Tag Archives: concrete floor

Fear of Concrete Slab Cracking at Post Corners

Fear of Concrete Slab Cracking at Post Corners

Nothing appears to add to the self-importance of a contractor more than instilling fear into the hearts and minds of their clients. If I had a dollar for every fear mongering story I have heard over the years, I would be a wealthy man!

Hansen Pole Buildings’ client PAUL writes:

“Hello, I’m Paul in McCall Idaho and I purchased a 14′ x 36′ pole building last fall from you and I had a quick question.  I am getting ready to pour the concrete floor and the concrete guy helping me was concerned that the floor will crack on all the post corners and wants to do some changes to prevent it. I have never heard that that was a concern and thought I would consult you guys as I know you’ll have the correct answer. SO, is that something to be concerned about??  Thanks for the help and I know my account is closed by now but figured you’d have a quick answer for me.  Thanks a lot.”  

Mike the Pole Barn Guru responds:

We’ve never heard this as a concern either, so perhaps you can get your concrete finisher to share research studies he has read which elaborate upon this supposed challenge. I personally have owned (or still own) several post frame buildings with concrete slabs and have never experienced issues with floor cracks other than where they are supposed to be – along control joints or saw cuts.

The most important things to avoid cracking where not desired is to have dedicated allowance locations for cracks (e.g. expansion joints or saw cuts should be located every eight to 12 feet for a four inch thick slab), have a properly prepared and well compacted site, eliminate sources of water which would or could flow under the slab, reinforce the slab (by use of one or more of the following – fiberglass strands, wire mesh, rebar) and to have the slab tied into the columns by use of rebar hairpins through the columns. The clean sand between the vapor barrier and the concrete should be moistened prior to the pour as well. Concrete mix with too much water in it will lead to future cracking. It is more work to pour with less water, but the end result will be far better. Keeping the slab well hydrated (water on top of the slab) for the first month after the pour will retard the speed of curing making the slab not only stronger, but also will reduce the cracking.

When I was building myself, one thing I would always guarantee with concrete slabs – they will, at some point, crack. It’s the nature of concrete.

 

 

Finishing a 15 Year Old Pole Barn

Finishing a 15 Year Old Pole Barn

Reader BOB in WASHOUGAL writes:

“I have a 30’x60′ pole building. It was constructed in 2003. I would like to finish the inside with a concrete floor, Insulation, and sheet rock. My question is…How long do the posts last before they rot off at ground level? (I have a wooden fence that was built around the same time and 50% of the posts have rotted off at ground level!) I just don’t want to throw good money after bad. I want to end up with a permanent Building when I’m done.”

Mike the Pole Barn Guru responds:

Your fence posts rotted off because they were not treated to the same level of treatment as are your building columns. In fact, most fence posts are just dipped in a chemical solution, they are never actually treated under pressure. In many cases, fence posts are peeler cores (the center remaining after logs are peeled for plywood) which will not take a treatment to begin with, or they are a species which does not treat easily (or at all). I recently wrote an article about the lifespan of properly pressure preservative treated wood, which should put a rest to your fears: https://www.hansenpolebuildings.com/2017/12/will-poles-rot-off/.

Some nonstructural, yet important considerations – before your pour a concrete floor, make sure to install a good vapor barrier, which is well sealed. You should either unscrew the steel siding, place housewrap and reinstall, or spray closed cell foam insulation on the inside of the wall steel. In the event you create a dead attic space, make use of proper ventilation to prevent mold and mildew challenges later on.

I recommend you consult with a RDP (Registered Design Professional – architect or engineer) who can determine if your building is structurally adequate for the modifications you propose. Post frame buildings with steel siding, which have not been specifically designed for future drywall finish on the inside, often have deflection which is beyond the limitations of the gypsum wallboard – meaning the joints will end up cracking due to too much lateral movement. Chances are good your roof trusses are not designed to support the weight of a ceiling and will require some engineered upgrades in order to do so. You are about to make a big investment into upgrading your building, please do not take my recommendations lightly – as you stated, you do not want to throw good money after bad.

