Barn repair scheme specifications

All rebuilt masonry work is to match the existing in terms of the character of the coursing including through-stones, the thickness of the beds and joints, and the profile of the existing mortar. Any replacement stone should also match the original in colour, grain size and texture.

Defective masonry must be carefully cut out as to not damage any surrounding masonry. The face of new stone must be hand-tooled and finished in an identical manner to match the existing.

Some stone may be won from the collapsed rubble on site. Care must be taken to ensure that this does not cause further damage to the structure or increase the likelihood of further collapse.

Where stitch and pin is specified, this should be carried out by carefully removing any defective stones and raking out around any cracks. All friable material should be brushed away and beds and joints should be dampened before pointing. Larger gaps should be pinned using small stones and stainless steel ties should be laid into the beds (so they cannot be seen externally) at approx. 500mm rises. Beds and joints should be deep packed and finished appropriately (see mortar and pointing). Where short sections of underpinning are required, the wall should be supported on needle shores and the foundation excavated and cut out in 0.5-1.2m sections and then back filled with mass concrete. On removing the needles, one by one, grout should be poured in to make good any gaps between masonry and concrete. Slate packing or dry packing may also be used.

Re-pointing, mortar flashing and re-bedding masonry, ridge tiles or coping stones shall be in a hot lime mortar mix. No cement must be added. New mortar must match the original mortar as closely as possible.

Using a hot-mixed lime mortar, powdered or kibbled quicklime is mixed with aggregate and then ‘slaked’ with water. The process generates heat, popping and fizzing so appropriate PPE must be used. The mix ratio of lime to aggregate is 1 : 3. Aggregate will require a pozzolanic additive (up to 10% by volume) such as silica, Metakaolin or brick dust.

If a lime putty mix is used for external re-pointing, the 1:3 proportion of lime putty to (clean and washed) aggregate will require a pozzolanic additive (between 15-20%). Lime putty also requires more care if used externally, as the mortar takes longer to set and is more susceptible to frost damage.

The aggregate for the mix must match that of the original (lime) mortar in colour, shape and size. It is to be angular (sharp sand or grit), well graded washed sharp sand ranging in size from 2.3mm to 0.15mm supplied from an approved source and shall comply with grading type C or type M or BS882:1983 for concreting sands. Other types of aggregate such as limestone dust or brick dust can also be added to gain the correct colour or texture, provided that the overall proportion and appearance of the mix remains the same.

Mortar can be mixed with a mechanical mixer or hand batched. Boards should be laid down to protect the surface to protect vegetation etc. A steel bath should be used for slaking. Mortar mixes must be well knocked up before use. The finished mix should be as stiff as possible without being unworkable. It should be of the consistency to form a ball in the hand.

Any existing failed/failing mortars should be carefully removed, or to a depth slightly more than the width of the joint, avoiding damage to adjacent masonry. This should be largely achieved by use of hand tools such as skutch/ teeth chisels, plugging chisels (for rubble walls), tungsten tip chisels (for more delicate material such as ashlar), hacksaw blades and specially made steel hooks which can be used to avoid damage to stone arrises and widening of joints. Large chisels and any tools wider than the joint width itself would not be used.

All cement must be removed unless there is no feasible way of removing it without damaging the surrounding masonry. Care should be taken to ensure that any sound, original lime mortars are left in place, in accordance with the principle of minimum intervention. Where masonry is relatively impervious and a suction bond may be difficult to achieve, joints may need to be raked out further, to at least twice the depth of the joint width, to provide a level of mechanical anchoring of the new mortar into the joint.

Re-pointing is only needed where mortar has become so loose, powdery, decayed or eroded that water has started to penetrate the joints. All dust, debris, soil and vegetation growth should be cleaned from the joints and wall surface prior to damping down and repointing.

No mortar shall be laid during heavy rain, or in temperatures less than 5ºC or over 30ºC at any point in time during the curing period of a few weeks. All materials used must be stored well protected from damage by frost or moisture. All materials used must be free from snow, ice and frost.

Boards should be laid over the cleared ground surface before re-pointing takes place, to facilitate the clearance of debris following completion of works.

