Damp Information
Cellars
If a cellar is to be used purely as a store room for un-perishable goods.ie. bikes, boxes of junk, tool bench for odd jobs. Providing it doesn’t flood every time it rains heavily and the local water table doesn’t emerge through the floor, all that is necessary is sufficient ventilation and a dry floor. If the floor is a bit too damp, lay some duck boards down to walk on. On the other hand if it is decided to make a small office room with a desk and a few shelves etc it wont be much fun without dry walls, nice plain décor and some good lighting, in which case the conversion out-lay will be quite a bit more, but not necessarily inhibitive. The first important factor to consider is the headroom. In other words can a person stand up. Secondly, is there a known history of flooding. This can often be spotted by a tidemark that will show up around the edges of the plaster or brickwork and confirm both that it does flood and to what height the water last came up. If this problem exists, it will take the design into a different category and a submersible pump will need to be incorporated in the specification and preferably a good one with all the battery back up systems. Unfortunately this item could prove to be too expensive for the allowable or planned budget . So for the sake of this exercise we shall assume that there is no flooding history and it is decided to take a chance against the BS 8102 which states that before any underground waterproofing is done one should consider the need to allow for water ingress at some time during the life of the basement or cellar. However this example will be specified as a dry lining system and is purely cosmetic and cannot be referred to as tanking, (that is something else that will be gone into later.) So now we refer back to our sub-floor chamber which for sake of argument lies directly below the front room ground floor and is accessible via a stone or timber staircase located below the main staircase. Or even a hinged floor trap. This of course will need to be protected with a guard rail should the trap be removed or left open.
It is further emphasised that dry-lining, even with CDM insulation, will not be awarded a long term guarantee against water ingress or flood, and most reputable damp proofing companies will not carry out this type of contract without a pump and all other specific components that constitute a recognised tanking system that conforms to BS8102
Requirements.
At least 7’ headroom.
A fairly dry level floor.
An outside wall to fit ventilation or make use of existing air vents.
Electricity supply.
Heating or an extended central heating radiator.
If there is a light well this can be utilised, as can any recess that is part of the cellar structure, such as the alcove of the fireplace foundation buttresses, which can make an excellent cupboard.
The aim is to cover the cellar walls so that water vapour that emanates continuously from the mortar joints is confined. This and a covering over the floor will eliminate the musty smell that is usually prevalent in cellars. This can be achieved by use of one of the Cavity Drain Membranes, a specially designed polyethylene sheet material that is supplied in rolls. The main essence of these CDM’s is that as well as being waterproof, they are constructed in thickness of between 3mm and 25mm depending upon requirement, and comprised of little uniform indentations that allow air to circulate behind without the need for venting, and are supplied by various companies including Delta, Newton, Spry, Wykamol and quite a few others who are all contactable on the internet.
For walls, and floors a 3-5mm relief pattern is suitable.
Floor
Its best to start with the floor and for this once the CDM has been laid out over the existing screed or soft compo, sheets of floor quality tongued and grooved 22mm thick chip-boarding are fitted together on top of it, forming a platform that is fitted to within half an inch of the walls, to allow for expansion. Also ensure to up-stand the edges of the CDM by a few inches to protect the edges of the chipboard getting damp. This is known as a floating deck floor and relies upon a fairly flat base and gravity to remain intact.
Walls
The simplest way of fixing the sheeting to the walls is to unravel the roll and use temporary clout nails to secure it in position around the walls, then either using masonry nails or rawl-plugged screws, secure a framework of 2X1” pre-treated wooden battens around the walls, (Roofing battens are ideal) Incidentally now is the time to extend any pipe work if an existing radiator needs to be realigned. Once this has been completed sheets of Foil backed Gyproc plasterboard can be secured by screwing through the board into the underlying wooden frame. It can also be nailed using small galvanised or large head aluminium clouts. Make sure you have marked on the plasterboard, the location of any electrical wiring or pipe work.
To finish the new plasterboard surface joints can either be taped over and painted as it is, or for a more professional finish, plaster skimmed. It is also important to fix some form of skirting around the walls to help brace everything and form a nice tight line to the floor. There are usually a couple of services meter boards on one of the walls but these can be concealed by the construction of an MDF cupboard tailored around them.
Ceiling
Finally the ceiling. In most cases there would be floor joists of the room above that providentially form cavities that will take a few recessed spotlights. This will need to be done in consultation with a qualified electrician, before the plasterer tacks up the ceiling, as will any power sockets or other electrical appliance connections.
