I've come to believe that I can't just get contractors to do everything I want, so there are times I just have to do things myself.
This week, before the final interior touch-up (including painting the new--and very nicely designed if I do say so--shelves) I had, partly by fortune and partly by accident, two extra days to do some interior work.
The first I had to do was cleaning up surplus mud and sheetrock around the outlet boxes and switch boxes, and applying acoustical caulk to the gap between the boxes and the sheetrock. Surely the electrician could have done the cleanup, but not on a moments notice before the paint touch up, and I've decided to have the electrician come in only after the general contractor has finished everything anyway. But the acoustical caulking is not something they do, so far as I know. And I had to pick out the right caulk. I managed to pick up the right caulk from Hart Acoustics just before they closed on Monday afternoon.
The second was strengthening the flashing underneath the air conditioner case. The contractor had simply stapled a couple pieces of Lowes housewrap that were folded in from the outside, about 3/4 of the way into the opening, leaving bare a bit of the stud wood beyond that and the dusty ragged edge of sheetrock that had been crudely cut just above the wood trim.
I'll explain these two operations in two sections below, then explain the choice of acoustical caulking in a subsequent post.
*****
When the contractor texted me at 8am Monday morning about the interior paint touchup to be done on Tuesday, it was my good fortune to be able to schedule a vacation day at moments notice. I had previously been researching what kind of caulk to use to fill the gaps, some as large as 3/8's of an inch, between the sheetrock and the electrical boxes. I decided to get OSI SC-175 acoustical caulk because it is water based and low VOC, and could be quickly obtained locally. It is amazingly inexpensive too, I got two of the large size tubes for less than $6 apiece. I tried calling the dealer listed by OSI on Saturday but they were closed. Repeating the call on Monday I was asked for "company name" and told they were a distributor, not a dealer, and could not sell retail. However they were able to find a local dealer, Hart Acoustics, who fortunately still had 2 tubes in stock. I got over to their building less than an hour before they closed at 5pm, and quite a few staffers were already going home for the day. I was pleasantly surprised that they were charging exactly the same price listed by OSI. For the current work, I only needed one tube, but at that price, and with all the uncertainties involved, it was trivial to get two tubes. As I got back to my car the rain had started. On the way home I stopped at Home Depot and bought 3 gallons of Valspar Premium Plus semigloss white paint for the interior. There was still 2 gallons or so in the 5 gallon jug used by the contractor a couple of weeks ago, but it had been left outside exposed to sun, nearly freezing if not freezing cold, and I found the cap was loose. I'm sure the contractor would have decided this was OK anyway, but I felt better getting brand new paint. I'll have to find some way of legally disposing of the old paint, Home Depot won't take back paint in opened containers.
I got home around 6 and it was still raining too hard to go out back, in fact it was raining quite hard, but I could see at Weather Underground animated radar the rain would last an our or so and then go away entirely, with temps in the low 60's, what it was then, until 6 in the morning. So no need to hurry, I had dinner and rested, and was back on the project by 9pm.
The ground was still very wet, but I hauled all sorts of stuff into the workshop including vacuum (with Protection Plus synthetic bag and HEPA filter) and Verilux light on a stand, and hooked up electricity using heavy extension cord plugged into GFCI protected outlet on my back wall. The cord reached easily into the building.
Many of the outlet boxes were partially covered with sheetrock and/or mud on 2 sides, then left with big gaps on the other side. The first job was trimming the sheetrock and mud down to the very edge of the boxes. BTW, the boxes are all behind the sheetrock at this point. I think the electrician will extend the boxes out with extenders. Come to think of it, I should have gotten the story on that, my caulking may have to be cut. But I figured they will use outlet box extenders that go inside the existing boxes, and that appears to be correct from looking at some extender boxes online.
I was very careful not to cut sheetrock beyond any edges leaving gaps like the contractor had done. I got large fixed Lennox utility knife at Home Depot to do the cutting. Large pieces were put in trash can, dust and debris carefully vacuumed up with vacuum extension angled away from me...so no dust would be accelerated in my direction.