Work should proceed from the top of the area to be pointed down towards the bottom. Mortar must be well-knocked before use. Before any mortar is laid, thoroughly dampen the joints (e.g. with a hand sprayer) and allow water to be absorbed by the masonry. All large deep voids and joints over 15mm wide require packing/galleting with small stones or slate (and mortar), which must be hammered well back; several layers may need to be applied with required drying periods in between each and every layer. Joints shall be solidly packed with mortar as far back as possible and tamped using suitably sized tools. Newly laid mortar must never be allowed to exceed 15mm in thickness or width. After the initial set has taken place, the not-fully-hardened mortar shall be well compacted in the joint and stippled/brushed back with a stiff bristle brush to expose the aggregate and edges of the adjacent masonry and to seal with joint between the mortar and the stone. No brush marks or trowel marks should show. Joints must never be struck, finished proud of the masonry, or feathered over the edge of the stonework, but be flush. Where the masonry is eroded, the face of the mortar shall be kept back to the original thickness of the joint.

The dampness must be carefully controlled for fourteen days to enable successful curing. The mortar must at all times be adequately protected from the harmful effects of weather (i.e. too quick drying out through direct sun and/or wind, or moisture saturation through heavy rain) by covering with damp hessian drapes. Where there is a risk of frost this shall be supplemented with plastic sheeting and a further layer of hessian. The Principal Contractor shall identify arrangements to monitor and keep the protection in place until the mortar has hardened. All stonework is to be left clean of mortar after pointing. The use of hydrochloric acid for cleaning off mortar stains will not be permitted. Finished pointing must be indistinguishable from sound sections of the wall.

This work concerns the treatment of exposed areas of core masonry, including broken wall faces and wall tops. It requires a high level of skill and experience to achieve the desired result, which is to reproduce the appearance of exposed corework and at the same time to provide adequate protection and stability for the wall. The distinction between corework and pointing to the finished face of a wall must be clear – there will always be a higher proportion of exposed mortar in corework than in facing stonework. Should corework form part of any openings, the necessary space allowance must be made for the missing facing stones, by keeping the core back sufficiently.

The use of an appropriate lime mortar is essential. The original aggregates should be as closely copied in type, size and distribution as possible, although it may be necessary to modify the mix slightly to improve its weathering characteristics. Sometimes it is possible to reuse original aggregates in with the new mix.

Where vegetation is growing into the wall tops or broken wall faces, it is to be cut out and the surface of the stonework cleaned of all soil. Where existing mortar is found to be loose or defective, it is to be carefully raked out to a depth of not less than 25mm, allowing for the lifting and re-bedding of loose stones as required. Joints are to be prepared and re-pointed using lime mortar of an appropriate strength, allowing for the formation of falls to allow water to be effectively shed from the wall tops. All mortar work shall be protected after pointing (e.g. damp hessian cover), the degree of protection depending upon ambient conditions.

Soft capping describes the treatment of exposed wall tops and core masonry using soil and turf, or other vegetation, which acts to protect the stonework below. Its aim is to reduce water ingress into exposed walls, reduce the amount of run-off to wall faces, and protect walling from extreme weather conditions. Soft capping will be most effective on more extensive, level areas of exposed wall head, where extremes in weather can cause unprotected lime corework to fail or erode rapidly. It can provide a more effective, long-lasting and cost-effective solution than rough racking, although it can also have a greater impact upon the character and appearance of a wall. Therefore, it is important that finished soft capping does not appear as a deliberate and obvious wall treatment, but rather as a natural accumulation of vegetation over time.

Prior to the introduction of soft capping, the exposed wall head should first be cleared of soil and loose debris. Where practicable, organic and mineral materials shall be bagged and stored for re-use as a rooting medium on consolidated wall tops. All existing rough turfs should be removed to expose the extent of root growth. Turf shall, where practicable, be lifted from the wall head and retained for re-use. Additional turfs shall be obtained from an agreed location on site to avoid the importation of foreign flora and fauna. All loose and failed masonry is to be carefully lifted and set aside to allow for consolidation of the remaining wall top. Sufficient curing time shall be allowed for mortar before soil and turfs are laid. Reserved soil shall be dampened and placed to a convex profile on the consolidated wall tops to follow the natural contours of the wall. Turfs shall be laid on the consolidated wall tops and bedded, where necessary, using a latticed arrangement of hemp or jute twine and cleft oak pegs. Exposed edges of turfs shall be folded under.

New soft capping requires regular watering to prevent drying out and die-back. This can be undertaken using hand watering or, where a suitable supply is available, by securing a perforated pipe along the wall top to provide a trickle system. Saturation of the soft capped wall top is to be avoided. The system must be removed upon completion of the works.

