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Richard L. Hird P.E. CCS
Senior Member
Username: dick_hird

Post Number: 30
Registered: 02-2004
Posted on Saturday, July 16, 2005 - 10:45 pm:   Edit PostDelete PostPrint Post

In investigating TPO roofing membranes on my clients behalf, a Roofing contractor that I have a great deal of respect for, said that TPO membranes thermoset in a relatively short period of time. This makes repairs of during construction, as well as future modifications, a problem. The membrane can not be heat welded for repairs.

I have used Hypalon and PVC membranes roofs in the past and have never heard that they can not be repaired or modified. Has anyone had any experience with modifications or repairs to thermoset membranes.
John Bunzick, CCS, CCCA
Senior Member
Username: bunzick

Post Number: 380
Registered: 03-2002
Posted on Monday, July 18, 2005 - 11:59 am:   Edit PostDelete PostPrint Post

My recollection is that Hypalon, a thermoplastic, would become 'thermoset' on the surface after weather exposure. PVC, however, does not have this effect. I have not heard that the TPOs have experience this phenomenon, but would also like to hear more. Have you contacted any TPO manufacturers?
Robin Dale Rund
Junior Member
Username: rdrund

Post Number: 2
Registered: 06-2005
Posted on Monday, July 18, 2005 - 06:19 pm:   Edit PostDelete PostPrint Post

There seems to be some confusion here.

Thermoplastic materials, like PVC and TPO, melt and flow when heated, or upon application of a solvent, at any time during their life. Theoretically, there should be very little difference between patching PVC and TPO.

Thermosetting materials like Hypalon and EPDM, are produced in a raw, uncured state, but once cured under heat and pressure (thermoset) become non-weldable and unable to be solvent-adhered. The interesting feature of Hypalon is that it is shipped in the uncured state, which allows seams to be field welded. The membrane then cures in-situ with the natural heat and moisture in the environment.

The term "thermoset" does not apply to TPO, but does apply to CSPE. Furthermore, roofers do seem to have more trouble with field patching CSPE than EPDM. One told me that he considered it impossible to make a permanent repair in a damaged CSPE membrane. So it does seem likely that Richard's contractor was confusing the TPO and CSPE.

However, I've also heard reports that some TPO membranes are fussy about the exact temperature and timing required to get adhesion between flashings and the field membrane (this was on new roof). Richard, I wonder if you could pursue this with your contractor. If he really has had a bad experience trying to repair TPO, I'd like to hear more about it.
Richard L. Hird P.E. CCS
Senior Member
Username: dick_hird

Post Number: 31
Registered: 02-2004
Posted on Monday, July 18, 2005 - 09:42 pm:   Edit PostDelete PostPrint Post

Must admit that I talked to material suppliers before I had my conversation with the Contractor. I do need to go back to the supplier folks at some time. Before I contacted them I thought I would float the problem on 4 Spec, then I could explain my concern in a manner that was not one person's opinion. Promise I will let you know what they say.
Interested in your differentiaion between Hypalon and PVC and TPO. I had assumed that Hypalon (CSPE?)was a thermoplastic because I recalled that we heat welded the joints. Could not find any of my old specs to confirm that however.

With regard to repairing the TPO, the Contractor told me he inherited another roofers "problem" after some legal rangling. He could not get the bad seams to reseal because of the time lapse during the rangling. It certainly is an unusual situation, but it does cast light on a potential long term maintenance problem. As mentioned above I will continue to gather information and post it. Not sure I fully understand the ramifications at this time, and I do not want to mislead anyone.
Anne Whitacre, CCS CSI
Senior Member
Username: awhitacre

Post Number: 220
Registered: 07-2002
Posted on Wednesday, July 20, 2005 - 11:31 am:   Edit PostDelete PostPrint Post

keep in mind that it has only been two or three years since there was an applicable ASTM standard regarding TPO membranes and its possible that varying formulations caused the issues you described. I have not heard of any repair problems with TPO membranes, but think its probably worth a call to the larger manufacturers of the products.
Richard L. Hird P.E. CCS
Senior Member
Username: dick_hird

Post Number: 32
Registered: 02-2004
Posted on Friday, August 05, 2005 - 10:12 am:   Edit PostDelete PostPrint Post

Sorry to take so long to get my findings posted, but a vacation, and making up for a vacation, has kept me busy.

Most importantly there is no evidence that old seams in TPO membranes can not be welded. However, they must be “properly” cleaned before welding. The older the membrane the more care must be taken in cleaning, because it is dirtier not older. “Properly” means cleaning with the manufacturer’s recommended chemical cleaners, not water and brushes. In fact that latter is what happened on the job that initiated this string. The Contractor who originally had the project cleaned the membrane in a manner that made it impossible to get a good weld even after proper cleaning. Subsequent attempts to fix the problem were unsuccessful.

The product is sold by reputable companies, is cost competitive and has several features that make it desirable. My only concerns about TPO are as follows:
It has been on the market for only 15 years. Installers may not be familiar with the product and warranties will be of shorter duration than products with longer track records
Subsequent welded seam modifications require enough electrical power to heat the seam to 750 degrees F. This could lead to a roofer to take short cuts in making repairs. Flashed joints can be taped but joints in membranes must be welded to maintain the Warranty
Although the membrane is less expensive than EPDM, installation costs can make the whole system more expensive.

More information is available from the manufacturers, Carlisle and Firestone most prominently, and at the following location. Single Ply Roofing Institute - www.spri.org/news_7.html [changed URL - Colin]
Posted on Friday, August 05, 2005 - 12:02 pm:   Edit PostDelete PostPrint Post


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