Efflorescence Treatment: What the White Salt on Your Wall Means

White powder on walls: check what the salt is telling you

White powder on walls, white salt patches on new plaster, a crusty tide line near the floor and paint peeling at the bottom of the wall are all the same thing: efflorescence. Water moves through the wall, dissolves the salts in the brick, sand, cement and mixing water, and leaves them behind where it evaporates. So the salt is a symptom. It tells you there is moisture in the wall. It does not tell you where the moisture comes from. Efflorescence treatment works when the water is stopped first and the salt is dealt with second. Six checks tell you which wall you have.

Find the right efflorescence treatment for your wall

Match your wall to one route. Each route says what is done and takes you to its section.

Water first, salt second. A salt barrier primer on a wall that is still getting wet only delays the next round of white patches.

Efflorescence treatment finder

Answer three questions for a starting recommendation, then confirm it with an Armstrong expert. Salt is a symptom, so where the answers do not fit one pattern, ask for a site assessment before buying material.

How to stop efflorescence permanently: find the moisture source

Salt cannot travel without water. Every efflorescence treatment that lasts begins by cutting off the water that feeds it. There are four places the water comes from, and each has its own fix on its own page. This page covers the salt. Use the cards below to reach the right source repair, then come back for the salt treatment.

When you cannot tell which source it is

A band of salt near the floor is not proof of rising damp, and a moisture meter alone does not settle it, because salt makes a meter read high even on a dry wall. If the pattern does not fit one source, work through the checks on the wall dampness treatment page, or ask for a site assessment by an Armstrong applicator or distributor before buying material.

Efflorescence treatment on a plastered wall: brush dry, prime, then paint

This is the usual treatment for white salt patches where the plaster is still sound: the source has been stopped, the wall has dried, and the salt is on the surface or just under the paint. The Armstrong product for this job is RAPIDSTRONG SALT FLUSHER, an anti-efflorescence primer for concrete, plastered, brick and masonry surfaces, inside and outside.

1. 1
   Wait until the wall is dry

   The source must be stopped and the wall given time to dry. Priming a wall that is still wet seals moisture in behind the primer.Why: Priming a wet wall seals moisture in behind the primer, and the paint blisters.
2. 2
   Remove all loose, old and flaking material

   Scrape off blistered and peeling paint, loose putty and any powdery skin until a firm surface is reached. Where putty has gone soft or chalky it comes off fully.Why: Primer and paint only grip a firm surface. Anything loose under them comes away and takes them with it.
3. 3
   Brush the salt off dry

   Use a stiff brush and collect the powder so it is not trodden back in. Do not wash the wall. Water dissolves the salt and carries it back into the plaster, and it comes out again as the wall dries.Why: Water dissolves the salt and carries it back into the plaster, from where it comes out again. Dry brushing removes it for good.
4. 4
   Check the plaster

   Tap the wall. Sound plaster rings solid. If it sounds hollow, crumbles under the scraper or has salt crystals through its thickness, go to the replastering route instead of priming over it.Why: Primer cannot hold on plaster that is hollow or full of salt. Tapping tells you whether to prime or replaster.
5. 5
   Apply the first coat of RAPIDSTRONG SALT FLUSHER

   The surface must be clean and dry with no loose particles. Apply by brush and work the coat in until the surface is saturated. The data sheet lists dilution with 50% potable water.Why: The first coat soaks in and builds the physical barrier to water and the chemical barrier to salt.
6. 6
   Apply the second coat

   Apply the second coat across the direction of the first, 4 to 6 hours after it.Why: Working across the first coat closes gaps and gives the stated dry film thickness.
7. 7
   Leave it 24 hours

   Any paint coating can go on after 24 hours.Why: The primer must cure before the topcoat goes on, or the topcoat blisters.
8. 8
   Level, prime and paint

   On inside walls, level with RAINCARE WALL PUTTY in two coats of 1 to 2 mm, prime with RAINCARE CP Primer and finish with SHINESHIELD Interior Emulsion or SHINESHIELD PREMIUM Interior Emulsion. On outside walls prime with RAINCARE CP Primer or RAINCARE WP Exterior Primer, which is thinned with 20% water and covers 60 sq.ft per litre, and finish with SHINESHIELD Exterior Emulsion or an elastomeric coating from the external wall waterproofing page.Why: The putty levels the surface, the primer seals it, and the emulsion finishes it. Each layer depends on the one under it.

