Slab preparation requires a ton of physical work and is visually unrewarding. Last week I became much too familiar with the word wheelbarrow. The site is nearly flat, with a minor 8-inch grade change between the north and south side of the house. We had to add earth to the interior footprint to bring everything up to one level.
Because the CMU foundation wall is above grade, a bobcat cannot drive over the wall to move earth, so hauling is all done with a wheelbarrow. Bruce and I armed with shovels and wheelbarrows, backfilled and compacted the crusher fines in the trench and then worked our way towards the center of the building footprint.
After the interior grade was leveled and compacted, we laid down 48” wide rolls of Ayr-Foil over the entire footprint of the house. This step is satisfies code by insulating below the concrete slab. Recently Ayr-Foil replaced the foam board insulation code requirement. Trying to compact earth over foam is a Sisyphean task at best; foam, once released from pressure, springs back and disturbs compaction.
Ayr-Foil is similar to a sheet of bubble wrap, except that one side is coated in a layer of foil, (which, in theory, reflects the heat from the radiant flooring back into the concrete slab) and the other side is white. In truth, it is a delicate material, and it doesn’t have near the R-value of two inches of foam, but it satisfies the building code requirement.
While researching the spelling of Ayr-Foil, I stumbled upon their technical literature, and according the manufacturers, sub-slab applications should be laid with white side facing up and concrete poured directly on top. In Northern New Mexico the installation is done a little differently: Ayr-Foil Is laid foil side up, then two inches of crusher fines are compacted on top of the foil. The two inches of earth between foil and concrete achieves a couple of things; first, it provides mass, which retains heat from the radiant flooring, and second, it sets the concrete slab faster because the water in the concrete is both evaporated upward, and pulled downward into the compacted earth. If the concrete were to be poured directly on top of the Ayr-Foil the water would only be able to evaporate, and the concrete would cure much slower. Ayr-Foil laid foil side up, also makes sense, as it is the reflective side, which will come in contact with heat and be reflected back in to the slab.
To recap, the earth is leveled and compacted before and after Ayr-Foil. The following images are Greg and Weasel (Weas) covering 2,000 square feet of Ayr-Foil in 2-inches of crusher fines. Who needs the gym when you haul earth for a living!
Once all the earth is leveled it needs to be screeded, which is further fine-tuning. The screed that we used was a piece of 2×6 lumber guided by string lines.
By standing the 2x on edge and manually pulling the dirt with the lumber, so that the top of the wood is directly flush with the bottom of the string, you can get a surprisingly level substrate. To make sure all that hard work stays put the earth is hosed down. The weight of the wet dirt holds it in place and compacts it again.
Next came the plate compactor. Normally Weasels favorite task, unfortunately the machine we rented was on its last legs and was coughing a steady plume of noxious fumes into Weas’ face. It didn’t take him too long to make his way around the entire house, and I am sure he popped a beer immediately after just to wash the gassy flavor from his mouth.
After using the plate compactor we laid down sheets of metal mesh, 8-feet wide by 20-feet long. The mesh acts as slab reinforcement and provides an organizing grid for tying on the radiant tubing.
While we were playing in the dirt the plumbers and the electricians were installing their rough-ins, which also take place in the dirt below the slab. This means that all locations of plumbing fixtures (sinks, toilets, baths, washers, water heaters) need to be finalized, and in the case of freestanding bathtubs, the exact model needs to be chosen. It seems early to be choosing final plumbing fixtures, but really it is important to design with their dimensions in mind, or at the last minute you will be frantically looking for a fixture that will fit into the space!
A lot of jokes are told on the jobsite; this is one of my dad’s favorites:
Ed: “What are three things you need to know to be a Plumber?”
Ed: “Hot is on the left, payday is Friday, and shit runs downhill!
I am sure Jason and Jose, the Plumbers would disagree, but at this phase of the plumbing aka the “rough-in,” it is quite straightforward. It boils down to two different types of tube material. PVC and PEX. PVC is the large white pipe that carries wastewater and requires a slope of ¼” per foot to move solids. Anything less than that prevents solids from being flushed out by water and gravity, and anything steeper has difficulties flushing solids because the water flows out too quickly. PEX carries clean potable water to all the wet rooms in the house. It is also color coded: Red PEX = hot water, Blue PEX = cold water.
Manifold is another term frequently used at this stage of plumbing. The manifold ties all the PEX tubes together (hot with hot and cold with cold), so that they are on a continuous loop. The 1” diameter clear PEX pipe is the main supply line which delivers water to the smaller color-coded PEX.
All water enters the house through the mechanical room, which serves as the “heart of the home.” It stores the hot water heater, which is why it is the first point of contact for water. The radiant flooring manifold is also in the mechanical room. By locating everything in this room it is easy for plumbers to test the tubes for any punctures and to retrace their footsteps for any issues down the road.
The radiant flooring is also made out of PEX tubing, clear. It is tied onto the metal mesh and is directly set into the concrete flooring. Before laying out the tubing, zones need to be established. This means that you can turn on the radiant floor heating in different areas of the house. We set individual zones as follows:
While laying the tubing, closest to the perimeter, two continuous tubes are 6” apart from each other effectively creating a heat wall. Because most heat in a home is lost through windows and doors this acts as a buffer to heat loss. After the perimeter is laid tubing is space 12” apart and uncoiled toward the center of the zone.
The last step in the plumbing “rough-in”, are the “box-out’s”. It is critical that we are able to access the PCV pipe once the slab is poured.
Under slab electrical is small part of the whole house wiring, and services outlets that are floating in a room, for example an outlet in the floor or in a kitchen island. It must be installed before the slab is poured.
We are using Maes Electric. Sound familiar? Same guys that do our earthwork. When Dan isn’t operating the bobcat he is an electrician. However they sent out Robert that day, Dan’s uncle, and his son Robert Jr. It’s all about Family aqui en Taos.
Next Monday the first slab is getting poured. We had to tie-up a couple of loose ends before then.
P.S. We finally got the construction site signs up!