Shims to level joists

[Hickory]

worksite: 7x11' bathroom in my old house,

problem: the low point in the joists is about 3/16" below the high point.

question: To level the joists before putting down the plywood underlayment, can I use the following:

-- the small shims that are sold in packs at Home Depot, etc.
-- wider cedar shakes
-- masonite/ "peg board"

The joists are quite solid: 2x9" cross-braced. On top of the joists, I'll be adding 3/4" plywood, thinset, Hardi-backer, thinset, and tile.

Sistering the joists to level them would be problematic due to wiring and cross-bracing.

Thanks!

-- Hickory

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[Paulfm]

Is the sub floor plywood or is it planks now?

[Hickory]

Right now it is bare joists -- I will be putting down 3/4" plywood over the levelled joists.

I am trying to avoid the need for SLC.

[gof]

I wouldn't recommend the shims as you describe. The angle of the shim isn't going to be right. What you want is continous support. Do you have one joist that is lower than the others, or are they all uneven, or is it a general pitch?

If it's just one, you can use single thickness shims (like lath strips). Masonite might work, but I'd worry about it ever getting wet since it would swell rapidly, but not shrink back. The shims would only work if they were close enough to the pitch you need to match the error in the joist.

In my case, I had two joists to "fix". On one it was just a bit, perhaps 1/8". For that I took some lath and used my planar to thin it down to 1/8" and glued it on with carpenters glue, taked with construction staples (pneumatic stapler) . For the other, it was closer to 1/4", but diminishing to 1/8" on the other end of a 6' span. For that one I glued and stapled 1/4" lath down and after it dried used a hand plane to thin down the 1/8" end. Now I've got 100% support. To put down the plywood (Sturdi-Floor) I'll use construction adhesive and 2" construction ("gold") screws, predrilling the plywood to prevent jacking (where the screw threads engage the plywood completely and don't pull it down tight). The construction adhesive is heavy bodied enough to fill any small gaps in height that might exist and eliminate any potential squeaks or movement.

[Hickory]

Thanks for the information; you may have saved me from myself.

I have five joists, all of which need to be leveled. That means lots of shimming, and I don't have a planer, so I was planning to use sections of the broad cedar shake shingles, placed perpendicular to the joist so it doesn't change height - simulating the lath idea.

You are saying that it is vital to have an intimate connection all along the joist, with the plywood. In my case, it would be joist-shim-plywood, with some gaps. Bad idea?

I hate to say this, but I wonder where common sense and perfectionism diverge here. Am I making a mountain out of a 1/4" molehill?

Instead of shimming the joists, would it be better to just put the plywood down over the unleveled joists (max. depression is about 1/4" or less), and then deal with the out-of-level by one of these methods:

(1) Adjust the height a little by putting down a little more of the thinset on the low spots (of which there will be two layers: between plywood and CBU, and between CBU and tile).

(2) ignore it. It's an old house. The sag is less than 1/4" over five feet. I'm using big tiles on a diagonal anyway, and it won't be that noticeable.

(3) use SLC.

(4) use an additional layer of plywood: 1/4" over the shimmed joists, then the 3/4"

(5) the right idea from you experts....?

Thanks!

-- Hick

[chassis]

I say go with the shims, or cut some strips of 1/8' whatever, like masonite.

Or you could forget the shimming, and go with SLC. It's really not that big of a deal. I was concerned about it before I poured some SLC, and found my concerns to be unfounded. I'm a first time (tile/shower) DIYer BTW.

Or you could forget the shimming and SLC and take care of the unevenness with thinset as you set the tiles. This option depends on your specific situation. For example, if the low spot is underneath your vanity, it would be much easier to soak up the wavyness with thinset since it won't be visible or under heavy loading.

[cx]

Trying to shim under the subflooring is usually not a good eye-dee, Hick, as Jerry has 'splained. You need another plan.

1. No, that's a bad plan, too.

2. It's gonna be too much to ignore.

3. You could do that.

4. Nope, 'nother bad eye-dee.

5. My personal choice would be to sister a 2x4 along the top edge of the sagging joists to flatten/level them. You shouldn't have any wires or pipes goin' through the center part of the span where the sagging is anyway, eh? You can cut the X bracing and pewt it back against the new wood.

My second choice would be to fasten the new plywood very firmly to the old joists with glue and screws, then instal my CBU (assuming that's the plan) and see just how far off flat I am. Chances are the floor will have flattened out some already and you can just pewt some thinset over the low spots, let it set up, then tile away.

You want a really flat floor for them big ol' tiles. :shades:

My opinion; worth price charged.

[gof]

Building of CX's suggestions, if you don't want to shim the "hard" way, you could put the floor down as-is. Then, go over the entire floor with a LONG level, as long as possible in the space and perhaps use two if you've got a narrow section your longest won't fit in. Mark all the depressions as areas. Then, skim coat those areas with 1/2 the distance in thinset. Why half? To avoid too thick thinset in a single pass. Since you max error is 1/4 inch, your thinset fix will be 1/8". Let it dry. Now install the CBU as recommended. Once that's dry, you could then go over the floor with a level again and repeat the fills.

