💧 Water Absorption of Masonry Units

Construction PN-EN 772-21

Overview

STATUS (as of 06.11.2026). PN-EN 772-21:2011 “Metody badań elementów murowych — Część 21: Określanie absorpcji wody ceramicznych i silikatowych elementów murowych przez absorpcję zimnej wody” (Methods of test for masonry units — Part 21: Determination of water absorption of clay and calcium silicate masonry units by cold water absorption) — English version, published 26.08.2011, implements EN 772-21:2011 [IDT]. The card has no withdrawal note — the standard is current. In PCA accreditation scopes (copy of the database of 06.11.2026) laboratories cite it as PN-EN 772-21:2011.

SCOPE (clause 1). The standard specifies a method of determining the water absorption of clay and calcium silicate masonry units by immersing them in cold water. Units are sampled according to the relevant part of EN 771 (EN 771-1 — clay, EN 771-2 — calcium silicate); this part of the standard does not cover other types of masonry units.

PRINCIPLE (clause 3). The masonry unit is dried to constant mass, immersed in water and the increase in mass is determined.

PROCEDURE (clauses 5–7). At least six units are tested — unless the product specification requires a larger number. The specimens are dried in a ventilated oven at (105 ± 5) °C to constant mass Md: constant mass is reached when, in two subsequent weighings at an interval of not less than 24 h, the loss in mass does not exceed 0.2 % of the total mass. Before weighing, the specimens are allowed to cool to ambient temperature. Each unit is placed in the water tank, supported off the base so that water is in contact with all its faces. Clay units remain submerged for (24 ± 0.5) h, calcium silicate units for (48 ± 0.5) h. After removal, the water is wiped from the surface with a damp cloth or sponge and the unit is weighed (mass Ms). The balance shall weigh to an accuracy of 0.1 % of the dry specimen mass.

RESULT (clauses 8–10). Water absorption of each unit Ws = (Ms − Md) / Md · 100 %, rounded to 1 %; the result is the mean, also rounded to 1 %. The test report gives, among other things, the sampling method, the description of the units according to EN 771-1 or EN 771-2, the number of specimens, the dry and soaked mass of each specimen, the soaking period in hours and the individual and mean values.

WHAT WE DO NOT GIVE HERE. The test standard gives no requirements or limit values for water absorption — these follow from the product specification and the manufacturer's declaration; nor do we give “typical” water absorption values or a relation between water absorption and frost resistance, because none of the available sources gives them. The standard does not specify the water temperature, other than that the test is carried out in cold water.

Method principle

A masonry unit is dried in a ventilated oven at (105 ± 5) °C to constant mass, weighed (Md) and immersed in cold water — a clay unit for 24 h, a calcium silicate unit for 48 h. After removal and wiping the water from the surface with a damp cloth or sponge, it is weighed again (Ms).

Ws = (Ms − Md) / Md · 100 %

Constant mass: loss of not more than 0.2 % between two weighings at least 24 h apart; immersion time with a tolerance of ± 0.5 h. The result for each unit and the mean are given rounded to 1 %.

Applications

• Clay masonry units (bricks and other units according to EN 771-1) — water absorption by immersion in cold water
• Calcium silicate masonry units (according to EN 771-2) — water absorption after 48 h immersion
• Testing of a sample taken according to the relevant part of EN 771 — water absorption requirements are set by the product specification

Key parameters

Standard

Standard number

PN-EN 772-21:2011

Title (PL)

Metody badań elementów murowych — Część 21: Określanie absorpcji wody ceramicznych i silikatowych elementów murowych przez absorpcję zimnej wody

Title (EN)

Methods of test for masonry units — Part 21: Determination of water absorption of clay and calcium silicate masonry units by cold water absorption

Step-by-step procedure

1. Sampling

   Take the units according to the relevant part of EN 771 — at least six, or more if required by the product specification (6.1).

2. Drying to constant mass

   Dry in a ventilated oven at (105 ± 5) °C until, in two subsequent weighings at an interval of not less than 24 h, the loss in mass does not exceed 0.2 % of the total mass. Allow the specimens to cool to ambient temperature before weighing; record the mass Md (6.2).

   🌡 Temperature: 105 ± 5 °C

3. Immersion

   Place each unit in the water tank (supported off the base, water at all faces). Leave clay units submerged for (24 ± 0.5) h, calcium silicate units for (48 ± 0.5) h (clause 7).

   ⏱ Time: (24 ± 0.5) h — clay; (48 ± 0.5) h — calcium silicate

4. Weighing after soaking

   Take out the unit, wipe the water from the surface with a damp cloth or sponge and weigh; record the mass Ms (clause 7).

5. Calculations

   For each unit Ws = (Ms − Md) / Md · 100 %, rounded to 1 %; calculate the mean, also rounded to 1 % (clauses 8–9).

6. Test report

   Give the standard, the organization and method of sampling, the date of testing, the description of the units according to EN 771-1 or EN 771-2, the number of specimens, the dry and soaked masses, the soaking period in hours, the individual and mean values and any remarks (clause 10).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard gives no safety requirements — the rules for working with a hot oven and heavy masonry units are set by the laboratory on the basis of a risk assessment

Frequently asked questions