Final Stages Before the Slab Pour...and the Pour!

The forecast was showing two good days at the end of the week (June 8 and June 9).  Pouring a slab requires good weather.  I was told, to be safe, we really needed 36 hours.  This would provide time to pour, wait for the slab to be finished and have another 24 hours for it to really set up hard before bad weather.  It was already Wednesday morning and we had discovered that the company that I had originally approached had a backlog of slab pours due to bad weather.  They recommended another company, East Coast Concrete Finishing, to pour and finish the slab.  I called them and they were good to go!  We had a lot of work to complete before we could pour a slab.  We had to lay the vapour barrier, seal all overlaps and penetrations, and lay rebar for the thickened load bearing slab.

We were in such a rush I really didn't get any photos till the next morning but I will describe our procedure for laying the vapour barrier.  The vapour barrier was a 15 mil polyolefin film from Raven Industries (  It's available in a sheets that are 12'x200'.  Local code (at least in St. johns) requires and approved polyethylene vapour barrier tape.  Most builders are using a blue Tuck Tape.  Personally, I have found that this tape is brittle and although it works well for tyvek,  doesn't stand up well to the abuse a vapour barrier receives before the concrete pour.  The slightest tug can easily start a perpetuating tear that opens the seams of  a vapour barrier.  I opted to use 3M 8067 ( mainly because its tenacious, it stretches, and its thick i.e. 5 mil.  The manufacturers specifications also says that it can be used in this application.  The split back on the tape makes it easy to work with.  Release one side to position the tape and the peel and stick as you go.  The key is to make sure you apply some pressure to the tape where the paper backing is being released.  To ensure there were no "veins" at the seam that could leak outward through the bottom of the tape, we did find it was easier to apply as a two person team.  One person pulling the paper backing off while another applied pressure and made sure that the tape stuck flat on the vapour barrier.  It is useful to always look at whats happening ahead of you.  as you work along the vapour barrier it may shift and start to pucker in places.  The key is not to panic, if the tape starts to wander, it can be stretched slowly in another direction and brought back straight along the course of the seam.  Keep working along the seam until the seam until it is completely sealed.  After this we went back and removed the other piece of backing from the tape, working slowly to ensure there was no puckering or "veining" of the tape that could lead to excessive air leakage.   After the seam was taped, we inspected along the seam and corrected any areas that looked suspicious.  My method for dealing with this was a small bead of acoustical sealant followed by a flat patch of 3M 8067 over the area to cover the acoustical sealant.

To seal around pipe and conduit penetrations Raven Industries makes a boot (  It didn't surprise me when the distributor said that this wasn't available locally and the ordering time wasn't acceptable for this build.  Creating your own pipe boots on site is not that difficult.  Using scrap vapour barrier I cut square/rectangular pieces of Vaporblock.  I laid the Vaporblock over the top of the pipe.  I could see the shadow of the pipe through the blue vapour block.  While holding the boot firmly against the top of the pipe, I cut slits in the top about every 45 degrees from the center.  The length of the slits was equal to the inside diameter of the pipe.  The boot was then slowly worked onto the pipe while making sure not to excessively stretch in any one direction.  A 1/4" bead of acoustical sealant was placed around the outside circumference of the pipe at the base.  The boot was slowly pulled down until the acoustical sealant started to squeeze out between the boot and the pipe.  The corners of the boot were lifted and a bead of acoustical sealant was caulked onto the bottom edge of the boot about 1/2" in from the edge.  The boot was pressed lightly in place.  Working from the inside edge of the boot, the acoustical sealant was forced out to the edge of the boot where it could be seen.  3M tape was then used to seal the boot to the vapour barrier.  Where the pipe penetrates the boot there was about a 1/4" surface to stick tape. A bead of acoustical sealant was placed about 1/4"-1/2" up from the base of the boot and then tape was applied all the way around the pipe making sure to seal the tape against the vapour block boot and the pipe uniformly without puckering.  To temporarily secure the vapour barrier we laid 2x4's at the edges.

