Gypcrete Installation

radmix

A few questions about a staple down/Gypcrete installation. The way Ive done this in the past is have the homeowner double the sill plates so there is a nailer for the sheet rock. The gypcrete company doing the pour wants the sheetrock installed before the pour without doubling the plates. I have also put the heat on only one day after the pour but Im told by this company it should cure a minimum of 14 days before applying heat. Ive read in the past where the heat was on during the pour. Is there a proper method of sheetrock install and a cure time?

mars_6

I would have the gypecrete company provide a statement saying they will cover any and all damages possible to the installed sheet rock, and insulation. When gyp dries water in the mix creates a very humid environment. This is not SOP in my region. As to firing the floor, it has been my experience that firing at a low temp 70 to 80 is not a bad practice depending on ventilation of the project. One more thing to bear in mind is If the gypecrete company wants the drywall installed then the insulation will be installed, insulation is a great absorber of moisture, if you are using fiberglass or blown cellulose, This can have some consequences that are not desirable. In short I would not do this on one of my projects. I hope this helps Matt

Zman

I absolutely agree with Mars.
I would throw the drywall in the swimming pool before I would soak it in gyp.
Gypcrete should go in first, the insulation, then drywall.
I prefer 2x2 blocks between the studs over double plates. You get better insulation.
Carl

Rich_49

Agree with Carl . Moist drywall and insulation is not good . Doubling the thermal bridging by adding a double plate is also not good . Twice the area of direct connection between outside and inside is terrible . Since you already have the double plate you should really think about a thermal break as with any slab floor and use at least 3/4" foam between the framing and your slab so all those BTUs dont go right outside through conduction . remember , conduction is King .
Maybe the Gyp installer will sign some document that states he will be responsible for any mold issues should this house happen to be well airsealed and unable to dry to the outside in the wall . Building Science can not be ignored either . I would run dehumidifiers until most of the moisture is wrung out of that Gyp . Watch how much fluid you capture also and remember that it would have gone straight into the drywall , insulation and sheathing . It'll certainly make you think .

radmix

Thank You for the responses. What about length of time before adding heat or can you run the heat while the gypcrete is being poured.

Rich_49

Just to avoid added conflict and possible warranty issues with your Gyp guy leave it off until he leaves . As soon as he goes though I have used 70 - 80 * fluid through them right away . I think Mars stated those temps above already .

hot_rod

I have seen some commercial applications where the gyp pours to the wallboard. Apparently to get the flame spread and smoke seal for hotels, etc? It does seal that infiltration point nicely to pour against the sheetrock.

But there is a lot of water in gyp and you would need to somehow dry out any moisture in the sheetrock.

That same moisture gets into the plywood or subfloor that the gyp is poured over also, unless you use a latex sealer first.

We were told to put a square of plastic over the gyp and look for condensation, not to install the hardwood until all the moisture was out of the gyp. Heat AND air movement is needed to dry it out, look for condensation inside the windows after a gyp pour.

One huge mistake we made was to pour a gyp floor with all the exposed exterior wall insulation in place. it was winter and the builder wanted to heat the floor, but after the blow in insulation.

That shredded paper insulation product they used sucked up all the moisture and took weeks to dry out.

See what the manufacturer of the gyp products suggests.

Zman

The only thing about heat that concerns me is the expansion and contraction of the tubing. I would go with the low temps suggested above and keep it on for several days.

Gordy

Gypcrete cure time is when the gypcrete reaches equilibrium with the rest of the ambient temp in the structure so long as that ambient is being in manufacturer spec for cure. Its cementatious, and uses chemical reaction just like concrete to harden. DO NOT put heat to it with in the slab until it has cured. raising the internal temperature will cause cracking, and poor curing lowering its strength.

As far as curing for flooring detail. Its just like HOT ROD says in his post. plastic over gypcrete till no moisture condenses. Could be 3 weeks depends on ambient conditions.

Rich_49

In the warmer months I would agree Gordy . This time of year the guy that I use for the occasional gotta have a huge mass floor job wants me to keep that material as close to what it will be when the heat goes on . His theory , whether he has had a bad experience or not I don't know is that during a cooler period of the year without the heat on that slab could cure and be , say maybe 45 * , then you turn the heat on and it almost immediately starts to expand which will crack and stress it for sure . Just what my therma floor guy says .

Gordy

I can agree with that Rich to a point. Strictly speaking Gypcrete on its own I would say the cure should be met by holding ambient temps by external means (supplemental heat). To get the most strength.

If that is met, and flooring temps brought on line slowly temperature wise 70-80 is fine should be no problems. What I would worry about is moisture leaving at a different rate from the tubing area verses in between the lay out. During the cure process.

I was strictly speaking getting the most out of the product by meeting proper cure specs. If you have had no problems, and the therma floor installer is on the same page that's great, and what counts.

Gordy

A bit off topic, but I would be willing to bet that if the dwelling or structure was brought up to ambient occupancy temp before the floor was brought online to take over there would never be a problem.

Most don't understand the compress a war in the winter time of the inner skin of the dwelling trying to expand, and the outer shell trying to shrink. The greater that delta the more force involved. Ever awake in the night to an ungodly pop, bang when the temps dip way below zero-25 or-30* That's what it is. The opposite happens in the summer, but those deltas, are not quite as drastic. 100 delta in winter verses 20-40 in the summer.

So my point is the slab is heating up, and the inner skin of the structure is lagging.


.....Holy crap I better go pour a Manhattan I feel myself crossing over the event horizon.

Does anyone else's ipad freeze up while trying to post?