LAYING A CONCRETE FLOOR

Dominion, Volume 20, Issue 57, 1 December 1926, Page 17

LAYING A CONCRETE FLOOR

WORKING RULES IMPORTANCE OF FOUNDATION The first thing to be considered in laying a concrete floor is the nature of the foundation. If the ground is at all spongy, it will be necessary to .take out enough of the soft stuff to give a good firm bottom, which should then be made roughly level. On a clay or rotten rock foundation the preparation amounts simply to tire removal of soil or loose material, subject, of course, tp there being space for at least a few inches of concrete even on a solid foundation. Forms or guide boards are needed all round the outer- margin of the floor. These may consist of 8 or 9 by 1 boards, set up on edge and nailed firmly to pegs which hare previously been so driven in that levels will be maintained. The “lay” or finished surface of the floor will be determined by the care with which the guide boards are set up and aligned. In concreting a cellar you could set them on tlufe dead level each .way, but for an out-house or garage it is usually best to give a fall towards the doorway for swiliirog-out purposes. This fall need only be slight, lin. in 6ft. being plenty for the surface drainage, though you can witffi advantage make it steeper at the entrance, and form side channels, if desired, bv setting in wooden moulds or us/ng half-round gutter as shapers. The guide-boards may then be set true to rfie finished surface by means of a spimt level and a long straight-edge. ® the floor is a large one it may be iiiobessary to provide an extra board across .the short way, so that yon may parry out the concreting in 4ft, or sft, •Wjfiths. The thickness of the floor may be .anything up to nine inches, though on good foundations half this thickness may suffice. Where a deep floor is laid, the lower two-thirds of the concrete may consist of a six to one mixture made up as follows:—Five parts of coarse gravel or ballast, 1 part of clean coarse sand, 1 part of Portland cement Tire top layer will be of 4 to 1 concrete, consisting of 4 parts of fine gravel and 1 part of Portland cement. If an extra sm,oo,th finish ; is required use rather less of the 4 to 1 mixture and float the -floor last with cement mortar (1 of sand and 1 of portland cement). To mix the concrete lay some rough boards down close by the site, and. have the gravel, etc., measured and tipped on to these. The stuff Should be turned over thoroughly with a shovel once or twice in the dry state first, as this ensures the even distribution of the cement through the aggregate, which is important. Water is then added gradually, as the turning process is continued until the material will just run off the shovel with tolerable ease. Fill the concrete into buckets and dump these -over the site, roughly spreading with the shove! until the required thickness is 01/ti'ined for the lower layer, when it may be left until next day for the finishing layer. No more concrete must be made than can be u'sed up in one day. For the finishing layer measure and mix the fine gravel and cement as in the former case. If you do not require the fine mortar top, one operation will now give the finished surface. Here a float-rule will be required, which is merely a stout wooden straight-edge long enough to span over the guide-boards. Dump the fine gravel as before, and spread roughly with the spade. Then pass the float-rule down from the top end of the-floor by a gentle sideways movement, which will have the effect of carrying down the surplus concrete

and leaving a smooth surface behind A little judicious watering with a finerose watercan greatly aids the .floating off. With care you' should get a perfect, true surface, which .can 'then ,be left ’to set hard. The floor should not be used for at least a week after the final floating off, though it is better, if possible, to avoid putting any heavy material on it for a fortnight, after which it should be as hard as a rock.

On soft or marshy gro.und it may; be necessary to reinforce the floor. This is easily managed by pegging down on the’ lower layer of coarse material some patent mesh or stout wire netting. Over ‘this the fine gravel concrete is laid, so as com- i pletely to cover the netting, no portion of which should on any account be exposed. -When set this floor-will remain permanently free from cracks, > and will not yield to any ;Settlenie,nt j of the ground -beneath it.