Water Intrusion Control Projects in the 2021–22 Fiscal Year: The Rest of the Story

PHASE II OF THE FLAGSTONE RESTORATION PROJECT was undertaken in late 2021, mainly to control ongoing water intrusion into the sanctuary building. Three smaller projects meanwhile also had the same goal. As this fiscal year comes to a close, here is a blog post that gathers those threads, weaving them into the fabric of a loosely told story.…

Sealing the Void

In our last episode on controlling water intrusion into the sanctuary building (8/31/21), our masonry contractor had uncovered an underground void between our building and the neighboring one. It was about 5" wide, 8' deep, and at least 20' long. We faced the challenge of closing up that void in such a manner as to enable a stable concrete pad to be poured on the patio—without the dirt (sand) underneath it collapsing down into the void. 

I had surmised that our masonry contractor would come up with something workable. It turned out, however, that he made no effort to do so; rather, he waited for me to fix the problem so that he could continue his work. (Lesson learned: When dealing with old buildings that have little documentation, it’s best to select a contractor with a problem-solving bent, who will be our engaged partner in dealing with surprises.)

After consulting with various parties, I designed the void’s cover: a piece of stainless-steel sheet metal, bent at a right angle and set vertically across the opening. (Stainless steel resists corrosion better than galvanized steel.) One leg of the metal piece would be anchored with construction adhesive to the wall of our neighbor’s building, while the other would be left free to float across the front foundation wall of our building. Both sides would be sealed against their respective wall with flexible caulk, to keep dirt (sand) and rainwater from eroding past the metal and dropping into the void. To prevent similar erosion at the bottom of the metal piece, we would place a concrete block as a stabilizing base.

I procured the custom-bent sheet metal, and Ruben and I installed it.

Hole cover in place, with its protective plastic sheet left on

Hole cover in the corner, next to FDC inlet

Next, the wall's stucco was refinished, because the original placement of the fire department connection (FDC) inlet for the basement’s sprinkler system had prevented a smooth finish, leaving a marred wall surface (visible above, to left of the new inlet pipe). 

September 15, 2021: After stucco refinishing

Then a plumber came and reinstalled an underground drainpipe to carry away stormwater from the corner downspout. 

After the underground drainpipe was reinstalled

Then the masonry contractor returned and fully buried the sheet metal piece, before pouring a concrete pad across the patio area, as mentioned above.

Checking the surface slope, before grouting

Sealing the Void

Stormwater coming off the roof had been finding its way into the basement for many years. I.e., it was not being channeled away from the building in a reliable manner. This was due to several factors: 

• The FDC inlet was located too close to the corner: there wasn’t enough room for a good connection between the corner downspout and the underground drainpipe that led the water out to the street gutter.
• The underground drainpipe was undersized, due to its being constricted by the narrow passage under the city sidewalk. 
• The underground drainpipe had gotten clogged with debris. It was eventually covered over altogether.
• The flagstone patio surface was permeable to water: it lacked a waterproof concrete pad beneath it; the grout between stones had cracked over time; and the surface sealant had not been maintained. 

In 2018 or 2019, the B&G Committee had adopted the admittedly short-term expedient of sealing the surface by applying a cementitious coating over the flagstone over the entire patio in front of the double doors. By 2021, however, that coating had predictably developed significant cracks.

In 2021, while restoring the flagstone patio, we attended to each of the factors identified above. The photos below show aspects of the following efforts:

• When the badly corroded FDC inlet was replaced, it was moved away from the corner, to make room for a tighter connection between downspout and drainpipe.
• The clogged underground drainpipe was replaced and provided with a clean-out and an overflow relief opening (see photo, below). 
• A waterproof pad was laid underneath the patio and sealed along both walls.
• The grout included a waterproofing compound.
• A (2-year) sealant was applied to the surface. 

Overflow drain opening, with mosquito screen

Seal at the old railing posts on front steps

After Master Masonry removed the stubs of old railing posts on the front steps, exposing the bare concrete below, I had them apply a waterproof coating in that area, before covering it with new flagstone. This was a change order during the Flagstone Restoration Project, as recommended by our water intrusion consultant. The idea was to reduce the known water intrusion through the steps in that area. (Unfortunately, it didn’t seem to help.)

Filling in hole around vent pipe at south wall

After Master Masonry opened up the void at the south wall, it proved to be much larger than we had imagined. Apparently over the years, underground water flows had carried away the dirt under that strip of driveway. 

So they filled the void with crushed rock, and then poured new concrete on top (not shown).

Enlarged downspout at northeast corner

One additional step that we took for the purpose of controlling water intrusion was to enlarge the downspout at the northeast corner of the sanctuary building. Apparently it was undersized, which in a heavy rain could cause problems. 

Ironically, during the first downpour of the rainy season, the new downspout apparently caused water to pour into the adjacent school/office building. Our roofer diagnosed the problem as a combination of holes and cracks in the stucco wall directly beneath the downspout (a ready entry point), plus a leaking seam in the new downspout directly above those openings.

The roofers kindly fixed that problem under our warranty, even though they had nothing to do with the faulty downspout installation.