Sunday, June 26, 2016

Construction - Garage Floor; Addition of Earth Contact East Wall

The garage floor was not poured at the same time as the house floor.  One reason for the delay was to kick the cost of it down the road.  But the major reason was that it would be doubling as a part of the insulation/water umbrella and I was not ready at that time to commit mind space to its exact design.  As noted below, the garage was under-excavated simply because I had not given an umbrella-floor combination enough thought.  

Reality Check
Progress on the entire house-building project has been and will continue to be snail-paced mostly because of the limited amount of work a DIYer alone can accomplish. The agreement I had with the Building Director when applying for a permit is that, since I was responsible for the design of the house, the architectural drawings did not need to be as detailed as is typical.  The upside of this arrangement is lower architect fees but the downside is that I have more stuff to keep track of on the fly. Not committing mind space to the garage floor at the time the site was excavated is a perfect example of how difficult it is for one person to prioritize and coordinate the myriad facets of construction.  Some things have to be back-burnered until they are more pressing and some simply drop through the cracks.  

Finally, the time came when the garage floor had to be dealt with and, by delaying, I created extra labor to get it right.

The original excavation would have been pretty accurate if it were not necessary to install the insulation/watershed umbrella under the floor as that part extending eastward from the house proper.  But the excavation needed to be lowered at least by the thickness of the foam insulation board for the umbrella.  So I tried to catch the soil at just the right time after a rain that it worked easily with hand tools -- which leads into an interesting discussion about our unique bluff soil.

Factoid About Our Unique Soil
In-letting for 4" of foam insulation
Smooth sand base for the insulation
Most of the soil covering the bluffs originated in the Mississippi River flood plane where it was deposited by receding glaciers.  The finer particles in the deposit were picked up by the wind and dropped on the bluffs (which themselves were left standing by the glaciers). The fine-grained silty soil, called "wind-blown loess", is extremely rich and drains reasonably well except that, when it dries out, it is almost as dense as plaster-of-paris and hard to work with.  Underlying the loess at depths that vary greatly throughout the bluffs, is a layer of what the local soil conservation agent calls "glacial till" and what we old-timers call "hardpan".  It is a layer that, when it is dry, is almost impossible to penetrate with hand tools. It is a layer that I had to dig through with the trackloader when excavating the hillside for the house such that the loader was often over-matched.  However, both the loess and, to some extent, the hardpan are somewhat more manageable if one catches them between the mud and dry stages.  Hence, my hesitancy to start digging until after a rain.   

Insulating the Garage Floor as Part of the Umbrella
Middle section of insulation in place
The foam board insulation under the garage floor needs to be 4" thick for the first 8' from the house then 3" for the next 4" followed by 2" to complete the coverage.  I started the inletting for the foam with the first 8' next to house.  When it was reasonably accurate as to depth and levelness, I coated the soil with enough sand to be able to make a smooth bed for the foam.  I laid the insulation in place over the wide footing next to the wall, stood foam board against the leading edge of the footing then installed two layers of  2" thick XPS in the new excavation.  To stabilize the foam and protect it from the wind temporarily, I covered it with a little more sand. Eventually, more sand would have to be added before the floor could be poured; more on this later.

Final section of insulation in place
Next, I hand-excavated for and installed the middle 3" section of insulation.  The 2" section was handled in the same fashion. Finally, I added sand in lifts and hand-compacted them after soaking the sand with a lawn sprinkler to make it more compactable.  By the time Jamie Schultz and crew came to do the pour the sand had dried to the extent that I soaked it thoroughly the night before so they could compact properly with a plate compactor just before covering with plastic and pouring the concrete.

Raising the Height of the East Wall of the Garage
In retrospect, I should have designed a higher concrete east wall for the garage in order to
Rebar and door buck in place for adding four feet to the
height of the east wall; notice also the 2 x 10 forms bridging
the garage door openings
have more flexibility for contouring the final grade of the soil east of the garage. The more I tried to justify leaving most of the wall stick-built, the more it became apparent that a higher concrete wall was necessary.  Consequently, on the day that Jamie Schultz and crew came to pour the slab for the screened porch (previous post), they erected forms and poured a four-foot high wall on top of the insulated concrete foundation.  The cost was probably twice what it would have been at the time the rest of the walls were poured.

