TEMPERATURE & HUMIDITY WHILE HANGING AND FINISHING DRYWALL AND AFTER (Before, During, and After)

On my recent project of hanging and taping a new house we had to hang all the ceilings before drywall was even brought in for the walls because blown in  cellulose was being installed . Just before  the insulators were scheduled to come,  I visited the job  to inspect all the air sealing that was completed by the contractor in the wall cavities and in the attic. After the inspection, I was confident that along the thermal boundary there was an excellent air barrier. The heat was on for several weeks, which allowed  the  building  to dry out. The moisture content of the framing was tested and was at  8 percent, which is excellent. After the insulation was installed and inspected  the drywall then was delivered.  A few days later we started hanging the walls. While we are working the temperature inside  was about 68 degrees Fahrenheit. Fans were runs to help circulate the air and even  some windows  were partway open  to help dump humid air created while taping. This was like a dream job so I better do a great job because I won’t have any excuses.

I live in upstate NY and the temperature  this January was a average of 20 degrees Fahrenheit. It  has been in the single degrees in the evening . Some days were even  below zero.  The outside humidity has been 90% or higher. I didn’t expect it to be that  high. The humidity inside my jobsite is what I typically worry about. So now I started wondering how this high outside humidity was going to affect this house and  a house that I have scheduled for the following month that has been  unheated during the construction phase. The reason I was surprised that the humidity was so high is because I had always heard that cold winter air is dry. I know if I am out hiking in the winter exposed skin is often dry and chapped.  To better understand temperature and humidity I decided that I needed to study my building science . What I needed to figure out was how temperature, relative humidity, absolute humidity, and dew point affect my drywall jobs.  I discovered in my studies the following:

Relative humidity is a ratio of the actual water vapor content of the air to the amount of water vapor needed to reach saturation. Absolute humidity is the mass of water vapor contained in a given volume of air. The relative humidity of a volume of air changes as the temperature changes. The absolute humidity of that volume of air does not.

 

  • Temperature is easy to understand. I know I can hang and tape a house when it is only 45 to 50 degrees Fahrenheit ,but I know it will dry better and have less potential problems if the temperature is 65 to 70 degrees Fahrenheit. But the question I have is what if the low temperature also had a low humidity and I compared that to a higher temperature with a high humidity. Would the two different scenarios ever reach a point where the drying time would be the same. (Look at chart below).  I found a few that would work. At  50 degrees Fahrenheit with 30% humidity and at 70 degrees Fahrenheit with 70% humidity the drying time between coats of compound should be about 26 hours.
  • Relative Humidity: I also understand that when the temperature is hot and the relative humidity is high I sweat easily and have to wait longer for the compound to dry. I am more comfortable working at a lower temperature but also worry about drying.  But as long as the humidity is lower at either temperature the compound will dry. Often when discussing best conditions only the temperature is mentioned, this is not sufficient. I have always believed that there are very few perfect drying days for finishing drywall. So to live by the standard of waiting 24 hours between coats of joint compound can lead to problems as temperature and humidity change.
  • Absolute humidity is the actual amount of moisture in the air. If you know the temperature of the air and the relative humidity you can use a psychrometrics chart {see below} to determine the actual amount of water in that air. The actual amount of moisture in the air and how this would affect my drywall work is what I needed to understand better.

Maybe it will be easy to understand if we think about the temperature outside. Today it is 21 degrees Fahrenheit and the sun is shining so from inside the house I am thinking that 21 won’t feel very cold so I decided to go for a walk. It was then that I realized there is a 10 to 15 mph wind. Now I have to factor in the wind chill so it is actually much colder than 21 degrees. It actually feels like 10 degrees – Brrr.

Chart from gypsum association www.gypsum.org

Water vapor in air has a maximum storage capacity, depending on temperature. Warm air can store lots of moisture as vapor in the air, cold air can store only very little.

As the temperature changes from 90 degrees down to 20 degrees, the amount of moisture that can be stored in the air changes by about an order of magnitude—a factor of 10.

