32 Figure 2 Stainless steel ladder reinforcement to strengthen brick arch are shown to give a guide as to the possibilities for the use of these materials. Where a front wall is not bonded to the return wall, the generally accepted conservation system was to cut out the comer and incorporate a concrete 'elbow' around the comer to bond the two together. It can be seen from Figure 1that the use of a purpose-made stainless steel wire angle around the comer will serve the same tying purpose whilst retaining the flexibility. The constantly reoccurring problem of brick arches that have deflected, distorted or cracked can be dealt with by taking some of the load away from the arch and distributing it to the window reveals by the use of stainless steel ladder reinforcement in the brick courses immediately over the arch, as Figure 2. Although the sketch indicates reinforcement in one course, we have on occasions reinforced, say, f<?urcourses directly above the arch in this manner. The question that should be ask is "why go to all this effort when the brick arch could simply be rebuilt?" Experience suggest that it is very difficult indeed to repair a brick arch so that it retains reasonable load-bearing capability without making the repair very obvious, and of course to replace the arch will make it look pristine and new even if constmcted in traditional materials. If one is dealing with a Georgian building with rather fine brickwork, with cracks mnning up through the external face, then rather than taking out substantial areas of brickwork and rebonding across we have used the 50 mm wide ladder reinforcement simply let into the brick joints by cutting back some 55mm and bedding the stainless steel into the joint with a lime mortar. The effect of this is to spread the load around the crack rather than concentrating it all at one point. The lack of lateral restraint referred to many time in these articles can be dealt with using the simple 'BAT' strap linked to the floors, but there are also now available helical bars that can be used into the end ofa particular floor joists. This system works by a hole being drilled through the masonry; a helical bar inserted and twisted into the joist end, and then the hole filled with resin with the external hole made good with mortar to match existing. As a practice we have Figure 3 Mortar to match existing wall in texture and colour for many years, been using the conventional stainless steel threaded bar set into resin to tie the external skin of a Georgian wall to the inner skin, but we have recently been made aware of a very much better design which we have now adopted on most of our repair projects. The problem always was that if you drilled into a cavity you were never really sure where the grout went once in that cavity. Indeed I can remember at a Church in Bedford where we poured many litres of grout into a stone column simply because we could not contain it. The system illustrated in Sketch 3. gives a very much better fixing into a wall when one is not sure of the extent of the cavities. The system works on the basis of drilling the hole through the wall and inserting either a solid or hollow stainless steel tube of round or square section. Surroundingthetubeorbarasitisinserted is a fibrous bag into which a cementitious grout is pumped from one end. The pressure of the grout is carefully controlled and the bag is strong enough to follow the profile of the cavity, bonding the whole stmcture together. Again I am content that the flexibility of the stmcture is maintained using this system. The company manufacturing these fixings provides a back-up service to the consulting engineer, advising on the suitability of the particular type of fixing for the particular problem and if necessary giving the strength characteristics of the various fixings. I am advised that these fixings have been drilled over very substantial lengths through, for example, bridge abutments giving the stmctures a substantially extended life. On a similar subject related to walls but not on new materials for repair, we have recently been looking at the use of hydraulic lime mortars which particularly interests us because of the requirement o, ·:r?cq· : . ~ : • d d - - y -,~_-:-:;===d '17,. Cementitious grout pumped into fabric bag after stainless steel tie is placed in repairing an historic stmcture, to have an initial set without having all the problems of using Portland cement. On two occasions recently I have been to Belgium to look at stmctures which have been repaired using hydraulic mortars that are being imported through Belgium to the United Kingdom from a quarry in Italy which has been in operation since the 12thcentury. Thecompanyimporting the hydraulic lime has carried out a great deal of experimentation and trials and I have been able to see some very successful results. The company sells the mortar mixes by the bag in various grades for various uses. They have, for example, an insulating grade, a water-resistant grade forthe base of walls, a normal-use external grade, and combinations of materials which they can put together for particular purposes. The buildings I was able to see in Belgium suggest that the material performs extremely well without the cracking problems associated with cement-based mortars and the application problems associated with setting times of the lime putty mortars. We are endeavouring to find a project where we can use the hydraulic lime which would be linked with advice from the company. We are advised that the company would look at the particular problem and advise a specification and give a guarantee as to the suitability of their material. I have only touched on the methods and materials of repairwhich are available to the Conservation Officer, architect and engineer. Many more are available and there are now companies which have, or appearto have the interest of the building at heart. I believe this to be very encouraging. Brian Morton is Consultant to The Morton Partnership Ltd CONTEXT49
RkJQdWJsaXNoZXIy MjgyMjA=