Pouring the Garage Floor
The floor was designed to be 1 1/2" lower than the house floor at the back of the garage and 3" below at the front.  I snapped chalk
The new east wall uncovered (in the background);
the slab pour underway
lines on the back wall and along the side foundation walls to mark the height of the pour. Across the openings in the insulated concrete forms underlying the garage door locations, I installed 2 x 10 forms to confine the concrete and for screeding at the 3" level.  

When Jamie and crew arrived, they removed the wall forms and, while waiting for the ready-mix truck, plate-compacted the sand that I had soaked the night before and installed 6 mil plastic sheeting.  The day was warm so the pour cured rather fast and could be finished by early afternoon.

Handling the Cold Joint Between the Wall Addition and the Foundation
My design and management of the east wall of the garage was driven too much by cost.
There are three deadmen in the middle of the north wall;
the fourth and fifth are affected by turning the corners
and involving the east and west walls
We turned the north wall southward into a short section of east wall in order for it function as one of the critical deadmen for the long north wall that was to be backfilled without internal support.  I should have had the entire east wall of the garage poured in concrete by at least half way up in order to have more flexibility for managing the grade east of the house.

The disadvantage of retrofitting the east wall is that a cold joint is formed between the concrete of the insulated concrete form foundation and the new wall.  My concern was that the joint would leak water into the garage.  So how to fix it?

One possibility was to gunk up the joint on the exterior with tar-like materials and hope that
they would not lose their effectiveness with age, assuming they adequately sealed the joint in the first place, given the contamination of the surfaces by deposited dirt. The other possibility was to install a proper French drain opposite the joint to siphon water away before it could infiltrate the joint.  I oped for the latter.

Typical French Drain Installation
So I more or less followed the typical protocol for French drains albeit with some customizing in order to use up some left-over materials. After the ditch for the drain was dug, I threw in a few inches of sand to level the ditch and to deepen the drainage plane below the drain (first photo). Then instead of buying pre-perforated corrugated pipe with a geo-textile sock already on it, I used some pipe left over from the solar collector conduits and geo-textile material left over from the French drains that under-gird the house.  I used the same technique for perforating the pipe that I had used early on for converting culverts to French drains (DIY French drains made from culverts).  I also used the same technique for attaching the material to the pipe as I used with the culverts. 

There was already a footing-level French drain so it was a matter of  uncovering it and inserting a wye for the new drain (first photo).  I then lined the ditch with left-over geo-textile fabric and fastened it to the wall temporarily (second photo).  As is typical with French drains, I covered the bottom of the fabric with a couple of inches of  3/4" clean rock before laying in the pipe and connecting it to the wye (third photo). More rock was added to cover the pipe.  The edges of the fabric were overlapped to cover the rock and secured with hog rings (third photo).

The drain was left exposed instead of backfilling immediately because the outside of the garage wall will have to be insulated before the soil is added.  It will be insulated in the manner that was described in an earlier post .  As soon as the wall is insulated and covered with stucco, I will backfill nearly to the top of the wall at the back and sloped towards the bottom of the wall at the front.

The footing French drain for the west and north concrete walls, as well as the east wall into which I tapped for the new drain, was not as carefully done because it will be covered by the insulation/watershed umbrella and the backfill sloped so severely away from the house that it is unlikely that it will ever see water once the umbrella is in place.  It's function, besides meeting code, is to siphon off enough water to eliminate hydrostatic pressure on the walls while the uncompacted backfill settles on its own before the umbrella goes in. 

Consequently, I used home center perforated pipe with a sock, no fabric lining for the ditch and sand instead of rock for the drainage plane.  If there were to be no umbrella, I would have bought perforated pipe and covered it myself with the geo-textile material shown here that has been scientifically designed for fine silt soil like we have.  The store-bought fabric that I did use instead of the special fabric can be expected, in the absence of an umbrella, to admit enough silt to clog the pipe and render the drain useless eventually.  The same would be true for lining the ditch with local store-bought material -- it would not filter the silt sufficiently to keep the gravel bed clean and unclogged indefinitely.


  1. I wanted to thank you for this great read!! I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post.
    daytona beach epoxy garage floor installers

    1. Thanks for the positive input. What is your role with the epoxy floor installers?


  2. Thanks for this great post, i find it very interesting and very well thought out and put together. I look forward to reading your work in the future.
    bed lining

  3. I appreciate your input. FYI: a retaining wall has been installed at the SE corner of the garage and the entire east wall of the garage has been backfilled to within 8" of its top. There has been no leakage through the cold joint nearly two years later.


As a do-it-selfer-in-training, I welcome your comments.