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Anonymous
 
Posted on Friday, July 21, 2006 - 02:14 pm:   Edit PostDelete PostPrint Post

Can anyone tell me pros of cons of using gypcrete 2000 vs standard lightweight concrete? This is a commercial hotel application over plywood subfloor.
John Carter (Unregistered Guest)
Unregistered guest
Posted on Saturday, April 28, 2007 - 09:52 am:   Edit PostDelete PostPrint Post

Gypsum is suitable for walls, but not for floors. It is not adequate for floors because it is soft and it absorbs water.

Lightweight concrete is portland cement and lightweight aggregates. Much better durability.
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec

Post Number: 368
Registered: 05-2003
Posted on Saturday, April 28, 2007 - 01:20 pm:   Edit PostDelete PostPrint Post

I am not a big fan of gypsum based leveling products, like gypcrete, we usually specify cementitious based products; it would be important to check with the manufacturer of the flooring that is to be applied over the gypcrete, gypcrete re-emulsifies when exposed to moisture, and will suck moisture out of the flooring application, which can lead to cracking of the gypcrete, so typically gypcrete has to be sealed (other problems can develop) or an additional WP membrane placed over the gypcrete. The only time I have voluntarily used gypcrete is when there is a sound proofing issue, espically in wood construction.
John Regener, AIA, CCS, CCCA, CSI, SCIP
Senior Member
Username: john_regener

Post Number: 294
Registered: 04-2002
Posted on Sunday, April 29, 2007 - 01:11 pm:   Edit PostDelete PostPrint Post

I frequently encounter mis-use of the term "lightweight concrete" for floor fill material. There are four cementitious floor fill products that I know.

1. Lightweight concrete: This is a structural product. It is commonly a component of composite construction of steel floor deck and concrete fill. The "lightweight" attribute is found in the aggregate. It is lighter weight than typical concrete. The aggregate is often something like an expanded or volcanic aggregate.

2. I usually specify "cementitious underlayment" for filling and leveling an existing concrete floor. Products by Ardex and others, which have high compressive strength, rapid curing and self-leveling are specified. When a floor is "floated", a thin layer of self-leveling, portland cement-based underlayment is applied and self-levels into a hard, smooth finish.

3. One of the two non-structural floor fill products is cellular concrete. Elastizell is a common brand. It is portland cement and sand with a foaming agent that is mixed and pumped to the application point. It has high water content and levels out with minimal manual troweling. As it dries, cellular concrete cracks. It must. It has a lot of water content. After the initial placement is dry, some quality-conscious contractors apply another thin layer of cellular concrete to fill the cracks and lock the fill segments together.

4. The final type is gypsum based, with the common brand named Gypcrete. There are two types of Gypcrete: regular Gypcrete and Gypcrete 2000. The latter has 2000 psi compressive strength when cured while the regular is something like 1700 psi. The compressive strength issue is important when considering rolling loads across the floor which could cause breakdown of the fill. As to water-resistance of the product, it is a less severe problem than it was about 20 years ago. Gypsum cement floor fill should not be used in bathrooms, in my opinion, although the manufacturer may tout some coatings to deal with the problem. The big advantage of gypsum cement floor fill, in addition to self-leveling, is that it does not shrink like cellular concrete. Dusting of the surface means a conditioner or sealer is needed for adhesive application of floor coverings. I think it is unsuitable for mortar set ceramic tile, even thinset.

I agree with the recommendation to contact a manufacturer's rep. Ask for the advantages and disadvantages of the product, including fire resistance and acoustical properties.
Anne Whitacre, FCSI CCS
Senior Member
Username: awhitacre

Post Number: 540
Registered: 07-2002
Posted on Wednesday, May 02, 2007 - 06:44 pm:   Edit PostDelete PostPrint Post

the underlayments I use are all in the self-leveling, 4000 psi type. the gypsum based products do absorb water and also break up too easily under point loading; I use only cementitious products -- the same ones that John has under his point 2 above.
John Regener, AIA, CCS, CCCA, CSI, SCIP
Senior Member
Username: john_regener

Post Number: 296
Registered: 04-2002
Posted on Thursday, May 03, 2007 - 02:06 am:   Edit PostDelete PostPrint Post

Cellular concrete fill and gypsum floor fill, especially for application over plywood sheathing, are part of fire and acoustical rated assemblies, from the gypsum board on the underside, resilient furring, framing (e.g., wood I-joists), acoustical batt insulation, plywood (check the thickness according to the fire and acoustical tests) and the floor fill.

The building code (at least the good ol' UBC) mandates use of a proprietary floor/ceiling assembly because of required fire and acoustical properties. The prescribed 1-hour fire rated assembly (double wood floor, 2x floor joists and 5/8" Type X gyp board) does not meet the impact (IIC) and sound transmission (STC) requirements of the Code.

Check ICC Evaluation Service Research Report ER-3433 for 1-hour sound control floors. It is an interesting example of the evolution of building materials in wood frame construction, from the old "double wood floor" to plywood sheathing and from sawn lumber to engineered wood framing such as TrusJoist's plywood web I-joists.

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