Lime wash is to be made from a well-matured lime putty, diluted until very thin with water – ratio (roughly): 1 lime to 2 water – and well sieved to remove any particles of unslaked lime or bits of debris which might have got into the putty. The putty and water is then mixed. As the water becomes cloudy with lime, pour it off into a large vessel through a sieve, add more water to the bucket and keep mixing. Water and putty may be added to the mixing bucket as necessary.

If lime wash is properly made from mature lime putty and applied thinly, no additives are necessary for all internal and most external work.

Lime wash must be applied in several thin coats, as many as six over new surfaces, and unless it is not put on almost invisibly thin it will drag, craze and brush off when dry. The initial coat should be put onto a damp wall, brushing in all directions to scrub well into the surface. Each coat must be allowed to dry before the next is applied. Under normal conditions, a coat of lime wash should dry sufficiently overnight. The action of brushing helps bond the lime to the surface. Lime wash should not be sprayed. The lime wash should feel and look like water when being brushed into the wall; as it dries it will become opaque.

New lime render needs no preparation other than a light spraying with water to dampen the surface. Newly built walls or those re-pointed with lime mortar will need vigorous brushing with a stiff bristle brush to remove all dust and debris. It may be appropriate to use a fungicide to kill off moulds and lichen yet this will not be permitted.

Where render is in good condition, a new coat of lime wash will consolidate the surface.

New render must match the original in surface finish as well as composition. As with mortars, renders shall be of lime mixed with aggregate which has a good variation of particle sizes. No cement must be added to the mix.

Organic acids that are produced through the tendrils of creepers and climbers can damage stonework and mortar. Woody roots can also cause serious problems in beds and joints not only from creepers but other herbaceous plants. The roots of larger plants such as trees can burrow under walls and cause structural problems.

For climbers and other plants growing on masonry and into joints, care must be taken to remove them to not damage any surrounding masonry. Joints where the roots have penetrated must be thoroughly raked out and brushed.

Stumps should be drilled and plugged with a biocide and left to decay naturally.

All existing timbers of historic value shall be retained or reused, where possible.

Defrassing of worm-affected timbers is to be kept to a minimum to avoid unnecessary loss of original fabric. If replacement is justified, it is likely that matching timber of a similar section will be required.

Only ‘bat-friendly’ products based on permethrin or cypermethrin may be used.  Even these can harm bats which come into direct contact with them, so a careful check must be made for bats before spraying begins. If bats are present spraying must not take place.

All new softwood shall comply with B.S.1186 in respect of quality of timber and workmanship. All joiner’s work is to be accurately set out in accordance with detailed drawings which must however be checked against site dimensions. The whole of the carpentry’s softwood shall be good quality, free from disease and reasonably free from any edges, shakes and sapwood and well-seasoned. It should be dried to moisture content of between 15 and 20%, and be of matching size and species to that being replaced. Softwood is to be pressure-impregnated with a preservative before being brought onto the site and any cut ends or bored holed should be liberally treated with insecticide/fungicide (not harmful to bats) before being built in. All carpentry/jointing details to match the existing where applicable. New to fit old. All carpentry details must match the existing.

All joinery is to be protected against damage during the progress of the works and in transit thereto. The Principal Contractor is to allow for any coverings required, for protecting the floors with clean sawdust and for cleaning this away on completion. Should any shrinkage or warping occur or any other defects appear in the joiner’s work before the end of the maintenance period, such defective work is to be taken down and renewed. Any work disturbed in consequence must be made good at the Principal Contractor’s expense.

All doors and other framed work to be put together upon the general work being commenced, but gluing and wedging is to be left until the joinery is ready for fixing.

Original doors and shutters or their remnants must be retained wherever possible. Where they are beyond repair, replacements must be exact copies of the originals, replicating for instance the moulding (or absence of it) where verticals boards are butted together. Frames shall not be introduced where the door or shutter closes directly against the stonework. Painting or staining must be in muted colours.

Original windows must be repaired or, if too decayed, renewed on an exact like-for-like basis. Where windows are being restored to a more appropriate design, they shall be single glazed to a traditional pattern and traditionally detailed. Frames shall be kept to the minimum size possible and glazing bars should be 18-20mm thick, with a profiled section internally. Putty or mastic shall be used to fix the glass rather than timber beads. Any opening casement shall have flush frames rather than storm-proof detailing. All frames must be set back in their openings to the original measurement.

Existing ironwork of hinges and pins shall be reused wherever possible. Where iron pins have eroded and cracked the stonework, they shall be reset in a lead sleeve into the replacement stones or be replaced with new pins of the same pattern made in non-ferrous material metal.

