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It’s a little awkward sitting in this tub like this, but it’s rock solid. And today we’re going to show you how to install bathtub, make it rock solid, and get your DIY bathroom remodel off on the right foot. Let’s dive into the blog right now.
We now have all the subfloor, all the existing flooring, all the vinyl, all the extra piled on flooring out of the way, and now we’re down to the original hardwood flooring that was original to the house. Now one thing about this hardwood is if you want to do tile, you can’t just tile over this. You can’t put DITRA over it and tile it. And the main reason is because these 3” planks, there’s too much expansion and contraction between these joists. So when it gets real humid, it expands. When it gets cold, it contracts. And that’s going to create a transfer of cracking to the tile and the grout. So what you have to do is either: one, remove it all and do plywood; or go over top of it with another layer of plywood. So we’re going to go with a ½” layer of plywood over top of all this. And that will keep that expansion and contraction from going through the tile. But there’s obviously a lot of mismatch patchwork that was done a long time ago. We’re going to get rid of that. So we’re going to be pulling up some of this stuff and putting some ¾” plywood that will be even with this, and then we’ll put the ½” layer over top of it. But there’s no sense of keeping all these little patch pieces in here. It’s just going to make it harder. And you really want to have that plywood being connected to the subfloor all the way throughout. You don’t want it like this right here about ¼” lower. So when I try to glue that plywood in, it wouldn’t even be hitting that wood. So we’ll just tear up the whole area underneath the toilet. This obviously had some rotting issue here. So it would be good to get a good solid surface underneath of that. Some of this is not even anchored. You can pull up boards using either a hammer or a super bar. Once you get the boards up, pull all the nails or pound them down into the joists. The last thing you want is a nail popping out. Now in this case, we had to tear out some of the plumbing. Steve just used a Sawzall. Sorry, man. It’s a mess. Don’t worry about it. Apply liquid nail to all of the joists. In this case, I think we had about, I don’t know, 5 or 6 different joists that we had to apply the liquid nail to. And the reason why you’re doing this is to make sure that whenever you apply the plywood to it, it’ll be a nice, solid surface. So that’s what we’re doing here. We’re placing the ¾” plywood down, and Steve’s nailing it in place using his gun. So you could also use deck screws if you don’t have a gun like Steve here. But make sure—and this is an absolute must—make sure that you’re nailing down into the joists and that you skip over any plumbing that is in the floor. The reason why you want to do this is pretty obvious.
You don’t want to drive a nail or screw into that plumbing. Also apply liquid nail to any subfloor that you’re going to put plywood over. That’s what Steve is doing here. Plenty of liquid nail and then putting the ½” on top of that. So the reason we’re putting this ½” plywood on here is because this wall is kind of a partition wall that they built. You’ll find this in a lot of 100-year old homes. Instead of having a regular 2” x 4” width where I’d have 3 ½”, they just turn the studs sideways. I guess it was just a way for them to save some room. And I mean really, they used to have lathe and plasters, so with an inch of buildup on each side, you still have like a good 3” thick wall. So their jambs for the doors and stuff still worked out. But that causes a problem because it’s such a short wall, and this is going to be the valve wall. We need some more depth for our valve. On Delta, you need 2 ¾” from the back of the valve to the finished tile surface. So we have just ½” layer on here. So that’s 2” and we’ll have ½” backer board—the WEDI or Schluter—whatever your backer board is. It’s going to be ½”, and then you’ll have your tile. So that’ll make 2 ¾”. So that’s why we’re kind of buffing this up a little bit Okay, so what I plan to do… a lot of these old homes there’s like nothing square anywhere, so it’s really hard to frame in a wall for the tub and make sure that you’re going to be sitting well. So we just dry fitted the tub and placed it in the room and just made sure that it looked somewhat square. We have it flush against that wall. So now that we’re got the tub in, I’m just going to mark where I want this stud wall up to enclose the tub. So were just going to put a level mark on the floor, and then we’re just going to build a little wall that goes all the way across. So what Steve did there was mark the position of the tub on that plumbing wall and