jeffhed
Structural
- Mar 23, 2007
- 286
I apologize for the length of this post but i tried to give as much background info as possible. I have designed a condominium project where the architect specified a sound mat with 1-1/2" gypcrete topping. This is the first time I have designed a project with this type of floor underlayment. The buildings are finished and I received a call from the contractor to come and investigate some distress that was occurring in the flooring. The flooring is glued down vinyl planking and there were spots where the floor had wrinkled. My first thought was that the gypcrete had cracked due to deflection of the floor. The manufacturer specified that the floor be designed for at least L/360 live load deflection. The architect requested that the floor be designed for L/480. The trusses are spaced at 24" o.c. the floor sheathing is 3/4" T&G with a 48/24 span rating. When I check the sheathing deflection we are better than L/360 but not quite L/480. We pulled up the vinyl planking in the questionable areas and there were hairline cracks in the gypcrete parallel with the floor trusses. When you step on one side of the crack you can see the gypcrete move as the sound mat compresses. The movement of the gypcrete appears to be stretching the vinyl flooring causing the wrinkles.
I met with the gypcrete installer and the contractor and the gypcrete guy claims that gypcrete never cracks unless there are structural problems. He also claims that gypcrete does not shrink. I find both difficult to believe. There has been no noticeable settlement or drywall cracking and the footing trenches had to be chipped out because the sub grade is hard caliche so settlement really shouldn't be an issue. All of the cracks appear in areas of the gypcrete that are long uninterrupted runs with the cracks perpendicular to the long direction of the gypcrete. One unit that is the worst is 49'-4" from the front door to the back door with no interruptions besides some minor 12" pop outs. The cracks have occurred between the pop outs and perpendicular to the long direction of the gypcrete which is also parallel with the floor trusses. I think the cracks are occurring from thermal expansion/contraction with the gypcrete getting hung up on the pop outs and the gypcrete then cracks near the pop outs where it can't shrink. The first cracks occurred only a few days after the gypcrete was poured. On the days around the pour there were multiple temperature swings of 40+ degrees. As time went on, more and more cracks appeared in the gypcrete but it was not considered to be a problem until the flooring was laid and the wrinkles began to appear.
I think it has to be the temperature change that has caused the cracking. Especially because it hasn't occurred in any of the smaller rooms only in the areas where the gypcrete is a long uninterrupted runs of 40+ feet. Everywhere else there are no cracks to be found. At this point we are ready to start building 2 and building three is in the architectural design phase. We need to figure out what is causing the cracking so we can prevent it on the next building but we also need to figure out how to fix the floor on this building as owners want to be moving in in the next week. The sound mat manufacturer recommends metal lathe in high traffic areas and inside corners, this was not done. But if thermal shrinkage is the cause I don't think the lathe would have solved the problem unless the lathe was installed throughout rather than just in specific spots. If it was installed in specific spots the gypcrete would have cracked where the lathe ended. There are some fracture guard products that can be rolled on, but I don't want to recommend anything until we have determined the cause. Anyone else have similar problems with sound mats telegraphing the gypcrete movement through sensitive flooring? If so how did you remediate the problem? Also is there any truth to gypcrete not shrinking due to temperature change? I think that is bull shit and I even found an old document with a coefficient of their,al expansion for gypcrete that is 0.0000085 in/in/degree Fahrenheit. My calculations show a shrinkage of up to 0.2" with a 40 degree temperature change. The cracks aren't even really the issue as much as the vertical movement that occurs after the cracks appear.
I met with the gypcrete installer and the contractor and the gypcrete guy claims that gypcrete never cracks unless there are structural problems. He also claims that gypcrete does not shrink. I find both difficult to believe. There has been no noticeable settlement or drywall cracking and the footing trenches had to be chipped out because the sub grade is hard caliche so settlement really shouldn't be an issue. All of the cracks appear in areas of the gypcrete that are long uninterrupted runs with the cracks perpendicular to the long direction of the gypcrete. One unit that is the worst is 49'-4" from the front door to the back door with no interruptions besides some minor 12" pop outs. The cracks have occurred between the pop outs and perpendicular to the long direction of the gypcrete which is also parallel with the floor trusses. I think the cracks are occurring from thermal expansion/contraction with the gypcrete getting hung up on the pop outs and the gypcrete then cracks near the pop outs where it can't shrink. The first cracks occurred only a few days after the gypcrete was poured. On the days around the pour there were multiple temperature swings of 40+ degrees. As time went on, more and more cracks appeared in the gypcrete but it was not considered to be a problem until the flooring was laid and the wrinkles began to appear.
I think it has to be the temperature change that has caused the cracking. Especially because it hasn't occurred in any of the smaller rooms only in the areas where the gypcrete is a long uninterrupted runs of 40+ feet. Everywhere else there are no cracks to be found. At this point we are ready to start building 2 and building three is in the architectural design phase. We need to figure out what is causing the cracking so we can prevent it on the next building but we also need to figure out how to fix the floor on this building as owners want to be moving in in the next week. The sound mat manufacturer recommends metal lathe in high traffic areas and inside corners, this was not done. But if thermal shrinkage is the cause I don't think the lathe would have solved the problem unless the lathe was installed throughout rather than just in specific spots. If it was installed in specific spots the gypcrete would have cracked where the lathe ended. There are some fracture guard products that can be rolled on, but I don't want to recommend anything until we have determined the cause. Anyone else have similar problems with sound mats telegraphing the gypcrete movement through sensitive flooring? If so how did you remediate the problem? Also is there any truth to gypcrete not shrinking due to temperature change? I think that is bull shit and I even found an old document with a coefficient of their,al expansion for gypcrete that is 0.0000085 in/in/degree Fahrenheit. My calculations show a shrinkage of up to 0.2" with a 40 degree temperature change. The cracks aren't even really the issue as much as the vertical movement that occurs after the cracks appear.
