Moisture: A natural disaster BY DARRYL WILSON, MAPEI TECHNICAL SERVICES
View of moisture issue with wood flooring.
View of moisture underneath carpet moisture.
Moisture issue underneath tile.
Vinyl sheet glue re-emulsification through seam.
30 Ops Talk • Fall 2010
There are many types of beautiful and stylish floors in schools – marble foyers in school entrances, ceramic tile in laboratories, coloured and crafted sheet vinyl in hallways and class rooms, hardwood floors in gymnasiums, carpet in administrative offices, and rubber flooring in areas surrounding aquatic centres. The average cost for installed flooring runs around $4 to $15/square foot for carpeting; $10 to $14/square foot for hardwood; $19 to 60/square foot for marble; $7 to $14/square foot for tile and $3 to $7/square foot for vinyl (according to www.costhelper.com). When work is complete, the flooring represents a significant investment by school facilities’ management. In certain circumstances, the concrete subfloor can compromise this investment, causing costly defects in the floor covering. If the water-to-cement ratio in the concrete mix is too high, or if the concrete slab does not cure properly, it can become overly porous. As a result, the tiny channels within the concrete may remain permanently connected, increasing the permeability of the concrete slab and the likelihood of moisture movement up through the slab to the flooring. In the absence of a vapour barrier/retarder, natural moisture such as ground water can become a problem. Artificial sources of moisture like irrigation problems, incorrect exterior grading or broken plumbing can also lead to problems with moisture control. The result can be serious failures in the flooring. In wood floors, moisture could lead to wood crowning or cupping, making that smooth gym floor more like an obstacle course. Carpet could start to buckle and smell due to excess moisture, mould and mildew. Moisture could cause efflorescence of cement-based grout in tile joints, leaving unattractive salt deposits in the grout lines separating the tiles. Stone is known for being sensitive to moisture and could sometimes change colours and/or curl in the presence of too much moisture. When sheet vinyl and other resilients are installed in conditions of excess moisture, adhesives will emulsify, turning gooey and losing their bonding strength. These conditions occur because moisture vapour is governed by the laws of physics. Water vapour travels from one area to another whenever a vapour pressure difference exists. In a controlled climate (HVAC), the temperature in a room is usually 70 to 80 degrees Fahrenheit, and the relative humidity is 30 to 50 per cent. Under these conditions, the air above the water-laden slab wants to hold more moisture and satisfies itself by pulling moisture from the slab. The warmer the room is, the more water is absorbed. Calcium chloride testing, which is
