Waterproofing exterior wall on slab

[AmateurGarageMan]

First post here, be gentle

We ordered a big arch building and outsourced the slab. Blueprints were provided to the slab guys, but I guess they didn't get the memo. Long story short, slab was out of square a few inches short, meaning that we were forced to frame up our end walls inside the shell instead of on the edge. What this means is that our end walls are sitting 2' in from the edge of the slab (See photos). This isn't a big deal to me and I'm not fussed about it. Annoying, but eh we'll deal with it.

We have already mostly framed one end wall and now I'm thinking about how I'm going to waterproof the sheathing. The standard flashing over the edge of the slab isn't going to work now, since we're 2' in. Everything in the wall is PT lumber, including the sheathing, but I still want to prevent water from wicking up through the edge of the sheathing. I also need to figure out a good way to waterproof the sill plate and keep water from flowing under. We put some polybutylene (I think) caulk under the sill plate down the middle and outside edge, but that's not a permanent solution, I'm sure.

Any thoughts are more than welcome. I'm just trying to do the best I can with what I have here.

 

[adespain]

You have yourself a very challenging battle here. My primary suggestion would be to make sure the overhangs on your structure go out as far as possible to limit the amount of water that will actually land on your slab (if this is even possible with your building). You could possibly have the ends of the slab cut off and remove it and flash over what's left. I'd also suggest using a liquid flashing to cover as much as possible.

 

[billconner]

Is the grade also such that it directs run off onto that slab and walk?

 

[AmateurGarageMan]

You have yourself a very challenging battle here. My primary suggestion would be to make sure the overhangs on your structure go out as far as possible to limit the amount of water that will actually land on your slab (if this is even possible with your building). You could possibly have the ends of the slab cut off and remove it and flash over what's left. I'd also suggest using a liquid flashing to cover as much as possible.

The wall is built 2' in from the ends. Unfortunately the rain always comes from that direction and it rains every day here so the slab is going to get wet there. I had thought of maybe cutting a groove into the slab and installing z flashing down into it. Also thought about maybe doing that and then tiling over it (which is pretty common here - my garage is tiled). What is this liquid flashing you're referring to? Sounds interesting.

Is the grade also such that it directs run off onto that slab and walk?

We'll be working on regrading as soon as the new tractor arrives and will be installing some sort of perimeter drain to direct water away from the building at that time as well.

 

[nadogail]

Welcome to the Forum.

Several things to bring to your attention: Should Happen and what gets done are not always the same. You have a beef with whomever was directed to check the placement of the forms prior to the pour.

If your contract specified the details of the slab, or included by reference the slab plans, your contractors errors and omissions insurance should make you whole.

Who failed to check the slab before beginning the framing?

 

[AmateurGarageMan]

Welcome to the Forum.

Several things to bring to your attention: Should Happen and what gets done are not always the same. You have a beef with whomever was directed to check the placement of the forms prior to the pour.

If your contract specified the details of the slab, or included by reference the slab plans, your contractors errors and omissions insurance should make you whole.

Who failed to check the slab before beginning the framing?

Things run differently down here. It's easier for me to just deal with what I've got. I deducted my annoyance from the contractor's final payment and I'm fine with where we're at now.

 

[acer66]

Welcome to the forum,

This is one type/manufacturer of liquid flashing.
https://www.huberwood.com/zip-system/liquid-flash

If it would be me I would only use that as a last line of defense.

I would either grind the concrete down or build it up so there is a slope away from the building.
Would tiles be an option?

If you decide to build up I would spend a lot of effort to waterproof the transition to the building and have the finish wall overhang the build up so the water has an uphill battle.

Still early for me so I hope this all makes sense.

Good luck.

 

[Natty Bumppo]

Is that the front or back of the building? If the back, could you build some kind of a shed roof coming off the wall? If the front, some kind of a nice looking porch roof?

Either that or cut the slab.

 

[AmateurGarageMan]

Welcome to the forum,

This is one type/manufacturer of liquid flashing.
https://www.huberwood.com/zip-system/liquid-flash

If it would be me I would only use that as a last line of defense.

I would either grind the concrete down or build it up so there is a slope away from the building.
Would tiles be an option?

If you decide to build up I would spend a lot of effort to waterproof the transition to the building and have the finish wall overhang the build up so the water has an uphill battle.

Still early for me so I hope this all makes sense.

Good luck.

Tiles are 100% an option, and is kind of where my mind was going since everything here is tiled. Including this wall in the future. So let's assume we're going to tile the wall (We are) and that we're going to tile the outside floor on this little stoop. I still am not 100% sure on the best way to waterproof things. I was thinking I could do something like

Install the sheathing, keep it 1/4" up from the ground (Or more)
Cut a groove in the concrete
Install Z Flashing on front of sheathing and into groove
Flashing tape over sheathing and onto wall surface
Tile over flashing on both floor and wall

This seems like it would be extremely water tight, but I'm no builder. In hindsight, I wish I had laid a row of block first and then built the wall on top of that. Then I could've flashed the wall easily and the block base to slab would be water tight as well. This may be the course I take on the front wall.