then mark the position on the floor using his level in a plumb position. So make sure that you do this. And it’s critical because you want that new wall to be sitting flush. And just double check that all your framing is plumb, and then you can nail it or screw it to your framing in the wall. So in this case, that’s what we did. And then we measured out evenly on both sides of the front and the back of the tub. So you want to double check, triple check, and then you can nail or screw that 2” x 4” to the floor if you’re in a similar position. But no matter what, make sure that you’re double and triple checking the framing for plumbness and level. Even if you’re not tackling a project that is specific like ours, like specific to our projects, it’s always a good idea to double and triple check that plumbness because after all, what you’re doing is attaching the tub to that wall. And if that wall is not level or plumb, your tile is going to be all wonky. Now what Steve did here is put a chalk line across the framing, and then he used that chalk line to make sure that all the new framing that we put in place was nice and plumb. Now this is how we’re building out the knee wall. We measured it beforehand. And then once we got our dimensions, Steve is just marking the position of the studs on the header and the footer of framing and nailing them in place. And the reason why he’s marking the positions is so that they’re even across the span. It’s pretty simple math to do this. You just need to plan ahead of time and then put 2 or 3 nails or 2 or 3 screws into the bottom and the top plates. So this is pretty basic carpentry, and you can definitely do it yourself if you’re building out a knee wall. Now what you want to do is dry fit the tub again. So you want to put it into place, and then make sure that your knee wall is plumb. Mark the position of the drain on the floor, and then cut it out either using a jigsaw like this or a reciprocating saw. Now in our particular project, we actually had to carve out a section of the joist because it was right in the middle of our drain, which totally sucked, but we did not compromise the joist’s structural ability when we did that. So what I recommend before you go setting your tub into place is to put together the drain assembly and then make your trap connection after you install the tub. Unless you have two people, it’s going to make it a lot easier to be able to put this whole assembly together prior to putting in the tub than to try to fight trying to put it together after the tub is set. So this is for a special drain for the Kohler tub. It’s a neat, little overflow area. It kind of looks like a line drain at the top. So it’s a kind of a special drain. That’s why you always want to make sure whenever you order a tub, make sure you order the drain assembly that is either required or recommended for that tub because a lot of tubs there’s always different drain assemblies. So but this particular drain set system will be all glued in so there won’t be any way for this to leak, essentially. I kind of like the glued in fittings better than the slip fitting type for cheaper tubs. So I always use 100% silicone on everything. It’s something I’ve always just had good success in keeping anything from leaking. Obviously they have a rubber gasket for it which should eliminate that, but I find that using silicone just gives you a little bit of extra insurance that everything’s sitting tightly. What Steve is doing is applying his silicone sealant to the overflow here, and then placing the rubber gasket over top of it. Like he said, this is just insurance that it’s not going to fail over time. And then applying another bead of silicone to the tub itself where that rubber gasket is going to be placed and then placing a second bead on top of the rubber gasket, and then putting that into the silicone that’s already on the tub. This makes for a 100% waterproof seal. You’re just providing yourself with extra insurance by using the 100% silicone. Now if you use an impact driver like Steve is doing here, do not over-tighten these screws because you could crack the tub. So this just has like a little slip nut that actually just connects for the overflow. It gives you a little bit more flexibility as far as where this needs to be for your overflow. So you have like a little bit of movement that you can allow yourself to adjust. So I just kind of set that on. Don’t tighten it all the way until you’re ready to do the bottom. But, yeah, you can see how like the silicone isn’t oozing out around this, so it’s a real good, water-tight… I just find it to be a little bit of extra insurance. Put on the drain piece as well. Again, I like to do the silicone on everything on this as well, and put on the bottom of the tub. And the most important part is the drain piece itself. Put