by Joel Hirshberg Originally published October 3, 2012 in the Green Home Guide, a service of the U.S. Green Building Council

Q: I would like to put a sealer on our gypcrete floor before we move in because we don't have enough money to cover the whole floor. The heating is in the floor. Later we would like to install tile in some areas and click together wood like flooring in others. We live in Interior Alaska there for have the additional difficulties and have fewer places to shop for products in stores and when shipping the cost and freezing conditions come into concern.
—Asked by James Sharp, Healy, AK

A: Gyp-Crete, an underlayment manufactured by Maxxon, was not designed to be used as flooring by itself as it is too soft and porous. It’s a light weight concrete used primarily as an underlayment for sound control and fire resistance in multi-family buildings, but is also used in residential areas to smooth out rough subfloors or to provide a substrate for radiant heated floors.

Primers and Adhesives

Although it’s very stable chemically speaking, Gyp-Crete is relatively soft and becomes dusty which makes it challenging for flooring contractors. There are lots of posts on the internet about problems related to trying to glue wood, concrete or tile directly to Gyp-Crete. This is because nothing sticks very well to it unless you use the proper primers and adhesives.

These specialty primers and adhesives are expensive, hard to find and usually toxic. Look up Maxxon, Hacker or Dependable as they all make a variety of products for professional use only. These primers and adhesives are not DIY type products. They require experienced professionals to install and I don’t recommend that you do it by yourself.

Flooring on Gyp-Crete

When used under floating floors, Gyp-Crete does not need to be sealed or primed as there is no off-gassing of VOCs, and no adhesive is required. However, you should still exercise caution if you plan on walking on the Gyp-Crete before you put flooring over it. If you can’t afford to buy flooring at this time, you could lay down some 6ml plastic to control the dust and then some plywood or RamBoard (a recycled protective covering) on top to hold you over.

Health Considerations

FYI--Gyp-Crete is made with gypsum which is mainly calcium sulfate, Portland cement, silicates and small amounts of titanium dioxide. The silicates and titanium dioxides are possible lung carcinogens. The dust from calcium sulfate and silicates has an irritant action on mucous membranes of the respiratory tract and eyes. There have been reports of conjunctivitis, chronic rhinitis, laryngitis, pharyngitis, impaired sense of smell and taste, bleeding from the nose and reactions of tracheal and bronchial membranes in exposed workers. Most of these symptoms arise from over-exposure of the dust on a daily basis which you might encounter if walking on it every day.

Some of Maxxon's Gyp-Crete products are Green-Guard Children and Schools certified, which means they’re compliant with very low VOC levels; however, this does not mean they are safe for people with chemical sensitivities or pregnant women; and low VOC does not always equate with non-toxicity or health. (For more info on VOCs and health refer to: Your Health: A Deeper Look at VOCs and Formaldehyde)

To avoid exposing yourself to unknown chemicals requires knowledge and experience. You have to do your homework.