Why, how and when should I seal my subfloor concrete?

February 11, 2012 by Renzo

The subfloor deck of a data center (computer room) is typically made of concrete and carries the physical load of the room, while at the same time directing the conditioned air to the equipment that rests on it. Concrete is a great structural foundation for most building applications, however, if concrete is not properly sealed – it can cause downtime in a data center environment. Some common dangers concrete floors can pose to data centers are outlined in this document.

Particulate Trapping

Unsealed concrete causes issues to a data center in multiple ways. Concrete is extremely porous, so it regularly traps and releases particles with which it comes into contact. Over time gravity helps this porous surface loosely collect many contaminants such as metal oxides, biological growth, and dust contamination. Air pressure or other environmental changes can then release plumes of these contaminants into the air-cooled equipment thereby causing downtime.

Concrete Dusting

Another point of concern is the composition and curing process of unsealed concrete. Concrete continues to cure continually over its lifespan, growing harder and continually turning back into its natural elements (efflorescence process), thus creating concrete dust. Concrete dusting occurs when the elements from the efflorescence process become airborne in the subfloor plenum and migrate to air-cooled equipment.

Three conditions must be present for efflorescence to occur: (1) presence of soluble salts, (2) availability of water to carry the salts in solution, and (3) a pathway for the solution’s migration to the surface (and water evaporation). Of the most common efflorescence salts — calcium carbonate, sodium sulfate, and potassium sulfate — the most prevalent and deleterious, by far, is calcium carbonate. During the cement hydration process, calcium hydroxide, Ca(OH)2, which is slightly soluble in water, is formed. The Ca(OH)2 dissolves and is carried to the concrete surface, where it reacts with carbon dioxide, CO2, in the air to form calcium carbonate, CaCO3, plus water (as shown below).

Ca(OH)2(dissolved) + CO2(dissolved) → CaCO3(solid) + H2O(liquid)

The water evaporates, leaving insoluble CaCO3 on the surface. Since the residue cannot be simply rinsed off with plain water, its removal requires the application of weak acid and/or abrasion; which may be impossible to do on a circuit board. If properly sealed or encapsulated, efflorescence may be stopped.

Improper Sealants For A Data Center

Normal to high profile seals applied to homes, garages or industrial buildings are not adequate for data centers – even if they adequately provide a moisture barrier. Most sealers are made with conductive elements such as minerals, metals and other cross-linking elements. As little as 250 volts of static electricity can cause data and memory loss, resets, erroneous commands, and damage to sensitive micro-circuitry.

LOW P.S.I. RATING – A p.s.i. (pounds per square inch) rating less than 100,000 should not be used. A data center needs a mechanical seal that will adequately withstand the constant air pressure coming from the CRAC units, while still providing a moisture barrier. Normal seals deteriorate too quickly.
COLORED SEALS & COLORED EPOXY SEALANTS – Color is held in seals by the use of metals. Metals create cross-linking which easily conduct static charges. Some colored seals claim to be anti-static; however, static may still occur due to the metals within the seal once the seal has cured. Although the room is grounded, static events still can occur throughout the data center and cause downtime. It is has been learned that as little as 250 volts of static electricity can cause data and memory loss, resets, erroneous commands, and damage to sensitive micro-circuitry.
MINERAL SEALS – Mineral sealants are made of conductive elements. Since static can only be dissipated and cannot be controlled, use of a mineral seal is not sufficient for a data center and may increase the risk of static caused downtime.

Proper Data Center Subfloor Deck Sealant Application

Only a 100,000 p.s.i., low odor, non-conductive seal should be used in a data center. The seal should be clear and not have a colorful finish. It is best to apply the seal before installing the equipment in the room; however, if the data center is already in operation, a seal can still be put in place utilizing proper line-flow techniques from a professional data center sealing company. It is important to check the references of the company before allowing them into the data center, as this process is specialized. Normal contractors that provide floor sealers will not have adequate training to work safely in the data center without causing downtime. A trained technician for data center subfloor seal applications should be able to provide the proper chemical with the above stated qualities and have a track record of successfully working in a data center environment applying the sealant.

REFERENCES
American Concrete Institute, ACI 116R
Technical report — “Evaluation of the Causes of Efflorescence in Concrete Masonry Products and Recommended Guidelines for Efflorescence Control,” Degussa Admixtures (Barbour, Culton, & Nmai), 2005