Cracks in new render on bathroom wall?

[Albumen]

I've had somebody render wall where the bath is going to be. I stripped off the old plaster/sand and cement myself back to bare brickwork, wirebrushed it.

He's left it with a scratched finish, presumably as a key for tile adhesive. I'll be doing the tiling.

But there are lots of cracks and a couple of spots where it sounds like it's blown. Should there be cracks in this? The whole point of having it sand and cement rendered (with waterproofer added) was to create a waterproof substrate for tiling. I told the plasterer to treat it as a 'tanking' job. It's obviously not waterproof if its full of cracks.

 

[roughcaster]

Did he give the old brickwork a good soak down?? It could be that the render has dried in too quickly, onto the brickwork. Is this 2 coat render? ie, did he scratch coat, then top coat render,,, (left off the scratch float), or did he bring it out in "one" coat? It's not much good for tiling onto if areas are cracked/sounding hollow!

 

[JMLanders]

delete

 

[roughcaster]

deleted.

 

[Albumen]

Not sure how he did it, I wasn't here.

There's no sign of much wetting/PVA having been applied - i.e. not sign of stuff running down the wall on the 18 inches of unrendered stuff at the bottom.

It looks to me like it dried to quick

 

[Micilin]

Not sure how he did it, I wasn't here.

There's no sign of much wetting/PVA having been applied - i.e. not sign of stuff running down the wall on the 18 inches of unrendered stuff at the bottom.

It looks to me like it dried to quick

As RC says. It could be

dried too quickly

coat too heavy

one coat where two needed

sand too 'soft' (3mm down for rendering, not builders/brickies sand)

combination of above

 

[Albumen]

Thanks for you replies.

As it cures, which I assume is what's happening as it turns a lighter shade of gray, more small cracks are appearing. Or maybe I'm just noticing them.

It appears from my looking on th'internet that sand and cement render often cracks.

The small cracks I can cope with. I'll fill with something (external filler?) and move on. What worries me a LOT more is that the render isn't adhering to the wall properly. It generally sounds OK, thought I've found 3 small spots, all next to larger cracks where it sounds hollow.

But if this is going to get worse over the years then I need to sort it now.

The WHOLE point of using a strong, hard, rigid and waterproof substrate like sand and cement was to do a job that would last years. Like 30. I told the plasterer this.

He said he didn't think s&c was the best backing for tiles, but didn't present and alternative or say why it wasn't the best backing and didn't say it would crack.

Should I just get it all off and start again? I guess when I get the 3 hollow patches off I'll get an idea of how well it's stuck to the wall.

I REALLY don't fancy hacking it all off myself. After all, I've just done all that once, and it was filthy dirty hard work.

Obviously he should do that, if we agree it's not up to standard. But there comes a point with tradesmen where if you've forced them to do a job a second time, for no extra money, they aint' going to be committed to the job, so I might not get any better work, but that won't be clear for years to come.

 

[1john]

Is there direct sunlight on the wall through a window or have you been helping it dry out at all?

 

[Micilin]

Hairline cracks are not so much of an issue IF it is sound, ie not hollow . I would not bother filling them if you are tiling over.

As for saying s/c is not ideal for tiles, then the man is, politely, wrong. Sand and cement render onto block (or brick) is the industry standard for tiling onto, for a variety of reasons.
If he does not know this, then he really does not know about rendering, with obviously no experience of rendering for tiling. Not giving you an acceptable alternative (perhaps hardwall and set) just highlights this.This makes you doubt if he did it properly - ie prep, mix , application etc.

You don't need the render to be rock hard, too strong can lead to cracking.

A standard application would be 4:1 sand and cement with w/p (or plasticiser) onto a dampened , dust free surface . Done properly, it will last as long as the house is standing. Most tilers dont even want it devilled up (the scratch marks)


What ever about it being plumb and true for tiles (which it should be) , you have every right to insist that it has adhered to the wall before you tile it.

If you get the 'live' patches off, you may be able to get in behind the render and get more off. Sight unseen, if you have checked it all and just have a fgew patches, then re doing them should be okay - but chek that it is acceptable for tiling -reveals all square with even margins, angles plumb, ceiling other lines straight (where your bath goes, if you are putting a mirror up etc.

Why did you leave 18" with no render - is it inaccessible because of pipes?

 

[Albumen]

Is there direct sunlight on the wall through a window or have you been helping it dry out at all?

Nope. It's a corner. Some of it may just get a bit of sunlight at about 2 in the afternoon, through a 4 by 4 window. But the worse cracks are on the wall that never gets any sunlight. No dehumidifiers or fires have been used. It's been warm weather, and I opened the upper lights in the window to get some air in.

But no, I've not done anything atall to encourage the render to dry. I'm aware that cement sets by chemical action and that it's best to let it do it like that.

 

[Albumen]

Why did you leave 18" with no render - is it inaccessible because of pipes?

On the 'long' wall just because it doesn't need doing. On the short wall it doesn't need doing, and the extra space just gives me a little more room to swing a spanner for doing the taps.

 

[Albumen]

Thanks for your advice folks.

I'm not a tradesmen. I'm always loath to say this, especially to people I employ, but I did spend 5 years in the construction industry. 3 of them as a setting out engineer in civil engineering.

So my attitude is to do things so they last forever. I can't seem to find tradesmen who share that attitude.

That was why I asked for s/c with waterproofer. In fact I've now got a worse job than non waterproofed plaster, because the hairline cracks will actually draw water towards the brickwork by capillary attraction.

If I want to bite the bullet and get all this off and get somebody to do it who shares my approach (called 'doing the job properly') should a get it off now? It looks half cured to me. Light grey patches and dark. He finished it Friday afternoon, it's now lunchtime Sunday.

 

[Micilin]

Why did you leave 18" with no render - is it inaccessible because of pipes?

On the 'long' wall just because it doesn't need doing. On the short wall it doesn't need doing, and the extra space just gives me a little more room to swing a spanner for doing the taps.

Bathrooms would be easy to work in -if it wasn't for the bath, sink, loo and all the plumbing!

 

[Albumen]

OK, just to find out I did this, just now.

Took a 4lb lump hammer and 1 inch cold chisel to a few edges that would be hidden by the bath.

It fell away very very easily. I hardly put any effort in and I'm a 52 year old sedentary worker!!

It fell away from the wall in one piece and didn't leave anything on the bricks. It appears there's no adherence worth speaking of.

If the rest of it comes away that easily I feel quite happy to get it all off now. But is it going to get a lot stronger as it cures?

 

[Albumen]

Here's a couple of pictures:

this area is about a foot wide:

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• Albumen
• 20 Jun 2010
• 1

this is about 2 feet wide:

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• Albumen
• 20 Jun 2010
• 1