Why does salt leave white marks on carpet?
Road salt dissolves into slush, the slush comes in on boots, and the salty water soaks into the pile. When the water evaporates the salt stays behind as a stiff, white crust along the tips of the fibres. The City of Hamilton's snow clearing page explains that before a storm it applies "a salt brine solution that helps keep snow and ice from bonding to the roadway", so from the first forecast of snow, every driveway, sidewalk and parking lot in the region is a source. The carpet just inside the door, the stairs and the front hall take almost all of it.
What does the Carpet and Rug Institute say to do?
The CRI's Spot Solver entry for salt lists three things in order: vacuum, a detergent solution, and warm water, then a professional if the mark stays.
| Step | What to do | What the CRI says |
|---|---|---|
| 1. Vacuum | Vacuum the dry salt crust slowly, in two directions, before any water touches it | "Pouring any liquid into a dry spill may create additional problems." |
| 2. Pretest | Try the solution on a hidden patch, such as inside a closet | Pretest for colour transfer or damage "in an inconspicuous area" |
| 3. Detergent | One quarter teaspoon of liquid dish detergent in one cup of lukewarm water | "NEVER USE A STRONGER CONCENTRATION!" |
| 4. Work it in | A little on a white cloth, from the edge of the mark toward the centre, then blot | "work in gently", "do not rub", and "be patient" |
| 5. Rinse | Blot with plain lukewarm water, several times | Detergent left in the fibre "may cause accelerated soiling" |
| 6. Dry | Blot with a dry white cloth until no more moisture comes up | Blot "until all moisture is removed" |
Which detergents should never go on carpet?
The CRI is specific. Never use laundry detergent of any kind, because laundry detergents "may contain optical brighteners (fluorescent dyes) that dye the fiber". Do not use automatic dishwasher detergent either, because many "contain bleaching agents that destroy dyes and some fibers". Plain liquid dish soap, at the weak strength above, is the one it names.
What about vinegar and water?
Vinegar and water is the most common home remedy for salt, and you will find it all over the internet. It is not in the CRI's salt entry, which names only detergent solution and warm water. If you try vinegar anyway, pretest it in a hidden spot first, as the CRI says of any solution, and rinse it out afterwards like anything else you put into the pile.
Why does the white mark come back after it dries?
Because salt or soap is still down in the pile. As the carpet dries, water wicks up the fibres and carries whatever is dissolved in it to the tips, where it dries into the same white ring. More rinsing and more blotting is usually the answer, not more detergent. A mark that has come back two or three times is a good sign that it needs hot water extraction, which rinses the whole depth of the pile and vacuums the water straight back out.
How do I stop salt getting into the carpet every winter?
- Mats on both sides of the door. The CRI's care advice is to "stop dirt at the door by using mats outside and in, taking your shoes off when you enter".
- A boot tray inside the door, so wet boots never stand on carpet.
- Vacuum the entrance and the stairs more often from December to March, before the salt is ground in.
- Deal with fresh slush the same day by blotting it up, before it dries into a crust.
When is it time to call a professional?
When the marks keep coming back, when they are across a whole hallway or staircase rather than a spot or two, or when the carpet has been salted all winter. The CRI's own last step is "Call a Professional", because professional cleaners "have the ability and the equipment to use more aggressive cleaning solutions to remove stubborn spills". Spring is when most homes need it. See stair carpet cleaning for the stairs, and commercial carpet cleaning for business entrances, which take the most salt of all.