What ever you do, don't expect to try and "level as you go" by adding extra thinset to some tiles. I made that mistake ONCE. The floor came out dead level, but took forever since I could only do a few tiles at a time working out the extra thinset and later digging out the grout lines :cry:

[Scooter]

I do very old homes for a living. I wouldn't even bother trying to level or shim the joists and/or substrate. I'd just nail the subfloor on and let it be wavey--who cares?

Then I'd float a mud bed which will make your floor dead flat and dead level.

Take it from me, a guy who fought flooring for years, with belt sanders, portable planes, shims, etc at every level, only to find the finished floor still had peaks and valleys. Then I did a mud bed, and now I'm hooked.

It is positively the easiest way to deal with flooring, and you could float 100 sq ft in about a half a day. Easier than shims, guy.

[gof]

How is floating a mud floor (for a small depression) any different from using SLC? In fact, I would assume SLC would be the preferred method for correcting a 1/4" variance. Shouldn't a mud float be at least 1" to 1-1/2" from what I've read??

[cx]

Mud beds are wonderful if a fella has room for them. In this case Hick could drop his floor down between the joists on cleats and use mud, but he may not be inclined to do that since his floor doesn't really need much repair.

The mud would be an advantage over his having only a minimal subfloor under his CBU, and it would be flat and level. Dealer's choice. Those of us who have laid mud beds just naturally want them under every piece of tile we lay when there's a choice.

Besides, Scooter's old and cranky and hasta live in California. Cut him a little slack. :D

My opinion; worth price charged.

[silverfox]

FWIW...I had the same problem and I went to Harbor Freight and got an electric hand planer on sale for 39 bucks. I didn't really think it would work on the two inch thick oak joists but it did...fast and slick as you please. I used a combination of different thicknesses of wood for shimming and the planer. My floor is now flatter than my head. :)
Mike

[Hickory]

I put the plywood directly over the joists, and did the Jump Test -- ahhh. Feels great. I did use a few shims between sheets of plywood to fill a gap, but only after screwing down the plywood everywhere else first.

Thanks for your advice. I'll most likely be using SLC for this one, but all of the advice will come in handy for the next bathroom (the "Taj") but I can't even think about that one in front of my wife, as she will just say, "and when do you think you'll finish THIS one???"

-- Hick

[jadnashua]

I did a major remodel on my first floor - tore out all of the subflooring, planed, shimmed, and installed new subflooring. A laser level was very useful as was a long straightedge. I probably have less than 1/16" across the entire floor (28x20'). The engineered wood flooring really went down easy.

[gof]

I did a major remodel on my first floor - tore out all of the subflooring, planed, shimmed, and installed new subflooring. A laser level was very useful as was a long straightedge. I probably have less than 1/16" across the entire floor (28x20'). The engineered wood flooring really went down easy.
Sure, you say that now, but what about come mid-summer and the humidity has shifted :rofl:

Seriously, unless you've got a very "pro" laser level, it probably doesn't even support that 1/16" tolerance across a 20 foot span. That's only one part in 320 error about 0.2 degrees. The bubble level on top of it probably has more error than that.

But I'm impressed none the less. That's some serious leveling. I'll have to stop complaining about leveling my little bathroom :)

[flatfloor]

Hick, don't forget to use lath, pastic or metal, with the SLC going over ply and double prime it. :whip:

[jadnashua]

The spec on the level was 1/8" or less in 100' (no bubble level here - self-leveling pendulum mechanism), so I think it was adequate...I'm kind of compulsive - once I decide, I try to do it right. Upstairs in the bathroom, I used slc...much easier!

[Hickory]

Jim, do you need lath even on the thin portions that SLC is covering? What's the limit? I think I read somewhere that SLC has both a Max and a MINIMUM depth. But I saw some "pichers" here on the Forum of SLC where it wasn't covering the entire floor.

[jadnashua]

First, I'm not a pro and have exactly one slc job done to my name...

slc comes in different flavors. Many of them are spec'ed to be able to go to a feather edge. Some of them can be poured to practically any depth (read lots of$$) if you need it. I poured over an inch to do what I needed, and they specified lath for that. Lath is preferred if you are going to be using it over plywood, if you will be using enough depth. If you are only going to use a little depth, then you really can't use lath. If I remember, they specify lath when the depth exceeds a certain value. Now, it wouldn't hurt to use it if you were going to make a pour that would cover it by some minimum.

Your best bet is to get one of the pros, and to read the manufacturer's detailed installation info.

[flatfloor]

If you are pouring on wood you should use a lath. Wood flexes and the lath gives the SLC a mechanical as well as a chemical bond. Your overall floor height will increase by1/4"-3/8".

I think Mapei says you don't need lath in small residential rooms but I'm not sure. Personally I wouldn't do it.

[Hickory]

Is there any standard for levelness? A certain deviation over a certain distance?

--Hick