Where an inside wall also needs a damp-proof coating, such as ROOFCOAT FLEXI 100 or ROOFBOND RFX PLUS 210 applied to the wall before primer and paint, the sequence is on the wall dampness treatment page.

Salt damaged plaster repair: when the plaster has to come off

This is the extreme case, and it is the last resort. Most walls with white patches are saved by stopping the water and priming. But plaster that has carried salty water for years ends up full of salt. The crystals grow inside it, break it apart from within and keep drawing moisture out of humid air, so the wall looks damp even after the source is fixed. No primer holds on plaster like that. The damaged plaster is removed and the wall is replastered with a mix that resists water.

1. 1
   Confirm the source is stopped

   Replastering a wall that is still fed by the ground, the rain or a leak wastes the work. Fix the source first. For a wall with no working damp-proof course, see damp-proof course.Why: Replastering a wall that is still fed by water wastes the work, since the salt returns.
2. 2
   Remove the salt-damaged plaster

   Hack off all loose, hollow and crumbling plaster back to the masonry. Go beyond the visible damage: at least 1 m above the floor on a wall with a salt band, or 500 mm above the highest salt line, whichever is higher.Why: Plaster with salt crystals inside keeps pulling moisture from the air. It has to come off, well beyond the visible damage.
3. 3
   Rake the joints and brush dry

   Rake out soft mortar joints, then brush the masonry down dry with a stiff brush. Do not wash it. Remove the debris from the room, because the dust is full of salt.Why: Soft joints hold salt. Raking them out removes it and gives the new plaster a key.
4. 4
   Let the bare wall dry

   A bare wall dries much faster than a plastered one. Give it as long as the job allows.Why: A bare wall dries much faster than a plastered one, so this is the best place to lose the moisture.
5. 5
   Apply a bond coat

   Brush on a bond coat of ROOFBOND SBR 401 mixed in equal parts with cement. Stated coverage as a bond coat is 40 to 65 sq.ft per litre per coat. Plaster onto it while it is still tacky.Why: The bond coat ties the new plaster to the old masonry. Plastering into the tacky coat gives a monolithic bond.
6. 6
   Replaster with a waterproofing compound

   Use a sand and cement plaster dosed with one of the Armstrong integral compounds: CONPROOF 500 at 500 ml per 50 kg bag of cement, CONPROOF LW 200 at 200 ml per bag, or CONPROOF No. 1 at 100 ml per bag. Use clean sand and clean water. Salty borewell water and unwashed sand put new salt into the new plaster.Why: The compound makes the plaster resist water and carries less salt into the face.
7. 7
   Do not use gypsum

   Do not use gypsum plaster or gypsum-based putty on a wall that has had salt. It holds moisture and salt and fails again.Why: Gypsum holds moisture and salt, and fails again on a salted wall.
8. 8
   Cure, then let it dry

   Cure the new plaster for at least 7 days, then let it dry fully before any coating.Why: Cement gains strength while it is kept moist. A coating over damp plaster blisters.
9. 9
   Seal the salts, then finish

   Apply RAPIDSTRONG SALT FLUSHER in two coats on the dry plaster, leave it 24 hours, then putty, prime and paint as in the previous section.Why: The primer is the salt barrier that protects the new finish from whatever salt is left in the wall.

Prevent efflorescence on new walls, exposed brick and stone

Salt is easiest to deal with before it shows. On a new building that means keeping water out of the plaster and concrete from the first day. On exposed brick, stone and fair-faced concrete, where there is no paint, it means keeping rain out of the face without sealing the wall.

New construction: three steps that keep salt out of the finish

1. 1
   Put an integral waterproofing compound in the plaster

   Dose the plaster for outside walls and wet-area walls with CONPROOF 500 at 500 ml per 50 kg bag of cement, CONPROOF No. 1 at 100 ml per bag or CONPROOF LW 200 at 200 ml per bag. These reduce the capillary paths that water and salt travel through. External wall plaster is a listed use for CONPROOF No. 1, for efflorescence resistance. For ready-mix concrete, CONPROOF RMC ADMIX 88 is added to the transit mixer at site.Why: The compound reduces the capillary paths through the plaster, so there is less water to carry salt to the face.
2. 2
   Build the damp-proof course and keep it clear

   A damp-proof course at plinth level stops ground moisture, a main source of salt at the base of walls. See damp-proof course.Why: Ground moisture is the main source of salt at the base of a wall. The DPC stops it at its source.
3. 3
   Cure, dry, then prime with a salt barrier

   Cure the plaster for at least 7 days and let it dry. New plaster and concrete are highly alkaline. RAPIDSTRONG SALT FLUSHER is listed for high alkaline concrete and new plastered walls, and is applied in two coats before the first paint. Painting a new wall before it has dried is a common reason for white patches in the first year.Why: New plaster is highly alkaline, and the salt barrier protects the paint from it as well as from salts.