The porch is an unheated space and the garage will be occasionally heated so air sealing the slab wasn't really that big of a concern so I just followed the designer's recommendations:  Lay the vapour barrier out flat and pour over it.  To avoid using my expensive 3M 8067 tape we opted for the cheaper Tuck Tape for this application.  We tape sealed the vapour barrier to the EPS foam check that was poured into the foundation wall to secure it before the pour

A local company, Allstar Rebar, pre-bent the rebar necessary for the load supporting thickened slab.  This company was great to work with!  They typically don't deal with residential work and rarely do work where somebody else supplies the rebar.  I dropped off the drawings and my rebar and they had it ready in about half a day.  They weren't sure what to charge for the job so the estimator told me to give a $20 tip to the guy in the warehouse that did the work!  Rebar stands (2") were used to lift the rebar above the vapour barrier.  The trench rebar was laid 2' on centre perpendicular to the trench and then 10' long rebar was laid parallel to the trench 6" on centre.    The rebar was tied together with rebar ties and tightened by twisting with pliers.

This was all completed just in time.....The pump truck was on site 1 hour early! They were quickly followed by the four guys from East Coast Concrete Finishing and the concrete truck!  They set up a laser level and did a quick grade measurement to ensure the slab would be level as they work.  I did one last survey of the vapour barrier to inspect for holes and with a thumbs up the pour started!  If you ever get a chance to watch a slab pour it is worth your time to hang around and watch how a team of people work collectively to level and float a slab.  There is very little talking back and forth.  They all seem to behave as a collective:  Each one knowing what the other is doing, working closely in unison.  One guy trowels a patch thats level to the grade taken previously and marks a visible line so the other guys know where they are working towards.  One or two guys level with long straight sticks, pulling the concrete around to fill the areas between the level reference patches.  another guy is inspecting and adding concrete to low areas.  They switch up jobs sometimes.  As they were working along the edges, I would pull the vapour barrier tight and work the vapour barrier into the corner of the slab trying to keep the vapour barrier as flat as possible agains the foundation, knowing it will be much easier to work with later in the build.  At the corners,  I have often seen people often slit the vapour barrier to get it to fold down.  Every time I have seen this detail I cringe.  There is almost no way to air seal it.  To avoid a difficult air sealing detail,  I opted to do a kind of folded inside corner that looked kind of the reverse of wrapping the corner of a gift box with wrapping paper.  In about an hour the pour was completed.  Watching a pour like this is pretty satisfying.  You get to see how all of your hard work pays off.

Now we have a foundation.  Time to start planning for the next stage:  Framing!

Photo 1-1 Vapour and rebar completed for the pour.  you can see the white 3M tape used to seal the seams of the vapour barrier on the house slab.  We used Tuck Tape for the garage slab.

Photo 1-2 Workers doing a quick look over the slab and shooting grades on the foundation for level.

Photo 2-1 Concrete starts flowing from the pump truck.

Photo 2-2 The edges were levelled with the level established from the foundation grade.  The centre of the trench was then levelled and the concrete was levelled in between using long flat sticks.

Photo 2-3 Once a section was completed a long float was used to further flatten the concrete.  In this picture you can see the Vaporblock boots that I made on site for sealing the pipe and conduit penetrations.  Rebar can be seen in the thickened slab section.

Photo 2-4  House slab 60% complete.

Photo 2-5  Working around penetrations.

Photo 2-6  pulling excess concrete and levelling to references.

Photo 2-7  Using a float to smooth the concrete.

Photo 2-8  House slab almost completed.

Photo 3-1 Leveling the porch slab.

Photo 4-1  pouring the garage slab.

Photo 4-2  Garage slab almost complete

Photo 4-3 Working the area around the slope for the garage door.

Photo 5-1 Slab Complete!

Photo 5-2 Power troweling the slabs

Photo 5-3  Complete!


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