Kindly tell me...if very low viscosity epoxy used for injection of cracks in building can be used successfully in vacuum infusion...or any experience of usage ...thanks

It will probably infuse fine due to the low viscosity.  However the cure profile and mechanical performance may not be there for a composite infused part.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I have tried Megapoxy HX before. Infused great, but the final composite component was extremely flexible, especially for the first 5 or 6 days. After that, or after a post cure, it was a bit stiffer but still no where near what I would have expected for the layup. I was only doing test panels, but I would be concerned about the potential for distortion.