Is gypcrete DIYable?

Only in very small quantities, like a 5 gallon buckets worth for patches. It really needs to be blended and pumped by a pro to get the best results.

I have done plenty of pea gravel, concrete mix pours. 1-1/2 - 2" pours are possible. You want 3 times the aggregate size over the tube. With 3/8 or 1/2 pex you can get down to a 1-1/2" pour with pea gravel mixes.

Double up the fiber to 3 lbs per yard with thin slabs. 6 mil poly over wood subfloors to prevent the wood from sucking the water from the mix and as a slip sheet. Add a shrinkage reduction ad mix, see WR Grace Products. In hot weather a bit more fly ash helps the work-ability. Your local concrete supplier should be able to help you with a custom mix.

Don't be tempted to water down the mix, any concrete mix, every gallon of water added to a yard of concrete reduces the psi rating by 200 lbs.

Concrete mixs are not self leveling like the gyp products and you end up with a rougher finish, but they are cheaper and readily available from any redi-mix provider. They can be pumped or wheeled into place.

hr

SolarAndWood said:

How much does 1 1/2" of pea gravel weigh per sq ft? I haven't framed the floor system yet, have a 20' open span, 16' if I put a 500 gallon propane tank in the lower level.

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Gravel itself would be 90-100 lb / cubic foot, about 12 lb per square foot 1 1/2" thick.

Concrete is about 140-150 lb / cubic foot, about 18 lb per square foot 1 1/2' thick.

Five feet of snow would be about 30 lb / square foot.

--ewd

Gyp, when dry weighs in at @ 14.4 lbs./sq. ft. Figure 18 lbs./ sq. ft. for concrete mixes.

Here is a recipe for a lightweight concrete mix you can mix yourself or have delivered. Formulated by Harvey Youker.

517 lbs Type 1 portland cement
1639 lbs. concrete sand
1485 lbs. #1A (1/4" minus aggregates)
166 lbs. (20 gallons water)
4.14 oz. air entrainment agent
3lbs. fiber
51.7 oz. superplasticizer (WR Grace)

You can also substitute lightweight aggregates like Perlite, Vermuclite, volcanic rock, etc. but the thermal properties also change when putting "air" into the mix.

Check the Joist Span Tables to assure you have enough framing to provide a bounce free floor when adding dead loads like concrete, rock, brick, etc to wood frame floors.

hr

Adding 1-1/2 to a floor does have some challenges like doorways, dishwashers, toe kicks, bath tubs and fixtures, etc.

I prefer a low mass, dry system, unless a slab on grade is in the plan already.

With low mass you have the ability to respond quickly to changing weather and temperatures. It is often much easier to retro fit. Properly sized it can work with low operating temperatures, conducive to solar, even in chilly NY.

I'm excited by the new radiators from www.jaga.com. With that small room reset-able fan module you can get very good performance even with supply temperatures down in the mid 90's.

Most can be fed with 3/8 or 1/2" pex or PAP. Home run piping from a typical radiant manifold provides zoning and isolation. There are a lot of nice panel and other types of low mass radiators available these days. They are easily removed for cleaning and wall painting also.

Dry radiant with panels are another option. Look for brands with an aluminum covering for best conductive transfer from tube to floor surfaces.

hr

My advice is don't do it! I put gypcrete on my main floor and the second floor (basement was regular concrete). I had to go with 2x4 web joist that were 12" apart for a span of 18'1" in my living room. Try fitting plumbing, ac duct work, etc thru the remaining 8.5"! When considering all the extra joists, extra cost of plumbing and AC installation as well as difficulty in locating pex tubes once it is poured (for example, when you want to run extra electrical or audio/video wires to another floor), it was probably the same amount of money and alot easier if I would have used warmboard, with the bonus of much faster construction and installation.

Yeah, that 20' span may be a deal killer, but don't let the haters get you down. I did concrete overlay in my barn home and I love it, for much of the year I can leave the windows open for a nice breeze and the temp evens out real nicely. There was just one week in August when we turned on AC for the humidity. If you have any significant south facing glass, I'd try to go with the mass.

Haters? I think most are giving first hand experience pros and cons. Gyp or concrete thin slabs do have a place and benefits. Sound and fire proofing are a few others. Gyp is mainly used in hotels for this reason.

There is at least one gyp manufacturer that now offers a high psi version that can be and used as a final flooring surface, that is a big plus.

Gyp hates water, be sure it is sealed properly.

hr

Consider the floor coverings also. Floating engineered hardwoods work great, as will any other floating product. Proper sealing is crucial if you plan to tile over gyp. Check with the installers some brands recommend against tile glued to gyp products. I learned this the hard way on my own home. The entry got a lot of snow from boots, etc. The melt water worked it's way around the edges of the pour. Gyp is a lot like sheetrock when it gets wet. It comes "un-gluded"

I'd have a tile installer do a dry pack over the radiant tube in the bathrooms, it's a much better substrate for tile installation and conducts heat as well as gyp.

Nail down hardwood can be a lot of work as you need to nail down 2X2 or 2X4 sleepers first.

I still advise against any carpet and pad over radiant, throw rugs are not so bad, but wall to wall carpet can be a deal breaker depending on output required.

USG is the company that offers the high PSI "LevelRock" product. They claim these can be used as the final flooring? I don't have an experience with the brand and version, but I have installed 10's of thousands of square feet of the Infloor and Hacker brand gyp over radiant.

Thermal mass can be your friend, or it can work against you as we learned in the "over glassed" passive homes we built in the 70 & 80's. A method to turn off the solar gain when the room gets un-comfortably warm is important. Motorized shades or glass with operate-able louvers built in can give you better control.

hr

All I will add to this discussion is this........there's a good reason the gypcrete installers show up at a job site with equipment that runs into 6 figures.