Can you get mould in a bathroom with MVHR?

[Adsibob]

I'm trying to work out if the following could give rise to mould. We are tiling a wet room. The substrate has been tanked and we are installing a series of 6mm thick porcelain tiles on a curved wall, in long narrow strips. The strips are 40mm wide and very long (about 60mm long). Photo below. You can't tell from this photo but each strip is exactly the same width, the visual distortion in widths is because each is on a slightly different plane to the next one so that after 13 or strips the wall curves through 90 degrees.

I wasn't expecting the tiles to be so close together. In my head, when we were considering this design i assumed grout would go in between the strips and that whilst that would break up the pattern of the stone a bit, as long as we kept the grout lines thin, say 1.5mm or 2mm, one would still be able to appreciate the pattern. But when the tiler put this in, for some reason that didn't happen, so this part of the shower area will be groutless, with tiny gaps between each strip of tile that is probably just under a 1mm wide and no more than 6mm deep. I queried it with both my builder and my architect (who designed this) and they both said that there is such little room for water in there, that I shouldn't worry. They also mentioned that with MVHR and external wall insulation (only single brick solid wall, but recently upgraded with a 45mm external wall insulation system) mould just won't be an issue. Are they right?

 

What about mould on niches in showers? We were going to have a slight fall in a niche, but it's going to make the tiling much harder. Much easier if the niche is flat, but would that attract mould?

 

 

 

 

[JohnMo]

My option is and it could be wrong.

 

Any small gap water will settle, the smaller the gap, then more capillary action will hold it there.  Give mould half a change it will take hold.  I would say it needs to be grouted or sealed in someway. 

 

The only thing if the sides of the tile are glazed that may help, if they are not, they may absorb moisture and make thing worse.

 

Doing nothing, may be a high maintenance finish, needing plenty of cleaning.

[Temp]

19 minutes ago, Adsibob said:

They also mentioned that with MVHR and external wall insulation (only single brick solid wall, but recently upgraded with a 45mm external wall insulation system) mould just won't be an issue. Are they right?

 

I doubt it will be an issue on walls. We have a relatively  low ceiling in our bathroom and have had mould on ceilings radiating out from the shower even with MVHR (but no extractor fan). Zinsser paint sorted the problem. 

[Adsibob]

So it turns out the gap is only 2mm deep and probably even thinner than I thought. Probably just another example of me worrying excessively.

[tonyshouse]

Grout it!  Insulation seems awfully thin and can’t possibly comply with regs unless it is aerogel or VIP’s . 
 

if you have humidity above 80% for extended periods then you risk condensation 

 

allowing water to seep into the gaps will cause saturation of the cement and potentially the backing, leading to growth. 
 

does showering water hit the tiles? 

 

 

[Gordo]

I agree. Grout it. The small crevices will hold water and you will have lime scale and mould even if your substrate isn’t soaking. Not worth the risk

[Adsibob]

2 hours ago, tonyshouse said:

if you have humidity above 80% for extended periods then you risk condensation 

Why would I have that when there is MVHR with an integrated humidity sensor. 

[Andehh]

If the gaps less then 1mm you'll be probably struggle to grout it? I'd be tempted to try the LTP grout sealing spray thoroughly into the gaps to seal the concete behind & then just leave it.

 

You could try grouting a small area as a test, but I'd be more worried about visual risks then damp risks, esp if it isn't directly in the shower area. 

[tonyshouse]

The answer to the op is yes, lots of factors, flow rates, shapes of rooms, use of bathroom, insulation levels, shapes of gaps between the tiles, type of grout, type of silicone. 
 

MVHR sensor will pick up average and not what is low down in a wet area.

 

we don’t get any with ours but it is possible 

[Adsibob]

1 hour ago, Andehh said:

If the gaps less then 1mm you'll be probably struggle to grout it?

Yes, I was worried about this. Is that because the grout line will be so weak it will just fall out?

 Are there any specialist resins which might work? What do “magic men” use to fill tiny cracks, for example?

[JohnMo]

We had a very small hidden leak, which dripped once every couple of hours, we got plenty of mould by the time we spotted it.  Localised humidity will have little affect on the total room humidity and would not trigger the humidity sensor.

[Andehh]

You could try silicone, in a colour very similar to your tiles? Use a silicone scraper to ensure a flush finish & clean up of over spill. 

 

Might take some time & patience, but im sure it'd do the job? 

 

Again, test in a small discrete area first. 

[Adsibob]

Yes, that’sa good idea. I will give it a try.

 What is the difference between silicone and grout? Why is grout used in some places and silicone in others?

[Andehh]

My very layman's description:

 

Grout is cement based and used for tiles etc where there is no movement & reasonable gaps. Slightly porous.

 

Silicon is the super flexible stuff that goes on around wall to floor interfaces etc. Showers, shower trays, toilet to floor, around sinks etc etc.Totally water proof 

 

Very very different method for application. 

 

For a novice, silicone can be tricky to get the hang of! Spend plenty of time on YouTube researching techniques & tools, then practise several times before you try it for real! Eith those gaps you will probably only have one go at doing it neatly. 

