How do you repair deep cracks in the Roof

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How do you repair deep cracks in the Roof

May 01, 2011, 03:56:45 pm

I FINALLY was able to get my GV out of storage. The first step was to wash all the dirt and algae off of it. In the process I discovered several cracks on the roof, see attached photos. The first crack does not seem to be too serious although it radiates out from the FM antenna at the right rear. The second one seems much worse. You can not tell it from the photo but the crack opening is raised up from the roof.

How serious are these cracks and how do I go about repairing them?

Re: How do you repair deep cracks in the Roof

Reply #1 – May 01, 2011, 04:11:07 pm

John, I had a 93 GV before this one and guess what, I had a couple of similar ones too at the time. I was not worried about making it look like new, so I took off the antennas etc, cleaned the area up about 6" each side of crack then got my angle grinder and cut a small V groove thru the gel coat and then mixed up some resin and hardner and just brushed it into crack quickly and also either side of the crack. Once this set up I then cut some Fibreglass matting and mixed up some more resin etc and pasted these over the repair. I did 2 coats and next day sanded it smooth carefully, then painted it. The repair was still good 2 yrs later when I sold it and told the new owner to keep an eye on it

Re: How do you repair deep cracks in the Roof

Reply #2 – May 01, 2011, 07:17:28 pm

John, the first step is to determine if there is subsequent delamination. Take a hard object like a plastic hammer or screwdriver handle and start tapping all along each side of the crack or anywhere the roof looks blistered. You should be able to hear a difference in the sound where the glass is firmly bonded to the plywood substrate and where it has come loose. If you hear any hollow sounds, that is a problem. If you are not familiar with fiberglass repairs I would take it to a good fiberglass shop that does motorhome or boat repairs. Sections may need to be cut out and re-glassed and painted. I have done quite a bit of fiberglass repair in the past but I took my coach to Xtreme in NAC to have a 3' X 8' section removed and repaired. The bill was under $1,000 for the repair but it was well worth the cost to me. They were painting the roof anyhow and Rance is as good as they come on fiberglass.

If everything is sound and there are no signs of delamination then you can follow Johns repair methods, or a little bit easier repair would be to open the crack with a grinder and apply a good quality, exterior grade, pure urethane caulk of a similar color. Do not use acrylic or silicon as they do not have adequate adhesion and poor long term performance. The width of the opened crack should be opened up to twice as wide as the depth of the crack. This will allow the caulk to expand and contract.

If you use caulk, be sure to check the crack periodically. If the caulk breaks bond you could develop a leak it could result in delamination. The chances are you will not have any further problems for years but repairing the caulk is very easy if it ever fails.

Re: How do you repair deep cracks in the Roof

Reply #3 – May 01, 2011, 08:40:23 pm

John,
While you are at it take that antenna off of there. It is mounted into only the Fiberglass and 1/4" plywood that composes the roof covering. In my opinion that is not strong enough to take the beating the antenna takes from wind and branches. That is a prime area for leaks. I just took it off and glassed over the holes and keep the antenna in the bedroom closet, it works fine in there. You might want to use an epoxy resin for the repair.
Good luck,

Re: How do you repair deep cracks in the Roof

Reply #4 – May 01, 2011, 10:04:01 pm

Rick, are you certain that the plywood roof sheeting is just 1/4" on a Grand Villa? I sure thought mine was either 1/2" or 5/8" when I replaced the Sky Light.

Re: How do you repair deep cracks in the Roof

Reply #5 – May 01, 2011, 10:58:00 pm

John,

Sounds like you have a lot of good advise so far. I use an epoxy resin like "system three". It has almost no smell, cleans off your hands fairly easily with soap and water, less chance of an allergic reaction, resistive to gasoline and diesel and best of all, it sticks to almost anything super well and for a long time. I have repaired plastic holding tanks with it after everything else failed. The repair is still holding about 10 years later. 3 types or so for different applications.

Use fiberglas cloth only. If it can be seen from the outside, you can get fine weave cloth that will lie flat and barely be noticed. You won't have to worry about that on the roof. Over 90 percent of the strength comes from the cloth, not the resin. Cloth does not cost that much more than mat. Epoxy resin may dissolve certain binders in mat, another reason not to use mat.

I have pounded on rocks at in a 36,000 lb. sailboat at the entrance to Manila Bay in the Philippines for 15 minutes or so. Sounded and felt like the next hit was coming through the bottom of the boat. When I hauled out, there was a fifty cent sized piece missing perhaps an eighth of an inch thick. Multi layer fliberglas layups with low resin to cloth ratio (excess resin squeeged off between cloth applications) are amazingly strong.

Sadly, to save money, mat is used on RVs. It is stiff but lacks the strength of cloth. Southern California boats got a terrible rep in the 70s' for making chopper gun, mat hulls.

For a good primer, see: Fiberglass Cloth Fiberglass Mat Fiberglass Roving Fiberglass Tap - Clark Craft

My 2 cents.

