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Discussion Starter · #1 ·
I did some driveway caulking yesterday and today the caulk is lumpy in the areas that got direct sun in the afternoon. Some background on the work: I used NP1 and backer where needed; The joints are at least 1/2" deep per NP1 data sheet; It was shady when applied and got hit with afternoon sun at 90deg F; and it rained about 18 hours after application.
I'm guessing the direct sun caused the issue rather than the rain, but not sure. The integrity of the joints is good, just not aesthetically pleasing. I spoke with the client about it and they have no issues, but I would like to avoid this problem in the future. Does anyone know what would cause this? My first thought was off-gassing and skinning over too quick due to the direct sun. Thanks for any insight.


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Check dates on tubes. I didn’t check & picked up some year over date tubes once & it came out fine but did lump in spots. Could be the conditions as well. I didn’t use mine on concrete. Check out Rufus Walker products San Antonio. They have caulk & sealants for every app

Mike
 

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Discussion Starter · #3 ·
No dates on the tubes, just product codes. However, the supplier I use specializes in sealants and a few other products for commercial/industrial apps, so I would be surprised if it was expired.
 

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Discussion Starter · #6 ·
It's about 1" between the slabs and 1-1/4" at the top as it hits the radius edge. Wide but definitely within range of the products capabilities. I did some caulking on their back patio last year with similar size joints. That gets hit with morning sun, then shade the rest of the day and those joints look good. That's why I suspect the direct sun might have caused this.
 

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Looks to me like edges of caulk stiffened, center stayed more liquid & flowed longer. Hence it sagged at the center.
 

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Discussion Starter · #8 ·
It's hard to tell from the pic, but there is no sagging. The joint is flat except for the lumpy areas which feel like there is air under them.
 

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I had that exact thing happen in my driveway. I used Sikaflex self leveling. It was on about a two foot long section that my concrete guy didn’t do. It was deep enough that I put some over it a few days later and it looked good then.
Nicko
 

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Discussion Starter · #10 ·
Do you have a theory on the cause, Nickko? What were the weather conditions like? I only ever used SL sealant once many years ago and it was in direct sunlight and in the 90s. That stuff actually bubbled up and looked like complete dog chit the next day. I have had air bubbles form on exterior caulking occasionally using quad, vulkem, and solar seal and all were in areas of direct sun. The only thing I can think of is off-gassing continuing after the sun has sped up the skinning of the sealant.
 

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Discussion Starter · #12 ·
Some of the edges are raised due to the lumps, but they also are found in the middle. This problem is only in the areas that got hit with direct light after the joints were laid. A 12' section in front of the garage is good.
 
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