Then I applied the caulk only inside the large gaps the contractor left. The water based caulk was easy to clean off the wall which I needed to do once. I didn't get any on the floor, and I used a large tarp to be sure, but I got lots on my fingers and hands and shoes. It easily washed off within 30 minutes. In some cases, pieces of spray foam were poking out of the gaps, I trimmed them off, and I'm glad my caulk is now covering up gaps in which the foam could be outgassing and releasing foam dust into the room. Preventing that outgassing and outdusting was actually the major concern behind this activity, the acoustics and sealing-from-the-outside are probably already handled by the foam insulation itself, the low VOC acoustic caulk only helps by doing-no-harm, not creating rigid couplings between wall and boxes that might cause rattling, otherwise non-acoustical caulk might have been fine.
After all this work was done, I removed all my items from the workshop and lawn and I put the paint and Alex 230 Ultra caulk (for the contractor) inside the shed from the garage. Walking around the gate to the garage there were pools of water in the dormant grass. I was all finished by 3 am. Yes it takes me 6 hours to do work it might take a pro 30 minutes to do. But they won't do it.
*****
That night, unfortunately, I was unpleasantly surprised that a toilet was gurgling all by itself when I ran the washing machine to clean my only slightly dusty project work clothes. Then I noticed water backing up into both tubs, and an unpleasant smell.
I feared that now the problem I had feared in early January after the spray foaming had come to pass. I feared that the heavy spray foam truck, which left deep tracks in my lawn several inches deep, had cracked the sewer pipe. It hadn't caused a problem right away, but with the heavy rain, high clay mud had leaked into the pipe causing it to become blocked at a point which might also be slightly compressed.
I feared how things would go in the morning when I needed to use the toilet. I feared ripoff plumbers. I feared paying $10,000 for sewer pipe replacement and having to find motel to stay in. I decided not to call any 24 hour services and wait until 7 am, when I am usually sound asleep, to call plumbers. I would first call my usual plumber, but I didn't know if they did router and video camera work. I noticed the Yellow Pages repeated the names of Roto Rooter and a few others on nearly every page, no doubt they have to pay a lot for all those listing...costs which indirectly get added to your bill. I checked Angie's list for recommended drain cleaners. I was almost 5:30 before I got to sleep and then I only slept until about 7am.
The first two plumbers didn't answer, nor did my insurance agent. I made an appointment for 2:30-4 with the third plumber I called, who had one of the highest ratings on Angie's List. I was pleased that I was getting both drain cleaning and video inspection for about $360 combined. I was now believing that the cleaning would at least get me back online even without replacing the pipe, though I might have to do that ASAP. The toilets were working--one flush at a time, and I was able to take a quick shower in the rarely used master bath shower (relatively clean) without serious trouble. I refrained from eating or drinking anything until the blockage was fixed.
The plumbers found only a root clog near the cleanout opening, all the rest of the pipe was clearly undamaged from the video. Whew! They gave me the quoted price, and estimated replacing the first 5 feet of sewer pipe to prevent future root invasions. I'm not sure when I'll do that, I've gone 20 years in this house without a root problem before. The only nearby plants I've tried to kill off before, and grass. A friend has volunteered to relocate the plants away from the drain.
So finally I was able to eat, use the toilet, and relax. I had scheduled this day off as "emergency leave" because of the blocked sewer, so I didn't need to go to work. Earlier in the day, the contractor had texted saying that they weren't coming out today after all.
Only then did it occur to me I might fix up the flashing on the horizontal stud underneath the A/C chassis. I'm sure the contractor would say it was good enough. But as said above, the housewrap only went part way across, leaving exposed rough sheetrock edge. I imagined water condensing on the bottom of A/C chassic dripping on to this, and eating way the sheetrock over time. And sheetrock dust would blow into the room through the crack. The A/C case goes around the sides and top, with only rails at the bottom, leaving the center bottom open. The A/C chassis slides on top of the rails. While the A/C chassis itself is sealed at the bottom, it is insulated only by a piece of plastic. This might be colder than the air in the crack beneath it, causing condensation and dripping.