 

 

Pouring a Concrete Floor in a Post Frame Building

Another great question from a loyal reader:

DEAR POLE BARN GURU: How would you install a concrete floor in one of your pole buildings. RICK in TOLEDO

DEAR RICK: Here is the chapter from the Hansen Pole Buildings Construction Manual:

Chapter 18: Concrete Slabs

While preference is to have building shell completed prior to pouring concrete slabs, at the very least, roof should be installed.

Building columns tend to grow “bull’s-eyes” in the presence of pre-mix concrete trucks. A completed building shell is far more resistant to potential damage. Pouring slabs with columns only in place, adds to the risk of one inadvertently being knocked out of plumb.

This section is not meant to provide the necessary instruction to pour a building slab. This is not because the task is beyond a novice’s abilities, although many do contract out this job. Pouring a slab is within most people’s abilities. However, unlike wood framing, which can be corrected if improperly constructed, work on a slab is “set in stone”. Due to this, and the fact so many local codes and practices apply to concrete slabs, we have only touched on this subject. If deciding to personally undertake, we suggest talking with local professionals to know what you are getting into. Have building inspector (usually a requirement in permitted situations) or a professional inspect work before pouring concrete. If under 100% confident, hire a professional to work alongside during the concrete pour.

If in “frost country” a sub-base 6” or thicker should be first placed across the site. To maintain frost-free soils sub-base should be such as no more than 5% (by weight) will pass the No. 200 sieve, and it is further desired no more than 2% be finer than .02 mm.

Prior to pouring, 2” to 6” of clean and drained sand or sandy gravel is spread below where concrete is to be poured. Mechanically compact fill to at least 90% of a Modified Proctor Density, so as not to cause slab to sink. ALWAYS install a good vapor barrier (such as A2V reflective insulation, available through Hansen Buildings) below any interior pour, to stop moisture from traveling up into slab through capillary action. Place 3” to 4” of clean and drained sand on top of the vapor barrier, to decrease differential drying shrinkage and floor curling.  If not using fiber-mesh or similar reinforcement additives to concrete mixture, place wire mesh or rebar (reinforcing steel rods) in slab center to add rigidity to concrete to aid in minimizing cracking.

Insulation Underneath Concrete Slabs

Best product to use is A2V reflective insulation. Unroll reflective insulation over prepared site sand or gravel, with aluminum side facing ground (white side up). Overlap by 2” at seams. Run reflective insulation up skirt board inside by 6”. Seal seams with reflective insulation white vinyl tape or white duct tape. Pour concrete on top of reflective insulation.

Aluminum side faces away from the concrete as concrete’s high alkalinity attacks aluminum causing facing to degrade.

Adding sand over reflective insulation will facilitate water drainage during curing time and accelerate installation.

Local code will dictate such things as slab thickness (usually 4” nominal), wire mesh sizing, gravel or sand layer thickness, and size and rebar location. Many garage or shop slabs also have a center drain. In the event structural engineering for a concrete floor (or any concrete or other masonry footings, foundations, walls, or retaining walls) is required or requested by you, or a building official, this is outside our engineer’s scope.

On solid walls of building, pressure treated skirt board will serve as forms for pouring slab. In open wall areas, or across sliding or overhead doors, a 2×4 will need to be temporarily place as a form.

Prior to pouring a nominal 4” (3-1/2” actual completed) thick concrete slab in building, finished, graded compacted fill TOP will be even with skirt board BOTTOM. If a thicker floor is desired, excavate below skirt board bottom, by any slab thickness greater than 4”. In no case, will concrete floor top, be even with either top or skirt board bottom. Using any other measure for the concrete slab top, will result in wall steel and doors not properly fitting, as well as interior clear height loss.

In other terms – after the floor is poured, when standing inside building, approximately 3-3/4” of the skirt board will be visible above the top of the slab.

