Roof repair and renewal

[theotherbart]

Looking at the roof of my 2000 Thor 21RB Class C, there's significant cracking in all of the caulked seams and the roof surface itself looks a little worn. I'd like to redo it in the spring but I wanted some input into the process. This is our first RV, but I'm fairly handy. I want a reliable system that will last, but at the same time it doesn't make sense spending more money than necessary on a relatively old rig. So here's what I had in mind:

Eternabond tape over all of the seams and around all of the penetrations (antenna, vents, etc.). But which flavor of Eternabond? Their website has many options and the differences aren't clear to me.

Then recoat the entire roof. But with what? The literature I have on this model says it's a "rubberized" roof, but doesn't specify the actual material.

The other big question mark is a "soft" area around one of the plumbing vents. Obviously there's been a failure there that has let some water in, but not enough to show any signs of leakage inside the motorhome. I have no idea how to even begin approaching that repair. I know it isn't ideal, but what happens if I just seal the seam with the tape, recoat the roof, and leave it be? If I do need to cut into it and repair, what does that process look like?

[JimMartin]

Chopperbob wrote:
Sorry, that was Google Bus Kote.

Bus Kote is for metal roofs only

[theotherbart]

Jose, the process you've laid out sounds like exactly the right way to tackle this. For now though I've decided to take the "patch it up" approach instead. To fix it the way you describe I'd have to remove a plumbing vent and a roof vent that are either in or adjacent to the soft spot, and I'm afraid I just don't have the time to dig that deeply into it.

Instead I'm going to seal up all of the caulked seams with Eternabond Webseal. The bulk of the soft spot is in the 12" or so between the rear seam where the roof meets the rear fiberglass cap and the plumbing vent, so I'm going to reinforce that area with slightly overlapping layers of the Eternabond. Then in the spring I'll recoat the whole roof with Liquid Roof or something similar. My theory is that 1) the soft spot isn't that big, 2) it shouldn't get worse if I seal it up tight, and 3) if it does get worse I can always open 'er up sometime next summer and effect a more permanent repair. If it comes to that I'll follow your instructions to the letter.

[tenbear]

When there is a heavy dew I can look at my roof and see exactly where all the joists (studs) are.

[DaHose]

Well Paul, my simple guess is cost. Sealing the wood would greatly increase production cost.

CPES is not cheap and for it to seal fresh wood, you have to get a good two or three coats with some drying time in between. So in theory, if you use good wood and don't have leaks it should all last a very long time.

I do think that if you ever open up a wall or get access to any framing wood, you should slap some sealant on it.

Jose

[panamea]

This might be a dumb question but I have to ask it. Is there any reason why the framing is not painted or coated with something to make the wood waterproof?

Thanks,

Paul

[DaHose]

Knowing what I do now, a soft spot in the roof would get the following treatment.

I would make small X cut where the roof is soft and work my way out from the center. I would make the X just big enough so that I could get to good lauan and then cut a hole making SURE I was out to good wood.

With the lauan cleaned up, it would also be critical that the main roof spars are in good shape. If you are repairing water damage, you will probably need to replace the insulation too.

Next, I would use some CPES (clear penetrating epoxy sealant) to seal the existing wood and cleanup the underside of rubber roof sheet too.

Once all the prep was done, I'd cut an appropriate sized roof patch from lauan, staple it back down and treat with CPES. If the seams could be felt, I would use wood putty to fill them and sand the whole patch area when the CPES dries. The sanding will make it possible to just use some 3M 90 contact cement to adhere the EPDM back down.

The last step would be to seal the X cut in the roof with some Eternabond and she would be good to go!

Jose

[theotherbart]

ScottnSherrie wrote:
Agree with DaHose above. Mine seemed like it was all glued as one big piece then laid in top. There was the occasional 2x3 cross piece, usually adjacent to any opening such as vent, AC opening or skylight. Other than that there were some other 2x2 pieces strategically placed to hold up the cabinets.

If the area that need patched is not lined up with an opening, it could be only foam insulation under the luan in that area.

If that's a case I wonder what would keep a person from cutting out the luan with a circular saw set for a very shallow cut, then patching back in with just some foam-safe construction adhesive, then an EPDM patch, then an overall roll-on coating.

[ScottnSherrie]

Agree with DaHose above. Mine seemed like it was all glued as one big piece then laid in top. There was the occasional 2x3 cross piece, usually adjacent to any opening such as vent, AC opening or skylight. Other than that there were some other 2x2 pieces strategically placed to hold up the cabinets.

If the area that need patched is not lined up with an opening, it could be only foam insulation under the luan in that area.

[DaHose]

Depending on your RV's age, the roof is most likely rubber, then some lauan. Lauan is 1/16" or so plywood. The rubber top layer is glued to the lauan. The lauan is probably just stapled to the roof cross beams.

Jose

[theotherbart]

ScottnSherrie wrote:
As far as the patch goes, I'm afraid you won't know where the supports are until you start hacking into it. A stud finder may help but can't say for sure. Be aware the area to patch may have wiring so dismantle carefully.

I like the look the Webseal variant of Eternabond gave given that I did recoat the entire roof. I think the vinyl backed product would be easier where the roof is sound but the edge seams are the problem area.

I'm new to this, and I know different manufacturers will be slightly different, but can you give me some idea of how the roof is likely to be constructed? I'm assuming rubber on top of plywood, how thick is the plywood typically? Then some kind of horizontal beams that the plywood is fastened to? Plywood screwed down? Is there some kind of foam in there somewhere, like between the beams?

My thought is, if the plywood is screwed down then I should be able to cut away a square of rubber bigger than the soft area, use the screws to locate the structure underneath, cut away the plywood along the centerline of the structure where the screws were, then patch in a piece. If there's any open space under the plywood I thought another alternative would be to cut away the plywood in between the structure and then use plywood doublers underneath to support the patch.

I don't know if I'm explaining that well enough, but does any of it make sense? I'm still not convinced I can't just Eternabond and Liquid Roof over what's there and leave it be.

[myway2rv]

I used this Brushable Sealant a few weeks ago to re-seal all the cracked caulking. One quart covered all the joints and it seems to have stopped my leak. Real easy to apply. Just clean the old caulk with denatured alcohol and glop it on with a small brush. It has the consistency of honey and sticks to old caulk, plastic roof, whatever.

[ScottnSherrie]

As far as the patch goes, I'm afraid you won't know where the supports are until you start hacking into it. A stud finder may help but can't say for sure. Be aware the area to patch may have wiring so dismantle carefully.

I like the look the Webseal variant of Eternabond gave given that I did recoat the entire roof. I think the vinyl backed product would be easier where the roof is sound but the edge seams are the problem area.

[theotherbart]

Great suggestions so far, thanks. Calamus, how did you "patch" your roof? Did you actually fix the water damaged wood under the rubber roof membrane or just patch over the rubber?

Scott, what an epic project that was! Obviously you've been deep into the structure, if I wanted to cut out maybe a 2'x2' section of roof and replace the wood under the rubber how would I go about that? Going in I'd have no idea where the underlying structure is, or any idea how to fasten in the wood patch. And it isn't something I'd want to figure out as I went either, I'd rather have a solid plan before I started cutting stuff.

No one has weighed in on which Eternabond product I should be using. It seems like WebSeal is the right stuff if I'm going to be coating over with something like Liquid Roof or the Dicor EPDM coating, is that correct?

[Chopperbob]

Sorry, that was Google Bus Kote.