IS 10850 : 1984Specification for apparatus for measurement of water retentivity of masonry cement

IS 10850:1984 is the specification for the apparatus to measure the water retentivity of masonry cement — the test plate, dish/funnel, vacuum (suction) arrangement, tamper and balance used to quantify water retentivity, the property that *defines* a good masonry cement. Water retentivity is why masonry-cement mortar bonds and cures against thirsty bricks instead of being sucked dry.

It sits with the masonry stack:

• IS 3466 — masonry cement (water retentivity is its key acceptance property, measured by this apparatus)
• IS 2250 — masonry mortars practice · IS 4031 Part 1 — cement physical tests · IS 456 — concrete (where OPC, not masonry cement, belongs)

An absorbent brick sucks water out of fresh mortar by capillarity. If the mortar can't *hold* its water, it dries before the cement hydrates → a chalky, weak, debonded joint. Water retentivity measures the mortar's resistance to that suction, and IS 10850 standardises how it is measured:

• A flow measurement before suction, then the mortar is subjected to a defined vacuum (suction) for a fixed time through a perforated plate/dish, then a flow measurement after suction
• Water retentivity = (flow after suction / flow before suction) × 100, which must meet a defined minimum for the cement to qualify as a masonry cement
• The apparatus (test plate, dish, controlled vacuum, tamper, balance) must be standard or the suction energy — hence the result — is not comparable

The engineering point: water retentivity is the single most characteristic masonry-cement property, and it is meaningless unless the suction is standardised — which is exactly what this apparatus spec exists to do.

Scenario: acceptance of a masonry cement consignment for brickwork/plaster.

Step 1 — apparatus check: confirm the IS 10850 test plate/dish, the controlled vacuum level and duration, tamper and balance are to spec (non-standard suction = non-comparable result).

Step 2 — flow before: prepare the standard mortar, measure initial flow.

Step 3 — apply suction: subject the mortar to the defined vacuum for the fixed time through the perforated plate (simulating the brick's pull).

Step 4 — flow after & compute: measure flow after suction; water retentivity = after/before × 100.

Step 5 — judge vs IS 3466: above the minimum → the cement will hold water against absorbent bricks (full, bonded, properly-cured joints); below → expect dry, chalky, debonded masonry regardless of strength.

The whole acceptance turns on a standardised suction — get the apparatus wrong and you accept a masonry cement that won't perform on a real, thirsty brick wall.

1. Non-standard vacuum level/duration. Water retentivity is defined by a *fixed* suction; any deviation makes the result incomparable and meaningless.

2. Ignoring water retentivity in masonry-cement acceptance. It is *the* characteristic property — accepting on strength alone misses why masonry cement exists.

3. Worn/leaking suction plate or dish. Bypass or inconsistent suction biases the after-flow and the retentivity figure.

4. Treating retentivity as 'nice to have'. Low retentivity directly causes chalky, debonded joints and crazed plaster on absorbent bricks.

5. Forgetting the field corollary. Even a high-retentivity cement still needs pre-wetted bricks and curing — the test predicts behaviour, it doesn't excuse bad practice.

• IS 3466 — masonry cement (water retentivity is its defining acceptance property)
• IS 2250 — preparation & use of masonry mortars · IS 4031 Part 1 — cement physical tests
• IS 456 — concrete (OPC domain — masonry cement is for mortar/plaster)
• IS 5512 — flow table (flow measurement is part of this test)

IS 10850 is a small apparatus standard standing behind the property that *is* masonry cement: water retentivity. Masonry defects are overwhelmingly mortar/plaster defects, and the most insidious mechanism is a thirsty brick pulling water out of the joint before hydration — water retentivity is the engineered resistance to exactly that, and IS 3466 acceptance hinges on it. The result only means something if the suction is standardised, which is the entire reason for this spec. The practitioner point: when assessing a masonry cement, water retentivity is not a footnote to strength — it is the headline property, measured by a standardised suction, and a cement that fails it will give chalky, debonded brickwork and crazed plaster no matter how the strength certificate reads.