood outswing double door that sits on an old stone slab that is halfway in and out of the building. It is preferred to keep as much original structure as possible as they want the door set in the same opening on the stone slab. However, there will now be a single outswing door with side panels. The door can receive some sort of sweep system but there will still be wood-on -stone contact from the side panels. Do any of you guys that build a lot of exterior doors ever use a vapor barrier tape around your jamb and under the threshold when it will be in contact with stone/masonry, etc.? If not what is your preferred method for protecting against moisture under a threshold/sill? Please bear in mind the door will be pre-hung and the stone can certainly be out of level.

Forum Responses
(Architectural Woodworking Forum)
From Gary Katz, forum technical advisor::
Yes, absolutely. You should use some type of membrane to both seal the bottom of the opening and isolate the stone from the wood. We make sill pans from membranes like "Ice and Water" all the time. And before I install the membrane, I level the sill of the rough opening, then lay in the self-adhesive self-healing material. In most cases, I install a cant strip first, so any moisture that gets in there travels toward the outside of the wall, rather than the inside and does not puddle under the jamb. I imagine if your stone sill is way out of level, you may have to add some type of molding at the bottom of the side lights. I'd definitely make the door long and plan on scribing/cutting it to the stone sill after it's hung, then installing the sweep.

From Contributor O:
We typically seal the ends of the jambs - or anything - with epoxy if they are going to sit on stone or be in contact with rain/snow. Recently, I have started adding some sheet rubber as an isolator between the epoxied wood and stone. The rubber is about 3/32" thick and easily cut to the foot print of the jamb. The material is scrap pond liner, black rubber. I agree with Gary on the long door and scribing to the stone. Then I would paint the door bottom with epoxy to seal it up well prior to adding the sweep. We have also used the automatic door bottoms on stone sills before (Pemko).

From contributor D:
Will they consider a steel jamb? The last church doors I completed were mahogany in steel jambs. Itís a spring-loaded door sweep that comes up into the door when it swings. They are still going strong after the install, in 1997.