Let’s say it’s around freezing outside (32 degrees F) and the relative humidity is 90% , so if I take that air and bring it into the building and heat it up to 70 degrees the amount of moisture in the air stays exactly the same. All I did was heat it. I didn’t add any moisture; I’m just heating it. But because the storage capacity of the air has increased with temperature, the relative humidity drops. And we can get down to less than 25% relative humidity. According to the chart 32degrees at 90% humidity would take 13 days for compound under tape to dry. But at 70 degrees and 25% humidity all you need is 11.5 hours.

So if I want to know what the actual moisture in the air is I need to know both the temperature and the relative humidity. If I put those two pieces together, (temperature and  relative humidity)and then refer to a psychrometric chart the absolute humidity can be calculated.

Now I know that understanding how much moisture is in the air is even more  important than I thought when finishing drywall. Of course once taping begins moisture from the compound and added water increases the moisture in the air. So ventilation and circulation is important. Maybe even opening a few windows now and then when it is cold outside to dump some of the moisture in the air.  This will also work in summer weather if there is more moisture inside the house because high goes to low (high moisture wants to move toward low moisture)

Psychrometric chart

 Other Cold Weather Tips

  • Provide heat. When a temporary heat source is used, the temperature should not exceed 95 degrees Fahrenheit (35degrees C)  in any given room or area. Heaters should not be allowed to blow directly on wall surfaces. Excessive localized heating can cause joint compound to dry too rapidly resulting in cracking and localized delaminating.
  • Provide sufficient ventilation to ensure normal drying conditions. Certain temporary heaters introduce large amounts of water vapor into the air causing high humidity conditions if not properly ventilated.
  • Joint compound and tape should not be applied to cold or damp surfaces. Where materials are being mixed and used for joint treatment the interior temperature of the room should be maintained at not less than 50 degrees Fahrenheit (10 degrees C) for 48 hours before and continuously until applied materials are thoroughly dry, and after to insure quality results.
  • Protect ready-mixed joint compounds against freezing in storage. Use setting-type compounds to avoid many cold weather related problems.

 

Copyright 2013-Myron R. Ferguson

 

25 thoughts on “TEMPERATURE & HUMIDITY WHILE HANGING AND FINISHING DRYWALL AND AFTER (Before, During, and After)

  1. Hi Myron; I really enjoyed your article on humidity and drywall.
    I had a new build in Ontario. Drywall was completed in Dec and Jan. and primed and painted in Feb.
    I moved in at the start of May.
    By July, I could see noticeable bulges on the horizontal seams of a cathedral ceiling. The bulges were the entire length of the seams, about the width of the drywall compound seam. The vertical butt joints are not visible.
    The angle of the light definitely may make the seams more pronounced.
    My drywaller seems to feel that the problem was high humidity in the house during June. He feels that the drywall absorbed the moisture and then “fossilized” along the seam. The problem is not evident in other areas of the house including the bathroom. There is also no evidence of mold.
    Do you have any thoughts about the effects of humidity on drywall and drywall compound during the first and subsequent years.

  2. The visible seams could just be the result of shadowing along the slight bump that was created while taping. Even a slightly raised area will be visible under certain lighting conditions. The cross lighting on cathedrals will show any defect. A level 5 finish should have been applied to the entire ceiling.
    Possibly the finishing was done properly to a level 5 and the ridge you are seeing was caused by compression of the panel edges. This compression is caused by expansion of the drywall and the result is panel edges being forced together. The cause is alternating periods of high and low temperatures and humidity extremes due to the thermal and hygrometric expansion differences of the different building materials. This is common in cold weather construction.

    Let the drywall system stabilize before attempting repairs. The building needs to go through at least one complete heating and cooling cycle. Do the repairs in a warm dry environment similar to what the building would be in when occupied.
    Sounds like the seams are not cracked so just feathering out the bump is all you can really do. Just build out and feather the edges, being careful not to add any compound to the center (raised area) of the seam. When finished it will be necessary to skim coat the entire ceiling to equalize the texture and porosity of the ceiling. This will reduce the possibility of joint flashing after painting.