One way to understand this (it was hard to make close-up photograph to do it justice) is that there's bare horizontal framing piece exposed by a rough opening in the wall beneath the AC. If the AC had a full wraparound sleeve, like many AC units designed for through-wall installation, it would have been simple enough to apply expanding foam insulation all around to seal the sleeve into the wall. In fact that was done on the two sides and top, so the A/C outer case (similar to a sleeve) is now effectively part of the wall. But this AC was a hybrid designed either for through-wall or window installs. The bottom of the case is open. For window installs, there is a crosspiece that would go across the bottom to rest on the window ledge, but for through-wall installs that crosspiece is removed.
Now, knowing this, I should have specified that the contractor create a window sill beneath the AC. Such a sill would have protected the wall from moisture dripping from the AC. In the place of that, they ragged perforated housewrap only going part way across the horizontal framing. The framing on the inside of the wall doesn't protect the gap, it merely covers it from normal view. Neither side of the gap has proper drainage, the inside had bare rough sheetrock extending above the board, and the outside has relatively smooth cut Hardi Panel siding extending above the board. There isn't enough room in the gap to place any kind of wood board, but there is enough room to place something thinner like a piece of polycarbonate sheeting (and conveniently, the angle from the inside of the interior trim to the hardi panel slopes slightly downward).
At minimum, I needed a piece of wood to go on top of the roughly cut sheetrock, protecting it from dripping moisture and condensation. The piece of wood would need to be at least 1" wide to completely cover the sheetrock and beyond. The only scrap shims I could find left by contractor were about 1/2 inch, and they were sloped. I wanted a flat piece.
All the shims I could find for sale at Home Depot were similarly sloped, but I found a scrap piece used as a spacer for lumber which was exactly what I needed. It was about two feet long, one inch wide, and about 1/8 thick. I asked an assistant if they would have anything better like that, and he said other than sloped shims everything they sold would be at least 1/4" thick. But I could have the scrap for free. I looked all over the store and indeed could not find anything better. I also thought of using a polycarbonate sheet to cover the entire opening from front to back, so I bought a 12x24 inch piece with a cutter.
Though it was much dryer outside by now, I decided not to mess with extension cord and light and vacuum this time...too much hassle. I did everything with two flashlights and the big one needed a battery replacement in the middle of the job. I cleaned off the sheetrock dust in the wall gap which seemed endless, with wet paper towels and a few disposed of work cloths. It wasn't perfect, but was MUCH better.
I then further pasted down the sheetrock edge with acoustical caulk, and placed the wood piece on top, nailed down only in front (on the stud) so it tilts a bit away from the sheetrock. I did lots of extra pounding on the on the side going away from the sheetrock to make sure it has that tilt.
Then I layered on Tyvek tape. First a 1/2 thickness piece only in front, going over the scrap piece and attaching to the front trim. Then I put another piece at the edge of the scrap piece going forward and connecting to the Lowes housewrap. Then a couple of full width piece in between connecting the two, with the previous pieces providing consistent tilt away from the sheetrock. Then additional pieces at the sides so that the shims underneath the A/C case are also covered, and there is tilt away from them too. Then pieces in some damaged areas in the housewrap. Then I nailed the housewrap just next to the siding to provide drainage channels toward the exterior wrap (on this side, covered with felt for even better drainage). Previously the housewrap kind of bubbled up toward the outside, which would cause condensate to migrate toward the inside, and back to the most vulnerable sheetrock.
The result is plastic covering everything from the trim inside to the siding and mostly tilting toward the siding except for a few remaining bubbles in the housewrap which had been folded by the contractor on the inside of the siding. The sheetrock edge is covered with acoustical caulk, 1/8 thick wood scrap, with Tyvek permanent polyethylene tape on top of it all, stuck to frame in front.
By this time it was 2am and I was exhausted. I still wanted to cover the entire gap from trim to outside of siding, on top of all this plastic, with a piece of polycarbonate cut to the exact size. But I was too tired to go on with that intricate work, and was thinking at this point it would only add an additional R value of 1.0 so why bother. Whether it was dripping from the plastic bottom of the AC chassis or the bottom of the polycarbonate, it would still be dripping.