[SimonD]

On 28/01/2022 at 17:08, Adsibob said:

6mm thick porcelain tiles on a curved wall, in long narrow strips.

 

Have these been cut on site, or were they delivered as long and thin? Is this a porous porcelain and have they been fully sealed before installation?

 

Personally I think there are potentially several problems that might arise from this as even if the tiles are tightly butted together, if not sealed, moisture will get in there.

[Pocster]

Water always gets where you don’t want it . I can’t understand why the tiler thinks a gap ( no matter how small ) is ok in a wet area . It may be possible to grout that - certainly try before silicone on a small area .

[Adsibob]

Yeah, on reflection I really don't understand why they did it this way. They should have built out with a touch more adhesive to make slightly bigger gaps which could then be grouted.

[Adsibob]

51 minutes ago, SimonD said:

 

Have these been cut on site, or were they delivered as long and thin? Is this a porous porcelain and have they been fully sealed before installation?

 

Personally I think there are potentially several problems that might arise from this as even if the tiles are tightly butted together, if not sealed, moisture will get in there.

They were cut with a water jet cutter, off site, about 3 months ago. The porcelain is this stuff: https://www.marazzitile.co.uk/collections/grande_stone_look/piastrelle

I wouldn't have thought it was porous, but what do I know.

[TonyT]

Time to bin the Architect as per the worktop post.

[Adsibob]

5 minutes ago, TonyT said:

Time to bin the Architect as per the worktop post.

Architect is now saying they will fill it with very runny grout or ask the stone guy who is coming tomorrow to see if he can fill it with silicone. But I agree this is really starting to get ridiculous.

[SimonD]

13 minutes ago, Adsibob said:

They were cut with a water jet cutter, off site, about 3 months ago. The porcelain is this stuff: https://www.marazzitile.co.uk/collections/grande_stone_look/piastrelle

I wouldn't have thought it was porous, but what do I know.

 

Okay, so the laying guidelines from the company you link says this:

 

Quote

The company declines all responsibility for laying without joints; minimum
joint laying has a gap of 2 mm.
The joints must be positioned:
on structural joints;
between the floor and the wall (perimeter joints);
between one tile and another (laying joints);
between the tiles and other materials (e.g. combinations of ceramics/linoleum
/wood).

 

 

Secondly, for fine porcelain stoneware polished tiles, it says waterproof treatment required (this is sometimes only required when installed on floor).

 

Here is a link to the document: https://www.marazzitile.co.uk/media/filer_public/e9/5f/e95f3156-f66b-4e26-9ae8-c51edfe8bd14/posa_manutenzione_marazzi.pdf

 

I reckon you need to call the tile company to get their view of it.

[Adsibob]

29 minutes ago, SimonD said:

 

Okay, so the laying guidelines from the company you link says this:

 

 

 

Secondly, for fine porcelain stoneware polished tiles, it says waterproof treatment required (this is sometimes only required when installed on floor).

 

Here is a link to the document: https://www.marazzitile.co.uk/media/filer_public/e9/5f/e95f3156-f66b-4e26-9ae8-c51edfe8bd14/posa_manutenzione_marazzi.pdf

 

I reckon you need to call the tile company to get their view of it.

I think their view is clearly set out in the material you found, which is very helpful, thanks.

 I’ve emailed it to the architect and given him a telling off and told him to stop instructing non-standard working techniques. It is odd though, because the builder (who did some of the grouting himself) was also reassuring me that this wouldn’t cause a mould issue because the amount of water in question was so tiny and almost all of the 6mm thickness of the tile has been packed out with adhesive.

 

 Does it make a difference that all water in that shower area is softened with salt?

 

Reminding everyone that we are talking about a crevice that is less than 0.5mm thin and 2mm deep.

Edited January 30, 2022 by Adsibob

[Faz]

You have to seal it mate one way or another. If you don't then water will be getting through and will destroy something which will inevitably lead to stripping the whole bathroom out and redoing it. If it doesn't attach the boarding it will eventually destroy something else be it joist or truss.

 

I had a purchaser who let his dog scratch out bits of grout as the twat showered it - water got through and attacked the wetroom board - this was the black board system - best you can get. Over time mould and rot set in and everything was destroyed. Green board would have been toast in months.

 

Premier Guarantee, in their infinate wisdom, made me do it.  Muppets.

 

Rot loves both hard and soft water - it just needs to be damp and the stuff is has a party!

[Mr Punter]

I have used silicone between tiles on a kitchen wall and got a really good finish.  Yours look doable.  Don't trim the nozzle on the tube and keep it at 90 degrees.  Remove surplus and finish with a Fugi tool.

[Adsibob]

2 hours ago, Mr Punter said:

I have used silicone between tiles on a kitchen wall and got a really good finish.  Yours look doable.  Don't trim the nozzle on the tube and keep it at 90 degrees.  Remove surplus and finish with a Fugi tool.

Thanks.  Any particular silicone you recommend?