Damaged purlins should be retained wherever possible, with new purlins in matching timber being secured to the lower side of the existing by fixing to the truss or gable wall generally in an identical manner to the existing or, when this is impractical, with joist hangers. Damaged principal rafters or truss ties are to be repaired by plating with new timbers or steel plates to each side, bolted at approximately 1m centres.

Individual loose or slipped roofing slates can be re-fixed using 6mm oak or aluminium pegs, by wedging up adjacent slates to allow the replacement, complete with peg, to slide into position on short rollers of about 10mm diameter.

Before the stripping of slates/tiles, the Principal Contractor must count and record the number of courses on each roof slope and the slate/tile length of each course from head hole to tail. Carefully strip to ground level all stone ridges and slates/tiles and set aside all sound material on a clean safe hardstanding for re-use, including any which can be dressed down in size. Sound salvaged slates are to be cleaned of all loose debris, sorted to length and thickness and arranged in stacks equivalent to each course length. Care should be taken to unload the roof on both sides equally and simultaneously to avoid excessively uneven load on one side. Carefully remove all slating laths and de-nail all rafters if nailed down. Clean down all timbers and remove all loose debris that falls the floor. All slates/tiles and ridges that are incapable of re-use must be kept on site for inspection and measurement.

Existing slates/tiles must be re-used wherever possible. Any shortfall shall be made up with matching new or sound second-hand slates of the appropriate type, colour and thickness. Sound salvaged slates/tiles are to be cleaned of all loose debris, sorted to length and thickness, and arranged in stacks equivalent to each course length. Diminishing coursing or local patterning must be retained. Imported slates/tiles shall not be used. Stone slates can be cut mechanically with a saw but each must be finished with hand tools to ensure a cropped not sawn finish to all edges.

If slates/tiles are found to be pegged, then this should be recorded and new or re-used slates/tiles be re-fitted with new pegs to match existing; otherwise slates/tiles are to be nailed with copper or aluminium nails (appropriate gauge). Each course of slates/tiles is to have a minimum head and side lap of 75mm to ensure the roof is fully waterproof. Slates should lie evenly without rocking and be graded in thickness where necessary. Sudden changes in thickness and gaps between courses must be avoided. Wide slates should be used to close the half-bond at verges and abutments. The slates are to be laid in diminishing courses from eaves to ridge. No slate or stone slate is to be cut to a width less than half its length and only wide slates are to be used at abutments and verges. Lay double course at eaves, projecting 50mm over the gutters. Verges to project 75mm, pointed under.

All flashings, soakers, cappings, valley and gutter linings and other weatherings should replace the original material such as lead. If the original material is unknown, modern materials would be appropriate.

Sandstone ridge pieces are to be re-laid on a lime mortar bed (see above). The joints should be carefully finished with a minimum of exposed mortar.

Roofing felt shall generally be not be used when re-roofing traditional farm outbuildings. Leave the underside of the slates/tiles exposed or to apply lime mortar as torching.

Existing cast-iron or timber rainwater goods shall always be repaired and made good rather than replaced. Any new or replacement rainwater goods must match the original material and pattern. If the original material is unknown, modern materials would be acceptable. Gutters and downpipes shall have a black painted finish. All joints should be made watertight with mastic joining compound. Downpipes should be secured with nails or screws and wooden bobbins, and downpipe joints wedged and putty pointed.

The floors of old buildings may retain archaeological deposits and artefacts which reflect their past use. For this reason, wherever possible, original floors must remain undisturbed.

Original floor coverings often still exist under layers of concrete. It is possible with care to remove the concrete without too much damage to the materials below — these can then be repaired as necessary.

Upper-floor repairs shall be carried out with timber boards of matching material, width and thickness. Every effort shall be made to retain floor beams and joists. Repairs to their bearing ends are often all that is required.

Regarding surface treatment of old floor boards, these should never be sanded. Solvent (non-caustic) strippers are successful in removing oil paints, tar and some emulsions. Used in poultice form they help to dislodge paint embedded in grooves. Appropriate methods should be used to avoid damaging the material.

Existing cobbles of suitable dimension are to be re-used where possible. New cobbles need to match the existing in size, colour and texture.

All cobbles are to be laid very tightly jointed and interlocking, with their long axis pointing downwards, with as level a top surface as possible and with surface joints no more than 10-12mm wide.

Cobbles should be bedded into a material to match the original; earth, sand or mortar (see mortar).