Fiberglass experts! Adhering new CSM to uncoated old layers exposed to elements?

[hanktruck]

Hi all, first post here, feel free to shame me for posting in the wrong section (forum altogether lol), but you boat guys seem to know more about fiberglass than anyone else.

I have a box truck with a fiberglass roof, and small leaks have developed in places, just drips here and there. The roof is composed of a sturdy fiberglass around the perimeter of 2.5ish feet, and the center 2ft x 5ft section is a very thin layer of chopped strand mat, with NO signs of resin at all applied to the top, only on the inside is there resin.

My goal is to prevent leaks through this area by stripping the whole roof with some kind of stripping pad/steel brush/sandpaper, and applying a new coating to the sturdy perimeter, and reinforcing the CSM with an additional layer or two.

My fear is that new layers may not adhere properly to the exposed CSM that has lived years getting dirty and weathered, and that aggressive cleaning may be too much for it and it could be destroyed or horribly frayed. Please see attached pic and advise. I can add additional ones if needed. Thank you!

 

[todhunter]

You need to sand with something like 40 grit then wipe with a good soaking of acetone right before you lay new glass, to make a good mechanical bonding surface. You won't get any chemical bonding with the original glass already having been fully cured.

 

[hanktruck]

You need to sand with something like 40 grit then wipe with a good soaking of acetone right before you lay new glass, to make a good mechanical bonding surface. You won't get any chemical bonding with the original glass already having been fully cured

Sand directly on the uncoated CSM? I assume you're talking about the sturdy coated stuff on the left which makes sense and thats what I'm planning. My main concern is how to deal with preparing the raw uncovered CSM or if I even have to.

I hope you can see the loose fibers sticking out in the pic

 

[stresspoint]

easiest way would be to get a 80 sanding disc , sand the whole lot down to remove the furry bits and lay a couple of new layers of CSM over the top.
most of the older truck stuff was done on the cheap , chopper gun , a quick rollout and flash cured , very little resin used so it was thick but no body.

don't be too fussed with sanding and prep the new CSM will bond just fine.

 

[Scott Danforth]

40 grit sanding disc on DA.

make sure you have your proper PPE or fiberglass dust will kill you

when you think you sanded enough, sand some more.

go thru some of the restoration threads. 4th sticky down, link 14 is a good one.

 

[hanktruck]

Thanks all, I'll add more progress pics in case this thread is useful to anyone else in the future.