  3. Okay, similar problem, I guess. Excessive humidity this Spring as building was being enclosed. Used huge dehumidifiers to remove so that work could continue with the drywalls. Now are experiencing cracks in the taping. Repair the cracks and within a couple of days they are back. Testing the drywall…it is extremely moist. What is the problem and how can we fix it?

    • Hanging and taping of drywall should be done under the conditions that the building will be under when occupied. Of course an unheated garage should not be taped in the winter because it will be difficult to keep temp and humidity at proper levels while working and then if heat is shut off problems can occur. If that garage was taped in the summer when temp is 70 and humidity is low it should hold up fine when winter hits. But if that garage is heated to 40 degrees in the winter and wet cars are brought in or cars are washed and the humidity is not controlled then cracks will occur.
      Sounds to me like your tempt and humidity are unstable
      Get things dried out and under control. Wait a full cycle of seasons and repair when tempt is about 70 and humidity is 40% or lower. May want to check moisture content of drywall before taping. 15% or lower should be fine.

  4. I hired a contractor to put up an addition. The sheet rock was installed at the beginning of February. I was surprised to find a worker applying joint compound when the temperature was 37 degrees outside, and no heat in the addition where he was mudding. Furthermore, that night, the temp was going to drop to 27 degrees. What will happen to the joint compound? Can I expect long term problems? I want to hold the contractor accountable, given he well knew the conditions!!

  5. A great source of information for working with drywall can be found at http://www.gypsum.org.

    FROM GYPSUM.ORG: GYPSUM BOARD WINTER RELATED INSTALLATION – RECOMMENDATIONS- (GA-220-06)
    (These recommendations apply to gypsum board installed on interior walls, partitions and ceilings. For gypsum
    sheathing recommendations, see Recommended Specifications for the Application of Gypsum Sheathing (GA-253).
    For information on joint treatment drying conditions, see Joint Treatment Under Extreme Weather Conditions (GA-236)

    Cold and damp weather conditions can contribute to joint compound bond failure, delayed shrinkage, beading, nail popping, joint shadowing and board sagging. Observing the following precautions during periods of cold and damp weather will reduce job problems.
     -Gypsum board and joint treatment should not be applied to cold or damp surfaces.
     -For mechanical installation of gypsum board, room temperature should be maintained at not less than 40oF
    (5oC).
    - not less than 50oF (10oC) for adhesive application of gypsum board and for joint treatment, texturing and
    decoration.
     -Interior temperatures should be maintained at not less than 50oF (10oC) for a minimum of 48 hours and the
    gypsum board should be completely dry before taping and finishing. Subsequent finishing and texturing
    should not proceed until previous applications are completely dry. Ready-mixed joint compounds and textures
    shall be protected against freezing in storage.
     -Where materials are being mixed and used for joint treatment or the laminating of one layer of board to
    another, the temperature of the building should be maintained at not less than 50oF (10oC) for 48 hours before
    and continuously until applied materials are thoroughly dry.
     -When a temporary heat source is used, the temperature should not exceed 95oF (35oC) in any given room or
    area.
    - Ventilation shall be provided to ensure normal drying conditions.
    (Note: Gas-fired heaters generate considerable quantities of water. The use of gas-fired temporary heat
    equipment may result in unusually high humidity conditions.)
     -The use of setting type joint compounds can help avoid many cold weather related finishing problems.
    - A latex primer should be applied and allowed to dry before decorating. This often takes between 36 and 48
    hours when the weather is cool or damp.
     -The proper thicknesses and types of gypsum board should be used to avoid sagging when ceilings are to be
    textured.
     -Where a vapor retarder is required, it is suggested that foil backed gypsum board or vapor retarder faced
    mineral or glass fiber insulation batts be used.
    - When a polyethylene vapor retarder film is installed on ceilings behind the gypsum board, it is important to
    install the batt or blanket ceiling insulation BEFORE the gypsum board; when loose fill insulation is used,
    install the insulation IMMEDIATELY after the gypsum board.

