54 Feature/Bricks & Blocks
HOUSEBUILDING TARGETS: Thin Joint Technique Can Help, Says Hanson
THE THIN JOINT SYSTEM OF MASONRY CONSTRUCTION HAS BEEN USED IN MAINLAND EUROPE FOR THE PAST THREE DECADES BUT HAS ONLY APPEARED ON UK BUILDING SITES OVER THE LAST DECADE AND IS STILL NOT YET IN WIDESPREAD USE ALTHOUGH IT CONTINUES TO FIND FAVOUR WITH A GROWING NUMBER OF BUILDING CONTRACTORS.
Hanson Building Products is a leading proponent of the thin joint system using Thermalite Thin Mortar r and Aircrete blocks.
The advantages claimed for this method of construction cover speed, accuracy, reduced waste, cost effectiveness and, in an industry increasingly dominated by rigorous energy-saving requirements, a contribution to reducing heat lost through the building envelope.
This sounds impressive for a system that uses a pre-mixed cement-based mortar that is mixed in a bucket. Just add to water and stir. Thin joint is in fact the only method of on-site build involving masonry now recognised as a modern method of construction or MMC. As the name confirms, thin joint reduces the thickness of the mortar course between blocks to a minimum. A traditional sand and cement joint is 10mm whereas thin joint does the job with a depth of just 3mm. The consistency of the joint is determined by use of a purpose-designed serrated scoop applicator.. For longer runs of blockwork a pumped system of application is available to further enhance speed of build. Just how fast is the process? An independent test
commissioned by Thermalite and carried out by chartered surveyors Percy Howes concluded that thin joint blockwork can be laid twice as fast as the traditional sand and cement method. Speed trials on 6m lengths of wall with a return, found Thermalite Shield blocks and general purpose mortar taking 302 minutes and 30 seconds to lay while the same type of block laid with thin layer mortar clocked up just 146 minutes and 20 seconds. So as to eliminate the all-to-inconsistent human element, the same brickie laid the blocks in all cases.
The tests recorded a laying rate of 9.72m2/hour when using the traditional method against 20.66m2/hour using the thin joint system. The area laid can be enhanced still further if the builder uses Thermalite’s Large Format Blocks which have a face size equal to two traditional blocks. Typically, walls constructed using Thermalite blocks and thin layer mortar will be stable after 60 minutes. This allows the amount of walling that can be built to be increased allowing the early installation of other components, such as floors and roof timbers.
In monitoring the tests Percy Howes also noted that areas surrounding the work were “significantly cleaner.” With the thin joint system there was “No mortar build up at the base of the panels, unlike the panels where traditional mortar had been utilised.”
By reducing the amount of mortar in any given area of wall by at least 70%, compared to a general purpose mortar joint, heat loss through the mortar joints is also reduced. An improvement in U-Values of up to 10% can be achieved using Hanson’s Thermalite Thin Joint System.
Walls built with thin layer mortar also offer increased air tightness of the construction which reduces the amount of ventilation heat loss through the building fabric. Independent tests carried out by the Building Services Research and Information Association (BSRIA) gave air tightness results for Thermalite 100mm blockwork and Thermalite Thin Layer Mortar of better than 0.10m3/hm2, the lowest possible score.
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