Poulton Remedial Services - Rising Damp

Rising damp results from capillary flow of water from the ground, most building materials i.e. bricks/blocks/mortar are porous and therefore wettable, the pores are fine and therefore water rises in them, sometimes to a considerable height, in a similar way to blotting paper.

Ground water is a dilute solution of soluble materials such as chlorides and nitrates, as the dampness evaporates these are left in the building and eventually over many years become highly concentrated at the wall surface.

These salts can be Hygroscopic which means in periods where high humidity occurs the salts will become soluble and therefore damp.

For this reason replastering has to be carried out in conjunction with DPC injection to remove the contaminated plaster. If a DPC is injected without replastering the damp will no longer rise but Hygroscopic dampness will occur.

Dryzone Damp Proof Course System

Poulton Remedial Services Use the Dryzone Damp Proof Course System (www.safeguardchem.com) which is installed in accordance with the British Standard Code of Practice BS6576 and is covered by British Board of Agreement Certificates Nos. 97/3363. It is designed to prevent the upward movement of moisture in the capillaries of brickwork, mortar or stonework. It is used in the following situations:

1. Where there is no existing Damp Proof Course.
2. Where the existing Damp Proof Course has broken down.
3. Where the existing Damp Proof Course is bridged by solid floors, external ground levels, internal wall plaster etc.

1. METHOD

Holes are drilled in the masonry 12mm in diameter along the line of the proposed damp proof course and spaced at 115mm centres to a depth determined by the thickness of the wall, but generally two thirds of the wall thickness.

The Dryzone Paste is then inserted with a Dryzone application gun. When installed it uses moisture contained within the damp wall to diffuse where it cures to form a water repellent resin.

The course to be injected is chosen so that the position of the horizontal damp course is at least 150 mm above the external ground level.

Complimentary vertical damp proof courses are injected where required to isolate treated walls from the effects of rising dampness in adjoining walls as for example in semi detached or terraced properties with abutting walls. Where injection is carried out above high ground levels the walls beneath will be subject to lateral moisture penetration. (Referred to as tanking).

Timbers below damp course level will be subject to damp conditions and should be protected wherever possible.

Rising dampness brings salts from the ground (chlorides Nitrates etc) that are hygroscopic. These salts have the ability of attracting and retaining airborne moisture. Therefore it is essential that the salt contaminated plaster is removed and replaced in strict accordance with our replastering specification.

2. TYPICAL SPECIFICATION

Remove internal plaster affected by rising damp to a minimum height of 1 metre or 450mm above the maximum level of rising damp. Remove internal skirting where necessary to expose the treatment area. Carry out drilling along the proposed line of the damp course. Inject the Dryzone paste into the hole with an application gun.

Replaster using a 3:1 ratio mix of sharp washed sand (BS119 or M Zone BS 882). The mix also contains a waterproof salt retardant additive. The first and second coats are required to be a nominal thickness of 10mm. The finish used is 'Thistle multi finish'. On no account should lightweight plasters be used.

All plasterwork to be finished approx. 25 mm from floor level to form a bridging gap. The gap is then covered with skirting which is plugged and screwed to the wall using PVC plugs.

The skirting should be pre-treated with a timber preservative.

Where party walls are involved, the Party Wall Act 1996 applies. This requires the owner of the property to notify his/her neighbours of proposed works and obtain their consent before proceeding. A neighbour cannot unreasonably withhold consent but should you require further information please contact our office.

In order to obtain the full benefit of the damp proof course, it is essential that all actual and potential sources of moisture ingress are rectified and thereafter the property is properly maintained.

The installed damp course must not be bridged in any way by paths, gardens, solid floors etc. External renderings should be stopped above the level of the damp proof course and terminated in a bell cast mould.

Fungal decay in timber is related to high moisture content and timber bearing into damp walls below DPC level should be re-supported on metal joist hangers, brick piers or joist ends protected by PVC Damp Proof Membrane

Walls that have been accumulating dampness for a number of years will not immediately dry out after the insertion of a damp proof course. The residual dampness within the wall above the damp proof course will take a considerable time to disperse. As a rule of thumb guide in the British climate, residual dampness disperses at the rate of approx. 25mm per month dependant on humidity, temperature, rainfall etc and how damp the wall was prior to the insertion of the damp course e.g. 230mm wall = 9 to 12 months.