Architectural Concrete (SC) Installation Specifications
The repair areas must be cut to regular geometry (no sharp angled corners or curved edges). The minimum patch depth for this material is 2.5” but the average patch depth should be more like 3-4” deep. Ideally, the concrete substrate should be sandblasted to remove all loose material and to provide for a textured surface. Chiseling out the repair area also provides for a rough texture which increases bond strength. The rougher the bond surface the stronger the bond will be.
There must be a minimum 1” spacing between the rebar and the concrete substrate in order to allow the repair material to consolidate properly around the reinforcing. Cathodic anodes shall be linear and roughly the same width as the rebar itself. The anodes shall be installed on the top or bottom of the rebar and NOT on the sides between the rebar and formwork or between the rebar and concrete substrate. Anodes installed on the sides of rebar can restrict the flow and consolidation of the repair material within the repair area.
Prior to installing the repair material, the existing concrete substrate must be flooded with water to achieve SSD (saturated surface dry). This means the existing concrete retained so much moisture that it can no longer absorb any additional water but remains dry on the surface. To achieve SSD it is necessary to water the repair area with a hose for 10+ continuous minutes and then allow all standing water to evaporate. The more moisture that is pushed into the substrate the less mix water it will absorb from the repair mortar and it will make for a strong bond and a more durable repair.
We do not have a preference for the type of plywood that is used to form the repair areas. However, it is strongly encouraged that the forms be sprayed with a Euclid Formshield PURE on the inside surface the day the patches will be poured. The form release agent will help reduce friction against the forms and will aid in the flow and consolidation of the repair mortar. Release agent will also help reduce absorption of mix water into the wood forms which will change the water to cement ratio in the mix and can also restrict flow of the repair mortar.
We advise that the bottom of the birds mouths be placed at the very top of the repair area to help spread the repair mortar to both ends of the repair area. Birds mouths that are placed below the top of the repair can cause a mounding effect as the mortar is poured which may restrict flow to the edges of the repair area. Make the birds mouths as wide as possible. Multiple birds mouths should be installed on patches that are longer than 12-14 inches so there is no more than 12” between birds mouths. The area of the existing concrete directly behind the birds mouths shall be removed to the full depth of the patch to provide for additional space for the repair mortar to be poured into. This keyway above the patch area shall be filled with the same repair mortar. Whenever possible, cut the patch area to the top of the spandrel so the entire length of the form can be exposed for pouring the patching material.
Each pail of repair mortar shall be mixed with the specific water content provided by Centurywerks. It is critical that the correct amount of water is used to mix each pail or workability, performance and coloration may be altered. It is acceptable to fabricate measuring devises by weighing out the correct water amount in a clear vessel and marking a fill line on the vessel. MIX WATER MUST BE MEASURED OUT ACCURATELY FOR EACH PAIL.
Pour carefully measured water into the pail of pre-blended repair mortar. Using a variable speed, high speed mixer with a heavy-duty ribbon paddle, mix each pail for approximately 180 seconds total. Consider using an Eibenstock EHR 20.1R mixer which provided excellent results during our trial batches and the site mockups.
Start the mixing process on a low speed so as not to slosh out ingredients before they are incorporated into the mix. After mixing for 120 second, tilt the pail and scrape the bottom corners of the bucket with a margin trowel to remove any unmixed powder. Continue mixing at a low speed for another 60 seconds. Immediately after mixing, pour the pail of repair mortar into the form.
While one person is slowly pouring the mixed pail of repair mortar into the form, a second person shall tap the face of the form to help spread the repair mortar into all corners of the void. Hammering the face also removes air pockets trapped along the formwork which can appear as unsightly voids after the patch has been cured and sandblasted. Rodding or vibrating the repair mortar within the form is not advisable because this can cause segregation of the course aggregates.
Subsequent pails of repair mortar shall be prepared by another worker while the preceding pail is being poured into the form so that each pail of mortar is poured on top of the other almost immediately. This process will help reduce unsightly pour lines within the patch. DO NOT SCRAPE RESIDUAL REPAIR MORTAR FROM SIDES OF AN EMPTY PAIL INTO THE FORM. If this is done you will see a layer of cement paste without any course aggregate in your patch which will be unsightly and may perform poorly overtime. You may scrape residual material into a fresh bucket of repair mortar and mix it into the next batch if you so desire.
As the patch area fills to the top with repair mortar, you will need to be extra vigilant to ensure the repair mortar flows evenly to the edges of the patch area and makes contact with the top edge of the patch area. To do this you will want to pour more slowly and wait for the material to settle into the form before pouring again. Use a hammer to continue tapping somewhat aggressively along the top edge of the form to help the material flow and consolidate along the top of the void via vibration. Consider rodding a few times in short rapid motions in the middle of the birds mouth at the very top of the pour to help jiggle the repair mortar into the sides of the form. Do not rod the material deeper than an inch or so from the surface or you will cause unwanted aggregate segregation deeper within the patch. Continue this slow process until you believe the top of the void is 100% consolidated with concrete.
The formwork can be removed within 24 hours but the repairs must be kept damp for a minimum of 3-days. This can be achieved by leaving the formwork on for that three-day period and shading the area against wind, sun and heat. If you remove the formwork earlier then shade the areas and mist them with water several times a day for three days.
Experiment with removing the birds mouth from the poured patch about 4-8 hours after pouring. The repair mortar should be stiff enough to remain in tack but soft enough to be able to carve the protrusion down to the appropriate finished surface. If this process works but leaves too rough a surface, consider taking some paste from a pail of mixed repair mortar and brushing or troweling it onto this rough surface to help smooth it out. Allow this area to damp cure for three days prior to sandblasting. Avoid scraping out large aggregate which will leave large voids in the patch.
After a 12 hour cure use a sandblaster and Back Diamond grade 3060 (fine) blasting sand to carefully remove the paste from the surface of the patches. The nozzleman should hold the nozzle at least 3-4 feet away from the face if at all possible.
He will need to read the aggregate exposure on the surrounding existing concrete as he is blasting the repair areas to mimic the same weathering patterns in the repair area. Some repair areas may only require a very light sandblast to expose only the sand while other repairs may require a heavier sandblast to expose varying amounts of course aggregate. Most patches on this building may even require several varying degrees of blasting within a single patch to produce an uneven weathering effect that matches the weathering patterns on the building.
Paste can also be removed through powerwashing, scrubbing, or acid wash. The surface cleaning should be determined by the exposure needed to replicate the original concrete.
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