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<\/a>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 This is a problem caused by electrolysis,\u00a0 where a steel post, flash-coated with zinc, is in contact with concrete, damp, and air.<\/p>\nIn most cases the SHS is in good condition within a few centimetres of the surface of the embedding concrete, rusting taking place at the junction.<\/p>\n
In concrete slab construction, for decades it was allowable to have the SHS posts exposed at the slab perimeter, with no insulation.\u00a0 Properly hot-dipped galvanised posts survive longer in this situation, but unprotected posts straight from the shop are susceptible, es THE FIX is tedious and time-consuming.<\/p>\n 1)\u00a0 Clear all obstructions (paths, bricks, garden, sheds, water tanks etc..) from around each steel post.<\/p>\n 2)\u00a0 Excavate a good-sized hole (say 500mm square at least) exposing the post where it penetrates the slab, down to the concrete footing.\u00a0 This could be any depth.<\/p>\n 3)\u00a0 The extent of the corrosion should now be apparent.\u00a0 In the event that the post has completely rusted through, read further, but in most cases it is now necessary to expose the rust area by chipping away concrete both at the slab and footing until clean steel appears.\u00a0 Use a small rotary hammer with a 25mm chisel.\u00a0 This will entail creating a shallow pit in the footing around the post.<\/p>\n 4)\u00a0 Having exposed the post to clean steel, chip off all loose rust.\u00a0 A rattler attachment on the hammer-drill is ideal.\u00a0 It is not necessary to grind down to bright steel.\u00a0 Clean out the hole; a drum vacuum-cleaner is useful.<\/p>\n 5)\u00a0 Coat the post with phosphoric acid (a Rust-Converter type of product), which will pool in a beneficial way at the footing. Brush the liquid 6)\u00a0 At this stage prepare steel boxing that will contain concrete which will case the exposed post from the footing to the slab-capping.\u00a0 Order a top-hat section of sheet (say 0.75mm)\u00a0 that can be trimmed to the lengths needed for each post.\u00a0 The section must be 300mm wide and 100mm deep, with flanges of say 50mm against the slab. Corners need a bigger section, shaped similarly to cover the post 100mm thick and extending 100mm on each side.\u00a0 Order the stuff in long lengths and cut off what you need.<\/p>\n 7)\u00a0 When each post has its boxing prepared and tested, have ready a good mix of waterproof concrete 10mm blend with some added Bond-Crete.\u00a0 Brush-coat Bond-Crete onto the post and surrounding concrete, put the boxing in place and carefully back-fill to hold it there.\u00a0 Fill the boxing with the concrete mix, and slope the top to just under the capping.\u00a0 Th Whether this 100mm cladding of concrete requires any anchor-bolts is a point, but the Bond-Crete usually makes a satisfactory adhesion.\u00a0 Time will tell.\u00a0 It’s a bodge anyway, trying to fix a bad initia POSTS RUSTED THROUGH;\u00a0 Should this be the situation, the only answer is welding.\u00a0 Free-standing SHS posts into individual footings We’re all learning here.<\/p>\n","protected":false},"excerpt":{"rendered":" SHS (square hollow section) STEEL CORROSION\u00a0 AT CONCRETE SLAB PENETRATION. \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 This is a problem caused by electrolysis,\u00a0 where a steel post, flash-coated with zinc, is in contact with concrete, damp, and air. In most cases the SHS is in … Continue reading <\/a>pecially when soil, garden-beds, et cetera are built up against the footings.<\/p>\n<\/a>The necessity of having a good-sized hole in which to work will now be obvious: all debris must be cleaned out neatly.<\/p>\n<\/a>liberally for a few minutes, then leave to dry, when it will form a protective coating, slightly glossy.\u00a0\u00a0 Any termite-proofing that may be exposed should be left undamaged if possible.<\/p>\n<\/a>ere is no reason why this boxing should not stay in place: it’s an added chore to remove later.\u00a0 Perhaps use Color-bond.\u00a0 Job done.<\/p>\n<\/a>l design.\u00a0 Posts now must be well-wrapped at penetration to prevent electrolysis, and encased in concrete, not exposed at slab-edge.<\/p>\n<\/a>often separate completely, unseen and buried in soil.\u00a0 A total replacement bolted onto the original footing\u00a0 (the hole filled with concrete) is quicker than a repair.\u00a0 If the post is part of the house structure, repair is the only fix.\u00a0 Blast away the slab and footing as above, to expose good steel, grind it clean, cut some corner sections from an offcut of SHS and weld them like splints to the post.\u00a0 Then rust-converter etc. as above.<\/p>\n<\/a>I have photos of this process, taken for the benefit of the building inspector, and following the advice of a friendly engineer.\u00a0 I’ll try and get them up.<\/p>\n