The next morning the contractor texted and woke me at 10am saying he would arrive at 11 for the A/C installation. Now, with 6 hours sleep, I decided to go ahead with tcutting the polycarbonate piece. I now figured it could be caulked all around, completely and permanently sealing the stud and drywall and sheathing from any condensate, like a window sill, maybe better since polycarbonate is strong and non-porous. No new moisture-laden air would be flowing into the vulnerable area at all, therefore little or no condensation would occur on the bottom side of the polycarbonate. Sitting on top of the trim, and the opening in the siding, it would tilt slightly toward the outside, serving like a drip edge by extending somewhat beyond the siding. Unlike the Tyvek tape to housewrap flashing I had done, which wraps inside the siding (the siding juts up 1/2 inch at that point), a plastic piece on top would direct moisture to beyond the outside of the siding, getting the condensate entirely outside the building, through the wide opening in the bottom of the A/C case.
I got to work re-measuring the opening and marking and then scoring the polycarbonate. It was not at all easy to score right on top of any existing score. Scoring is supposed to be done to a depth of 6. I did the best I could and then tried breaking the polycarbonate. No matter how much I bent or pounded it, it would not break. By this time, the contractor had arrived and was sitting in his car. I checked the Home Depot website and it didn't say they cut polycarbonate, I don't believe they do, only glass, and I didn't want to use that as it's dangerous to handle. I called Samuels Glass and they said they would sell custom cut polycarbonate if I came down to order. I figured that would take at least a day.
So now I went to the contractor in an attempt to delay the A/C installation for a day so I could get a polycarbonate flashing piece. I had great trouble explaining the need for this. He suggested simply putting some gap sealing foam rubber pieces like people use for doors and windows into the inside and outside gaps, and that having a piece like I described would get in the way of installing such pieces. I went along with his plan to install the AC chassis right away. The job went OK, though I wasn't entirely happy with the way the contractor installed the foam weatherstrip provided by Friedrich for the top and sides before pusing the AC in all the way. It was OK, though, at least it got installed. Also I kept them from jamming on the plastic front panel. I feared they might break it, so I insisted that I would take care of that myself. Plus I want to do other things like straighten out a few of the the aluminum evaporator fins which got bent by me (they are little thicker than aluminum foil) when I was unpacking the AC.
I still figure it would be better to have the polycarbonate piece to keep moisture out of the wall system. If there is a tiny remaining gap for air to flow into the room, I am not as concerned about that, any moisture condensing would simply be drained outward on top of the polycarbonate, and the effect of such a thin (1/16" or less) gap would be fairly small, maybe even beneficial. And if the only protection of a very vulnerable area in the wall is a foam rubber gasket--those don't last forever, and when it fails I'd never know until damage to wall, most likely to the sheetrock, happened.
Maybe I'll find some way to do the polycarbonate piece in the future. I'm worried that if I wait too long, my carefully applied Tyvek tape and so on will have ceased to work as I intended (this is WAY off lable usage). Or perhaps the best thing would be to figure out how to have such a polycarbonate piece AND have the foam rubber end seals as well.
But I'm greatly satisfied that at least I did a much better of flashing underneath the A/C. I'm sure the way the contractor had done it would have caused problems within a few years or less.
I've also thought about the weather stripping. Even with a sill-like polycarbonate piece below the AC, or not, the gaps in front and back need to be filled with weather stripping. Friedrich provided a second foam piece for through-window installations which would work for this purpose...so long as I don't add the sill (which would probably make the remaining gap too small for the thick foam). Also, my plan is not just to use the foam strips, I plan to augment the outside with special duct tape intended for exterior use, and possibly on the inside with Tyvek tape.
Update: Now that the AC has been installed, I can see it won't be so easy to seal up the bottom, particularly at the outside. The bottom of the AC chassis is not flat, it has a 1/2 beams in a cellular pattern, obviously intended to give the polyethylene plastic sufficient strength. There is no flat surface that can be taped to, and a foam weatherstrip would need to be very flexible to reach the inside of each cell while still being compressed by the beams. Furthermore, despite this reinforcement, the bottom has a slightly bowed contour, so it hangs deeper, maybe by a millimeter or so, right in the center. That bowing denies sufficient clearance to shove a polycarbonate panel underneath. It can be shoved past the outer trim frame, but sticks right at the rough Hardi Panel edge.
