Creating level roof surface for AC? - Fiberglass RV


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Old 09-11-2007, 03:44 PM   #1
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The AC leak prior to our owning our 1988 Bigfoot B19 (mentioned in my post about the fiberglass ripples or wrinkles)caused some of the core to swell, creating an uneven surface around the AC roof opening. Per the suggestion of a fiberglass repairperson, I did my best to seal the areas where the fiberglass had separated from the core, but the roof is still uneven around the AC opening. The instructions for the AC state that it must be placed on a level surface and suggest creating a shim if the surface is uneven. Well, if there were an uneven slope in only one direction, that would be easier to do, but in this case one or more of the 14 x 14 sides of the opening has an undulation in it so one could not just slap a shim the length of it and have it be even. It needs an indentation filled in in one part, but then there's a raised area before there's another indentation. So, I am at a bit of a loss on how to create a level square surface upon which to place the gasket and then the AC (and make it all water tight) and we want to go to that Rally this weekend, but I am starting to feel that I won't possibly get this done in time.

Has anyone else had to remove and then reinstall an AC on an uneven roof...and if so, how did you even it? Thanks for your suggestions!

I just had the idea of sanding the gel part of the finish off of the surface to be leveled, then using epoxy paste or putty to create a level surface, which I could then paint. Since it would be under the AC body and shroud, it wouldn't be visible, so as long as it is waterproof and holds up well, it doesn't matter if it matches the rest of the trailer body.
Any thoughts on this before I go to Home Depot to buy these supplies? Is there some other material I should be aware of? I am going to call the fiberglass repairmen to see what he thinks.
Val
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Old 09-11-2007, 04:13 PM   #2
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Butyl tape is excellent for leveling out imperfections, and I think it would work well for you. When you attach your AC the excess tape will squeeze out, creating a tight seal. Plus it's very forgiving, and if you find it doesn't work as well as you hoped, it's fairly easy to remove and try a different approach. With the butyl tape I don't think you'd want to use your gasket though - just go directly from the tape to your AC.

Jeanne
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Old 09-11-2007, 09:54 PM   #3
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Just wondering how far out of level is it? That might have some bearing on the best approach to reseal this.
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Old 09-12-2007, 12:23 AM   #4
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Update:

The fiberglass repairman thought the gasket would be enough, but Kayla and I both felt that wasn't going to cut it, so after much searching for an appropriate material, I found some heavy duty styrofoam insulation at Home Depot that is not easily compressed, though I imagine it will give a little under the weight of the AC, but it should fill in the gaps well to create a level enough surface to meet the manufacturer requirements for proper AC operating conditions and to allow the gasket to do its job without hoping that it will compensate for the uneveness around the AC opening.

There was over an inch difference in height between the highest corner (where the core had swollen, then dried after some past AC leak) and three other corners, so unfortunately, butyl tape was not going to work because it couldn't fill such a large gap, plus, we needed to make a hard enough surface to support the weight of the AC, so that it is evenly disbursed over the roof, not leaning to one side... anything too soft or spongy would just allow it to tilt. Kayla cut the styrofoam pieces tonight (while we watched a wonderful made for TV HBO movie about the life of Josephine Baker... I know this is off topic, but I highly recommend it... we got it through Netflix).

I will use 3M Marine adhesive to install the pieces tomorrow, and to seal any cracks and crevices. They are solid enough that the gasket should have an excellent surface to adhere to. I will post results.

Val
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