Q: I have an old concrete porch that has never been painted. I will paint it with terrace latex paint. I plan to clean it with TSP (Trisodium Phosphate) and then apply a concrete bonding primer. Do I need to etch before applying primer?
Answer: It is wise to be cautious when performing the necessary preparation steps. Getting paint to stick to concrete is much more difficult than sticking to wood. The last thing you want is paint peeling, especially on porches that have survived without paint in these years.
When the paint does not stick to the concrete well, it is sometimes because moisture enters through the concrete from below. To check, place a relatively thick piece of clear plastic (such as a 3-inch square cut from a resealable plastic bag) on the unpainted area. If water drops appear the next day, you may want to leave the porch as it is.
Another important reason why paint sometimes does not stick to concrete: the surface is too smooth and dense. The installer usually smears concrete on the porch and floor to form a very fine sand coated with grout. This makes the surface denser than the concrete further in the slab. When concrete appears in the weather, the surface will wear down over time, which is why you can often see exposed sand and even gravel on old concrete walkways and terraces. However, on the porch, the color of the surface may be almost as dense and uniform as when the concrete is poured. Etching is a way to roughen the surface and make the paint adhere better.
But etching products only work if the concrete is clean and uncoated. If the concrete is painted with paint, you can easily spot the paint, but the sealant that also prevents the paint from sticking may be invisible. One way to test the sealant is to pour some water. If it sinks into the water, the concrete is bare. If it forms a puddle on the surface and stays on the surface, it is assumed that the surface is sealed.
If the water sinks into the water, slide your hand across the surface. If the texture is similar to medium to rough sandpaper (150 grit is a good guide), you may not need to etch, although it will certainly not be harmed. If the surface is smooth, it must be etched.
However, an etching step is required after cleaning the concrete. According to the technical assistance staff of Savogran Co. (800-225-9872; savogran.com), which produces these two products, TSP and TSP alternatives are also suitable for this purpose. A pound of a box of TSP powder only costs $3.96 at Home Depot, and it may be enough, because half a cup of two gallons of water can clean about 800 square feet. If you use a high-pressure cleaner, a quart of liquid TSP replacement cleaner, priced at $5.48, will be easier to use and can clean about 1,000 square feet.
For etching, you will find a series of confusing products, including standard hydrochloric acid and products such as Klean-Strip Green Muriatic Acid ($7.84 per gallon for Home Depot) and Klean-Strip Phosphoric Prep & Etch ($15.78 per gallon). According to The company’s technical help staff said that the “green” hydrochloric acid had a low concentration and was not strong enough to etch the smoothed concrete. However, if you want to etch concrete that feels a bit rough, this is a good choice. Phosphoric acid is suitable for smooth or rough concrete, but you don’t need its big benefit, that is, it is suitable for concrete and rusty metal.
For any etching product, it is very important to follow all safety precautions. Wear full face or half face respirators with acid-resistant filters, goggles, chemical-resistant gloves covering the forearms, and rubber boots. Use a plastic spray can to apply the product, and use a non-metallic broom or a brush with a handle to apply the product to the surface. A high-pressure cleaner is best for flushing, but you can also use a hose. Read the complete label before opening the container.
After etching the concrete and letting it dry, wipe it with your hands or a black cloth to make sure it does not get any dust. If you do, rinse again. Then you can prepare the primer and painting.
On the other hand, if you find that your porch is sealed, you have several options: remove the sealant with chemicals, grind off the surface to expose exposed concrete or reconsider your options. Chemical peeling and grinding are really troublesome and boring, but it’s easy to switch to paint that sticks even on sealed concrete. Behr Porch & Patio Floor Paint seems to be the type of product in your mind, even if you use a primer, it will not stick to the sealed concrete. However, Behr’s 1-part epoxy concrete and garage floor paint is marked as suitable for directly covering previously sealed concrete, provided that you clean the floor, sand any shiny areas and scrape off any peeling sealant. (The “wet appearance” concrete sealant forms a surface film that can peel off, while penetrating the sealant will not change the appearance and never peel off.)
But before you promise to paint the entire porch with this or any similar product, paint a small area and make sure you are satisfied with the result. On the Behr website, only 62% of 52 reviewers said they would recommend this product to friends. The average ratings on the Home Depot website are roughly the same; among the more than 840 reviewers, nearly half gave it five stars, which is the highest rating, while about a quarter gave it only one star. Is the lowest. Therefore, your chances of being completely satisfied and completely depressed may be 2 to 1. However, many complaints involve the use of the product on the garage floor, the car tires will put pressure on the finish, so you may have a better chance of being happy on the porch.
Despite this, there are still many problems with painting concrete. No matter which finish you choose, or how careful you are in the preparation steps, it is still wise to paint on a small area, wait for a while and make sure the finish sticks. . Unpainted concrete always looks better than concrete with peeling paint.
Post time: Aug-30-2021