In the event a professional is hired to finish concrete, most often costs can be reduced by paying the local pre-mix company direct for the concrete. Many offer discounts for prompt payment, so do not be afraid to ask. On a properly leveled site, a pre-mix concrete yard will cover an 80 square feet area, nominally four inches thick.

Mike the Pole Barn Guru

Rebar Hairpins

When I began writing these articles a few short years ago, I assumed I would run out of subject matter after about 100 or so. Silly me – as I’ve now produced in excess of 1100 of them and I keep realizing I have totally skipped over some obvious subject matter.

One of those which has been totally missed by me is rebar hairpins.

So, what is a rebar hairpin?

A rebar hairpin is a piece of rebar (https://www.hansenpolebuildings.com/2016/01/rebar/) , in the case of a Hansen Pole Building, ½ inch in diameter and five feet in length. An oversized (5/8 inch diameter) hole is drilled through each column, 1-3/4 inches above grade and two inches in from the outside column face. The rebar is inserted into the column so an equal distance remains outside of each end of the hole.
The two rebar ends are then bent towards the interior of the building, at a 45 degree angle to the pressure preservative treated splash planks. When the nominal four inch thick concrete slab is poured inside of the building, the hairpins will be in the middle of the slab’s depth – effectively tying the columns and the concrete floor together.

Why might the hairpins be important?

Embedment formulas.

Not baby, or racing formulas.

Part of the calculations for every post frame building should be those for column embedment. There are two conditions of embedment – non-constrained, where the building will never have a concrete floor or the concrete floor and the columns will be affixed to each other. The other condition would be constrained where the building columns are “constrained” from lateral motion due to the contribution of the concrete slab on grade.

There are cases where the building columns being constrained can actual save money (sometimes significant amounts). This is due to the shear forces the building must resist are reduced to 75% from the contribution of the slab constraint.

When wind forces are relatively high, building is tall and/or the building length to width ratio is large, the savings in column sizes and additional materials for shearwalls can amount to significant savings.

Hairpins also function, in frost country, to keep the columns and slab from being moved at different rates due to the forces of frost. This should be negligible on a properly prepared building site.

And there you have it… everything you wanted to know about rebar hairpins, and a little more.

Voids Under Concrete Slabs

From Hansen Pole Buildings’ Designer Rachel:

“A nice lady from Pennsylvania called and said she was looking to get some advice.  Her husband died five months ago and she is having a pole building put up.  It sounds as though they have the poles up, skirtboard on and the concrete poured although there is a problem……she can put her entire hand under the concrete slab and she doesn’t think this is right.  She said they excavated the ground and then added fill to get it level.

So there are a couple issues she has. 

  1.  She is worried about what is under the concrete, as in wondering if the “fill” will wash away.  Should she be worried?
  2. How should it be properly fixed?  She is going to call the “engineer” who is doing the work but what if they fix it and don’t fix it right?  She said she is a girl and she’s a nurse and doesn’t know anything about building so wouldn’t know if they were doing it right or wrong.

Would you have any advice for her?”

Issue Numero Uno – yes, she should be worried. The “fill” (I will use the term loosely on purpose here) was probably not either the proper material, was inadequately compacted or both.

There is nothing more important to the quality of a concrete slab poured on grade than a properly prepared site. I’ve written about it extensively in the past:

https://www.hansenpolebuildings.com/blog/2011/11/site-preparation/ as well as how to do proper compaction: https://www.hansenpolebuildings.com/blog/2011/11/soil-compaction-how-to/

When voids occur under the concrete slab, if the concrete is not strong enough to span the void, the slab will crack, break, and collapse into the void.

Problem Part Deux – I’m lucky, my bride is a girl, a nurse and knows more about building construction than most males. Chances are good the person who is doing the work is not actually an engineer. If he is not, it would behoove her to require the contractor who poured the concrete to pay for an independent registered soils engineer to inspect the work and recommend the best fix.

