Tufnell Park Sash Window Repair, Draught Proofing, and Restoration
Sash Windows when poorly maintained can cause a variety of problems. We are going to look specifically at water ingress beneath the window sill itself. The obvious signs of water ingress beneath your sash window internally is a mouldy or cloudy wet look on your plaster. Not only is this unsightly and will ruin your decoration it has far more severe implications if let untreated. The biggest problem by far and away is that untreated for several months, can lead to the plaster becoming ‘live’. This effectively means that as a result of the continual water damage. the plasters ability to stick to the render is diminished to the point it is hanging onto the wall floating free of the main brickwork and render. A simple way of checking if this is the case is to touch the plaster that appears affected to see if there is clear movement.
We will forget the damage inside now and concentrate on our sash windows outside. Externally you will note your windows may be rotten or even in good condition. If rotten then this needs dealing with first and you will either contact a sash window specialist or attempt the repair yourself. If rotten it is likely the water damage is simply penetrating through the poorly decorated, damaged wood. This means by installing a new sill section or calling a sash window restoration expert to carry this out for you will solve the problem.
If your windows are in good condition it is almost certainly the seal between the wood and brickwork both at the sides and bottom of the window. Most sash windows will be sitting on a stone known as the sub sill. This gap will need sealing with an external pointing sealant like silicone. The sides will need pointing with a sand cement mix. These steps will need to be included if your window sill and style was rotten as they will have been removed anyway to perform an effective lasting sash repair. Once at this point you will have solved the real problem and can now concentrate on the remedial works internally.
Going back to the plaster being ‘live’ internally, if this is the case you will need to completely remove the plaster and most likely render beneath the windows until you come back to a solid base (usually back to brick) with no movement. Some people prefer to remove the mortar/plaster right to the bottom of the floor from beneath the window sill which is perfectly acceptable and probably better longterm. The draw back to this is that you create yourself far more work than is actually necessary at this point in time.
There are two main steps to take on here. Firstly you will dampen the wall and apply to the naked brickwork you have exposed, a sand cement render of normal mix strength, four sand to one cement, approximately 4 mm shy of the original flush plaster finish. Once this is applied evenly you will then score the render in a crossed patterned. This is then left to set. Usually a couple of days later this will be fully cured. You will now mix up your plaster and bring up to the flush finish which is left at either sides. You remember how we left the render 4mm lower than the flush finish of the original plaster? Well this is so that we can now bring the plaster up to the correct level on the wall to match everywhere else. You may also remember how we scored the render. This was for when the plaster is applied. A smooth render finish beneath the plaster would have been easier to break away whereas scored will give better bond between the plaster and render. Once the plaster is cured it is normal for a DIY effort to need to sand the joint between the old and new plaster. This is so that once decorated you will never know the problem was allowed to occur in the first place!