So in a bunch of ways, I'm between a rock and a hard place on this.
This week, before the final interior touch-up (including painting the new--and very nicely designed if I do say so--shelves) I had, partly by fortune and partly by accident, two extra days to do some interior work.
The first I had to do was cleaning up surplus mud and sheetrock around the outlet boxes and switch boxes, and applying acoustical caulk to the gap between the boxes and the sheetrock. Surely the electrician could have done the cleanup, but not on a moments notice before the paint touch up, and I've decided to have the electrician come in only after the general contractor has finished everything anyway. But the acoustical caulking is not something they do, so far as I know. And I had to pick out the right caulk. I managed to pick up the right caulk from Hart Acoustics just before they closed on Monday afternoon.
The second was strengthening the flashing underneath the air conditioner case. The contractor had simply stapled a couple pieces of Lowes housewrap that were folded in from the outside, about 3/4 of the way into the opening, leaving bare a bit of the stud wood beyond that and the dusty ragged edge of sheetrock that had been crudely cut just above the wood trim.
I'll explain these two operations in two sections below, then explain the choice of acoustical caulking in a subsequent post.
*****
When the contractor texted me at 8am Monday morning about the interior paint touchup to be done on Tuesday, it was my good fortune to be able to schedule a vacation day at moments notice. I had previously been researching what kind of caulk to use to fill the gaps, some as large as 3/8's of an inch, between the sheetrock and the electrical boxes. I decided to get OSI SC-175 acoustical caulk because it is water based and low VOC, and could be quickly obtained locally. It is amazingly inexpensive too, I got two of the large size tubes for less than $6 apiece. I tried calling the dealer listed by OSI on Saturday but they were closed. Repeating the call on Monday I was asked for "company name" and told they were a distributor, not a dealer, and could not sell retail. However they were able to find a local dealer, Hart Acoustics, who fortunately still had 2 tubes in stock. I got over to their building less than an hour before they closed at 5pm, and quite a few staffers were already going home for the day. I was pleasantly surprised that they were charging exactly the same price listed by OSI. For the current work, I only needed one tube, but at that price, and with all the uncertainties involved, it was trivial to get two tubes. As I got back to my car the rain had started. On the way home I stopped at Home Depot and bought 3 gallons of Valspar Premium Plus semigloss white paint for the interior. There was still 2 gallons or so in the 5 gallon jug used by the contractor a couple of weeks ago, but it had been left outside exposed to sun, nearly freezing if not freezing cold, and I found the cap was loose. I'm sure the contractor would have decided this was OK anyway, but I felt better getting brand new paint. I'll have to find some way of legally disposing of the old paint, Home Depot won't take back paint in opened containers.
I got home around 6 and it was still raining too hard to go out back, in fact it was raining quite hard, but I could see at Weather Underground animated radar the rain would last an our or so and then go away entirely, with temps in the low 60's, what it was then, until 6 in the morning. So no need to hurry, I had dinner and rested, and was back on the project by 9pm.
The ground was still very wet, but I hauled all sorts of stuff into the workshop including vacuum (with Protection Plus synthetic bag and HEPA filter) and Verilux light on a stand, and hooked up electricity using heavy extension cord plugged into GFCI protected outlet on my back wall. The cord reached easily into the building.
Many of the outlet boxes were partially covered with sheetrock and/or mud on 2 sides, then left with big gaps on the other side. The first job was trimming the sheetrock and mud down to the very edge of the boxes. BTW, the boxes are all behind the sheetrock at this point. I think the electrician will extend the boxes out with extenders. Come to think of it, I should have gotten the story on that, my caulking may have to be cut. But I figured they will use outlet box extenders that go inside the existing boxes, and that appears to be correct from looking at some extender boxes online.
I was very careful not to cut sheetrock beyond any edges leaving gaps like the contractor had done. I got large fixed Lennox utility knife at Home Depot to do the cutting. Large pieces were put in trash can, dust and debris carefully vacuumed up with vacuum extension angled away from me...so no dust would be accelerated in my direction.
