DEALING WITH DAMP
Though Spain enjoys a much drier climate than the UK, damp is still a common problem especially in older town houses. Most properties won’t include a damp proof course (DPC), therefore in order that the effects of rising damp are minimised, a number of other measures may have been taken to protect the lower walls. If these measures have not been included in the original design of the property, or formed part of renovation works, remedial measures may be required.
Buyer Beware!
The tiled area to dado level in many older town houses has normally been added due to a damp problem in the walls. Unless the tiles have been applied after a proper tanking system has been added, they will quickly lose their key and because they stop the wall from ‘breathing’ they often only serve to delay the seasonal drying out of the wall and can cause the moisture to track even higher in the wall. Some walls may also be covered in decorative plastic paneling, which again normally hides and aggravates damp problems.
MAIN CAUSES OF DAMP IN WALLS :-
Ground floor is the same level as, or below external ground.
Every opportunity should be taken at the time of construction to raise the main living area 0.5m or more above the surrounding ground level. Though damp will still be present in the lower walls, little if any will ever affect the walls within the living space and the property will cope better at times of flash flooding. Creation of a ventilated floor void will also eliminate the problem of damp in the floor structure and the need for a continuous membrane.
Most older properties are on solid floors (often just tiles on earth) and may sit at, or even below, ground level. Good room heights mean that floors can be raised as part of a complete renovation, but if money is limited, doorways, stairs etc will cause complications.
Many properties include ‘semi sotano’ underbuilds, cellars etc where at least one, if not all walls are below ground level. Ultimately these areas should be tanked from the outside at the time of construction, as the best systems are pushed onto the structure by the water pressure, rather than away from it. Unfortunately on existing properties this is often not a viable option, so a tanking system must be applied from the inside. (see specifications below). In cases of flooding a sump pump may be required, but it is not an infallible solution, and should ideally only be used as a back up to a full tanking system. The reason being, most flash floods are accompanied by power cuts, so the very time the sump pump needs to kick in, the power may be off. Hence the area could still flood in a matter of hours.
The quantity of water involved at times of flash flooding will normally be too much for the average pump to cope with, so flooding will occur anyway. While a petrol driven pump would solve the power problem, the occupants will need to be present to get it started and the petrol driven pump still be unable to cope with the shear quantity of water.
Ideally design any fully sub ground areas such that they act as a watertight bowl (Tank) and do whatever is necessary to allow water to drain around this tanking and away from the property as quickly as possible. Low level perimeter drains can be introduced around the inner wall of the area and a second inner tanking leaf built (effectively a dry room within a damp room), entrances e.g. garage doors should feature a storm drain to discourage water from entering, though these often become blocked at the very time they need to function.
Fortunately many basements suffer only minor damp, such that a cement based tanking system can be applied from within (see specification below). This can then be decorated, but as a secondary measure, it is better to build an inner leaf of ceramic bricks after tanking has been completed, not only does this reduce the risk of further damp effecting internal decoration, but it also allows for services to be tracked in the wall without breaching the water tight nature of the tanking system. (holes, channels etc should all be avoided on the tanked surface).
Wherever possible, never build below ground level unless at least one elevation sits above it (e.g. on a sloping site). Do not store valuable items or utilise any fully sub ground areas for purposes that would result in significant damage to the contents. Increasingly new houses are built in Spain with fully sub ground garages in which the boiler is often located, this is simply asking for problems and very bad design and planning on both the developer’s and town architect’s part. Garage entrances at the top of slopes are fine, but entrances at the bottom of slopes should be avoided.
Where the property is at ground level, but the site benefits from good drainage, consider excavating out a path area around the property hence, dropping the immediate ground level around the walls. The paths must be well drained, so as not to have the opposite effect and encourage water pooling. All surrounding paths should be laid to fall away from the walls and to shed water to an area below the property as quickly as possible. A narrow gravel filled trench immediately adjacent to the wall will reduce splash back, but again this must be well drained. Garden walls should incorporate drainage holes to stop water build up, which may cause water entry into the house and risk collapsing the wall itself.
The property sits on a slope such that there is higher ground above the house
Water fall off from higher ground can be considerable in Spain, in addition to occasional flash flooding e.g. every 5yrs or so, properties will normally have to cope with several heavy downpours throughout the year due to seasonal change (Autumn and Spring time) and thunderstorms.
