Concrete Flatwork Tips for Your Morton Building Project

August 4, 2020

Some of the most experienced concrete contractors may not be familiar with pouring a floor in a Morton building. If a Morton customer is working directly with their own concrete subcontractor, we highly recommend that they share the following information with their concrete contractor early in the building process.

The building height stated on our building contract is the distance from the bottom of the standard splashboard, also called GRADE, to the bottom of the truss heel. Concrete floors are typically poured with the top of the floor 4" above grade (the sill of the walkdoor that is cut into our splashboard indicates where top of floor should be). This reduces the overall inside clearance by the thickness of the concrete floor above grade (4" typical). Floors thicker than 4" have the additional thickness poured below grade (see details following). Use expansion joint material or ridged foam board insulation to prevent concrete from getting under the splashboard or framing for walk doors. Also, if you are pouring your floor in colder weather, be aware that it will take longer for the concrete to cure. You should never pour concrete flatwork over frozen ground.

To reduce the potential for condensation from ground moisture, a vapor retarder (6 mil minimum) is recommended under the concrete floor. If the building will have any interior finishes, a 6 mil minimum vapor retarder is to be installed continuously under the concrete floor slab extending up to the 2x4 baseboard or 2x laminated column. If interior liners are already installed, protect those areas with a sheet of plastic when placing the concrete.

Sliding Doors

Building features such as sliding doors, overhead doors and walk doors are all positioned assuming a concrete floor with floor level four inches above grade which is the bottom of the treated splashboard. If a thicker floor is poured it is assumed that the additional concrete will be lower than the splashboard. Either expansion joint material or rigid foam board insulation can be used to ensure the concrete does not extend under the splashboard.

If you plan to pour a concrete floor with a floor level greater than four inches above the bottom of the splashboard you must consult with your Sales Consultant or Crew Foreman to allow adjustment of other features in the building to ensure their proper function.

It is recommended that the concrete floor be poured to extend out to form a threshold under the sliding door panels as shown in the detail below. This threshold should be incorporated into a continuous trenched footing below the frost line or a well-designed post and beam footing through the door opening to help eliminate frost heaving problems. Good drainage, both surface and subsurface, also helps eliminate frost heaving problems. When digging a trenched or post and beam footing, remove the center door guide stub column. Save the center door guide for re-use when pouring the threshold. It must be placed in the same location that it was prior to its removal.

To form a concrete threshold at a sliding door, slope the 4" floor 3/4" from the inside of the jamb columns down to 3-1/4" above grade at the outside of the jambs. From this point, drop down 1-1/2" to form a lip for the door to seal against. If more durability is desired, the lip can be formed with a steel angle iron embedded in the concrete. The angle iron should have anchor rods or 9" long pieces of #4 rebar welded to it 16" on center to anchor it to the threshold. See the detail below.

If the door is adjusted properly, there should be approximately 1/2" of vertical clearance between the bottom of the door panel and the concrete at the bottom of the lip. At the bottom of the lip, slope the concrete away from the building at 1/4" per foot.

Overhead Doors

Floors poured for overhead doors can be sloped through the opening or sloped to the opening with a 1/2" recess behind the door. It is important that the elevation of the concrete under the door is three inches above grade and that this elevation extends to a point that is six inches beyond the door jambs (under the door track). Approaches are to have an expansion joint between the floor of the building and the approach.

If you have any questions or concerns regarding concrete work for a Morton building, please reach out to your local sales consultant.

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