Is that the front or back of the building? If the back, could you build some kind of a shed roof coming off the wall? If the front, some kind of a nice looking porch roof?

Either that or cut the slab.

The roof overhangs this by 2' already. It still will get wind driven rain almost daily because we live in the tropics and that's how things are here.

 

[jack stand]

Is this a "quansit hut" type building? (Rolled galvanized metal)
If this is what I'm saying, adding another section so that the "roof" fits the slab with a little extra....
It's not an easy fix but it's the right way. There's no water directed to the end by the roof, that's a plus but the driven rain sounds like a daily event and to be at the mercy of sealants forever warrants the extra effort. I'd imagine the one day in the future that's what you'll end up doing anyway.

 

[AmateurGarageMan]

It is a quonset hut, yes. I should have taken better pictures, but the roof already fits the slab with a little extra, because they built the slab just a little too small and out of square, so the side walls / roof overhang the slab by a couple of inches. That's why we built the end wall "in" one section, instead of flush with the outside, because flush with the outside would be hanging off the slab, if that makes any sense. So there's no room to add another roof section. This end wall we're building is 2' in from the outside of the slab AND the roof. The roof extends all the way to the edge of the slab plus a couple of inches.

 

[jack stand]

The end wall is not supporting anything but itself and hanging it off may be the best thing??
It's hard giving sound advice for a creative fix without actually being on site.
It seems like you have a great attitude towards this bump in the road and you'll figure it out.

 

[AmateurGarageMan]

The slab is out of square enough that on one side the wall would be completely off the slab. No bueno. (Also we already built in 2' in, so this is where we're at now lol). You gotta have a good attitude about bumps. Life's too short.

 

[mcbane]

Grinding a 2% slope on the slab, to drain away from the house, will improve the performance of any drainage detail at the slab/wall interface.

 

[AmateurGarageMan]

Grinding a 2% slope on the slab, to drain away from the house, will improve the performance of any drainage detail at the slab/wall interface.

That's easy enough to do. Thanks for your input!

 

[acer66]

If going with tile which would also allow you to dress up the sides of the slap I would do something like this.

1. Install a -12” durock band at the wall.
2. Seal durock and concrete with brush on sealer that is used for showers.
3. create a slope with thinset at least 1/4” per foot.
4. Seal the thinset and durock with the sealer again
5. tile over it



Come to think about it I would maybe also consider tiling up the wall 12” to get the siding away from splashing water.

 

[AmateurGarageMan]

If going with tile which would also allow you to dress up the sides of the slap I would do something like this.

1. Install a -12” durock band at the wall.
2. Seal durock and concrete with brush on sealer that is used for showers.
3. create a slope with thinset at least 1/4” per foot.
4. Seal the thinset and durock with the sealer again
5. tile over it



Come to think about it I would maybe also consider tiling up the wall 12” to get the siding away from splashing water.

I like this plan. So you're thinking no Z flashing at all, but instead just redguard, some slope, and some concrete?

The wall will be tiled to the ground already, so splash onto the plywood should be basically non existent.

 

[acer66]

No you are right a Z flashing between the tile band and the siding.

Grinding down the slap to create the slope before tiling would be the best imho.
That is just a lot of hard work at least for me and I think with sealing the slap first, building it up and sealing it again it is almost as good.

I would also use bigger tiles to minimize grout lines and that epoxy grout (?) which is hard to work with because you have to work very fast but I am very happy with results but I also have only used it indoors though.

 

[jack stand]

If tiling on the outside is an option, I'd treat it like you're building a shower stall.

 

[Joemctag]

Is that the front or back of the building? If the back, could you build some kind of a shed roof coming off the wall? If the front, some kind of a nice looking porch roof?

Either that or cut the slab.

This is what I’d consider. She’d roof going out 6 to 8 ft or more from wall. You could extend the slab with a deck a few feet to make it useful. Maybe some side screens, wouldn’t have to go to the ground, for that wind-driven rain.
The. You could have your door open when it’s raining. I do this a lot. She’d and awnings over doors are great. There’s stuff that you want to store under a roof, but ok if it gets a little wet because you got airflow. Like yard and garden equipment, shovels.
You’d want your wall siding to go as high as the shed roof tied in, then flashing over the roofing, then siding over that the rest of the way up.
A shed roof there would be a great idea even if there wasn’t the problem that you have. Good luck.
Where are you at?

 

[larry4406]

How about a picture from the outside showing that wall?

Perhaps make lemonade from lemons. Since that's a field framed wall, build another wall that follows the edge of the slab (2' more). Flash it like you wanted to with flashing overhanging the edge of the slab. Build a shed roof on this new wall and return the shed roof to the framed wall. Create 2' deep exterior closet storage for all your yard implements or install headers and add this space to your shop.