Pierce & Gaylie Stewart
93' U300/36

Re: How do you repair deep cracks in the Roof

Reply #6 – May 02, 2011, 01:22:47 am

I know nothing about fiberglass but from the pictures, it looks to like all the cracks start at a hole drilled for antenna etc. Maybe the screw/bolt size was too large for the drilled hole ??

Just a thought ? Pierce ?

Re: How do you repair deep cracks in the Roof

Reply #7 – May 02, 2011, 02:19:10 am

Dave,

Sure does look as if it started at the screw/bolt like you said. Probably a combination of that along with constant flexing from the antenna while underway or even parked in the wind. Years of UV rays have also weakened the roof and made it more prone to cracking. When I was shopping for my rig, I looked at one with really serious cracks. Had been outside it's whole life.

This looks like a super easy repair. Just a bit of sanding, brushing on a coat of epoxy, laying cloth on top, smoothing with the brush to get bubbles out, painting more epoxy on and then repeating if you want additional layers. depending on the weight of the fiberglas cloth. Then using a paint with good UV resistance. Lot of good "do it yourself" web sites and videos that make it easy. I have a much better time understanding if I can see a video rather than reading about it. I did a quick Google search and found lots of You Tube videos at: Google Probably good to try it on something small in the garage to get it down so the result on the roof is perfect.

I don't have any cracks but walk gingerly when up there. Not a super solid feeling. Perhaps other members have a recommended coating they have had good luck with. How about some input?

Pierce & Gaylie
93' U300/36

Re: How do you repair deep cracks in the Roof

Reply #8 – May 02, 2011, 07:10:38 am

Quote from: Kent Speers – May 01, 2011, 10:04:01 pm

Rick, are you certain that the plywood roof sheeting is just 1/4" on a Grand Villa? I sure thought mine was either 1/2" or 5/8" when I replaced the Sky Light.

Kent,
Not sure about the Grand Villa's, but my 1995 U-300 Unihome has 1/4". A call to the factory can probably define the roof construction for any given year.

Re: How do you repair deep cracks in the Roof

Reply #9 – May 02, 2011, 09:23:19 am

Repairing fiberglass does not require special skills or expensive tools. Its much easier than repairing metal. However, most people are somewhat intimidated by mixing chemicals. If one doesn't mind performing multiple steps of sanding, itching, application of epoxy and cloth, sanding, itching, epoxy cloth, sanding, itching, and more sanding, it certainly can be accomplished by almost anyone.

Pierce is correct in suggesting Epoxy rather than Polyester or Vinylester resins. The reaction is easier to control. If one stays with 100% solids epoxy, no solvent, you will avoid adverse reactions with substrates like Styrofoam, composite wood and plastics. The ester based resins can melt or dissolve other plastics. Cure rates are also easier to control with thermosetting Epoxy vs catalytic setting ester resins. With ester resins, one drop to many of the catalyst speeds up the cure time and shortens the working time. Thirdly, epoxy inherently has better long term flexibility and strength when compared to ester resins. It is washable with soap and hot water until it starts to set, then you will wear it off of your hands. Xylene or Acetone are good for cleaning tools for most epoxies depending upon the formula.

Adtech Plastics, ADTECH Plastic Systems, is a good source for different types of resins. You can use their website or call them at 800.344.7776. Also West Marine carries repair kits but cannot supply much technical assistance.

Re: How do you repair deep cracks in the Roof

Reply #10 – May 03, 2011, 06:00:14 am

In my days as an aircraft mechanic, we occasionally had to repair cracks in fiberglass and aluminum panels. Before prepping the area for a patch, we drilled a small hole (1/16 or so) through the material at the end of the crack(s). This is called "stop-drilling". The hole prevented further cracking. If you don't stop drill, the crack may continue developing even after the area is patched. Seen it happen.

Hope this helps. Guess I better go have a good look at my roof too.

Steve

Re: How do you repair deep cracks in the Roof

Reply #11 – May 03, 2011, 11:40:58 pm

One of the things I found out today from a race car mechanic is that "fiberglass" can either have an epoxy resin or a polyester resin and that the two are not compatible. Any one know what my my '91 GV on an Oshkosh chassis roof has?

Re: How do you repair deep cracks in the Roof

Reply #12 – May 04, 2011, 09:21:38 am

John, I don't know where you heard that fiberglass made with epoxy is not compatible with polyester fiberglass or vice versa. I spent 30 years making polymers. I have never heard of any compatibility issues regarding repairs.

The main thing is to try to roughly match the thickness of the existing repairs to the original fiberglass to avoid future stress cracks at or around the repair and to make sure the area to be repaired is prepared properly to insure a good bond. There will not be any chemical bond between the two, only a mechanical bond but if done correctly it will outlast you and the coach. Using epoxy is always the safe bet. I bonds better to all substrates better and is easier to use than the esters.

