White efflorescence salts or stains on building clay, concrete, or slate roofs.
Salt Deposits, Brown & White Bubbly or Fluffy Crystalline Deposits Diagnostic & Identification Photographs.
This article series illustrates and explains white or sometimes reddish brown bubbly surfaces on walls and white powdery or crystalline deposits left on walls, especially masonry walls, by moisture - efflorescence.
Our photo at page top shows white efflorescence on the under-side of a clay tile roof in San Miguel de Allende, Guanajuato, Mexico.
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White efflorescence can often appear on clay tile roofs, concrete roofs, and slate roofs as you can see in our slate roof photo here and on the clay tile roof at page-top.
[Click to enlarge any image]
On a slate roof round white deposits starting at the center of the slate and expanding towards its perimeter can be an indication of roof age and condition.
See those details at SLATE ROOF LIFE EXPECTANCY
On concrete or clay tile roofs efflorescence may be a sign of moisture absorption, deterioration, or it may be due to use of concrete mortar used to set the roof tiles along a clay or concrete tile hip or ridge.
See CLAY / CONCRETE ROOF TILE HIP & RIDGE MORTAR GENERATED SURFACE EFFLORESCENCE [PDF] (2014) Tile Roofing Industry Alliance TRIA - cited
Excerpt: Efflorescence is a temporary surface discoloration common to all concrete based building materials
including mortar and concrete roof tiles.
It is superficial and in no way detrimental to the overall quality, structural integrity, or functional properties of the tile.
see details at CLAY TILE ROOFING
While cleaning a natural slate roof we applied a rust stain remover. Once the rust remover effectively removed the rust we now have various areas of efflorescence where the remover was applied.
We tried vinegar and water with no results. We tried an efflorescence remover from powerwash.com with no results. Any suggestions? - Amanda Dooley, 2022/09/24
This question was posted originally
at EFFLORESCENCE REMOVAL & PREVENTION
@Amanda Dooley,
I've been thinking about your question for a time before trying a reply as I don't have a great answer. But in researching the effect of an acid cleaner on slate roofs we did find some information that I'll share below.]
I see that the Rust Remover Plus product sold by power wash (cited below) whom you cite, is intended to be used with a power washer.
I would not recommend power-washing a slate roof - but, then, perhaps you didn't apply a high-pressure spray to the roof: do tell me how you applied this chemical.
The manufacturer's instructions are simple:
1. Rust Remover Plus™ is a concentrated rust stain remover.
It can be applied directly, or diluted with water up to a 1:5
mixture.
The exact dilution ratio will depend on the severity of
the rust stain.
2. Apply product with a pump up garden or chemical sprayer
using a cone or fan tip.
Apply evenly with overlapping passes
to insure uniform coverage. Thoroughly wet area to be cleaned
with product.
3. Allow a 5 to 10 minute dwell time for product to soak into
surface.
When using product for rust stain removal, do not
proceed to step 4 until stain disappears. Reapply if necessary.
4. Pressure wash using high pressure with a 40 degree tip. Use overlapping passes approximately 6 inches from the surface.
5. Allow surface to dry before evaluating results. Product brightens concrete as it dries.
Do not allow product or overspray to come into contact with glass, metal or tile surfaces. Protect these areas from contact.
Always perform a test in an inconspicuous area to determine results achieved before using on a wide scale basis.
Allow surface to dry prior to evaluating results.
A one-gallon jug of Rust Remover Plus™ will cover approximately 150 to 300 square feet of concrete when used straight.
- IS THAT how you applied the chemical? Including testing it on a small area first?
FYI, at EFFLORESCENCE REMOVAL & PREVENTION we discuss some cleaning products that might be used safely on acid-sensitive stone materials such as slate.
So if you are up to answering my blizzard of technical questions we can continue to figure out what happened to your slate roof and what we can do about it.
at EFFLORESCENCE REMOVAL & PREVENTION - What steps should I do to remove efflorescence from my building?.
and
at WHITE STAINS on ROOFS - includes more References for Cause & Cure of White Calcium or Mineral Stains on Roofs
...
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