{"product_id":"concealed-post-base","title":"Knife Plate Post Base","description":"\u003cp\u003eA concealed post base holds the bottom of a timber post to a concrete slab or footing with a steel knife plate that goes up into a slot in the post's end, bolted through the post. Hide the plate in a mortise, so only the bolts show, or let its edge show through a slot sawn across the post. The post can stand on a standoff plate, which lifts its end grain off the base. Set your post's real size and the slot you'll cut below, and it's made to fit. Also called a knife plate post base or a concealed column base.\u003c\/p\u003e\n\u003ch2\u003eHidden or through\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eHidden in a mortise.\u003c\/strong\u003e The knife plate goes into a slot plunged into the post's end, with wood left at both ends, so only the bolt heads and nuts show. Its top corners are clipped to clear the radiused corners a mortiser's bar leaves. With a standoff plate, the knife plate widens below it into a foot as long as the standoff plate, and the standoff plate is slotted over the knife plate and sits on the foot's shoulders.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eThrough slot.\u003c\/strong\u003e The slot is sawn right across the post's end, so the knife plate's edge shows on two faces. The knife plate can be the post's full width, or a little short of it so a post that shrinks doesn't leave steel standing proud. With a standoff plate, it is two halves, one each side of the knife plate, on webbing.\u003c\/p\u003e\n\u003cp\u003eEither way, nothing is welded on top of the standoff plate, where the post bears. Its welds are underneath.\u003c\/p\u003e\n\u003ch2\u003eCutting the slot\u003c\/h2\u003e\n\u003cp\u003eThe configurator tells you the slot to cut: 1\/8\" wider than the knife plate, 1\/8\" deeper than it is tall above the post's end, and, for a mortise, 1\/8\" longer than the knife plate at each end. Center it on the post both ways, within 1\/16\". Lay it out from one face of the post, and cut the post's end square first: an end 1\/16\" out of square across 5 1\/2\" leans a 10-foot post about 1 3\/8\".\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eA mortise's corners.\u003c\/strong\u003e A chain mortiser's bar leaves its cut rounded at each end, to the radius of the bar's nose. Half the length of a single plunge, measured along the slot, is that radius. Choose a corner clip at least as large as your bar's nose radius, and cut the mortise the 1\/8\" deeper the configurator asks: the knife plate can then sit anywhere along its mortise and still clear the corners. The configurator shows the largest nose radius each clip clears. Match the knife plate's thickness to the slot your tool cuts, and if the slot is more than 1\/8\" wider than the knife plate, shim it tight. Check that your tool plunges as deep as the slot the configurator gives.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eA sawn slot.\u003c\/strong\u003e A circular saw leaves the slot's top curved where the blade stops. Carry the cut off both faces, finish its top square with a handsaw or chisel, or use a bandsaw.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eWith no standoff plate,\u003c\/strong\u003e the knife plate's welds run along the base where the post bears, so chamfer the slot's mouth 3\/8\" at 45 degrees to clear them.\u003c\/p\u003e\n\u003ch2\u003eThe standoff plate and webbing\u003c\/h2\u003e\n\u003cp\u003eThe standoff plate lifts the post's end off the base, so its end grain can drain and dry. The gap under it is at least 2\", or half the reach in from the plate's edge to the knife plate where that is more, so the welds under it can be made. Four 1\/2\" drain holes through the standoff plate, beside the knife plate, let water through to the base. Set the standoff plate a little inside the post's faces, about 1\/4\", so water running down the post drips past it rather than onto a ledge.\u003c\/p\u003e\n\u003cp\u003eWebbing is two upright plates welded under the standoff plate, one each side of the knife plate. It makes the standoff plate stiffer. Whether your post needs webbing, and how thick, is for your engineer. A through slot's standoff halves always have it.\u003c\/p\u003e\n\u003cp\u003eThe International Residential Code's rules on protecting wood from decay (section R317) are why builders look for a standoff. Whether your post needs one, and what else it needs, is for your local code and building official to say. With no standoff plate, end grain sits on steel, so that style suits covered or interior posts. Don't seal around the base, and keep the slot and the drain holes open: end grain that stays wet is where posts rot.\u003c\/p\u003e\n\u003ch2\u003eAnchors, and the nut under a standoff plate\u003c\/h2\u003e\n\u003cp\u003eThe base has four anchor holes, one near each corner. Their holes are the rod's diameter plus 1\/16\", or larger, as you choose, for cast-in rods that don't land exactly where the template says.\u003c\/p\u003e\n\u003cp\u003eFor a new pour, choose deformed bar anchors instead: two, one each side of the knife plate, or four near the corners, 1\/2\" x 8-1\/8\" or 3\/4\" x 12-3\/16\", each welded under the base with a fillet all around. Hold the base at its height and place the concrete around them. With no nuts, nothing has to clear the post or the standoff plate.\u003c\/p\u003e\n\u003cp\u003eWhere an anchor is clear of the post and the standoff plate, a socket reaches its nut from above, and you can set the base and tighten it before the post goes on. Where an anchor is under the standoff plate, a wrench has to come in from the side, and the nut needs room to be started: the configurator keeps the gap tall enough for a washer, a nut started on the rod's tip, and 1\/4\" of rod past it. It gives the window the rod must end in, measured above the concrete. Use a threaded rod that takes a washer and nut, ending inside this window, and set and cut it to length before setting the base. A taller gap widens the window.