Then I applied the caulk only inside the large gaps the contractor left. The water based caulk was easy to clean off the wall which I needed to do once. I didn't get any on the floor, and I used a large tarp to be sure, but I got lots on my fingers and hands and shoes. It easily washed off within 30 minutes. In some cases, pieces of spray foam were poking out of the gaps, I trimmed them off, and I'm glad my caulk is now covering up gaps in which the foam could be outgassing and releasing foam dust into the room. Preventing that outgassing and outdusting was actually the major concern behind this activity, the acoustics and sealing-from-the-outside are probably already handled by the foam insulation itself, the low VOC acoustic caulk only helps by doing-no-harm, not creating rigid couplings between wall and boxes that might cause rattling, otherwise non-acoustical caulk might have been fine.
After all this work was done, I removed all my items from the workshop and lawn and I put the paint and Alex 230 Ultra caulk (for the contractor) inside the shed from the garage. Walking around the gate to the garage there were pools of water in the dormant grass. I was all finished by 3 am. Yes it takes me 6 hours to do work it might take a pro 30 minutes to do. But they won't do it.
*****
That night, unfortunately, I was unpleasantly surprised that a toilet was gurgling all by itself when I ran the washing machine to clean my only slightly dusty project work clothes. Then I noticed water backing up into both tubs, and an unpleasant smell.
I feared that now the problem I had feared in early January after the spray foaming had come to pass. I feared that the heavy spray foam truck, which left deep tracks in my lawn several inches deep, had cracked the sewer pipe. It hadn't caused a problem right away, but with the heavy rain, high clay mud had leaked into the pipe causing it to become blocked at a point which might also be slightly compressed.
I feared how things would go in the morning when I needed to use the toilet. I feared ripoff plumbers. I feared paying $10,000 for sewer pipe replacement and having to find motel to stay in. I decided not to call any 24 hour services and wait until 7 am, when I am usually sound asleep, to call plumbers. I would first call my usual plumber, but I didn't know if they did router and video camera work. I noticed the Yellow Pages repeated the names of Roto Rooter and a few others on nearly every page, no doubt they have to pay a lot for all those listing...costs which indirectly get added to your bill. I checked Angie's list for recommended drain cleaners. I was almost 5:30 before I got to sleep and then I only slept until about 7am.
The first two plumbers didn't answer, nor did my insurance agent. I made an appointment for 2:30-4 with the third plumber I called, who had one of the highest ratings on Angie's List. I was pleased that I was getting both drain cleaning and video inspection for about $360 combined. I was now believing that the cleaning would at least get me back online even without replacing the pipe, though I might have to do that ASAP. The toilets were working--one flush at a time, and I was able to take a quick shower in the rarely used master bath shower (relatively clean) without serious trouble. I refrained from eating or drinking anything until the blockage was fixed.
The plumbers found only a root clog near the cleanout opening, all the rest of the pipe was clearly undamaged from the video. Whew! They gave me the quoted price, and estimated replacing the first 5 feet of sewer pipe to prevent future root invasions. I'm not sure when I'll do that, I've gone 20 years in this house without a root problem before. The only nearby plants I've tried to kill off before, and grass. A friend has volunteered to relocate the plants away from the drain.
So finally I was able to eat, use the toilet, and relax. I had scheduled this day off as "emergency leave" because of the blocked sewer, so I didn't need to go to work. Earlier in the day, the contractor had texted saying that they weren't coming out today after all.
Only then did it occur to me I might fix up the flashing on the horizontal stud underneath the A/C chassis. I'm sure the contractor would say it was good enough. But as said above, the housewrap only went part way across, leaving exposed rough sheetrock edge. I imagined water condensing on the bottom of A/C chassic dripping on to this, and eating way the sheetrock over time. And sheetrock dust would blow into the room through the crack. The A/C case goes around the sides and top, with only rails at the bottom, leaving the center bottom open. The A/C chassis slides on top of the rails. While the A/C chassis itself is sealed at the bottom, it is insulated only by a piece of plastic. This might be colder than the air in the crack beneath it, causing condensation and dripping.