  6. Our drywall was done a few weeks ago. We have spray foam insulation. The temperature has been normal in NC but is supposed to drop to 20s. We do not have a backdoor yet and the insulation keeps it constant at a very low temperature even though it was up to 79 today. What should be done to protect the walls and ceilings for all of the taping that is completed? Please help.

    • Hi Lani, I think you should close off the doorway opening and then run some dehumidifiers to keep the humidity low and fans to circulate the air. If you did choose to use some sort of space heaters make sure to circulate the air and only use vented heaters, unless the heat is electric.
      Myron

  7. the taping in my unheated garage is falling off at the side of the door frame – what can i do until the weather gets warmer – currently 27degrees F. The cold air is getting in ?? Can I use an all weather adhesive for now.

    • Hi Michael, You can remove the casing and insulate the space around the jams. Fiberglass will do a pretty good job but spray foam will be better. They do make a cold weather expanding foam.
      Are the walls insulated? If not you may continue to have problems. The problem with un heated and often un-insulated garages is that whenever you bring in a hot vehicle along with moisture the temperature extremes combined with the high humidity causes problems with the drywall. Some garages have exhaust fans with a humidistat connected with the switch. Which does help.
      Myron

    • Hi Thomas, It is not only about the temperature but also the humidity and airflow. The temperature should not be lower than 55F at any time during the day and should not fluctuate up to real high temperatures either. Humidity should be below 45% and have fans running all the time. There is info on this topic on the drywall finishing councils website. http://www.dwfc.org
      Myron

  8. Thank you so much for sharing your experience and your knowledge. Most people know that temperature and humidity have a large effect on paint, but it is not the only task to consider. Insulation will obviously help regulate the temperature of the interior, but anyone who wants to paint should be aware of the effects of the weather. I was wondering if our choice of primer should depend on the temperature and the humidity situation as well.
    Eli | shpaintingpa.com

  9. we are doing a commercial rock on wood project with a tight schedule. Started on level six and we are experiencing screw dimples after a level 4 finish on walls and level 5 finish on ceilings. Gypcrete was installed within a week after or finish was done. Having same problem on level 5. Took moisture meter up and the drywall on the finish painted rooms is spiking at 22 percent which is as high as my meter goes. Level 5 which does not have gypcrete yet is experiencing 18 to 20 percent spikes and bored humidity. It has been a damn cool spring so we have had days where it is below 50 degrees with dew points at 46 to 48 with constant fog in the mornings. My question is what should the drywall be in terms of measured humidity when we are applying joint compound. Is there anything else we can do to stop the dimples when we’re dealing with a contractor who is only worried about schedule but has SPECT smooth walls and smooth ceilings in these conditions?

    • Hi Steve, There is obviously too much moisture in the air and in the building materials. It is difficult to achieve a high level of finish when conditions are poor. I don’t think the light weight compounds perform as well either. The gypcrete is also a problem and I know it is common to install after the drywall work is done. Hopefully the drywall will be at least primed first.
      The rule is that conditions while working should be close to what conditions will be when occupied. Whenever I test moisture in drywall it is about 15% under good conditions. I have seen it up to 20%. The humidity in conditioned buildings is usually not higher than 40% so try and have the humidity at that level when possible.
      Regulate the humidity, temperature, and airflow while working even if you have to bring in heat, dehumidifiers and fans.
      Myron

  10. Thanks for the great insight on drywall. Have an interesting problem and local resources don’t have an answer. Our 20 year old house in MN has popcorn ceilings. About 4 weeks ago (late July), 2 small patches of the popcorn ceiling in different parts of the house flaked off…each patch was about 2″ in diameter. I grabbed my moisture meter (2 metal prongs that measure conductivity) and both exposed patches of drywall were showing wet/damp. However, there were no signs of water leakage (i.e. brown staining). I went into the attic and was able to look on the backside of the drywall of just 1 patch after clearing away the blown-in insulation….the drywall for the other patch is inaccessible. With the moisture meter, the drywall was showing dry. At this location, the poly vapor barrier did have an open seam in it. It must have been like this for 20 years. There are no signs of roof leaks or puddling. There are no plumbing lines in the vicinity. Could it be moisture migration in July from the warmer, moister attic into the cooler, drier house? The moisture gets past the open seam in the barrier and has accumulated on the backside to the point where it’s breaking the bond of the paint/popcorn to the drywall?

