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bulk density of sand - civil engineering

bulk density of sand - civil engineering

Sand is one of the fundamental ingredients in concrete. Density is an important parameter for sand. For sand, density is determined by multiplying the relative density (specific gravity) of the sand times the density of water.

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jointing and pointing for stone paving - dry grouting

jointing and pointing for stone paving - dry grouting

Dry grouting is method of using a dry mix of sand and cement to fill joints in paving, and then rely on natural moisture to hydrate the cement content. Does it work? This page looks at it in more detail.

Considered by some to be a suitable alternative to wet grouting , dry brush-in relies on the complete and total absence of water from the mortar mix and pavement surface during the placement phase to allow the water-free, bone-dry sand/cement mix to flow into the empty joints.

The surface of the paving must be completely dry. Any residual dampness will cause the sand/cement mix to "stick" and will probably result in a stain. Consequently, this is a technique that is only really practical during the summer months.

Use a dry-ish building sand, plastering sand or, if so desired, a Kiln Dried Jointing sand. Some installers like to use a coarser or sharp sand, but this can result in a rough-looking finish when used for dry grouting.

A 3:1 ratio of sand and cement are mixed without the addition of ANY water. None. At all. Not a drop. The resulting powder should be of a uniform colour indicating the sand and the cement are thoroughly mixed. It is then scattered onto the surface of the paving and swept into the joints using a soft brush.

Because the dry sand/cement mix is relatively light in weight, it rarely fills the joint properly; instead, it lies in the joint all fluffy and airy and not very convincing as a jointing medium. The better contractors will use a pointing bar or the blade of a trowel to press down the dry mix, compacting it into the joint and then brushing-in additional mix, repeating this sequence until all the joints are properly filled.

An allegedly easier alternative relies on the surface being sprayed with a fine mist or drizzle of clean water once the joints are filled. This has the effect of washing the dry mix into the joint, and simultaneously providing the moisture needed to initiate hydration of the cement content, but, as the surface is then wet, there is no opportunity to 'top up' joints with additional dry mix. On hot summer days, the surface may dry off in a matter of minutes and the whole process can be repeated until all the joints are properly filled, but these conditions exist on very few days over the course of a working year.

Left to its own devices, and when not wetted at all, dry brushing-in rarely creates a well-filled, structurally competent joint. The resultant mortar is often a crumbly, friable gap filler that has a very limited lifespan and usually offers an excellent home to all sorts of weeds. This is of little consequence to the less reputable installer, as they will be long gone and the money spent by the time problems start to become apparent.

If the contractor is conscientious and ensures joints are properly packed and filled before spraying with water, a reasonable quality joint is possible, but it is unlikely to be as sound as a wet slurry joint. A better joint is possible if dry brushing-in is combined with freshly-buttered joints when flag laying. The butter mortar (a standard wet mortar) contains sufficient moisture to initiate hydration (hardening) of the dry mix brushed in to top up the joint, and, as long as the dry mix is properly pressed down into the joint and the butter mortar, a reasonable joint can be achieved.

With regard to spraying with water, if care is not exercised the cement-rich brush-in mix may be splashed out of the joints to land on the now-damp pavement surface and result in staining or spotting, the avoidance of which, after all, was the reason for using the dry brush-in technique in the first place.

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sharp sand or builders sand ? - mybuilder

sharp sand or builders sand ? - mybuilder

I am laying a patio at home in a couple of weeks. The paving flags are between 22mm-30mm thick. Should I mix sharp sand with the cement or builders sand and should I use 5 parts sand to 1 part cement? Thanks.

Hi you use both. The mix is 4 sharp sand, 2 building sand, 1 cement,also put a bit of sbr bonding agent in.Keep the top surface of your flags minimum 150 mil below any damp courses and running away from your house if laying against your house. good luck John

There's more to laying paving than simply the ratio and type of mortar mix. Ask 5 different paviours and you'll get 5 different methods, some use a little sharp sand to strengthen the mortar and some prefer soft only, depending of course on the type of slabs, substrate / ground and how it's been prepared.

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