One way to understand this (it was hard to make close-up photograph to do it justice) is that there's bare horizontal framing piece exposed by a rough opening in the wall beneath the AC. If the AC had a full wraparound sleeve, like many AC units designed for through-wall installation, it would have been simple enough to apply expanding foam insulation all around to seal the sleeve into the wall. In fact that was done on the two sides and top, so the A/C outer case (similar to a sleeve) is now effectively part of the wall. But this AC was a hybrid designed either for through-wall or window installs. The bottom of the case is open. For window installs, there is a crosspiece that would go across the bottom to rest on the window ledge, but for through-wall installs that crosspiece is removed.
Now, knowing this, I should have specified that the contractor create a window sill beneath the AC. Such a sill would have protected the wall from moisture dripping from the AC. In the place of that, they ragged perforated housewrap only going part way across the horizontal framing. The framing on the inside of the wall doesn't protect the gap, it merely covers it from normal view. Neither side of the gap has proper drainage, the inside had bare rough sheetrock extending above the board, and the outside has relatively smooth cut Hardi Panel siding extending above the board. There isn't enough room in the gap to place any kind of wood board, but there is enough room to place something thinner like a piece of polycarbonate sheeting (and conveniently, the angle from the inside of the interior trim to the hardi panel slopes slightly downward).
At minimum, I needed a piece of wood to go on top of the roughly cut sheetrock, protecting it from dripping moisture and condensation. The piece of wood would need to be at least 1" wide to completely cover the sheetrock and beyond. The only scrap shims I could find left by contractor were about 1/2 inch, and they were sloped. I wanted a flat piece.
All the shims I could find for sale at Home Depot were similarly sloped, but I found a scrap piece used as a spacer for lumber which was exactly what I needed. It was about two feet long, one inch wide, and about 1/8 thick. I asked an assistant if they would have anything better like that, and he said other than sloped shims everything they sold would be at least 1/4" thick. But I could have the scrap for free. I looked all over the store and indeed could not find anything better. I also thought of using a polycarbonate sheet to cover the entire opening from front to back, so I bought a 12x24 inch piece with a cutter.
Though it was much dryer outside by now, I decided not to mess with extension cord and light and vacuum this time...too much hassle. I did everything with two flashlights and the big one needed a battery replacement in the middle of the job. I cleaned off the sheetrock dust in the wall gap which seemed endless, with wet paper towels and a few disposed of work cloths. It wasn't perfect, but was MUCH better.
I then further pasted down the sheetrock edge with acoustical caulk, and placed the wood piece on top, nailed down only in front (on the stud) so it tilts a bit away from the sheetrock. I did lots of extra pounding on the on the side going away from the sheetrock to make sure it has that tilt.
Then I layered on Tyvek tape. First a 1/2 thickness piece only in front, going over the scrap piece and attaching to the front trim. Then I put another piece at the edge of the scrap piece going forward and connecting to the Lowes housewrap. Then a couple of full width piece in between connecting the two, with the previous pieces providing consistent tilt away from the sheetrock. Then additional pieces at the sides so that the shims underneath the A/C case are also covered, and there is tilt away from them too. Then pieces in some damaged areas in the housewrap. Then I nailed the housewrap just next to the siding to provide drainage channels toward the exterior wrap (on this side, covered with felt for even better drainage). Previously the housewrap kind of bubbled up toward the outside, which would cause condensate to migrate toward the inside, and back to the most vulnerable sheetrock.
The result is plastic covering everything from the trim inside to the siding and mostly tilting toward the siding except for a few remaining bubbles in the housewrap which had been folded by the contractor on the inside of the siding. The sheetrock edge is covered with acoustical caulk, 1/8 thick wood scrap, with Tyvek permanent polyethylene tape on top of it all, stuck to frame in front.
By this time it was 2am and I was exhausted. I still wanted to cover the entire gap from trim to outside of siding, on top of all this plastic, with a piece of polycarbonate cut to the exact size. But I was too tired to go on with that intricate work, and was thinking at this point it would only add an additional R value of 1.0 so why bother. Whether it was dripping from the plastic bottom of the AC chassis or the bottom of the polycarbonate, it would still be dripping.
