CoatingsPro Magazine

MAR 2018

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Notes From the Blog COATINGSPRO MARCH 2018 17 the bottom of a floating roof tank. We are recommending the application of a polysulfide seam sealer on all welds and in the chime area before the appli- cation of the coating system over the entire bottom of the tank. e client, however, is questioning whether or not we need to use the seam sealer. Does anybody have any data or is familiar with any articles or documentation that addresses this issue? A: In my time with tanks, we both used a filler at chimes and not. Other operating companies weren't using a filler at chimes, so we dropped it. I don't believe we ever experienced a problem we could attribute to the absence of a filler, but this is all very subjective and a long way short of a definitive answer. Use of a filler along welds sounds like a good idea at first thought, but there is also the possibil- ity that the thicker material will fail under floor movement where the thin coating may not. We never used a filler, and I don't recall any specific problems resulting from our coating practice. We certainly had coating failures, but for other reasons and more general than specific to welds. A: First of all, the chime is a struc- tural component that acts as a stiffener for the tank wall and the most highly stressed weld on the tank or f loor to the shell weld. I've seen 0.5-in. (1.27 cm) glass reinforced asphalt mastic set into a 0.25-in. (0.635 cm) deep by 4 -in. (10.2 cm) groove on a tank concrete ring wall that proved to be well worth the minor expense on large ground storage tanks in the wet climate of south Louisiana. Being about 60 miles (96.6 km) from the Gulf probably added to that. T hese tank ring walls were in good condition w ith ver y minor settlement. Smaller tanks w ith no seal eventually required chime repairs due to bottom-side corrosion. None of these were coated from the bottom side. My memor y fades on the specifics of the mastic, but I think it was similar or equal to a heav y-grade roofing felt. With polysu lf ide, if the product stored is hot, be cer tain to consider ther ma l ex pansion of the f loor. Add ing a d isband ing tape to a l low for the movement is simple enough, but if the tank bottom doesn't have stops to prevent uneven movement, the tank may tend to crawl or move in one d irection or another. One ver y ser ious issue can be a sea l that par tia l ly fai ls or fai ls on a few spots. Water that enters w i l l usua l ly be Notes From the Blog DeFelsko Corporation l Ogdensburg, New York USA Tel: +1-315-393-4450 l Email: techsale@defelsko.com Measures Relative Humidity and Temperature in Concrete Floor Slabs CMM IS NEW 1 -800-448-3835 www.defelsko.com Concrete Moisture Meter - In Situ WiFi n No need to open the hole or remove the cap to take a measurement. Reusable smart probes remain powered on and broadcasting via while in situ for up to three weeks. n C ombined sleeve and probe design simplifies the installat ion process and does not require consumables U se probes with the f ree PosiTect or mobile app or the PosiTect or D P M A dvanced Re ad e r In qui r y at co ati n g sp ro m a g.co m /i n q0318

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