How to Install a Skim Coat for a Concrete Floor
Adding a skim coat is important because it will strengthen the floor, and when colored, acts as a primer coat for the second hand-trowelled coat of finish.
This project must begin with a completely clean concrete surface. The overlay will chemically bond with the concrete so any paint on the concrete must be removed. Using a grinder with a diamond blade, grind in smooth circular movements until the concrete is the only thing left (image 1). Use a 3000 psi power washer to clean the newly exposed surface and get rid of dirt and debris. The goal is to remove dirt that an ordinary hose would not (image 2).
In a clean bucket, mix eight parts water to one part muriatic acid. The acid will etch the concrete, exfoliating it and opening its pores. Muriatic acid is caustic and hazardous. Follow the manufacturer's safety precautions to the letter. In a separate bucket mix eight parts of water to one part ammonia. Flood the porch with the acid solution first. Spread it with a broom so everything is covered. Once the acid stops fizzing, flood the porch with the ammonia mixture to neutralize the acid and adjust the pH. The ammonia reacts immediately, don't wait to let it take effect. Power wash the porch again to rinse excess acid and ammonia from the porch.
Prep the house for the skim coat by taping the door jambs and edges of the house with painters tape. This step ensures that the skim coat doesn't bond to the house.
To mix the thin finish skim coat, use a mixing paddle and heavy duty mixing drill and place it in an empty five gallon bucket. Add seven to eight quarts of water to the bucket first, and then add a 55-lb bag of thin finish. Wear a mask, and mix the finish so that the consistency is very soupy, with no lumps. Let the material set for five minutes and then re-mix.
Make sure the concrete is wet, but with no puddles. Pour the skim coat out in sections and spread it in U-shaped motions with a squeegee (image 1). Start at the edge and work away from the house (image 2). Spread the skim coat evenly and without lines. Use a paintbrush for the edges, since the squeegee is too big. The skim coat should dry for several hours before beginning to apply the next stamping coat.
For the stamping layer, apply a thin bonding layer of Thin Finish®, and a thicker layer of Texture Pave®. To mix the Thin Finish, follow the same instructions and water ratio used for the skim coat. The texture pave is mixed similarly, but will be thicker – to create a stamping layer, mix four quarts of water per 55 lb. bag. This mix should also be thoroughly mixed first, allowed to set for five minutes and mixed again. Because several batches are required make sure the four quarts is exact to ensure consistency.
Wet the concrete substrate thoroughly. Leaving dry spots will create puddles when stamping. Squeegee off excess water (image 1). Squeegee on a layer of Thin Finish. Work in small sections, and apply the Texture Pave. Set the gauge rake to 1/4 of an inch. Pour out the Texture Pave and spread one bucket at a time. Use the gauge rake to spread and always keep the handle at the same height so the product spreads at the same thickness. Smooth out the lines by floating a squeegee across the surface (image 2). Don' t forget to paint the sides, and allow the texture pave to set up before stamping.
Allow the Texture Pave to dry according to the manufacturer's recommendations to the point it is stampable. Start at the outside edge of the concrete area and work towards the opposite end. Spray a liquid release agent on the bottom of the polyurethane stamp and the area of the porch to stamp. Apply the stamp to the concrete, and press down with hands or feet starting at the outside edge of the stamp and working towards the center. Set the next stamp adjacent to the first and overlap the edges by three to four inches. Alternate the orientation of the stamp to enhance a more random pattern. Allow it to dry for six to eight hours.
Use a rubbing stone to take out all the divots and lumps of concrete that have dried overnight. Rub the edges and clean the dust off.
Although not necessary, a border pattern can be added by scribing a groove in the Texture Pave parallel to the edges of the porch using a carbide-tipped tile scribe (Images 1,2 and 3).
Protect the house with paper and tape (image 1), and apply the stain by using a pump sprayer (image 2). Two coats are usually required with the first being a primer and the second being the finish color. Wait at least an hour between spraying coats. Use a broom to push any color out of puddles and keep a rag handy for any spills.
Apply sealer according to manufacturer's instructions. Usually application can be done with a paint roller.