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"Preserving the past for our future"

SWITCH TO MOBILE SITE

Ground water is contaminated with salts (sulphates, nitrates, etc.,).  These salts become concentrated in the plaster and masonry in the areas from which moisture is evaporating.  The ingress of moisture can also dissolve salts already present in the structure.  These salts are generally hygroscopic, i.e. they attract and absorb moisture from the atmosphere, with the result that on humid days, even though a damp course has been inserted damp patches can appear on the wall surface and may spoil decorations.  In addition to the contamination of the plaster, the underlying masonry also contains residual salts.


The removal of the original plaster will remove the majority of the salts, but unless the wall is re-rendered using a waterproof rendering system, the salts contained in the masonry can migrate back and spoil newly decorated surfaces.


If the existing rendering is deemed to be stable and removal thereof could prove detrimental to the sub-strata, we will in some situations apply our plaster directly onto existing rendering.


Preparation


Protect surrounding area by covering with dust sheets, where quoted for.


Remove timber skirtings, architraves, disconnect radiators and other fittings, where quoted for, as detailed in our report.


Remove old plaster back to brickwork or stone and up to specified height.


Remove all timber fixing grounds.


Rake out joints and hack brick or stonework to provide a good key.


Application


1.  First Rendering Coat


Mix:  Three parts washed sharp sand to one part sulphate resistant cement.


Apply render up to 10mm thick, incorporating waterproofing admixture, using only sufficient water to maintain workability. Water to be free from contaminants, the cement should be fresh and free flowing.  Do not over trowel.


On initial set, scratch to provide a mechanical key and apply floating coat before the scratch coat has finally gone off.


Leave a 25mm channel between the rendering coat and any solid floor.


2.  Second Rendering Coat


Mix:  Four parts washed sharp sand to one part sulphate resistant cement.  


Apply second coat up to 10mm thick, using only sufficient water to maintain workability.  Do not over trowel.


Scratch surface to provide a key for finishing plaster.


Leave a 25mm channel between the rendering coat and any solid floor.


3.  Third Rendering Coat


Material:  Multifinish or similar finish.


Apply plaster at a minimum 3mm thickness.  This coat to be porous and not over-trowelled.


Clear away and leave site tidy.


Important Notes


1.  Redecoration


It must be remembered that, even after the insertion of a damp-proofing course, the moisture already present in the wall can only escape by evaporation.  As a general guide, the drying rate is given as 1 month for every 25mm of wall thickness (BRE Digest 163, ‘Drying out buildings’).  Therefore, 230mm will take approximately 9 months to dry.  However, the drying out depends on conditions, ventilation and the type of masonry, so drying may take  considerably longer.  External finishes, e.g. paint/render, will considerably extend this time period.  Due to the potential prolonged drying of the wall, the following must be considered:



Note: It is not uncommon for cracks to appear in new plaster. Any cracks should be filled as part of the re-decorating process. The initial decorations should be regarded as temporary, the final decorations not taking place for at least 12 months after the completion of the damp proofing and ancillary works.


2.  Skirtings & Joinery


If sound, original timber skirtings and joinery may be re-fixed.  Alternatively, new timber skirtings and joinery may be required, these will be treated with fungicidal fluid prior to fixing, paying particular attention to all cut ends and joints.  The replacement or refitting of skirting boards and other fixtures and fittings is NOT included in the contract unless specifically agreed in writing beforehand.  Every care will be taken with the removal of skirtings. However, some damage may be unavoidable especially if they are fixed with cut nails or are decayed.


3.  Lightweight Plaster


Lightweight, gypsum plasters should not be used in this context.


4.  Need to Conform to Specification


It should be understood that the materials and methods used in plastering do not directly influence the effectiveness of the damp-proofing system.  However, a wall which has been subject to rising damp will be contaminated with salts which have been taken up from the soil.  Unless this specification is conformed with, these salts may migrate into the new plaster, and the plaster may afterwards remain damp by the absorption of atmospheric moisture, even though the damp-proofing system is fully effective.


5.  Drying Out Period


It is vitally important that the new system be allowed to dry out slowly.  Too rapid drying out will result in cracking, and eventual breakdown of the system.  Heating or forced drying should be avoided.


Please Note:


All re-plastering costs are based on thickness of up to 25mm.  Any thickness in excess of this will be subject to further costings.  Forced drying of newly re-plastered surfaces should be avoided as this may result in cracking to the finished plasterwork, under normal circumstances this should be made good when decorating.  Making good is not allowed for in our quotation & we cannot accept any responsibility for this.  The re-commissioning of radiators too soon will add to this effect.


We reserve the right to alter the provisions of this specification in such respects as may be found necessary during the course of the works.

Re-Plastering of Internal Wall Surfaces

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