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otrex 02-18-2019 03:41 PM

Okay, I added my location (Toronto, CANADA).

Bit of a letdown today tearing up the subfloor. We discovered that the floor joist in this area is 2x4! True 2x4s, mind you, with various doubles running here and there, but nevertheless that's going to completely destroy the ability to do a dry pack base anywhere because the deflection is so high and the weight probably too great. Some of the main beams are true 2x6s but they are several feet away.

The contractor involved said he wanted time to think about what to do and so has departed for the day. The trouble is with only some of the 2x4s bearing out onto the foundation, I cannot simply notch out the 1.5" that I need even with sistered 2x8s attached (so the contractor states). Now there is a challenge to find out how to make this subfloor stable enough for a mud base of any kind, let alone tile and a curbless format.

I don't know if you can notch 2x8s so they sit on the rather wide foundation wall and then sister them (with added jackposts down to something solid on the dirt crawlspace floor).


otrex 02-18-2019 04:02 PM

2 Attachment(s)
Just wanted to follow up that last post with a diagram and a picture.

The diagram shows the joist position. Hopefully that all makes sense.

The photo shows the current demo state as well as the joist.

Solutions are welcomed!

cx 02-18-2019 06:51 PM

What you have for joists is suitable for a ceramic tile installation, Kevin. The support under your beams is what you need to be looking at.

I think you can find a way to make that work.

My opinion; worth price charged.

otrex 02-18-2019 08:39 PM

The only problem is, I think, that I cannot get the 1.5" ripped out of the joist, right? Not sure how to make a curbless shower if I cannot safely rip out the necessary depth from the joist in the shower area. The double 2x4, in particular, would be down to just 2" of material left in a double after ripping it - not much to sister a joist onto even if I did make that sistering joist 2x8.

cx 02-18-2019 08:44 PM


Originally Posted by Kevin
Okay, I added my location (Toronto, CANADA).

Thanks. It was obvious that we weren't speaking the same language. :)

I wouldn't think about cutting down what you've got now that you see it, Kevin. I'd look more toward removal and replacement of what's in the way. May require setting at least one additional support for that center beam among other things, but I don't see why you can't take out a lot of what's there and install what you really need.

My opinion; worth price charged.

otrex 02-18-2019 11:06 PM

Thanks for your reply.

I am trying to see if I can replace that one double 2x4 beam and all the little singles with 2x8 joist running North/South and bridging in between, then rip those down by the amount needed.

The only thing I can think of that might accomplish that would be to lag bolt some 2x8 "clevices/bearing points" onto the inside of the foundation wall, and then hanger them back onto the double 2x6 on the other side (the one in the drawing). That might let me, if I'm careful, replace that wood, at least in that section, for the purpose of the bathroom that I wanted originally. It requires moving some plumbing, but that had to happen anyways. I'm just not sure if that's structurally-sound-enough, so perhaps if the carpenter will agree I can also put some jackpots down to the basement to help hold everything stable while also using bridge blocks between.

I should mention that when I first moved into the house 10 years ago, one of the first things I did was to jackpost the area where the two 2x4 doubles intersect the 2x6 double. The carpenter said I may have saved the house doing that because the double on the right is compromised to the tune of 80% because someone decided to put the toilet drain right through that beam! Then they just blocked it down to the dirt with a 4x4, which is a very lazy fix. May explain the sag in the floor! To that end, I certainly could add more jackposts if necessary. I tend to like to overbuild things a bit anyways.

When you say "... I don't see why you can't take out a lot of what's there and install what you really need", do you mean that I should consider replacing all those 2x4s where possible, or, reading that a different way, are you saying that I should modify my design to be a curbed mud deck shower to avoid ripping the 2x4s? Just want to be sure I'm understanding your opinion on that.

I suppose if the 2x8 replacement is a valid option, you wouldn't see any reason why I could revert back to the curbless option with the mud base, right?

Thanks again for your answers. It gives me lots of good options to think about.

otrex 02-19-2019 01:52 PM

Also, as a follow-up, assuming I can get all this to work, do you perceive any issue with using Laticrete 3701 Fortified Mortar Bed Mix for the Dry Pack Bed? I like the concept because it is premixed, but also it adds their 3701 latex. With the thinner mud base, that might be very helpful.

I spoke with Laticrete and though they have premixed "209 Floor Mud" they were adamant that 3701-fortified Mortar is superior in every way.

Lou_MA 02-19-2019 02:08 PM

How thin will the deck mud be at thinnest point?

