Cracks in penthouse top

[SierraHawk]

I have waxed my 2003 E350 SMB every 6 months. When I wax the PH top I use a heavy application of paste wax. During this semi annual cleaning/waxing ritual I noticed an eight inch hair line crack in the very top of the PH roof. There are also two quarter size spider cracks developing on the PH top near the rear of the PH. The area gets a lot of sun but it is not stressed by weight. I have never seen a profile of how the PH tops are constructed or understood what the "gel coat" is or does. Are the cracks evidence of another problem? How can the cracks be repaired?

[daveb]

In my case the cracks didn't pose a problem as far as I could tell. But I never cut open anything to look. I think most of the leaks are from where a hole has been drilled in the top for whatever purpose. Even My Bass boat has gel-coat cracks and I don't worry about them too much. I decided to have SMB spray my top with the Rhino type lining. No worry now and it is so much easier to clean. There are plenty of posts on this issue and some dealt with leaks but I don't know if it was proven that the cracks were the cause.

[witoke]

"I have never seen a profile of how the PH tops are constructed or understood what the "gel coat" is or does. Are the cracks evidence of another problem? How can the cracks be repaired?"

Gel coat is an airless cure polyester paint basically. When making something from GRP in a female mould with polyester resin (the cheaper stuff, most GRP is made using Poly for budgetary reasons), the gel coat is applied to the interior of the mould prior to the application of the glass/resin mix. It then becomes an integral part of the structure. GC is very hard, not too brittle and has excellent UV resistance. The resin has limited UV resistance so once the glass/resin is exposed, UV can break it down very quickly.

I have not taken down the lining of my PH but I am pretty sure it's made with chopped strand. This is short pieces of glass fiber shot onto the mould in alternating layers of resin and glass. It is quick, cheap and provides a reasonable product.

Most cracks you will see are in the GC itself. They are not usually too much of a problem since the glass mat is resin impregnated and so is fairly water resistant. Unless it's immersed in water all the time like a boat kept in the water, but I trust that will not be a problem with the PH top on your SMB. Eventually, like cracks in anything with a protective layer, it can become an avenue for breakdown.

Fixing is fairly simple. Clean it with a good solvent like acetone, sand the crack back to solid material, fair it with an epoxy putty or bondo for that matter, and paint it with a good UV resistant paint. If the crack is through the glass itself then it's a little more work but in a similar vein.

[PatO]

My cracks were so bad that they did take on moisture and it was oozing out as I prepared the top for Line-X.

[witoke]

Ah, nasty cracks you have there. If they are oozing moisture you need to get a bit more involved. It's still easy enough for a DIY but will take some work. I'm not much of a typist but if you PM me I'll give you my phone number or if you are live anywhere near me, I'd be happy to help you with it and I have all the materials you'll need. I'm in Albuquerque, NM.

Those may need reinforcement from the inside as well, depending on how deep they are. They are clearly more than just GC cracks. It would be good to figure out what caused them too so you can make sure it doesn't happen again. Was it an accident of some kind or someone walking on the roof?

[PatO]

Unknown reason for cracks but after the 1st year I never waxed it again. I sanded everything down and had 3/16" Line-X professionally applied about 1.5 years ago. It has had zero problems since then but it is extremely heavy now. After pictures in my Gallery.