Not only will ground water track under the property at times of heavy rain, but mid terraced houses may suffer water leaks from the old plumbing within unrenovated properties higher up the street. Most towns feature numerous fonts, some of which were private and located in basements, this water may also be tracking under the property.
In country areas especially low lying orange groves (which are design with irrigation channels and generally catch water), and worse still rice fields, ground water levels can raise significantly after heavy rain, which is why many casitas are raised above the surrounding land. If your prospective purchase is not raised, take a good look at the surrounding land and preferably ask locals if the area floods.
Poor roof overhang or failed gutters
All Spanish properties should be built with a good eaves overhang e.g. min 30cm for a single storey property and another 10cm for each extra storey. Importantly this should be on all elevations, but even on many new properties, (for the sake of quicker and cheaper construction), many gable ends have virtually no overhang. Poor overhang results in the wall being saturated at times of heavy rain (therefore it relies solely on the surface finish to stop water soaking into the outer leaf). The lower wall also suffers splash back. While gutters and stone cladding can help to solve the splash back problem, they will not stop upper wall saturation, the damp from which will aggravate damp in lower walls.
The ultimate but most costly solution would be a new roof design to include sufficient overhang, (always try and increase the overhang if your need to re-roof anyway), though a partial e.g. 20 –30cm overhang can be created by a good roofer with ceramic bricks and tiles alone.
Lower stone cladding painted with an ‘impregnante hidrofugo’ clear treatment e.g. Sikaguard, is ideal for cutting down maintenance to lower walls and reducing damp penetration. It must be high enough (preferably 0.75m +) so as to cover the whole area most prone to damp. The junction with the wall above should include a water resistant additive in the cement mix e.g. Sikacim, and the upper wall paint system (two coats 100% acrylic paint) should ideally be finished over this cement fillet to stop water tracking down behind the cladding. Alternatively the stone can be capped e.g. with marble, chased well into the render . Though in many cases stone cladding is applied straight onto the existing surface, ideally the failed existing render should be hacked off and the lower walls re-rendered with a water resistant mix (left keyed for good adhesion, not smooth) before cladding takes place
Leaking water pipes
As covered in a previous issue of IT, older water types, especially the iron type, will normally leak from the cast joints after about 25 years. Most older properties that are plumbed with this type of pipe will show some signs of water damage and damp in the lower walls. Re-plumbing of the effected area, and preferably the whole property should be carried out before any expensive refurbishment works are carried out, (e.g. fitting a new bathroom or kitchen). This problem is particularly evident in the summer, if walls are still damp when they would normally have dried out if rain or ground water were the culprit.
The property has a floor membrane only
Where the ground floor has been retiled a continuous sheet or liquid membrane may have been introduced to stop damp coming through to the living space. Unfortunately, unless the lower walls of the property have been properly tanked, the membrane only serves to retain more damp in the floor slab, such that it’s only method of ‘breathing’ (evaporation) is via the lower wall areas. The lower walls will therefore also need to be properly tanked, and importantly the floor membrane should ideally rise up the tanked walls slightly.
There are of course many other specific causes of damp, e.g. leaking water deposits, poor tiling in neighbour’s shower etc, therefore proper identification of the damp source is essential before the appropriate remedial works can take place.
When is a damp patch, not a damp patch?
Answer:- normally when the suspect area is covered in black or green mould without staining. This problem is almost always due to condensation rather than penetrating damp (e.g. from a roof leak, which would normally cause staining). This is aggravated by ‘cold bridging’ e.g. where walls are solid, rather than cavity and often occurs in bedroom on the north side of the property. Airborne water vapor from breathing, cooking, showering, drying clothes, gas bottle heaters and evaporating damp from other areas of the property (e.g. a leaking water pipe or rising damp in lower walls), condenses on these cold areas of wall or ceiling and mould growth occurs. Condensation can also cause periodic surface damp on floors.
(This topic including solutions will be dealt with in more depth in a coming issue of the IT soon).
REMEDIAL SPECIFICATIONS:-
The products included in the remedial works outlined below can be purchased from most Spanish builders merchants. Make sure your builder uses the right product, which has been specially designed for use in damp situations.
