B-73 Restoration in Antique and Classic Mack Trucks General Discussion Posted 3 hours ago Yes apply the high fill in 2-3 progressive layers over the LS but you must add approx 35 of flex additive to the high fill because the LS is flexible whereas the high fill is solid, by adding the flex add to the high fill then the high fill will move with the LS - when I say move it means the product is flexible, and that is ok, after each HF you apply let it dry thoroughly then sand it back to even it a bit then apply 2nd HF with flex add, let dry then rub back, if after 2nd coat you have a smooth surface then you can apply an undercoat also with flex add, let dry and rub back to get smooth finish and then apply the final red paint with flex add in the red. That is how we did our fire wall engine side and we have a mirror finish which you see in my picture. If you need to apply a 3rd coat of HF then that wont hurt because you are building up in layers to get a smooth surface before you spray the undercoat. It sounds like a lot of work but the final result you will be very happy and get the benefits - once done you will look back and forget the extra work, but it is done properly, which is what the LS inventor, Bob Call advised me to do. Remember the trick is to add the flex add so all the products can flex in parallel with the LS. And that is what I have seen with underside of our hood, it is aluminium we applied LS with some of our external green paint mixed in and the hood twists when it is opened and lifted, so far after 5 years no cracking or peeling of the LS because it is flexible - hence the name like the lizard skin. With your cab wall vents they serve no real purpose unless you want a permanent air flow. If not seal them with a thin aluminium or metal sheet, painted black facing the vents, and stick on with a long lasting glue so you dont have water leaking thru into the cab, (when you wash the truck) and no bugs or mice to damage the upholstery, do this before you spray the LS over internal cab walls. That is how Ian Lee did the vents in his Pal LTL, from outside the vents look as original. Congratulations on a craftsman workmanship, a credit to you sir.