I am planning to do a panel by panel paint job on my truck. I live on a gravel farm road. What do you think of the idea of using brush/roll on bed liner as undercoating under fenders, bed, under cab, etc.? If I masked the edge of the fenders for a clean line?

 

If the underside is rust free and has a good base of paint on it already, I'd say that's a great idea. If you have any rust, treat it first with Por15, the use the bedliner stuff. Take extra time to insure the surface is roughed up and is VERY clean.

 

So, I would prime and paint the underneath like usual and then rough up with like 320 sandpaper, then use the undercoating?

 

I wouldn't use 320 grit, I think something in the 100-120 range would do better for the bed liner. Hurculiner comes with a scour pad that they want you to use to scratch things up and it seems to work well, 320 seems too fine.

Careful about what you prime and paint over, I'm sandblasting mine right now and I'm finding rust spots under the paint that you can't see till you strip the paint. I'd check some of the problem areas for rust first. very rear of truck under bed, where flat bottom welds to sides, under fender wells... Epoxy primer is probably the best choice.

Let the new paint COMPLETELY dry for at least several days maybe more before applying the bed liner.

Just as a side note, I'm using Por15 for several reasons, but one nice thing about it is that it's near impossable to chip. I've heard you can hit it with a hammer and bend the metal and it won't chip. I paid about $90 for a gallon and that's about the same as a gallon of bed liner and you don't need to paint or prime, just clean and wire brush.

If you do go with the Por15, be sure to apply it in at least two VERY thin coats, don't let it puddle up, keep it thin. and be sure the surface is VERY dry and clean.

 

Undercoating and rustproofing are 2 different things. Undercoating will not fill the seams where 2 pieces of metal over lap. Only a rustproofing spray applied using a pressure gun will work. The rust proofing is far more fluid than undercoating and thus seeps under seams.

 

I ready to apply bed liner to the underbody of my cab (56 F100). I took it down to bare metal and sealed it with Eastwood Corroless, sealed seams with Eastwood seam sealer and am about to apply Gator Guard bed liner to the underside of the cab. I am stalling now, trying to decide spray or roll on or brush or a combo of the above. I have no plans to coat anything except the cab floor. Anybody ever use Gator Guard?

 

I have used GatorGaurd several times with good results. Only problem I have is with the quantity they give you. It comes in a gallon can and 1 quart can(activator). I have found that this is not enough to do a regular sized box only a short box or flare side. You need to apply enough of the product to cover all the painted surfaces.