I have Thunder alloy tg-18 thermal paste with 8.6Wm/k thermal conductivity shoud i use this paste for my GTX 1070. also tell me should i fully tight the gpu nuts which contain springs to 100%

 Install them using a cross tightening pattern until they all bottom out properly.  Do not tighten one all the way down, and then the next.
 
Their are  tons of guides how to reapply TIM and install thermal pads.
 
https://forums.evga.com/How-to-apply-the-Thermal-Pads-for-the-10701080-Cards-m2573413.aspx
 
if you have never done this read a bunch of them and watch youtube videos. it is a simple process if you are careful. Be careful and take pictures or use a computer to view info or pictures why you work I can not speak on the thermal paste. I prefer Artic MX4 because that is what i have used for the last decade. The TG 18 Is almost guaranteed to be better then old dry out thermal paste. Hope this helps

tattude69
 Install them using a cross tightening pattern until they all bottom out properly.  Do not tighten one all the way down, and then the next.
 
Their are  tons of guides how to reapply TIM and install thermal pads.
 
https://forums.evga.com/How-to-apply-the-Thermal-Pads-for-the-10701080-Cards-m2573413.aspx
 
if you have never done this read a bunch of them and watch youtube videos. it is a simple process if you are careful. Be careful and take pictures or use a computer to view info or pictures why you work I can not speak on the thermal paste. I prefer Artic MX4 because that is what i have used for the last decade. The TG 18 Is almost guaranteed to be better then old dry out thermal paste. Hope this helps

Install the screws in the X pattern in Small increments (1/2 to 1 turn at a time) in that X-pattern ---- while holding the cooler Flat against the GPU die
 
thermal past - read reviews, look at what is available to you & cost. 
 
Average PC use like for business or casual gaming does not require the expensive TIM