Complications in bathroom project

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This morning I started hacking off old tiles in order to re-tile. But at the lower left side of the window the plaster is definitely moist. I suspected this to be honest as tiles were a bit wobbly in that area, but it still is an unpleasant thing to find. I am anxious to find and correct the cause so that I don't re-tile over a problem that will then reoccur in due time. How do I trouble shoot a problem like this?

Most of the plaster in the affected area easily peels off due to the moisture. But I also need to understand how deeply into the wall this problem has gone. Do I need to worry about moisture having gone into the concrete in the external wall and if so how do I deal with that?

I am 90% sure that the cause is moisture building up on the wooden windowsill then being somehow wicked into the wall trough the wood itself. (Mind you the wood itself looks quite OK?) I am prepared to remove all wooden components of the windowsill and remake it with concrete and tiles, but must admit I am out of my depth here. And could there be other sources of moisture? There are no pipes in or near this section of the wall.



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Is there any ventilation ...it could be moisture sitting on the sill and has penetrated the wall...

but another cause could be the window is not sealed on the external wall and rain is driving in or there could be a broken gutter /drainpipe
 
Was there a bath there with a bath screen perchance?
Could have been a contributing factor.
 
Yes there is a bathtub below, but no bath screen. Why? Are bath screens bad in any way? Was thinking of installing one after the refurb.

See image below for how it used to be.



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BTW, I am keen to get rid of the wooden sill and recast it in concrete.

Can anyone point to good online resources for this kind of small scale concrete casting?
 
I thought the bath may have run along the other wall.
Do away with sill and just completely tile it.
That sill most get soaked when using the shower.
The shower screens gnerally weep water where the seal meets the wall plate,
They all weep eventually due to limescale making the rubber seals brittle.
 
I would take off all the damp plaster let the room dry use a fan with the window open don't put heat on it you'll cause condensation get a good plasterer in and get the Walls done properly with sand and cement the plaster skim let it dry then waterproof it with pva then tile with a waterproof adhesive and the a waterproof grout don't use a adhesive/grout use a proper waterproof grout then do the silicone properly and get a fan fitted toy can put it on a switch so you only use it when using the shower or bath but off when just washing hands
 
A round of thanks to everyone for advice so far. Following advice from you guys and other people I removed the entire wooden sill. Seems like a good idea as its underside and edges felt slightly damp.

I will now let it dry out a couple of days then I am moving onto casting a sill of waterproofed concrete. Anyone feel like giving me a few pointers on this?

My general plan was to fasten a plywood scaffolding to the wall and fill the cavity that used to be the sill with the concrete.
Do I need any form of reinforcement such as chicken wire or similar?
Should the concrete be on the runny side or a bit on the thick side?

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Why concrete cill?

One of those white plastic internal cills are cheap and off the shelf. Various styles, just cut to size and run a white mastic seal round all the edges.

If you are going for concrete I would run a dpc (heavy visqueen polythene) under the concrete to surface level effectively producing a waterproof cavity closure.
 
Just fix a piece of ply along the front of the wall. Cast the sill out of sharpsand cement4:1. Job done.
Defo tile it afterwards!
 
... get a good plasterer in and get the walls done properly with sand and cement then plaster skim, [then] let it dry then waterproof it with PVA ...

I've seen elsewhere on this forum that people recommend the PVA applied as a mix that is 25% PVA, 25% emulsion and 50 % water. Could I use this combo in my bathroom as well?

I am planning to repaint the whole bathroom anyway, so should I just use a PVA/emulsion mix as a skim coat over the whole room once plaster and cement is fixed and dried? Then I would tile over the PVA mix in the shower area and paint over it with eggshell in the rest of the room?

I only need to repair about 3 square feet of roughed up plaster which will then be covered by tiles anyway. I'm under the impression that easi-filler is simpler to work with? But will it be OK under tiles and PVA?
I am also curious about Homebase readymix plaster skim. Not that expensive and about the right quantity for my needs.
Polyfilla's readymix solutions seem to be unpopular mind you.

I have more or less set my mind on the Cementone Rapid Set cement kit that Homebase sells. Does anyone want to recommend a waterproofing agent?
 
If your fixing tiles IMO i would not bother fixing the plaster, bea bit more generous with the adeshive and just take a bit more time to level them up.
Ready mix plaster is tish!
Not to sure about the paint mix idea, im sure someoneelse will soon be along!
 
You should try posting this in the building/tiling/decorating forums, you will get a better response!
 
... get a good plasterer in and get the walls done properly with sand and cement then plaster skim, [then] let it dry then waterproof it with PVA ...

I've seen elsewhere on this forum that people recommend the PVA applied as a mix that is 25% PVA, 25% emulsion and 50 % water. Could I use this combo in my bathroom as well?
.... Then I would tile over the PVA mix in the shower area and paint over it with eggshell in the rest of the room?
...

Here I go answering my own questions as I've done a bit more research on PVA. Answer to my above question is NO. Not underneath tiles, not underneath bathroom paint. See these threads for more:

//www.diynot.com/forums/viewtopic.php?t=33645&start=0
//www.diynot.com/forums/viewtopic.php?p=1885743#1885743
 

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