    • Hi Bob, Whenever I see a painted surface discoloring or coming loose it is because of moisture. Plaster never starts to delaminate unless moisture is present. I think it will be hard to pinpoint the cause of your problem except to say it is moisture. Sounds like the condensation occurred on the living space side only caused by the warm temps of the attic somehow reaching the cool air of the living space. The gap in the plastic could be part of the problem but maybe there is also a screw that attaches the drywall in that area. The metal screw can transfer the heat of the attic and is more likely to create condensation from the air in the living space. The condensation could also be occurring on the attic side and just traveling to the ceiling below. Make sure you have enough insulation in the attic and seal all penetration where air can enter or exit through the ceiling.
      Myron

  11. About 8 years ago we built on a non-temp controlled sunroom in which we installed drywall on the ceiling. We used plain paper tape for finishing seams, but now (over the last few years) all of the tape is coming loose. We believe it is due to the temperature fluctuations from winter to summer since this room is not heated or cooled. If I tear out the tape and use self-adhesive mesh tape to re-finish, will this likely hold up? Our only other option is to put some type of wood board over the drywall or just boards trying to hide the ugly seams. Thanks for your advice!

    • Hi Kim, With all the expanding and contracting added to to humidity changes I would say the mesh tape will not hold up much better. It will most likely crack along the seam.. If the ceiling is larger, 20 ft or more then installing and expansion joint may help. Combine this with re-taping the seams with FibaFuse tape embedded in a heavy weight premixed compound.
      Myron

  12. We had the drywall person hang and tape a 24 by 32 addition with2x6 studalls and a valued ceiling. The addition is in western Washington where there is a lot of moisture. There wall cavity was dry when we started. They used hot mud to pre-fill and then taped the seams and finished with pre-mixed mud. The waited 4 days then primed with a PVA primer and textured over that. We noticed water leaking out of the bottom of one of the walls. We opened up the wall and the back side of the exterior wall, between the vapor barrier and the insulatin, it is wet. Dripping in some areas. We checked for leaks in the roof and siding, there were none. We checked for leaks in the Windows, again none. We checked under the house for standing water, it is dry. What would cause moisture to build p in the wall cavity and how do we get rid of the moisture?

    • Hi Mitchell,
      I have seen this many times over the years. It is condensation caused by air movement through the wall assembly. Air is moving through the walls and ceilings because not enough attention was paid to creating an air barrier. I believe in doing a great job with the air and moisture barrier on the exterior of the building but also creating an air barrier along the inside of the the heated and cooled areas. This air barrier should be continuous along where the insulation, is starting along the basement walls and including rim and ban joist areas as well as the ceilings that are adjacent to attics. So you have this air movement combined with high humidity in the interior because of all the moisture being introduced during the construction process that is causing the water to condense when it hits the cooler air in the wall cavity. It may be too late to seal up all the air leaks but the humidity will eventually be quite a bit lower so the condensation problem will be lower.
      So do as much air sealing as possible and control the humidity. You may want to hire a professional building performance contractor to help evaluate the problem.
      Good luck,
      Myron

    • Hi Rob, After insulating turn the heat on to around 70 degrees for at least a week. Run a dehumidifier if necessary. You will most likely have an air exchange system installed so run that also. The moisture content of most drywall that I have tested is around 15%.
      Myron

      • Hi Rob, After insulating turn the heat on to around 70 degrees for at least a week. Run a dehumidifier if necessary. You will most likely have an air exchange system installed so run that also. The moisture content of most drywall that I have tested is around 15%.
        Myron

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