You're exactly right. Not enough coffee - our bourbon for that matter. Kind of like getting a new truck instead of changing the oil.
Couple of questions: would you glue the underlayment to the deck or use screws and glue? Also, what adhesive would you recommend to secure the membrane? Gorilla glue or some type of RV adhesive?
We leave Monday for a five week trip to the Northeast. Not wanting to "hurry up and fix it" I'm going to leave well enough alone until we get back home. I don't want to take the risk of glue not setting up, rain, etc. The roof is secure right now and was fine on a huge trip we took out west back in March.
Thanks so much for reaching out to me. Appreciate your insights.
Yeah, do this repair when you can be stationary for a week at least, and it's always better to do these when there is low humidity (I manufacture commercial TPO roofing systems).
Here are the facts of the matter. The Alpha System's TPO on your rig is applied with a water-based acrylic emulsion - it's all they use with their TPO. I have not seen them sell it in small containers. However, there is nothing special about the formulation other than it is inferior to commercial product as it is designed for lower peel strength to facilitate re-roofing. You can find water-based acrylic emulsion adhesive for TPO of many brands in quart size. Make absolutely sure you use water-based! The super thin TPO for RVs is not compatible with solvent-based adhesive.
Regarding fixing the underlayment to the decking will really depend on what you find. Simple pulled fasteners would be nice, but that's a 50/50 in that the fasteners you are seeing probably have nothing substantial to bite into. The original roof decking is generally a specifically engineered oriented strand board (OS
for roofing applications (but I cannot tell you how many RV manufacturers do not police the production line because the product has two distinct faces and only one side prepared for proper bonding of membrane!!). Anyway, what often happens when peeling a membrane off the decking is that it'll take chunks and splinters of the OSB with it, particularly along the edges - either completely pulling them off or just freeing it out of the pressed composition. If you find this to be the case under the veneer underlayment and why the fasteners didn't hold, you will need to repair that first in order to have something to fasten to. If it's is a loosened piece, you may be able to inject a good polyurethane-based wood glue to bond it to the rest, but if it's real loose you want to pull that out and proceed to make a leveling repair. FYI - good re-roofs will actually do all these deck repairs before laying the underlayment, but I would not be surprised if an RV dealer did not. I'm going to try my best to explain the trick of the trade here to have such a repair, and you need to use a quick-curing, non-shrinking, two-part, PENETRATING epoxy-filler. This can be found in any quality boating supply house and I have even seen it in the big box stores in recent years.
After inspecting and determining this is the situation you have, you will need to drill 2 to 3 0.25-inch holes in the underlayment above the chunked-out area. Do your best to clean out the recess between the underlayment and decking - shop vac with an edge tool. Tape up everywhere you do not want to get epoxy on, including the underlayment on the side of the seam that is adhered. Mix up the epoxy and force it in under the underlayment in a quantity a bit more than that needed to fill the void. Then press the underlayment down - slowly, and the holes you drilled will eject the excess epoxy. Press the underlayment until flush to the adjacent piece and weight it down with a brick, sandbag or such after you use a putty knife to remove the ejected epoxy from the holes till it is flush with the surface. Let that repair dry for at least 48 hours. Once set, if you have an air stapler, that's best to use to secure the underlayment to the repair because the veneer is so thin (the penetrating epoxy will give you some bonding too). If you do not have one, I suggest you use wafer head screws for the additional bearing area of the large head and being a low-profile head. The screws need not be recessed since you are capping the repair area. The underlayment just needs to be secure.
Should you find that you aren't missing a chunk, but just have edge splitting of the decking such that the underlayment fasteners cannot hold, then bonding with any quality polyurethane based glue will work provided you clean the area of loose material and then apply pressure with the brick, sandbag, etc. till it cures.