Detailed Vertical and Overhead Instructions

 For a printer friendly version of the written instructions, please access the PDF Library.

Site Preparation

Ensure that Surface is Clean and Dry: For most vertical work such as Retaining Walls, Bridge Pillars, Columns, Ceiling Joists, and Curbs, there is very little preparation necessary to ensure the area is clean and free of contaminants. If needed, use chipping hammers, grinders, blasting equipment to mechanically remove loose concrete, corrosion, dirt and all contamination to produce a clean, dry, rough surface. Usually a wire brush is more than sufficient to clean the concrete or any rusting rebar. If you are fixing a curb where the damage has been painted over, you will want to grind the paint off with an angle grinder equipped with a diamond cup wheel or stone. You will want to use a leaf blower to get all the remaining dust and grit out of the cleaned area.

Tape or No Tape: If you want a flush to grade repair, you do not need to use duct tape, although some applicators use duct tape to mirror the damaged area. If you prefer an above grade-cut-out-look you will want to use duct tape to symmetrically tape off around the repair.

Mixing and Applying FlexPrime

(Same as Horizontal/Flatwork - Except for special priming)

Estimate Amount of FlexPrime:  You are going to mix enough FlexPrime to paint a VERY THIN coat that completely covers the concrete and voids within the repair area.  A simple way to estimate the amount needed is to estimate approximately 300 square foot of coverage per gallon. (i.e. 2.5 sf. an ounce) (38 sf. a pint) (75 sf. a quart).

Mix and Apply FlexPrime: Mix equal parts of A & B for 1 to 3 minutes, and apply a VERY THIN COAT with a brush, roller, or spray.

Allow FlexPrime to Tack: For vertical repairs it is critical to ensure that the FlexPrime is TACKY enough to hold the FlexKrete in place while it cures. The FlexPrime should be tacky enough to ensure the repair material achieves a mechanical bond to the repair area. Depending on the temperature, FlexPrime can take 15 to 30 minutes at 70 degrees and much longer when cold outside. If you do not want to wait for the FlexPrime to reach it's VERY STICKY stage, a torch can be used to preheat the concrete before applying FlexPrime so that it will tack more rapidly.

Special Priming

Fast Option - Overcoat Primer: If you are in a rush and cannot wait for the FlexPrime to completely tack up, you can mix up a FlexKrete Resin Priming Coat using the standard catalyst and our FlexTemp Accelerator / Additive. The FlexKrete resin painted on top of the FlexPrime can speed up the thermosetting and tackiness of both materials.

Fast Option 2 - FlexKrete Resin Priming Only - On dry concrete some contractors omit the FlexPrime altogether and substitute with a thick coat of the FlexKrete priming coat only.

Mixing and Applying FlexKrete

Estimate The Volume of FlexKrete Slurry Needed: Since you will want to mix enough slurry to fill the repair area but not throw any away, it is a good idea to have all the repair areas in the immediate area, primed and ready. The simplest method is to look at the repair and estimate the volume of sand required to completely fill the void, and then divide by 2 to determine the amount of FlexKrete needed. (Example: One gallon void 2 = gallon of FlexKrete to 1 gallon of fumed silica and 1 gallon of sand

Determine Consistency of FlexKrete Vertical/Overhead Slurry: A good starting point for a stiff batch is 1 part FlexKrete, 2 parts amorphous fumed silica, and 2 parts medium blasting sand. MORE FUMED SILICA MAKES IT STIIFFER, LESS SAND MAKES IT LIGHTER. If you are doing overhead repairs that are very thick, you may want to cut back on the sand to 1.5 parts to lighten up the slurry. For curbs, you can cut back on the parts of fumed silica and replace with sand if you do not need that stiff of a mixture. You can vary the ratios to meet your needs.

Vertical Applications: After measuring and catalyzing FlexKrete, mix in 2-parts blast sand and 2 to 3-parts fumed silica. 3-parts fumed silica produces a stiff, dough-like material that can be hand-placed and toweled smooth. 2-parts fumed silica and 2-parts sand produces a less-stiff material and recommended as a good starting point to evaluate ratios needed.

Overhead Applications: After measuring and catalyzing FlexKrete, mix 1-part blast sand and 2 to 3-parts fumed silica. If material is too heavy, decrease amount of sand.

Mixing the Vertical/Overhead Slurry: The easiest way to mix in the fluffy fumed silica is to catalyze the FlexKrete for one minute, then stop mixing. Then add fumed silica and load most of the sand on top of it, working it in manually with your rectangle paddle before paddle mixing. Some applicators also use cardboard covers over their mixing bucket to prevent loss of fumed silica. You should always wear respiratory protection when working around fumed silica.

Trowel Slurry: The vertical slurry mix is very stiff like bread dough or silly putty, therefore, the easiest way to get the material out of the bucket and onto the repair is to use a gloved hand to simply grab handfuls of material and pack them into the void above grade. Then you can then slice to grade or trowel above grade to the tape. Keep your stainless trowels clean by wiping with acetone frequently.

Retain Expansion Joints: On vertical and overhead repairs it is usually easiest to place expansion joint strips at the point of movement, while you are packing in the FlexKrete slurry.


Finishing: If you use the tape off method, you should pull the tape before the repair is set up. If you use the “Flush-to-Grade” method, and the area is not going to be painted, you may want to put some finishing touches on the cured repair with an angle grinder or stone for final smoothing, "dusting" and/or color matching.

Contact us for more info

On this page we have shown you how to easily repair vertical and overhead damage to concrete that includes how to repair a concrete stoop, how to repair voids in a concrete a wall, how to repair concrete steps, how to repair swimming pool concrete coping, how to repair a concrete wall or ceiling and many more applications.