MudjackingThe repair is typically going to be one of two options. The first is what is known as mudjacking or slabjacking. Used for decades, this process involves pumping a flowable (high-slump) cement-based liquid under the slab. The fill material then cures to form a solid concrete subbase.

A newer process is the use of dual component polyurethane foams. Compared to concrete replacement, polyurethane foam is inexpensive and exponentially faster. Repaired areas can be utilized within minutes and the process is far cleaner than traditional mudjacking.

In the event the new building owner is unable to receive a satisfactory resolution from the contractor, her only alternatives may be to seek competent legal counsel.

Ask The Pole Barn Guru: Where Can I Buy Concrete Brackets?

Greetings…and WELCOME to my new blog Feature – Dear Pole Barn Guru!

Starting today….each Monday I will post questions submitted to me about pole buildings and pole barn construction, products for use in pole buildings, along with my answers.  Scroll to the bottom if you have a burning question for the Pole Barn Guru, and look for the answer in an upcoming Monday segment of Dear Pole Barn Guru.

Concrete Bracket - Drill-SetDEAR POLE BARN GURU: Where can I buy the post to concrete heavy duty brackets? – DETACHED IN SOUTH CAROLINA

DEAR DETACHED: There are numerous brackets to attach pole building columns to concrete foundations. We’ve found only one which is capable of withstanding the moment (bending forces) which are introduced into the building columns by the wind. Contact Eric at Hansen Buildings (866)200-9657 for delivered pricing on concrete brackets.

 

DEAR POLE BARN GURU: When is the concrete floor installed and by whom?—FLAT IN LIVINGSTON

DEAR FLAT: If the pole building has a door or doors tall enough to get the premix truck inside the building, I prefer to have all of the roofing and siding on. This allows the pour to be done, without the threats of weather (baked by the sun, or whipped by winds which cause curing too fast, or rained upon). If this is not possible, at least have the building roofed, prior to the concrete floor being poured inside a pole building. For some reason, when slabs are poured with only the columns set and the pressure treated splash planks (splash boards) installed, the columns tend to grow bull’s-eyes (which are seen only by pre-mix trucks).  More than once, I’ve had a column knocked out of plumb by a truck during the pour.

 As to whom? I personally have an aversion to finishing concrete. If this is outside of your skill set, most pre-mix companies can furnish a list of finishers who service your area. My recommendation is to always purchase the pre-mix yourself and pay the finisher only for labor. I’ve seen estimates of 40-50 square feet of finished floor per finisher hour. This feels very low to me, as I know of several finishers who have no problems finishing 800-1000 square feet in a day by themselves.

 While flatwork is hard work, I’d have a hard time paying more than about 50 cents per square foot in labor costs.

 

DEAR POLE BARN GURU: Are the supports set in or on concrete pilings? – DIGGING IN TEXAS

 DEAR DIGGING: In an ideal scenario, holes are augured into the ground (in most cases a skid loader with an appropriate diameter augur bit will dig them), the pressure preservative treated timber columns are placed in the holes and then pre-mix concrete is poured to flow both below and around the columns. This is going to be the least expensive and most structurally sound scenario. Temporarily nailing a couple of 2×4’s horizontally to the post will help to keep the columns at the required distance “floating” above the bottom of the hole until the concrete is set.

Alternatively, the holes could be completely filled with pre-mix and engineered wet-set brackets are placed in the concrete to mount the columns to.

 

HAVE A QUESTION FOR THE GURU? https://www.hansenpolebuildings.com/ask-the-pole-barn-guru.php

 

 

Concrete Slab

I was talking with one of our clients yesterday. His builder was concerned because constructing the new pole building first, then pouring the concrete slab seemed backwards to him.

Here is the information I shared with the client:

While the preference is to have the building shell completed prior to pouring concrete slabs, at the very least roof should be installed.

Building columns tend to grow “bull’s-eyes” in the presence of pre-mix concrete trucks. A completed building shell is far more resistant to potential damage. Pouring slabs with columns only in place, adds to the risk of one inadvertently being knocked out of plumb.

