Quikrete and Sakrete don’t print a list of what concrete won’t stick to. They tell you to coat the form: Quikrete’s countertop data sheet calls for a light coat of form-release agent on every form, insert and knockout. To make new concrete hold on old concrete, Quikrete and Sakrete sell bonding agents.
Forms and molds
| Product or guide | Form or mold | What the maker says |
|---|---|---|
| Quikrete Countertop Mix (data sheet) | Forms, inserts and knockouts | A light application of form-release agent; leave the forms undisturbed for 18 or more hours |
| Quikrete countertop forming steps | Melamine, with the seams caulked in silicone after masking with painters tape | No release agent in the steps; cover with plastic sheeting and wait at least 18 hours |
| Smooth-On AquaCon | Smooth-On rubber molds, latex molds, melamine, metal and sealed wood | A water-based concrete release; use it straight for the first 10 castings in a new rubber mold |
| Sakrete slab guide | Lumber forms | Run an edging tool between the slab and the form “to encourage a clean release” |
From each maker’s data sheet, product page or project guide. Quikrete’s data sheet and its forming steps are for the same countertop mix; we’d follow the data sheet and coat the forms. Smooth-On says AquaCon contains no oils that will cause rubber molds to soften, shrink or swell, and not to use it below 45°F.
Quikrete also says to keep the curing tent of plastic sheeting off the fresh concrete, because it will leave surface imperfections, and to take extreme care removing inserts and knockouts.
New concrete on old concrete
Quikrete sells its Premium Concrete Bonding Adhesive to bond new concrete, plaster and stucco to existing concrete, plaster and stucco. Its data sheet says to remove dust, dirt, oil, grease, wax and paint first, and not to use it over previously painted surfaces or below 50°F. Quikrete’s FAQ adds that it isn’t for continuously wet places.
- 1 to 2 inches thick: Quikrete’s FAQ says to paint Concrete Bonding Adhesive on the old surface and let it dry before the new concrete or Sand Mix goes on.
- Thinner than 1 inch: Quikrete’s resurfacing FAQ says to add Concrete Acrylic Fortifier to the mix for toppings under 1 inch; its bonding FAQ says that for exterior work under 1 inch, but also says Bonding Adhesive can be used for interior applications. Its data sheet says not to use the two together.
- Sakrete Concrete Bonder & Fortifier: Sakrete says to clean off dirt, oil, grease, paint and loose material, and that the bonder should be tacky when the fresh patch goes on.
- Don’t soak it: Sakrete’s slab capping guide says not to bring the old slab to saturated surface dry (SSD) when you use a bond-enhancing admixture, since water can act as a bond breaker there.
Quikrete’s safety data sheet for its Portland cement concrete products says they cause severe skin burns and serious eye damage and may cause an allergic skin reaction, and that cement burns may not hurt right away. Quikrete says to always wear eye protection and waterproof gloves.
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