Exposed brick, stone and concrete: a clear water repellent

A facing brick wall, stone cladding or fair-faced concrete cannot be primed and painted without losing its look. Here the salt is brushed off dry and the face is treated with a transparent silicone water repellent. It lines the pores so rain is shed, while the wall stays breathable and can go on drying.

1. 1
   Stop the water behind the face first

   A repellent keeps rain out of the face. It does not stop ground moisture or a leak from behind. Deal with those first.Why: A repellent keeps rain off the face but does not stop water coming from behind. Fixing the source comes first.
2. 2
   Remove loose material and brush the salt off dry

   Remove loose mortar, flaking material and old failed sealer, then dry brush the salt.Why: The repellent soaks into sound surfaces only. Loose mortar and old sealer block it.
3. 3
   Repoint open joints and seal cracks

   Wider cracks and open joints are repaired before the repellent. See external wall waterproofing for crack and joint sealing.Why: Water goes through open joints and cracks faster than through the brick, so they are closed first.
4. 4
   Apply the water repellent wet on wet

   Apply RAINCARE WR or RAINCARE SWR as listed above, working from the bottom up so runs do not streak a dry face.Why: Wet on wet gives one even layer, and working bottom up stops runs streaking a dry face.
5. 5
   Wipe drips from glass and metal

   Remove run-downs on glass, frames and metal immediately.Why: Repellent dried on glass and metal leaves marks that are hard to remove.

Anti-efflorescence primer and salt treatment chemicals compared

Every Armstrong product below has a place in efflorescence treatment. They are not ranked. Each does a different job, and several jobs offer more than one product. Pick the one that fits the wall, and an Armstrong expert will help you choose.

Efflorescence on new walls and efflorescence that keeps returning

The two look the same and need different handling. The table sets them side by side.

Efflorescence treatment chemicals and products by stage

How much anti-efflorescence primer for 100 sq.ft of wall

Approximate quantities worked out from each product's stated coverage, for a wall 10 ft long treated to its full 10 ft height. Rough, porous or badly salted walls take more. An Armstrong expert confirms the final quantity after seeing the site.

Standards and test figures behind the salt treatment

• CONPROOF LW 200, CONPROOF 500 and CONPROOF No. 1 are integral waterproofing compounds to IS 2645, the Indian standard for integral waterproofing compounds for cement mortar and concrete. CONPROOF LW 200 states water permeability below 15% against the 50% the standard allows.
• RAINCARE WR and RAINCARE SWR comply with BS 3826-1969 Class A and Class B for silicone-based water repellents for masonry.
• RAPIDSTRONG SALT FLUSHER states a dry film of 30 to 40 microns per coat, an intercoat interval of 4 to 6 hours and a topcoat after 24 hours. Its data sheet lists no IS or ASTM standard, so none is quoted here.
• IS 3067:1988 is the Indian code of practice for damp-proofing and waterproofing of buildings, and covers the damp-proof course that keeps ground moisture, and the salt it carries, out of the wall.

Efflorescence treatment quantity calculator

Enter the wall size to see the material needed for the salt treatment. Quantities only.

Eight mistakes that bring white salt patches back

1. Washing the salt off with water. The salt dissolves, soaks back in and returns as the wall dries.
2. Priming or painting before the source is stopped. The water keeps coming and pushes the new finish off.
3. Painting before the wall has dried. Moisture trapped behind the paint carries salt to the surface and blisters the film.
4. Leaving salt-damaged plaster on the wall. Plaster full of salt keeps pulling moisture from the air and keeps failing.
5. Replastering with gypsum. Gypsum plaster and gypsum putty hold salt and moisture.
6. Using salty water or unwashed sand in the new plaster. It puts fresh salt into the repair.
7. Skipping the loose material. Primer applied over flaking paint and chalky putty comes away with them.
8. Treating every base-of-wall band as rising damp. Rain splash, raised paving and pipe leaks look the same and need a different repair.

Efflorescence treatment questions and answers