a good amount on this, and then just a little coating on the inside as well. Ah! Squeeze it out of there again. You got to be careful that this rubber gasket doesn’t slip out from underneath of it. Sometimes if it moves around too much you’re going to just finger the rest of that silicone off around there. This just kind of helps you put that drain assembly together for inside the tub. These notches go into that cross. So it just allows you to hand-tighten that. That’s all you really have to do on these drains. Just hand-tighten it. You don’t really want to crank on it with a wrench or anything because if you do, the rubber gasket on the other side ends up kind of squeezing out. So that’s more of just a firm hand-tighten, and this helps do that. The excess silicone is not going to hurt the tub, but just get rid of that excess. So with the drain assembly, it comes with two pieces of PVC pipe. And what I like to do is just make sure you hold this out. I mean you have a lot of flexibility with it; that’s why it’s made to rock around like that. But if you kind of keep it straighter it’ll make it easier for yourself. So 5 ¾” for the drain pipe. And once we get that on there, we’ll be able to get an accurate measurement for the top part. But this will be all glued together. Okay then you can just measure this—not really measure it, but just kind of reference where you need to mark it. So just dryfit that; make sure that fits well. That looks good. So we can just start priming and… So what I like to do is just glue this all together, put it in here, and press down. And then it’s a good, tight seal that way. So you go ahead and prime all your fittings. And just a word of caution: Do not get this primer or the PVC glue on the inside of the tub. It will not come off. It really gets stuck on there. I mean they might have some kind of solution that will help you get it off, but this primer, in my experience, I have never been able to really get it off of the coating of the inside of the tub. So whatever you do, just be careful with it. Just hold this together just for a couple of seconds. Make sure it’s well glued. We’ll glue both fittings here. So like I said, stick it in top here and then press down into your drain. I like the glued in fitting deal better because there’s really nothing that could go wrong with it. And once it’s all glued… Well you can obviously not get the right measurements on this… And once it’s glued, I mean you can snake everything well. There’s nothing that can really go wrong with it. Okay. So that will dryfit our tub again. And now it’ll just make it a lot easier. You can just connect your trap to this, and this difficult part of reaching around the tub and trying to put everything together… It’s just a lot simpler having this done beforehand. This is the heavy duty clear PVC cement and purple primer. This is what you use for not ABS but for PVC rather. After you get everything kind of dryfitted in terms of the overflow, you want to dryfit the tub again. You can see this is what it looks like when it’s in place. And just to double check to make sure that it’s level using your level on all four sides of the tub. This is absolutely critical to do this before you set it in any kind of mortar. So what we’re using here—you can just use a regular mortar mix—but I get this stuff from my local tile place. This is just a 4 to 1 sand mix. But really any type of mortar you can set this tub in. So here is like one bag is about what you need—this is a 50-pound bag. 55-pound actually. So I just mix a whole bag, and then that’s usually enough to embed the tub. Or you can have another bag in case you added too much water into it. You don’t want this too runny. You want it to be able to support the tub, and you don’t want it to just run down through the hole where your drain is either. There are two ways to install this tub. One is with a mortar bed, and one is with just straight adhesive. I’m a huge fan of the mortar. I think it makes the tub feel a lot more solid when you get in it. You could feel like the denseness of that concrete. And Kohler is a well-constructed tub. But any tub that you embed in mortar, it just gives it that much more rigidity to it. So you’re essentially just putting this completely underneath the tub where it’s being supported minus the drain assembly. So basically the drain assembly area where we have this notched out, this whole area back here, we’ll just be putting mortar down in the middle. So you just kind of want to even it out. It should be about 2” thick. And then once we set the tub down it’ll squoosh it to where it needs to be—if that’s a word. Okay, before you completely pound it down in, let’s get a level on this and get some screws. Predrill holes where studs are. So I’m going to put a screw in each one of those. You’re better off to predrill it