A helper cut the cement board too short - please check pic and advise

[Curiousv]

Please check mfg instruction where it says one should leave about 1/8" gap between tub deck and cement board(wallboard) -
A helper cut it too short and instead of having 1/8" he cut at 1" - (please check pic again)
so now cement board is just a bit over the tub flange instead of covering the flange
So is this ok or I have to remove wrong cut board and put a new board? @Terry

 

[wwhitney]

The bottom edge of the board needs to overlap the tub flange shingle style, so yes that will need to be redone.

Wayne

 

[Sponsor]

 

[Curiousv]

The bottom edge of the board needs to overlap the tub flange shingle style, so yes that will need to be redone.

Wayne

Not arguing but trying to understand -
What will happen if I leave the board over flange instead of board covering the flange?

 

[wwhitney]

Not arguing but trying to understand -
What will happen if I leave the board over flange instead of board covering the flange?

Tile and grout are not damaged by water, but they allow some water to pass. The area of missing cement board obviously can't be waterproofed. So the water that migrates through the tile and grout will encounter that void and be able to exit the tub enclosure and wet your wall framing.

For the same reason the waterproofed cement board has to lap over the flange--if it stops above the flange, water can pass under the bottom of the cement board and exit the tub enclosure.

Basically, before the application of any tile or grout, the tub enclosure should be waterproof, so that you could spray water anywhere and it would end up in the drain. Tile and grout are just the wear layer to protect the waterproofing.

Cheers, Wayne

 

[Curiousv]

Tile and grout are not damaged by water, but they allow some water to pass. The area of missing cement board obviously can't be waterproofed. So the water that migrates through the tile and grout will encounter that void and be able to exit the tub enclosure and wet your wall framing.

For the same reason the waterproofed cement board has to lap over the flange--if it stops above the flange, water can pass under the bottom of the cement board and exit the tub enclosure.

Basically, before the application of any tile or grout, the tub enclosure should be waterproof, so that you could spray water anywhere and it would end up in the drain. Tile and grout are just the wear layer to protect the waterproofing.

Cheers, Wayne

Ok may be off topic - but I read somewhere that to achieve waterproofing thru redgard you need to apply about 8 coats is this true?
Even the mfg document says for waterproofing - you need 25 mil thickness and there is a video on YouTube that shows it will take about 8-9 coats to achieve 25 mil when dry

 

[Jeff H Young]

I think its clear or you wouldn't ask that's poor workmanship , I'd put lath paper or something like a patch of vinyl behind the hole that is several inches longer and higher maybe a strip from stud to stud and 6 inches high . This isn't plumbers work but that's what I'd do might ask a pro I'm not a tile guy

 

[wwhitney]

Ok may be off topic - but I read somewhere that to achieve waterproofing thru redgard you need to apply about 8 coats is this true?

Only if you are very very skimpy in applying your coats. It should be 2-3 coats, but what matters is that you follow the manufacturer's directions including overall coverage rate. Plus for fluid applied waterproofing, use a wet film gauge as you go.

Cheers, Wayne

 

[Jeff H Young]

I think you'll be fine though with a little backup patch

 

[Curiousv]

Tile and grout are not damaged by water, but they allow some water to pass. The area of missing cement board obviously can't be waterproofed. So the water that migrates through the tile and grout will encounter that void and be able to exit the tub enclosure and wet your wall framing.

For the same reason the waterproofed cement board has to lap over the flange--if it stops above the flange, water can pass under the bottom of the cement board and exit the tub enclosure.

Basically, before the application of any tile or grout, the tub enclosure should be waterproof, so that you could spray water anywhere and it would end up in the drain. Tile and grout are just the wear layer to protect the waterproofing.

Cheers, Wayne

Coming back to the topic we were discussing before - on one wall he has left about half inch gap between tub deck and board (instead 1/8" ) so is it ok or I have to undo that wall too? so in this wall - about half inch portion is overlapping over flange

 

[Tuttles Revenge]

You need to buy that guy a new tape measure that has easy to read numbers on it in whatever language they speak fluently... Maybe take away the tape measure with "about" marks on it.

Leaving gaps over the top of the flange is not acceptable. Remove it now and do it correctly. Proper overlaps where specified.

Like my client who said he installed all his copper in the house and only socketed the fittings in half way.

 

[Curiousv]

You need to buy that guy a new tape measure that has easy to read numbers on it in whatever language they speak fluently... Maybe take away the tape measure with "about" marks on it.

Leaving gaps over the top of the flange is not acceptable. Remove it now and do it correctly. Proper overlaps where specified.

Like my client who said he installed all his copper in the house and only socketed the fittings in half way.