If the min thickness is 3/4" or more, I'd skip the fortified mud. It'll be overkill in the sense that it'll give you way more compressive strength than you'd ever need, plus it's more expensive and will be more difficult (sticky) to work with. Sand and portland work just fine, I wouldn't complicate things.

otrex 02-19-2019 06:27 PM

Thinnest side is 15/16" thick and thickest is about 1.5".

I also want to see how this floor joist issue turns out. I would think If I'm building on something with higher-than-normal deflection I would want much stiffer dry pack?

cx 02-19-2019 06:33 PM

Nope, you wanna correct any excessive deflection problem before you place any deck mud bed, Kevin. You're not depending upon your "dry pack" for any structural properties aside from compressive strength.

My opinion; worth price charged.

otrex 02-20-2019 06:02 PM

So, I had another chat with Laticrete today and they conceded that the 3701 fortified mortar is probably overkill for a dry pack bed.

They're back to recommending their 209 Floor Mud mixture:


Anyone work with this before? Is it a 5:1 mixture or something else? Given that I am going to build this dry pack bed myself (first time), I think maybe this is better than trying to mix up a batch myself.

cx 02-20-2019 08:53 PM

I disagree, Kevin. Not much in the world of construction simpler than mixing some sand and some Portland cement. Five scoops of this, one scoop of that. Mix. And there's nothing that makes better deck mud than that.

If you really wanna make life easier for yourownself, get you a Bucket Mortar Mixer.

Mix all your mud, plus a little, dry in 5 gallon buckets and have them sitting ready outside your shower. Add a little water and mix as needed. Less than 2 minutes each. Great when working alone, which is nearly always my case.

My opinion; worth price charged.

otrex 02-28-2019 03:02 PM

2 Attachment(s)
Just wanted to post some follow-up just in case anyone finds it useful.

After being told that all my joist were 2x4, I decided to hop into the crawlspace to inspect. I was delighted to see that the contractor had been fooled - I actually have dual 2x8s running out to the foundation with 2x4 crossers in between! He was deceived because 1940s construction did not use hangars, and in this case a thin strip of wood was positioned under the 2x4s to hold up insulation. Though I previously removed all the insulation from the floor in favour of making the entire crawlspace walls insulated (one of the best things I've ever done in this house), it left traces of insulation paper hanging from that strip which obscured the 2x8s and made them look like 2x4s.

So, long story short, in the diagram from earlier where I show double 2x4 beams, they're actually 2x8! :yipee:

I have directed that the 2x4 crossers be removed and new 2x6 crossers with hangars be placed instead. In addition, I have had the centers changed to 12" and bridging blocks added to reduce non-uniform movement across the floor. The shower area is on 6" centers with clearance left for the Kerdi Line drain.

Also, since the beams were 2x8, I was able to have the shower area framed with 2x6s and simply installed lower than the rest of the bathroom area. Coupled with the fact that my house has 3/4" plywood over 3/4" floorboards, leaving the shower area with only a single 3/4" plywood base means the depth that needed to be cut out of the 2x8 beams was only 11/16". Now I can make the dry mortar base the full thickness by using the extra depth provided by the double-thickness of the sheeting in the bathroom area.

Here are some photos!

jadnashua 02-28-2019 06:51 PM

The 'crossers' (called blocking) don't change the deflection rating for the subfloor. The will reduce the tendency for the joists to twist when exposed to a load, and will help change the resonant frequency of the floor which can make it appear to be stronger. They do add weight to the overall floor assembly. They do not need hangers. They help make the things safer prior to the installation of the flooring, but that isn't as big a deal when the joists are short. On a new construction, with longish lengths, they can wobble if you walk across them prior to the subflooring being installed...the blocking prevents that from happening. The subflooring, once properly attached does that, especially if there's a finished surface on the bottom, making it a box beam.

otrex 02-28-2019 07:24 PM

I was actually a professional framer for a time a few years back, so my use of "crossers" was not meant to mean the blocking (and yes, blocking definitely doesn't need hangars). I only stated it that way to be more clear on referencing the new joist running left-to-right in the picture rather than the foundation-bearing beam/joists running "top-to-bottom" in the picture.

Yes, I realize the deflection rating wouldn't change across the structure as a whole. I am just trying to reduce any "point deflection" by sharing the support across multiple crossers instead of the previous version of this floor which was independent 2x4s.

The plywood which is next to go down will be glued and screwed to help with that goal. There are now also two jack posts underneath the 2x8 beam which runs inside the bathroom. Again, just an attempt to reduce any point deflection.

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