The next morning the contractor texted and woke me at 10am saying he would arrive at 11 for the A/C installation. Now, with 6 hours sleep, I decided to go ahead with tcutting the polycarbonate piece. I now figured it could be caulked all around, completely and permanently sealing the stud and drywall and sheathing from any condensate, like a window sill, maybe better since polycarbonate is strong and non-porous. No new moisture-laden air would be flowing into the vulnerable area at all, therefore little or no condensation would occur on the bottom side of the polycarbonate. Sitting on top of the trim, and the opening in the siding, it would tilt slightly toward the outside, serving like a drip edge by extending somewhat beyond the siding. Unlike the Tyvek tape to housewrap flashing I had done, which wraps inside the siding (the siding juts up 1/2 inch at that point), a plastic piece on top would direct moisture to beyond the outside of the siding, getting the condensate entirely outside the building, through the wide opening in the bottom of the A/C case.
I got to work re-measuring the opening and marking and then scoring the polycarbonate. It was not at all easy to score right on top of any existing score. Scoring is supposed to be done to a depth of 6. I did the best I could and then tried breaking the polycarbonate. No matter how much I bent or pounded it, it would not break. By this time, the contractor had arrived and was sitting in his car. I checked the Home Depot website and it didn't say they cut polycarbonate, I don't believe they do, only glass, and I didn't want to use that as it's dangerous to handle. I called Samuels Glass and they said they would sell custom cut polycarbonate if I came down to order. I figured that would take at least a day.
So now I went to the contractor in an attempt to delay the A/C installation for a day so I could get a polycarbonate flashing piece. I had great trouble explaining the need for this. He suggested simply putting some gap sealing foam rubber pieces like people use for doors and windows into the inside and outside gaps, and that having a piece like I described would get in the way of installing such pieces. I went along with his plan to install the AC chassis right away. The job went OK, though I wasn't entirely happy with the way the contractor installed the foam weatherstrip provided by Friedrich for the top and sides before pusing the AC in all the way. It was OK, though, at least it got installed. Also I kept them from jamming on the plastic front panel. I feared they might break it, so I insisted that I would take care of that myself. Plus I want to do other things like straighten out a few of the the aluminum evaporator fins which got bent by me (they are little thicker than aluminum foil) when I was unpacking the AC.
I still figure it would be better to have the polycarbonate piece to keep moisture out of the wall system. If there is a tiny remaining gap for air to flow into the room, I am not as concerned about that, any moisture condensing would simply be drained outward on top of the polycarbonate, and the effect of such a thin (1/16" or less) gap would be fairly small, maybe even beneficial. And if the only protection of a very vulnerable area in the wall is a foam rubber gasket--those don't last forever, and when it fails I'd never know until damage to wall, most likely to the sheetrock, happened.
Maybe I'll find some way to do the polycarbonate piece in the future. I'm worried that if I wait too long, my carefully applied Tyvek tape and so on will have ceased to work as I intended (this is WAY off lable usage). Or perhaps the best thing would be to figure out how to have such a polycarbonate piece AND have the foam rubber end seals as well.
But I'm greatly satisfied that at least I did a much better of flashing underneath the A/C. I'm sure the way the contractor had done it would have caused problems within a few years or less.
I've also thought about the weather stripping. Even with a sill-like polycarbonate piece below the AC, or not, the gaps in front and back need to be filled with weather stripping. Friedrich provided a second foam piece for through-window installations which would work for this purpose...so long as I don't add the sill (which would probably make the remaining gap too small for the thick foam). Also, my plan is not just to use the foam strips, I plan to augment the outside with special duct tape intended for exterior use, and possibly on the inside with Tyvek tape.
Update: Now that the AC has been installed, I can see it won't be so easy to seal up the bottom, particularly at the outside. The bottom of the AC chassis is not flat, it has a 1/2 beams in a cellular pattern, obviously intended to give the polyethylene plastic sufficient strength. There is no flat surface that can be taped to, and a foam weatherstrip would need to be very flexible to reach the inside of each cell while still being compressed by the beams. Furthermore, despite this reinforcement, the bottom has a slightly bowed contour, so it hangs deeper, maybe by a millimeter or so, right in the center. That bowing denies sufficient clearance to shove a polycarbonate panel underneath. It can be shoved past the outer trim frame, but sticks right at the rough Hardi Panel edge.
So in a bunch of ways, I'm between a rock and a hard place on this.
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