Dealing with unsightly mineral deposits on brick
Darnestown, Md.
A: The flagstones can be removed, but that might not be the way to solve your problem.
Although you say the flagstone was installed over poured-concrete steps that are integral to the foundation, that would be an unusual way of building steps. Typically, concrete steps are cast separately, with flashing installed to keep water from seeping through the concrete into the section of the wall that’s between the foundation and the door threshold. Fill material — tamped soil, broken concrete, gravel — fills most of the space so that concrete is only along the sides, the risers and the treads.
Mineral deposits, known as efflorescence, form where mineral-laden water evaporates, leaving other ingredients that were in the water behind. Typically, the deposits form where water moves through the masonry and picks up minerals, either from the soil or from the masonry materials themselves. But they can also form where there are minerals on the surface.
In the picture you sent, the efflorescence appears to be only in the mortar joints next to the patio and on the patio paving itself — not on the higher risers or even in the mortar that’s right under the bottom tread. These are clues that the moisture probably isn’t coming through the flagstone, unless the bottom step was built differently from the higher ones.
Before you start dismantling things, look for other things that might explain what’s happening. Does a gutter dump water next to the bottom step, or is there a sprinkler for the nearby planter that could be soaking into the bottom step from the side? Is there a water line connecting planter beds on either side of the steps that might have sprung a leak? When the flagstones were added to the concrete patio and the installer struggled to keep the paving height next to the steps the same as it was, did he install the pavers so water puddles by the bottom step? Do you use a de-icing product in the winter that might have left salt splashed against the bottom row of bricks? Salt can greatly add to an efflorescence problem.
You might try scrubbing off the efflorescence, then watching to see whether the deposits reappear in sync with outdoor watering, de-icing treatments or anything else that might explain the underlying problem. Sometimes, efflorescence comes off just with a vigorous scrubbing with a stiff brush and water. Or you can use a half-and-half solution of white vinegar and water. If these don’t work, buy an efflorescence remover, such as Foundation Armor Concentrated Concrete and Brick Efflorescence Remover and Cleaner ($49.95 a gallon at Home Depot). Although muriatic acid also takes off efflorescence, using a product labeled as an efflorescence remover is better, because it has buffering ingredients. Straight muriatic acid can eat into the mortar and masonry. Follow all safety precautions on the label.
If you decide to remove the flagstones, be aware that adding or removing tread coverings alters the vertical distance between steps. Building codes generally require that riser heights can differ by only 3 / 8 of an inch at most, because any greater variation can cause people to trip. If it’s your house, you might be able, over time, to adjust for a greater difference, but visitors would still be vulnerable.
The picture you sent indicates that the step height might already be off, perhaps dating from when you installed the flagstones. Unless the camera angle explains things, it appears that the middle and bottom steps are separated by the height of 2½ bricks, while the other step heights are just two bricks apart.
If the steps are indeed uneven, safety, rather than just the visual annoyance of efflorescence, might warrant redoing them to make the riser heights equal. You probably can’t go back to what you had before you added the brick and flagstones, because the flagstone-covered patio is higher than the bare concrete patio used to be. To overcome a half-brick difference in step height, one idea might be to replace the bottom tread with thicker flagstone and redo the patio close to the steps with enough mortar underneath the nearby bricks and flagstones so the surface next to the steps is slightly higher than it is now. You would see the different thicknesses on the treads, but if safer steps result, the trade-off might be well worth it. Raising the nearby patio height might also make water less likely to pool at the base of the steps. And that would also have the effect of reducing icing there, which might be the way to permanently fix the efflorescence issue.