than to try to put screws into it because you might crack it. So I just like to use galvanized 2” screws. So I’ll just see what this looks like. Okay, so it looks like to me that that’s pretty level right there. So we’ll keep this level and then we’ll push down into the mortar bed to get this down to where we need it as well. Now that I have a little bit of weight in there by foot, I’m just going to go ahead and screw this in. Just one screw for right now. Okay, so that’s level that way. And let’s just go this way. So we actually have to get down here on this side a little bit. Okay, that’s good. Okay. Okay then I would just walk around on the tub to make sure that nothing’s moving from side to side. And it just kind of making sure that that mortar’s embedded underneath there. So wherever there’s spacing here, definitely use a shim because we don’t want to pull that hub flange back that far. So I mean that wall’s a little bit indented there, but you’ll be able to shim that out when putting the backer board in. Go ahead and install our knee wall to where we want that to be. And we’re going to try to make this minimal. So whether this is a knee wall or a wall, you kind of want to have at least 1 ½” on the outside of the tub just so that you can properly tile around this. We’re going to tile around this wall. But even if this were just a wall and this were drywall, you’d still want to have bullnose tile going down the edge of the tub. This is always a problematic area if you have just drywall here. It always ends up deteriorating. The paint falls apart, the drywall gets saturated. So I always recommend bringing tile down along the edge of the tub and then bringing your waterproofing down there as well. But 1 ½” is kind of nice because once you get ½” backer on there. You got 2”. Two inches looks nice. If you go less than that, it looks kind of forced. You’re just kind of making little slivers. So let’s go ahead and level this wall out here. Use wood shims to shim up the knee wall, and then tack it in place using your nailer. Now you want to nail through the shims if you have to use them across the span of the knee wall. And make sure that it is plumb before you apply screws through the tub flange and into the framing. Looks pretty good. Now what we had to do was apply some ABS cement to the existing ABS under the tub and attach some piping to it, and then dryfit your PVC to that ABS. So it’s really important that you dryfit everything before you apply your ABS cement. This is I think a 45° fitting. You’re going to have to play around with this. If you’re not comfortable with the plumbing, call in a licensed plumber; have them do it for you. But again, if you’re going to try it yourself, know all your plumbing codes. Apply ABS cement to the inside of the pipe fitting to the outside of the pipe. And then once you have it in place, you only have a few seconds to maneuver it. And now on this case, what Steve is doing is applying ABS to PVC cement. Now this isn’t to code in some places in the U. S. , so make sure that it is to code in your location. But you can use that cement to adhere ABS to the PVC. Okay, so now that you’ve got the tub set in the mortar, you don’t want to fill up with water. You probably pretty much want to let this sit overnight before you do anything else. You don’t want to be doing a lot of walking and moving around because that mortar supporting is to kind of level because our floor is not completely even. We’re about 3/8” and 4’ off. So that mortar is kind of holding this tub up level. So the more you walk around on this the more that it’s going to want to go unlevel. And you don’t want to put any more stress on these nailing flanges of the tub. So once you get this set, you can go ahead and hook up your plumbing or whatever, but wait for testing all the plumbing and stuff until the following day. So there you go. Now you know how to install a bathtub. It’s pretty cool, right, to see a professional do it? I want to thank Steve for taking his time and coming out here on a Saturday to do it on my 100-year old bathroom. Hopefully you got some great tips from today’s tutorial. Down in the comments, tell me what you think about it, what questions you have, and how to use this blog to help you out with your own DIY bathroom remodel if that’s something that you’re doing, all right? So that is it for today. If you are doing a DIY bathroom remodel, and you want a professional looking tile job, professional looking waterproofing, and a tub insulation, I know you’d really like BathromRepairTutor. com. So you can check out BathromRepairTutor. com. That’s where Steve and I put all of our blog tutorials and help you out step-by-step in our private Facebook group. All right? So that’s it. I’ll see you down in the comments. Take care. Thanks for reading. We’ll talk to you soon. .