Hi there, I have just bought a new house out here in Gibraltar, it is a funny layout and one bathroom wall is actually below ground so to speak. Consequently for 3 months of the year it will be damp, as i am about to rip the bathroom out and start again i am after some advice on how to seal the damp wall so i can tile over it.

How far is it under ground? and has it always been? are you able to dig a trench on the outside so it doesn't have earth stacked up against it? Or is a basment in the true sense? If so you could tank the room (i'm not talking about wetroom membranes here)

The house is built on a hill side, so one wall is in theory a basement

Same as Rob, dig the earth away which is up against the wall, are they solid walls

The wall is solid, about 14 inches thick, about 150 years old. When i say damp i dont mean running water but just slightly damp, and only now in the 2/3 month rainy season. I was wondering if i could just batten some plywood up to keep the tiles away from the damp wall and vent it at the top in several places

Well really you want to damp proof the walls at it first interior point i.e. at brickwork level. As it is on the hill you will get a fair amount of water running down it so you should always see what you can do to slow it down outside the property, even divert the water if at all possible, it just needs some common sense, also look out for any trees that many be up the hill from the property and close enough to cause problems, i.e. will the leaves block up your gutters every year? as this can be a major cause of damp if they are not kept clear

No, this is the same as an old lime wall in the uk, remove the earth thats up against the wall and this should solve the problem.

These old walls have no damp course.

i think i may have confused you both, the block that my house is in is built on a hill, the left hand wall of my bathroom is in effect dug down into the hill, above is a road, unable to remove the earth.

Tank the walls and floor with Oldroyd P tanking membrane and install a drain, This can then be dot and dabbed onto the Oldroyd plaster membrane plugs

Easy enough to DIY and Can be done for less than £1000

Gotcha, just a thought could you not dig down and slide a damp proof membrane down past your floor level against the wall.

I get the construction, the back of the house in underground but the front is not, right?

But you say now a 'block' so is it a flat? Doesn’t really matter too much but helps to visualise and also what you can and can't do outside the property

Like i said its built on a hill, it is a block of 4 houses/flats the ground floor has bedrooms etc, and downstairs has bathroom, lounge etc.

The wall needs to breath as it is part of the hill construction i gather....not like a traditional basement in the uk..

That is why Gib is called the rock... my neice lives on Gib..Army wife..

You should be ok to build a false wall in front but away from contact with the affected wall...but you have to be careful not to leave a haven for mould to grow.

A lot of uk barn conversions have that have damp isues have Metal stud stoothing walls so the damp doesn't effect them..

But without actually seeing the set up it is not easy to say either way..

sounds like a job for Mapei Idrosilex or Idrosilex Pronto

Originally Posted by dock

sounds like a job for Mapei Idrosilex or Idrosilex Pronto

Care to share how that one works? not seen it before, quick outline as I know we can get the full details from your website

Yes CR

Idrosilex Liquid is the best for resisting negative hydrostatic pressure. When mixed with cement:sand as directed on the data sheet the liquid component combines within the cement matrix such that water molecules cannot penetrate.

so similar to vandex?

Originally Posted by Dave

The wall needs to breath as it is part of the hill construction i gather....not like a traditional basement in the uk..

That is why Gib is called the rock... my neice lives on Gib..Army wife..

You should be ok to build a false wall in front but away from contact with the affected wall...but you have to be careful not to leave a haven for mould to grow.

A lot of uk barn conversions have that have damp isues have Metal stud stoothing walls so the damp doesn't effect them..

But without actually seeing the set up it is not easy to say either way..

This sounds like the easiest and cheapest option, if i leave some breathing vents at the top of the false wall should this be enough to alleviate the mould build up you mentioned? Also if i leave an inch is this sufficient??

Cheers

I do loads of these rob and i live in Spain, if the house is 150 years old it is built of rock and clay or rock and lime morter. There is no succesfull way of tanking these walls with chemicals, originaly it may have just have been animal quarters so they werent bothered by damp. If you cant remove the earth from the outside do as has been said build a false wall from metal stud boarded with MR plasterboard or cement board if you can get it and afford it, if you use 50mm stud make some brackets from the track and fix the studs to the wall midway or more depending on ceiling height to keep it rigid especialy if you are tiling it. You could increase the stud to 75mm if you feel the need or even I stud, make sure you put air bricks in top and bottom every 1.500 or so to ventilate the void.
Lucius.

There is the option of using Sovereign "Heydi K11" ... Its a cement based damp proofing system .. You will not find a better option and not have to lose space as with studding out you wall ... Sovereign Internet Goto Tanking ....
Under Video's & Literature There is a Video to see what it does and how it works etc..
I hope this helps ..

Ive used the Soverign Heydie system before and its great stuff but the problem with old Spanish buildings built of rock and clay or lime is that they are suffer from seasonal movement which can crack this kind of cement based tanking, ive seen sand and cement rendering crack on this type of building even when expanded metal has been used.
Lucius.

So what your saying Lucius is , that whichever system he uses . They will all crack ... Even a stud wall, as there will be movement in everything that is put in there to cure the problem through seasonal changes ?

Depending on movement there is a possibility of the stud wall cracking where the boards butt together but i have never experienced this, i always leave a penny gap between boards and keep them of the floor to help compensate for any movement but even if it does crack it dosent matter as it is only a false wall hiding the bad wall but if the tanking cracks it is compromised and will let in water though in this case i think it is only a damp problem not water gushing in, quite common in this type of house often due to other reasons like modern cement renders being used preventing the house from breathing.
Lucius

The reason he wants the information is, so that the wall that is damp can be tiled . Now what you are saying is no matter what it cant be tiled ....
I would go with the Heydi K11 before stud wall as, If it is a timber stud wall then the wood would end up with wood weevil and rot. If it is metal then that is going to rust away and end up falling apart ... Atleast with the Heydi K11 the internal fabric of the building is being sealed from the inside . The wall will still have the damp on the other side of the barrier so in my mind will not dry out and be less of a chance of cracking ... Than replacing a stud wall that will rot and need replacing every few years..
Just my opinion ... on what I would do ...

I dont remember saying it couldnt be tiled and as i said ive never had a problem with this type of stud wall suffering the same movement as the original structures do, you suggested it.I would never use timber for this kind of aplication in Spain as tanalised timber is difficult to source and all timber is expensive, we aint got many trees.Metal frame studding is electroplated which will pretty much protect it from rust unless it is in a saturated situation which is not the case here, it will not be in contact with the damp wall other than the brackets which can be isolated by using rubber or plastic washers if you feel the need. If the sole concern is the metal rusting another common practice in Spain is to build the wall with 30mm wide terracota blocks.The correct purist method here would be to expose the outside wall and coat with a lime putty morter and fix the tiles internaly in the same morter but this would be costly. As have said before cement based tanking systems are excelent but do not work well on this kind of substrate especialy if it is clay built i know i live in one.
Lucius.