\u003c\/p\u003e\n\u003cp\u003eThe anchor's type, size, depth, and distance from the concrete's edge are for the anchor maker's instructions and your engineer.\u003c\/p\u003e\n\u003ch2\u003ePutting it in\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eA hidden knife plate:\u003c\/strong\u003e fit the post over the knife plate on sawhorses, drill through the post from both faces using the knife plate's holes, and bolt it. Then stand the post up and anchor the base.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eA through slot:\u003c\/strong\u003e set and anchor the base first, then lower the post over the knife plate and bolt it.\u003c\/li\u003e\n  \u003cli\u003eMeasure the delivered part, not the drawing, before you drill: the bolt holes are cut where the configurator shows them, and the knife plate is square to the base within 1\/16\" over its height.\u003c\/li\u003e\n  \u003cli\u003eShims or grout under the base lift it: measure an anchor's projection from the base as set. A base 1\/16\" out of level across 8\" puts a 10-foot post about 15\/16\" out of plumb.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eThe welds\u003c\/h2\u003e\n\u003cp\u003eEvery joint is a fillet weld on both sides. You choose each joint's fillet, from 1\/4\" up to the thinner plate it joins: the knife plate to the base, the standoff plate to the knife plate, and the webs. A larger fillet takes more passes and costs more: 1\/4\" is one pass, 3\/8\" and 1\/2\" are three, and 3\/4\" is six. The cart line and the shop's paperwork list each one.\u003c\/p\u003e\n\u003ch2\u003eSizes it is made in\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePost:\u003c\/strong\u003e 5\" to 12\" each way, for 6x6 to 12x12 posts, surfaced or rough-sawn.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eKnife plate:\u003c\/strong\u003e 1\/4\", 3\/8\", 1\/2\", or 3\/4\", 2 1\/2\" to 12\" long, and 3\" to 18\" into the post.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eStandoff plate:\u003c\/strong\u003e 1\/4\", 3\/8\", 1\/2\", or 3\/4\", its gap 2\" or more, its size up to the base's.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBase plate:\u003c\/strong\u003e 3\/8\", 1\/2\", or 3\/4\", up to 24\" each way, with four anchor holes for 1\/2\" to 1\" rods, or two or four deformed bar anchors welded under it.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBolts through the post:\u003c\/strong\u003e 1\/4\" to 1\", in one row or two.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003eSizes are set to the 1\/8\". The configurator opens on a rough-sawn 6x6 in a mortise, on a 1\/2\" standoff plate 2\" up, with a 1\/4\" knife plate and two 5\/8\" bolts, on a 9 1\/2\" square base.\u003c\/p\u003e\n\u003ch2\u003eWhat a post base doesn't do\u003c\/h2\u003e\n\u003cp\u003eA post base holds the bottom of a post in place. A post base doesn't brace a post: it doesn't keep it from leaning, however many anchors and bolts it has. A post that stands alone, like the post of a carport or pergola with no bracing, needs to be braced some other way. Ask an engineer.\u003c\/p\u003e\n\u003ch2\u003eQuestions\u003c\/h2\u003e\n\u003ch3\u003eCan I see the knife plate in a through slot?\u003c\/h3\u003e\n\u003cp\u003eYes: its edge shows on the two faces the slot runs out through. Choose the hidden style to keep it out of sight.\u003c\/p\u003e\n\u003ch3\u003eIs the post treated?\u003c\/h3\u003e\n\u003cp\u003eIf your post is preservative-treated, ask your building official what finish the steel needs where it touches the wood. Galvanizing is by quote, and it adds substantially to the lead time.\u003c\/p\u003e\n\u003ch3\u003eWhat connects the top of the post?\u003c\/h3\u003e\n\u003cp\u003eA \u003ca href=\"\/en-ca\/products\/post-cap\"\u003epost cap\u003c\/a\u003e seats a beam on the post. For a plate in a slot between two timbers, see the \u003ca href=\"\/en-ca\/collections\/splice-and-knife-plates\"\u003esplice and knife plates\u003c\/a\u003e.\u003c\/p\u003e\n\u003ch3\u003eMy design is too large to buy online.\u003c\/h3\u003e\n\u003cp\u003eSend it through the \u003ca href=\"\/en-ca\/pages\/contact-us#quote\"\u003equote form\u003c\/a\u003e. Bases outside the configurator's range are made to order from your numbers or your plans, and custom design costs nothing extra: you pay for the steel and its welds.\u003c\/p\u003e\n\u003ch2\u003eThe basics\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eA36 steel plate, laser cut and welded in our ISO 9001 shop in Texas.\u003c\/li\u003e\n  \u003cli\u003eHoles are cut to the sizes you choose. Bolts and anchor rods aren't included; deformed bar anchors, if you choose them, come welded on.\u003c\/li\u003e\n  \u003cli\u003eEnter your timber's real size, not its name. \u003ca href=\"\/en-ca\/pages\/timber-connector-guide#measuring\"\u003eHow to measure a timber\u003c\/a\u003e.\u003c\/li\u003e\n  \u003cli\u003eBare steel, or matte black powder coat added in the cart. Galvanizing is by quote.\u003c\/li\u003e\n  \u003cli\u003eShips free in the lower 48 states.\u003c\/li\u003e\n  \u003cli\u003eNo published load ratings. Ask your engineer, and see \u003ca href=\"\/en-ca\/pages\/timber-connector-guide#load-ratings\"\u003ewhat to give them\u003c\/a\u003e.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Timberplates","offers":[{"title":"Default Title","offer_id":67732783989012,"sku":"knife-post-base","price":289.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0432\/5985\/files\/render-knife-base-mortise-10e5dfb6.png?v=1792422733","url":"https:\/\/www.timberplates.com\/en-ca\/products\/concealed-post-base","provider":"Timberplates","version":"1.0","type":"link"}