Pouring a concrete slab in a pole barnThis blog is not meant to provide the necessary instruction to pour a building slab. Not because the task is beyond a novice’s abilities, although many do contract out this job. Pouring a slab is within most people’s abilities. However, unlike wood framing, which can be corrected if improperly constructed, work on a slab is “set in stone”. Due to this, and the fact so many local codes and practices apply to concrete slabs, I am only going to touch on this subject. If deciding to personally undertake pouring your own concrete slab, I suggest talking with local professionals to know what you are getting into. Have  a building inspector (usually a requirement in permitted situations) or a professional inspect work before pouring concrete. If less than 100% confident, hire a professional to work alongside during the concrete pour.

If in “frost country” a sub-base 6” or thicker should be first placed across the site. To maintain frost-free soils sub-base should be such that no more than 5% (by weight) will pass the No. 200 sieve, and it is further desired no more than 2% be finer than .02 mm.

Prior to pouring, 2” to 6” of clean and drained sand or sandy gravel is spread below where concrete is to be poured. Mechanically compact fill to at least 90% of a Modified Proctor Density, so as not to cause slab to sink.

Install a good vapor barrier (15ml thickness conforming to ASTM E1745) below any interior pour, to stop moisture from traveling up into slab through capillary action. Run vapor barrier up inside of skirt board (splash plank) by six inches. Vapor barrier seams should be overlapped by six or more inches and sealed with vapor tape.

The best insulation product to use under concrete slabs is closed cell polystyrene with a minimum R -10 value. Place directly on top of vapor barrier and below concrete. Insulation board seams do not need to be taped.

If not using fiber-mesh or similar reinforcement additives to concrete mixture, place wire mesh or rebar (reinforcing steel rods) in slab center to add rigidity to concrete to aid in minimizing cracking. Concrete should have a low-water mix.

Local code will dictate such things as slab thickness (usually 4” nominal), wire mesh sizing, gravel or sand layer thickness, and size and rebar location. Many garage or shop slabs also have a center drain. In the event structural engineering for a concrete floor (or any concrete or other masonry footings, foundations, walls, or retaining walls) is required or requested by you, or a building official, a registered professional engineer should be consulted for the design.

On solid walls of building, the pressure treated 2×8 splash plank will serve as forms for pouring a slab. In open wall areas, or across sliding or overhead doors, a 2×4 will need to be temporarily placed as a form.

Prior to pouring a nominal 4” (3-1/2” actual completed) thick concrete slab in building, finished, graded compacted fill TOP will be even with splash plank BOTTOM. If a thicker floor is desired, excavate below splash plank bottom, by any slab thickness greater than 4”. In no case, will the concrete floor top, be even with either top or bottom of the splash plank. Using any other measure for the concrete slab top, will result in wall steel and doors not properly fitting, as well as interior clear height loss.

In other words – after the floor is poured, when standing inside your new building, approximately 3-3/4” of the splash plank will be visible above the top of the slab.  

In the event a professional is hired to finish your concrete slab, most often costs can be reduced by directly paying the local pre-mix company for the concrete. Many offer discounts for prompt payment, so do not be afraid to ask. On a properly leveled site, a pre-mix concrete yard will cover an 80 square feet area, nominally four inches thick.

My last words of wisdom here…my best concrete slabs, were always poured by someone else.  I have learned when DIY jobs are truly DIY, and when to leave them to…a concrete professional.

Hurl Your…Concrete Cookies

I know none of us has ever experienced this condition, but we all know of someone who has had the hurling issue, often after a period of personal discussion with some of the friends of George Thorogood.

In this instance, I’m not thinking either of the example above, or the tasty oatmeal raisin cookies my grandma made for us when we were kids. I am making specific reference to the pre-cast chunks of concrete usually four to six inches in thickness and 12 to 18 inches in diameter which are sold or provided for footings in pole buildings.

