Thread: Hydroscopic patching material ?

I did an inspection this week where the ceilngs on the east side of this home showed water stains. Most showed no evidence of moisture - and the roof is not leaking and the home has been sided with vinyl with a foam board underlayment. It appeared to be very tight fitting. One area, with some type of heavy patching material showed high moisture levels. I could not ascertain whether there really is an active leak or if this material is just highly dense (it appeared to be) and/or hydroscopic. The attic above this ceilng was accessible and I could not find any evidence of leakage from the roof, the wall, or any vents.
My suspicion is that the patching material is hydroscopic. Has anyone run into this???

Similar Threads:

• Acceptable drain and vent material?
• Mobile home ceiling material?????
• Valley material
• Primary drain line material
• Draft hoods , combustible material

Originally Posted by Ernie Simpson

or if this material is just highly dense (it appeared to be) and/or hydroscopic.

You had me on that word, so I had to look it up. I think you mean:

hygroscopic
One entry found.
Main Entry: hy·gro·scop·ic
Pronunciation: \ˌhī-grə-ˈskä-pik\
Function: adjective
Etymology: hygroscope, an instrument showing changes in humidity + 1-ic; from the use of such materials in the hygroscope
Date: 1790
1 : readily taking up and retaining moisture
2 : taken up and retained under some conditions of humidity and temperature <hygroscopic water in clay>
— hy&#183;gro&#183;scop&#183;ic&#183;i&#183;ty \-(ˌ)sk&#228;-ˈpi-sə-tē\ noun


Answer is, yes, it could be something like this: SHEETROCK Durabond Joint Compound


Unlike drywall setting compound, which "dries out" and hardens because it "dries out", those postive setting time compounds do not really "dry out", they "cure" by chemical reaction. Somewhat like concrete cures (concrete does not 'dry').


They are also more dense than regular drywall compound.

Good morning, Ernie:

Although the meters normally used in home inspections are commonly called “moisture meters,” contrary to common belief, most of these meters do not actually measure moisture; rather the meter measures electrical conductivity or capacitance and translates that parameter into general moisture equivalents. For example, with the Tramex&#174; PTM 6005 conductivity style moisture meter, if the meter probe was placed in 100&#37; pure water (also known as DI or “distilled” water), it would read less than 8% moisture. The reason being that pure water is a lousy conductor of electricity with an high dielectric strength.

If a small amount of salt was placed in the water, the “moisture content” would steadily increase linearly with the salt concentration until approximately 43%; indicating moisture saturation. Therefore, the moisture values given in any discussion on moisture content should be used with caution and within the limitations of the meter and parameters discussed.

The patch material may simply have a different conductance or capacitance and therefore give an apparently anomalous “moisture” reading.

Cheers!
Caoimh&#237;n P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG

In addition:

Use of Electrical Moisture Meters
Paper: Use of electrical moisture meters
Distribution of Moisture and Soluble salts
Hygroscopic salts

It is essential to appreciate the fact that on masonry substrates the readings may not always reflect moisture alone. For example, contaminant hygroscopic salts, mostly chloride and nitrate, even in very low concentrations in plasterwork/wallpaper, especially under conditions of high humidity, will cause moisture meters to respond quite positively. Therefore examination of, say, an exposed stone wall in a property that has been damp-proofed or a property that was once a barn (likely to be salt contaminated from past use), should be undertaken with extreme care; one cannot distinguish between residual hygroscopic salts and rising damp/dampness in these situations, and it might therefore be prudent to resort to other methods of moisture evaluation.
It is possible for the material itself to be significantly electrically conducting but this is rare and is generally quite evident to the investigator from the unusual distribution of readings; almost all plasters, bricks, cements and finishes are unlikely to cause such problems. Nevertheless, this factor should be borne in mind. But, most importantly, where the meter records zero readings the surface is both ‘dry’ and uncontaminated.

Which is why, such as with my Tramex, there is a switch to select the appropriate range, meaning, you (the operator) are selecting the meter calibration setting based on your experience with the different settings, i.e., wood, gypsum board, roofing, etc.

All you are really doing is "manipulating the reading" to fit to what you are measuring "moisture" in.

Not sure how big the patch is, but if it is one of those metal patch jobs, your meter will peg....

Thank you all (although I do like to add my own words to the dictionary (in this case, "hydroscopic" in place of "hygroscopic". After all, 'hydro' does refer to water so logically it seemed right. Anyhow, I'm leaning towards this material being hygroscopic, given the lack of evidence of current leakage at this site.

Originally Posted by Ernie Simpson

I did an inspection this week where the ceilngs on the east side of this home showed water stains. Most showed no evidence of moisture - and the roof is not leaking and the home has been sided with vinyl with a foam board underlayment. It appeared to be very tight fitting. One area, with some type of heavy patching material showed high moisture levels. I could not ascertain whether there really is an active leak or if this material is just highly dense (it appeared to be) and/or hydroscopic. The attic above this ceilng was accessible and I could not find any evidence of leakage from the roof, the wall, or any vents.
My suspicion is that the patching material is hydroscopic. Has anyone run into this???

Ernie,

Given that you see moisture stains, there is evidence that moisture has penetrated into that area in the past and a reasonable likelihood that it will again.

Ernie, could not tell where you are from, but here in the Northeast we have problems with ice daming on the eaves due to poor attic ventilation. I've seen where moisture gets beneath the roof and into the walls, causing water stains. A lot of times owners get over zealous with insulation and cover the soffit vents.