Its not the gap between flange and board this wall..its a gap between tub deck and wall.
I said instead of 1/8" - its 1/2" - is it ok ?

 

[Tuttles Revenge]

The 1/8" gap requirement is NOT the backer board distance. The diagram only shows generally overlap of the backerboard. The gap required is for the TILE so that the tile is not making contact to the tub surface and gets filled with a flexible caulk.

The backerboard needs to overlap the flange enough so that water can't migrate over that edge. The more overlap the better but it depends on how tall your flange is.

 

[wwhitney]

1/2" gap is too much, I assume you can see some of your flange screws through that gap? That's a point for water to get to your framing.

Rather than specify everything that is wrong, let me just briefly go over the correct procedure:

- Install tub per manufacturer's instructions. (Don't use any flat head screws, use wafer head if screws are required).
- Fir out all the studs so that each wall is in plane, those planes are plumb and square to each other in the corners, and the plane is proud of the flange and any fastener heads.
- Set down a temporary 1/8" spacer on the deck against the flange
- Cut the cement board (or I'd use waterproof faced foam board) to fit well, with a factory edge resting on the deck spacer. Install per manufacturer's instructions. That may involve leaving an 1/8" gap between pieces of cement board. Remove spacers.
- If using cement board and liquid applied waterproofing, use mesh tape and thinset on all the board to board seams to create a flat continuous substrate for the waterproofing.

Cheers, Wayne

 

[Curiousv]

The 1/8" gap requirement is NOT the backer board distance. The diagram only shows generally overlap of the backerboard. The gap required is for the TILE so that the tile is not making contact to the tub surface and gets filled with a flexible caulk.

The backerboard needs to overlap the flange enough so that water can't migrate over that edge. The more overlap the better but it depends on how tall your flange is.

Flange is 1" -

 

[wwhitney]

tiles should be touching tub deck

No, edges of tiles don't touch anything other than grout (if between another a tile on the same plane) or caulk (all other cases). Edit: or a purpose made tile profile, like the Schluter products.

Cheers, Wayne

 

[Jeff H Young]

the board being a half inch above the deck I don't see as a problem, but above the flange makes no sense.
As you can see in the funny papers it shows the tile an 1/8th off the tub and board looks according to my eyeball scale to be 3/8 above tub at least 5/16s the eye don't lye

 

[Jadnashua]

Industry guidelines call for any change of plane OR materials needs an expansion joint. That cannot be tile butted up to something, or grout, as neither of them is flexible or compressible.

RedGard and all similar paint on waterproofing membranes call for a certain wet film thickness. That's a bit harder to achieve than some think, and the only way to verify that it's the proper thickness is with a wet film thickness gauge. Those are cheap and easy to use, if you can follow instructions. Adjust your application until you can achieve the required wet film thickness. Extra coats are just as problematic as too thin, runs, or pinholes. I prefer a sheet membrane where you only need to worry about seams versus the entire surface with a liquid.

Your picture of the bottom of the cut cbu shows a very ragged, broken cut with a significant breakout. You don't have to replace the entire sheet, but you could cut it, and install a new strip then, apply the proper mesh tape and thinset the seam. That must be done and cured before you can apply the RedGard.

Unless you've notched your studs or shimmed out the cbu, lapping the cbu over the tub flange means it will end up bowed out, which makes tiling a flat plane harder.

 

[All Fug Duck]

If the wall is going to be tile, I'd not trust that gap. maybe if 3 solid walls where they're one section each, but just not a good way to go about it TBH.

 

[John Gayewski]

Flange is 1" -
and I disagree with you - that 1/8" distance is between wallboard and tub deck - tiles should be touching tub deck

Based on what?

 

[Jadnashua]

Tile should NEVER be butted up against dissimilar materials or changes of plane...that requires an expansion joint that can be either literally a gap, a flexible material like silicone, or an engineered profile joint.

Using cbu on the wall requires one of the following in a tub/shower:
- a vapor barrier behind the wall, lapping over the tile flange of the tub
- a sheet membrane sealed and bonded to the tub
- a surface waterproofing that is sealed to the tub (hard to do with that gap in the cbu!)
- a tileable waterproof panel like KerdiBoard, or WediBoard that is sealed to the tub.

You can cantilever tile over the end of the cbu as long as more than half of the tile is bonded to the material above it.

That picture shows the cement broken away, and just the mesh showing...no structure. You want structure there. If you were to use the RedGard's reinforcement band, and bond that to the tiling flange (if you had any of the cbu structure to support the uppoer section), that MIGHT suffice in being able to create a waterproof surface.

CBU is cheap in the scheme of things...fix it.