Where damp penetration is minor and substrate sound. Scrape off failed paint then paint with ‘Anti Humedad’ treatment e.g. Sika ‘Imper Yeso’ or ‘Sika Top 141 SP’ (if surface has not been previously decorated), before 2 coats of interior paint to match existing walls. Where substrate has lost key from wall or is soft or crumbly, hack off failed plaster (to 1m or more from floor level) render and re-plaster with damp proof plaster / render e.g. Weber ‘Terrasan’ renovating plaster (white finish). Alternatively lower walls could be hacked back and sealed with a brush on membrane e.g. sand blinded bituminous rubber e.g. Sika ‘Bitosol’, before finishing with a conventional render or plaster.
As the majority of such expenditure is generally on the labour, it is highly recommended that the best antihumedad, plaster and mortars are used. Sub soil walls, e.g. underbuilds / cellars should be properly tanked. Tapping large holes where water ingress is evident with Weber ‘motex dry obturador’, followed by full tanking with ‘motex dry capa gruesa’(applied as a render where damp is severe) or ‘motex dry capa fina’ applied as a brush on ‘slurry’ coat (where damp is moderate).
Injection
Specialist companies will be able to offer a number of DPC solutions including silicone injection, though the thickness and make up of some walls may make this method difficult and unreliable. If you decide to pay for a specialist contractor, try to see previous work.. Physical sheet DPC’s can also sometimes be chased into the wall by grinding out a channel from both sides in sections, once again thicker walls prove difficult. Other methods are also sometimes used including ventilation of the wall to aid evaporation Most DPC and non suppressive systems are still ideally complemented with a suppression tanking system as outlined below.
Quick guide:-
Problem Product
Minor damp above ground level Scrape of loose paint and apply Sika Imper Yeso or other ‘antihumedad’, then repaint. Clad external lower wall with stone treated with a clear antihumedad treatment e.g. Sikaguard.
Moderate damp above ground level
Hack off failed plaster and replaster with
Weber Terrasan renovating plaster, then paint. Clad external lower wall with stone treated with a clear antihumedad treatment e.g.
Sikaguard.
Severe damp above ground level Consider introducing a DPC as well as using the system for ‘moderate damp’ above. Wall may need rebuilding or lining with an inner leaf.
Minor damp below ground For sound but damp surfaces, apply Sika Bitosol (needs lining or plastering after) or Weber motex dry capa fina (for application on continuous smooth surfaces e.g. concrete), then paint.
Moderate damp below ground
Hack of failed render and apply
Weber motex dry capa gruesa (for application onto blocks, bricks, stone etc)
, then skim or paint.
Severe damp/ flooding below ground
Hack off failed render and use
Weber motex dry obturador for cracks / holes, followed by
motex dry capa gruesa.
Preferably an exterior plastic membrane e.g. Sika Lam should be applied including a land drain to the exterior of the wall. Where this is not possible consider an internal perimeter drain, secondary inner wall and back up sump pump. This type of work should be carried out by a specialist company (or good builder that has experience in this type of work).
Ground floor surface damp Ideally raise the floor with a new concrete floor slab over a continuous damp proof membrane e.g. Sika Membrana and/or add Sikacim water proofing additive to the concrete or screed mix before retiling. If you cannot raise the level (due to stairs, doors etc) excavate out enough to lay the new floor slab. All floor membranes should tie in to wall membranes or other tanking systems.
For all of the above, consider improving external land drainage and general water shed of surrounding paths, steps etc. Design drainage to take the water ‘around and away’ from the building as quickly as possible, thus reducing the amount of water any tanking systems have to cope with.
Summary:-
Most experienced builders/ plasterers, will be able to solve moderate damp problems
provided that they use the right systems and materials. While damp proofing productsare
more expensive than for example, standard sand cement renders, most of the cost willbe
in the preparation and labour, therefore a few more euros per sack of material is well
worth the money. Make sure your builder has read the product instructions properly and prepares both the substrate and product accordingly (some products are two part mixes and have limited working times, all products will need to be well keyed to the substrate, which may or may not need to be dry at the time of application). Remember that damp will affect structural timbers and steel reinforced concrete structures, so check that the
rest of the structure is sound, before spending money.
NB:- Information for advice purposes only. Proper safety precautions should be taken and legal procedures followed when carrying out all works.