LDPE plastic sheet for curing, damp-proofing and covering

Sheet specifications

Sheet is sold by weight, and that is where quotes get slippery. Two suppliers can quote the same rupees per kilo, but if one is 15 percent thinner you get more square metres for the money and less protection per metre. Always compare micron and per-kg rate together. How to compare LDPE quotes →

Which micron for which job

This is the table we read out on the phone to site engineers three times a week.

The rule of thumb underneath all of this: cost scales with weight, and weight scales with micron. Doubling micron doubles the cost of covering the same area. So specify for the abuse the sheet will actually take, not for peace of mind.

Working out how much sheet you need

Sheet is priced per kilo but used per square metre, so here is the conversion that keeps a purchase order honest.

The formula

Weight in kg = length (m) x width (m) x thickness (mm) x 0.92

That 0.92 is the density of LDPE, roughly 0.91 to 0.925 grams per cubic centimetre. Thickness in millimetres means 200 micron is 0.2.

A worked example

You need to cover a 20 x 15 metre slab in 150 micron sheet. That is 300 square metres. 300 x 0.15 mm x 0.92 = 41.4 kg. At a hypothetical 130 rupees per kilo, the sheet for that pour costs about 5,400 rupees, or 18 rupees per square metre.

Run the same slab in 200 micron and it is 55.2 kg. Same rate, roughly 7,175 rupees. That 33 percent extra buys you a sheet that will survive being walked on and probably re-used on the next pour, which is often the cheaper decision overall.

Two things that catch people out

• Lay-flat versus open width. A tube blown at 8 ft lay-flat opens to about 16 ft. If you order "8 feet" and mean 8 feet of coverage, say so, or you will get twice what you need.
• Overlap. For curing and DPC you need 150 to 300 mm of overlap at every joint. On a big area that is 5 to 10 percent more sheet than the bare floor area. Add it before you order, not after.

Related reading

LDPE sheet questions