Powdery white stains on your retaining wall are likely caused by efflorescence. As concrete cures, moisture slowly migrates to the surface of the block where it evaporates into the air.
Like a candle wick, the water brings dissolved salts and minerals from within the concrete mixture. As the water evaporates, those minerals are left on the surface of your block, giving it a whitish, hazy or streaky stain.
In most cases, this problem is temporary — eventually, the salts will all be removed from the concrete, and the efflorescence will stop. How long this takes depends on the ingredients with which the concrete was made, and how long it takes for the concrete to cure and dry out completely.
However, with landscape retaining walls, your blocks are continually being exposed to groundwater and hydrostatic pressure, which can force moisture (and more salts from the soil) into the blocks to later show up as efflorescence.
Here are some tips for dealing with efflorescence:
- Efflorescence is ugly, but it does not affect the strength or functioning of the block.
- Normal efflorescence should stop once the concrete is completely cured. Ongoing streaky stains or cakey buildup, particularly at joints and cracks, may indicate a problem with water infiltration and drainage.
- It’s important to reduce the amount of moisture that is getting into your wall. Mortared walls should be treated on both sides with a waterproofing sealer. Non-mortared, stackable retaining walls should be backfilled with gravel, with water drainage directed off to the sides. This prevents water pressure from building up in the soil behind the wall (and forcing itself into the concrete blocks).
- Avoid pressure-washing or overly wetting your blocks. This makes them look nice at the time, but it forces water into the concrete, inviting more efflorescence.
- Clean off light stains with a dry, stiff brush, then remove the dust with a damp sponge. If you have heavy stains, try scrubbing with white vinegar. Stubborn stains can be removed with a masonry cleaning solution.
- Cleaning solutions are often specialized to address particular mineral stains. Check their labels carefully.
Listen to the Today’s Homeowner Podcast for more home improvement tips!
- [1:29] How to prevent paint from cracking
- [7:38] How to get efflorescence off a concrete retaining wall
- [13:33 Best New Product: Behr Ultra Scuff Defense Paint
- [15:09] DIY-friendly way to repair creaky floors in a second-floor apartment
- [16:55] Tips for removing stains from vinyl flooring in a camper
- [19:48] Tips for choosing the right baseboard
- [24:52] Simple Solution: How to easily make a shelf that attaches to pegboard — followed by some general pegboard tips
- [28:12] Fan Feedback: Danny’s suggestion to use silicone caulk to prevent slipping worked perfectly for this listener’s workout mat
Simple Solutions
Pegboard Shelf — Perforated pegboard provides an easy way to organize hand tools by hanging them on metal hooks. Here’s how to add a shelf for storing items that aren’t easily hung by hooks, such as glue bottles, tape measures, and cans of machine oil. Start by cutting a 1×4 to eight or 10 in. long. Then measure in 1 in. from each end of the board and drill a 3/16-in.-dia. hole into the back edge. Be sure to bore the holes at least 1½ in. deep. Insert into each hole a short, straight pegboard hook, then use the two hooks to hang the shelf on the pegboard panel.
Watch How to Hang a Shelf on Pegboard
Untying Tight Knots — To loosen an especially tight knot in a rope, cable or twine, reach for your nail set. A nail set with its rigid shaft and narrow, tapering tip is perfect for busting loose stubborn knots. Start by forcing the tip of the nail set into the heart of the knot. Wiggle it around a little, then force it in a little deeper. Continue in this manner until the entire tapered tip has passed through the knot. Now use your fingers to the tip of the nail set to “hook” one of the rope strands and pull straight back. At this point there’s usually enough slack so that you can easily untie the rope. If you don’t have a nail set, try an awl or Phillips screwdriver.
Fan Feedback
“I was listening to one of your podcasts recently, and a suggestion you had about making a throw rug non-slip was a huge help to me!” TH fan Rosemary Rollman writes.
I am making my small living room into a workout room. My son bought me a ‘puzzle piece’ mat, and I was going to use a non-slip rug mat to keep it from sliding around.
“You suggested to a listener to use silicone caulk on his rug. So I did the same on each piece of my mat. It works perfectly! I can do jumping jacks or whatever I need to, and those pieces do not move. Thank you so much. What a great suggestion!
Other Products and Links Mentioned
- Simple Green Concrete Cleaner
- Zep Concrete Cleaner
- Rust-Oleum Concrete Cleaner
- Home Depot
- O’Berry Squeek No More
- Drylok