The basic concept is to throw concrete cookies in the bottom of the augered holes and place the building columns directly upon them. The general idea is for the cookies to support the weight of the building, to prevent settling.

My recommendation – RUN, DO NOT WALK, away from this as a design solution.

Why?

They are a failure looking for a place to happen.

Let’s look at what a footing is supposed to do. The dead weight of the building PLUS all imposed live loads must be distributed to the soils beneath the building. Sounds pretty simple, eh?

Concrete Cookie

Concrete Cookie

To begin with, the International Building Codes require concrete footings to be a minimum of six inches in thickness. This eliminates immediately any concrtete cookies which are less than this thickness (most of them).

Examine a fairly small example – a 30’ wide building with columns spaced every eight feet. The actual weight of the building (dead load) will vary greatly depending upon the materials used. Steel roofing and siding will be lighter than shingles and wood sidings. For the sake of this example, we will use a fairly light 10 psf (pounds per square foot) building weight. The Code specifies a minimum roof live load of 20 psf. This means each footing must carry the weight of one-half of the width (15 feet) times the column spacing (8 feet) times 30 psf. Doing the math, 3600 pounds.

In many parts of the country soil bearing pressures are as little as 1500 or even 1000 psf. Basically – the easier it is to dig, the lower the capacity of the soil to support a vertical load.

For every foot of depth below grade, the soil capacity is increased by 20%. Other than with 1000 psf soils, for every foot of width over one foot, the capacity also gets a 20% increase.

With 1500 psf soil, and the bottom of the footing four feet below grade, a 12 inch footing will support 2700 pounds per square foot.

A 12 inch diameter footing covers 0.785 square feet, a 16 inch 1.4, 18 inch 1.77, 24 inch 3.14.

The 16 inch footing would support exactly the 3600 pounds from the example above. However – lots of places in the country have snow loads (which the footings must support) and many buildings are wider than 30 feet, or have columns placed over eight feet apart.

Trying a 40 foot span, with a 40 psf roof snow load, same eight foot column spacing, would mean resisting an 8000 pound load! With 1500 psf soils, even a two foot diameter footing would be inadequate.

In most cases, the use of concrete cookies as footing pads proves to be both inadequate and a waste of good money. To insure a building won’t settle, (from inadequate footings), look for a plan produced by a registered design professional who is proficient in post frame building design. He/She will have the history and training to design your building to withstand the loads…which begins with the foundation.

Concrete Sealer to Moisture Proof an Existing Concrete Slab

We were at a vendor event for the DirectBuy in Beaverton, Oregon when a member approached us looking for advice on how to seal an existing concrete floor in her pole barn. It seems the floor is always damp.

I’ve always recommended placing an insulated vapor barrier beneath any new interior concrete floor. I’ve had great results personally with the A2V product available from www.buyreflectiveinsulation.com. For those who are too late, there is a solution.

Concrete floors are notoriously damp, as moisture will pass through concrete. Think of concrete not as a solid, but instead as being a sponge – albeit a very heavy sponge.

When a concrete slab floor is not sealed, the moisture in it becomes added humidity to the inside of your building.  Over time, this will encourage the growth of mold, mildew, rot, and dust mites in your pole building, leading to damage to your building materials along with adding unhealthy allergens to your interior air space.

By sealing the concrete with a penetrating concrete sealer, moisture-related issues with concrete floors can be quickly and easily avoided.

Concrete is a porous material which will accept water, moisture, and water vapor readily from the foundation soils beneath pole barns. This moisture can be passing through in the form of water vapor even when the slab floor doesn’t appear to be damp.

One way to test the amount of moisture passing through a slab floor is to lay a sheet of plastic on the floor for several days. If the surface under the plastic is damp, then there is evidence of moisture penetration through the concrete slab.

Along with moisture, water will bring a small amount of minerals with it. As the water passes into the air, this will be left behind as a mineral salt known as efflorescence, which appears on floors as a white, powdery substance.