If existing ventilation is not sufficient for some reason, it will be necessary to install a powered extractor fan that expels to the outside, and that preferably is fitted with a timer so that it is automatically triggered to activate at least every ten minutes on the hour. After all that work you do not want to encourage a build up of excessive humidity. One company who specialise in air control are the Nuaire Group who can be contacted at www.nuire.co.uk/company.shtml The cost of any powered extractors is not included below.
All that needs to be done now is the decorating.
COST:-
Taking a typical area of 7’ high X 10’ wide X 12’ long, with a floor and ceiling area of 120squ ft. and taking into account electrics, plumbing and carpentry, and the decorating of course, should be in the region of £6000.00 +Vat
This is probably the cheapest practical system available and could be carried out by any reputable jobbing builder and plasterer.
Cavity Drain Membrane system of tanking, incorporating a sump pump, that will qualify for a long term insurance backed guarantee. This system relies upon relieving the building of ground water pressure rather than holding it back.
Taking a similar area as before, but assuming that the property could be subject to water ingress or flood at some time, as contained in BS 8102, will require the following:-
Existing brickwork will need to be keyed out and re-pointed.
Any old plaster that is in a state of deterioration must be removed
Any defective brickwork made good
If the wall surfaces are particularly uneven they will need to be rendered and levelled off
Any external known cause of water entry must be rectified and sealed by plugging with a fast setting cement.
A floor screed will need to be laid so as to provide a fall to the sump
Subsequent to the above requirements, a plastic gulley is inserted around the perimeter of the floor screed and is connected directly to the sump so that should ground water enter the property it is automatically collected in the sump and discharged via the pump once a certain controlled level of water has been reached.
Some of the deeper recessed or studded CDM’s can be loaded with a cement screed to form a permanent floor, headroom allowing. Or a chipboard floating deck can be used. Again membrane edges are formed into up-stands so that they lap inside the wall membrane and form a seal that is bonded with butyl tape adhesive. With this system the membranes are fitted to the wall with special plastic plugs that are hammered into the brickwork. These have flanges designed to accept spot dab adhesive that are deposited onto the back of the plasterboard so that it coincides with the flanges. The plasterboard is then pressed onto the flanges and allowed to set. Alternatively the plasterboard can be screwed onto the flanges.
However although the membranes are jointed together with a special pliable sealant, this is for holding purposes only and does not make the joint waterproof above a certain pressure. This means that if too greater a volume of water entered the building suddenly, or if water was allowed to build up behind the membrane due to failure of the pump or perhaps because of silt and sludge blocking the gullies, the system would leak causing water to escape into the interior fabric of the room.
Final finish can be taped joints or plaster skim.
Ventilation again would need to be taken into account as would lighting and ceiling, and any c/heating arrangements..
COST:-
Probably around £10,000.00 plus VAT
The work would need to be carried out by a specialist company experienced in CDM tanking.
Another form of tanking using a laminate of cement renders that incorporates chemical additives, such as the Sika 1 system, has been in use for many years.
A well proven system, but one that is more structurally sensitive and relies entirely upon a rigid construction. There is very little flexibility, as in a CDM system.
Again taking the same area of cellar into account there are still certain preparatory requirements:-
Existing walls need to be plugged for any ground water leaks.
In most cases it is recommended to construct a new concrete floor slab, so if headroom is tight, the existing floor or soil will need to be lowered accordingly.
All fittings and obstructions need to be temporarily removed including service pipes and meters, and staircases that are fixed against the wall.
Walls need to be keyed up, either by needle gunning, bush hammer or grit blasting.
Usually 3 coats are applied, although more can be added if deemed necessary depending upon the ground water (hydro static) pressure.
The render coats are lapped onto the concrete to form a floor/wall joint, prior to laying of the final screed, and providing the works are carried out in accordance with the manufacturers instructions the final result will provide a totally waterproof box. At least up to the height of the ceiling, unless of course the specification included a brick or concrete ceiling, but this is not the case in this example. There are other similar systems such as the German Hey Di. In this system the walls still need to be plugged where necessary and cleared of flakey strata and is usually usually screeded with a tight coat to provide a workable base, with the exception that the covering material is applied with a brush or trowel, and is a thinner coating, than Sika. Another well-known name is Vandex. A Swedish company. They were quite early pioneers of waterproof chemical cement first used for chemical mortar damp course injection.
The important thing with cementicious tanking is to maintain it puncture free. So if there are any fittings or pictures to go on the walls, or skirtings etc, they must either be glued to the finished render or plaster, or some damp seal provision must be planned before hand.
Cost:- Allowing for the inclusion of a new concrete floor and screed, would be in the region of:-
£11,500.00 plus VAT.
Again works would need to be carried out by a specialist damp proofing company.
