ASTM C679:15 pdf free download – Standard Test Method for Tack-Free Time of Elastomeric Sealants.
8.4 Relative Tack-Free lime Unknown. If the relative tack- free time is unknown, the procedure is to pretest one of the test specimens by lightly touching the surface of the sealant with a film of polyethylene wrapped over the end of a finger. Touch the test piece in accordance with an appropriate time interval described in 8.5. Try 10 touch a different place on the surface each lime. After the polyethylene wrapped finger is lightly touched to the suriicc of the sealant, it is immediately removed and examined to see if sealant was picked up on the polyethylene film. When no sealant is picked up on the polyethylene strip. perlorm the next test as described in 8.6.
8.5 Time Intervals—If the relative tack-free time is unknown, the procedure is to pretest. as in 8.4. one test specimen each minute for the first 10 mm. each 2 mm for the next 10 mm. each 5 mm for the next 160 mm (3 h has elapsed). each hour for the next 69 h. each day until a positive result is achiesed or until 21 days has elapsed. Table I summari/es the time intervals.
Note 4—lnloimat.on provided hy the manuraciurer can save a great deal of lime and kad the ieier quickly to an appropriate time bracket.
8.6 After the pretest in 8.4 do the actual test by starting new, but just before the tack-free time estimated by the pretest. At the appropriate lime lay a polyethylene strip over half of the same test specimen and gently place the brass weight on the strip and allow it to remain there for 30 s.
8.7 Remove the weight anti then slowly withdraw the polyethylene strip pulling it with thumb and forefinger at 9tJ to the compound. at a constant rate of I inil5 s tsee Fig. I).
8.8 If the strip is clean or almost clean, repeat the test of 8.6 and 8.7 on a previously undisturbed test specimen.
8.9 If the strip is clean from the previously undisturbed test specimen. record the time from the moment the template was scraped level with a spatula until the pulling of this strip.
8.10 If the polyethylene strip still has sealant adhering to it. wait half the time of the preceding test lime interval arid repeat the test described in 8.6 and 8,7 on another undisturbed test piece.
8.11 If the strip is again not clean, repeat 8.10 until a clean strip is achieved.
8.12 If an approximate tack-free time is known, consult Table I and choose the total elapsed time interval that matches the supposed tack-free time, back down one interval and start the pretest there and proceed with the pretest and lest as described above.
8.13 If the tack-free time is shorter than anticipated, start with fresh specimens and pick a shorter elapsed time as the starting point.
8.14 If the tack-free time occurred at an occasion when no one was available to check it that is, night or weekend) start the test over, at such a time where the anticipated final point will occur during working hours.
Note 5—therefore should be closely watched prime imponance is performing the test at the called Out conditions.