A solution is a silane-based concrete sealer. These sealers penetrate deep into the pores of the concrete, activating with the minerals in the concrete to create a glass-like barrier deep within the concrete. They’re safe to use indoors, and contain little or no VOC’s (volatile organic compounds – brand depending).

A silane-based concrete sealer activates quickly, and can be applied to both cured and newly-placed concrete. It will not change the appearance of the concrete, efflorescence and acidity will not harm it, and the concrete floor is able to be painted over with ease. Installation is fast (done with a brush, roller, or sprayer), and they’re middle-of-the-road in overall cost.

There are several disadvantages to consider.  One, a concrete sealer provides moisture control only, thus will not be able to breach cracks or stop flooding water. Second, it’s meant only as a sealer for water vapor which would otherwise pass through the pores of the concrete. Third, care must be used when installing as silane-based sealers cause etching on glass, should they come in contact with it. When installing, be sure to protect and/or avoid glass surfaces. And lastly, when installing be careful to only use enough silane-based concrete sealer to damp the concrete, as too much will leave a white residue behind.

Silane-based sealers are the ideal choice for concrete slab floors which are damp but do not flood, as they are inexpensive, install quickly and subtly, and provide a lasting solution.

A How To: Pouring a Concrete Slab

I was talking with one of our clients yesterday. His builder was concerned because constructing the new pole building first, and then pouring the concrete slab seemed backwards to him.

Here is the information I shared with the client:

While the preference is to have the building shell completed prior to pouring concrete slabs, at the very least the roof should be installed.

Building columns tend to grow “bull’s-eyes” in the presence of pre-mix concrete trucks. A completed building shell is far more resistant to potential damage. Pouring slabs with columns only in place, adds to the risk of one inadvertently being knocked out of plumb.

This is not meant to provide the necessary instruction to pour a building slab. Not because the task is beyond a novice’s abilities, although many do contract out this job. Pouring a slab is within most people’s abilities. However, unlike wood framing, which can be corrected if improperly constructed, work on a slab is “set in stone”. Due to this, and the fact so many local codes and practices apply to concrete slabs, I am only touching on this subject. If deciding to personally undertake this task, I suggest talking with local professionals to find out exactly what you are getting into. Have the building inspector (usually a requirement in places requiring a building permit) or a professional inspect work before pouring concrete. If you are less than 100% confident, hire a professional to work alongside you during the concrete pour.

If in “frost country” a sub-base 6” or thicker should be first placed across the site. To maintain frost-free soils the sub-base should be such that no more than 5% (by weight) will pass through the No. 200 sieve, and it is further desired no more than 2% be finer than .02 mm.

Prior to pouring your concrete slab, 2” to 6” of clean and drained sand or sandy gravel is spread below where concrete is to be poured. Mechanically compact fill to at least 90% of a Modified Proctor Density, so as not to cause the slab to sink. Install a good vapor barrier (such as A2V reflective insulation, available through https://www.buyreflectiveinsulation.com ) below any interior pour, to stop moisture from traveling up into the slab through capillary action. Place 3” to 4” of clean and drained sand on top of the vapor barrier to decrease differential drying shrinkage and floor curling.  If not using fiber-mesh or similar reinforcement additives to the concrete mixture, place wire mesh or rebar (reinforcing steel rods) in slab center to add rigidity to the concrete to aid in minimizing cracking.

The best insulation product to use under concrete slabs is A2V reflective insulation. A2V is a double layer on air cells, sandwiched between a white vinyl facing on one side and a reflective aluminum facing on the other. Unroll reflective insulation over the prepared site sand or gravel, with aluminum side facing towards the ground (white side up). Overlap by 2” at seams. Run reflective insulation up the skirt board inside by 6”. Seal seams with reflective insulation white vinyl tape or white duct tape. Pour concrete on top of the reflective insulation.

Aluminum side faces away from the concrete because concrete’s high alkalinity attacks aluminum causing the facing to degrade.

