I have no idea why your coating has blisters, but my best guess is:

1) the roof was not cleaned properly before application of coating product – this causes delamination of coating from the rubber roof (substrate).

2) the coating thickness was insufficient (I believe it should be 30 mil minimum DRY thickness).

3) Most contractors who install small coating jobs, do so infrequently, thus do not have much experience with it. This might not apply in TX, as your climate is much hotter than here in MA, so coatingins are more popular.

4) Ponding water will damage coatings – break them down, and make coating separate from the substrate. This does not apply to ALL coatings, but to most.

Additional fact is the actual coating material AND the application (installation). There could be so many additional reasons for the coating to go bad.

HEAT wave – I don’t know if the heat was the factor in your coating going bad – in theory it shouldn’t have, but I am not really familiar with your particular material. Keep in mind – there are over 50 coating products on the market (maybe over 100). They are all different, and it’s impossible to know much about all of them.

I am right now dealing with a leaking roof that has a coating on it and coating is also blistering and bubbling, and in ponding areas is coming off the rubber. Additionally, the coating make it difficult to repair this roof, because the adhesive must be applied over coating – not directly to the rubber, and it does not hold up well.

Basically, from what I’ve seen, and in MY PERSONAL OPINION, people should avoid using a coating on membrane roof (i think it’s ok to use on metal roofs). Coatings will create more problems than they solve, as they make it very difficult to repair a roof, if there is a leak. Also most coatings are not water-proofing material, though they are advertised as such.

Leo.

The granules are only on the top, and when field seams are done, there is a 3-4″ strip on one side of Mod-Bit roll, that has no granules (for better field seams adhesion).

But when it comes to field flashing / detail work / termination at the wall, etc., that strip is usually not present, so granules are between the overlap. This is especially critical for skylight / chimney / curb flashings, as shown in this picture:

Therefore in real roof settings, the seam on a modified bitumen roof, often has granules in it, which reduces the longevity of such seam.

I thought that a cap sheet only had granules on the
top surface. You seem to say that it has granules
on the bottom?
thanks,
bill

Also, there are many limitations to it. You need a positive slope to the roof, and proper drainage.

I think built-up is definitely outdated – but also we are talking about a few types of flat roof at once – built-up can be tar + gravel roof or modified bitumen. These two are completely different animals. Mod. Bit. can be cold applied or torched, and I have issues with both methods, ans especially with the granular surface cap sheet. How do you expect to have proper adhesion / contact / bond between two sheets, when there are granules in between them. Yes it hold for some time, but not 30 years!

Coal tar pitch – man really? when was the last time you’ve seen a kettle? I last saw one 7 years ago – so two dudes that looked like miners from W. Virginia where doing magic tricks on a roof of a store. 3 month later, a new PVC roof went up on that roof… So much for hot tar roofing

Also, there are many limitations to it. You need a positive slope to the roof, and proper drainage.

I think built-up is definitely outdated – but also we are talking about a few types of flat roof at once – built-up can be tar + gravel roof or modified bitumen. These two are completely different animals. Mod. Bit. can be cold applied or torched, and I have issues with both methods, ans especially with the granular surface cap sheet. How do you expect to have proper adhesion / contact / bond between two sheets, when there are granules in between them. Yes it hold for some time, but not 30 years!

Coal tar pitch – man really? when was the last time you’ve seen a kettle? I last saw one 7 years ago – so two dudes that looked like miners from W. Virginia where doing magic tricks on a roof of a store. 3 month later, a new PVC roof went up on that roof… So much for hot tar roofing