Adding sand over reflective insulation will facilitate water drainage during curing time and accelerate installation.

Local building code will dictate such things as slab thickness (usually 4” nominal), wire mesh sizing, gravel or sand layer thickness, and size and rebar location. Many garage or shop slabs also have a center drain. In the event structural engineering for a concrete floor (or any concrete or other masonry footings, foundations, walls, or retaining walls) is required or requested by you, or a building official, a registered professional engineer should be consulted for the design.

On solid walls of building, the pressure treated 2×8 splash plank will serve as forms for pouring slab. In open wall areas, or across sliding or overhead doors, a 2×4 will need to be temporarily placed as a form.

Prior to pouring a nominal 4” (3-1/2” actual completed) thick concrete slab in building, finished, graded compacted fill TOP will be even with splash plank BOTTOM. If a thicker floor is desired, excavate below splash plank bottom, by any slab thickness greater than 4”. In no case will the concrete floor top be even with either the top or bottom of the splash plank. Using any other measure for the concrete slab top will result in wall steel and doors not properly fitting, as well as interior clear height loss.

In other terms – after the floor is poured, when standing inside the building, approximately 3-3/4” of the splash plank will be visible above the top of the slab.  

In the event a professional is hired to finish concrete, most often costs can be reduced by paying the local pre-mix company directly for the concrete. Many offer discounts for prompt payment, so do not be afraid to ask. On a properly leveled site, a pre-mix concrete yard will cover an 80 square feet area, nominally four inches thick.

It’s obviously a good idea to completely finish your building at time of construction by pouring your concrete slab.  However, I have known of several customers who chose to pour it “later”, thus spreading out costs of their project over time.  Whenever you add the concrete floor, carefully follow these introductory points to ensure a level concrete slab…at the correct height.

Where is the Top of the Concrete Slab?

This is not like Where’s Waldo?, or Where in the World is Carmen San Diego?

The relationship of the top of a concrete slab inside your new pole building, to the grade surrounding the building is critical not only during construction, but also in the lifetime of performance of your building.

Hansen Pole Buildings services pole building kit package clients for several major lumber yard chains. One of them kindly provided us with a set of the building plans they had been supplying to their everyday client base. As I began to review the plans, I was astounded to find the building was designed so any concrete floor being poured had the top of the slab even with the grade outside of the building.

In the event of a rainstorm, or heavy snow melt, water would easily coming pour into the building!

Your new Hansen Pole Building has as the bottom horizontal framing member, connecting pressure treated column to pressure treated column, is a pressure preservative treated splash plank. The building design is such so the top of any concrete floor is set at 3-1/2” above the bottom of the splash plank.

On the outside of your building, assuming it is steel sided, the base trim (also known as rat guard), is installed so the lowest point of the drip edge is four inches above grade. This allows for any concrete driveway approaches or doorway aprons to be poured appropriately in relationship to the top of the level of the interior slab. It also keeps any exterior concrete from being poured against steel trims or siding.

While proper jobsite preparation and compaction of fill beneath a concrete floor has more to do with the performance of the slab than does thickness, some clients want floors thicker than the typical nominal four (3-1/2” actual) inches. If a thicker floor is desired, excavate below skirt board bottom, by any slab thickness greater than 4”. In no case, will the top of the concrete floor be even with either the top or bottom of the splash plank.

Occasionally we have clients who ask why they can’t run the concrete to the top of the splash plank, as they want to use the splash plank to “screed” the concrete slab top.   Using any other measure for the concrete slab top, will result in wall steel and doors not properly fitting, as well as possible interior clear height loss.

TIP:  If you want to use a board for screeding the concrete slab, take a 2×4 pressure treated board and nail it to the inside of the splash plank with the bottom of the 2×4 even with the bottom of the splash plank.  This board stays concreted in around the perimeter of your concrete slab.  Quick.  Easy.  And ensures a level concrete slab, at just the right height.