Re: How do you repair deep cracks in the Roof

Reply #13 – May 04, 2011, 11:59:21 am

I have a little bit of experience working with fiberglass using both polyester and epoxy resin. Just hobby type work and repairs. A couple of strip plank canoes using epoxy and cloth, Polyester hatches for a sailboat, and repaired 2 basement doors on the FT.

Epoxy resin will bond to hardened polester, but polyester does not bond very well with hardened epoxy. Almost everything on the market including FT is made using polyester. Epoxy cures slowly and polyester tends to harden quickly or kick after a certain time of being mixed with hardener. At that point all you can do is quit and clean up. If you didn't get the job finished you may have to grind away some of it and try again later.

I would use polyester resin for almost all repairs on items that were made with polyester in the first place. Most fiberglass cloth and mat sold in stores have a coating designed to work with polyester resin. It can be used with epoxy, but a cloth with a coating designed to work with epoxy will wet out easier. Before it hardens polyester resin can be cleaned up with acetone. Epoxy is much harder to clean up. Plan on using throwaway brushes and other materials for both.

Working with fiberglass and resin is not difficult, but there is a learning process and it is messy. Read all you can about doing it, but your first job will probably be sort of amateurish. Polyester purchased in a store will probably have a wax in it. During the cure the wax floats to the surface to exclude air. With out the wax the surface will remain sticky. This is desirable if you are building a boat and need the layers to bond together. Wax is added to resin used in the final layer.

FT uses a higher grade of gel coat than found in most stores. There are shipping restrictions for resin and gel coat. FT probably does not have the license needed to ship, so you either have to go there and pick it up or have some one do that. One can brush or spray on gel coat and after it hardens sand it out to a polished finish. This requires going through many grades of sandpaper up to maybe 1500 grit and/or rottenstone. It is very likely while doing this to sand through the gel coat to the fiberglass underneath, in which case you get to start over. Have fun.

Re: How do you repair deep cracks in the Roof

Reply #14 – May 04, 2011, 07:16:11 pm

Jerry, overall a pretty accurate treatise for fiberglass repair. That's why even with my experience, I went to Xtreme to have my roof repaired. If I was still 21, I would have been foolish enough to do it myself.

Re: How do you repair deep cracks in the Roof

Reply #15 – May 05, 2011, 01:55:19 am

Jerry,

I has been my experience that GV gel coats could be better quality. I have been reading about chalking on forum posts and have experienced it on mine. Every morning I have to clean off the white powder off the windshield. The gel coat also seems to be very thin and easily damaged by the sun. When I have attempted to buff it with a 1400 RPM professional buffer, I can never get any kind of high gloss as a finished product. When I have removed a decal, the gel coat underneath looks great and buffs out nicely. I have worked with older Fiberglas sailboats that have been in the sun and have been able to restore a high gloss with a good buffer and machine rubbing compound.

I buy a box of inexpensive brushes at Harbor Freight and give them a toss after finishing using polyester or epoxy resin. I usually use System Three products mixed in a 2 to 1 ratio. The epoxy resin is available in different types and with fast or slow hardeners. If I am repairing something small like a crack, I usually mix in a paper Dixie cup and if in a real hurry, give it a few seconds in the microwave. After the application, it does not take too long to lose the tacky feel and by the next day, it is hard. If the mix is left in the cup, it will heat up and catch fire just like polyester resin. Where epoxy comes into it's own is bonding different materials like plastics, steel, etc. together. Polyester resin will go on, look good for a time but generally not provide a long lasting bond like epoxy. Polyester resin in contact with gasoline or diesel results results in softening and that nasty red color as it goes bad. Ethanol in the gas also speeds the process. Epoxy on the other hand can be used to make fuel tanks that look great years later. As noted, polyester resin does not do well when applied to epoxy surfaces.

Both are excellent products. Surfboards are super strong and looked like a million bucks long before epoxy was invented. My boat was cloth and polyester resin and was incredibly strong. I have both in my garage but where I have to repair an older weathered surface and or bring a different material into contact and need a secure, long lasting bond, I always choose epoxy.

An excellent source for all information and materials is at: Welcome to System Three.com - Epoxy Resin Products - System Three Resins, Inc.

Pierce & Gaylie
93' U300/36

Re: How do you repair deep cracks in the Roof

Reply #16 – May 05, 2011, 11:38:41 am

Pierce, I totally agree that epoxy is much stronger than polyester, especially when it is used with wood as I did with the canoes. Given enough time in the sun, I think all gelcoats will become chalky. I have been using Gel Coat Labs sealant on the roof and that has helped a lot with the chalky runoff. (See Barry's website about cleaning) It is difficult to polish the roof of an older coach to a high gloss, at least mine was. Eventually it may require a coat of epoxy paint to make it look good. I don't remember ever seeing a gelcoat for epoxy, but it may exist. I believe that most gelcoats, if not all, contain polyester, so if you do a repair with epoxy and want to finish it with gelcoat, will it stick? I had a polyester/fiberglass sailboat and eventually painted it. A friend had a custom sailboat built with fiberglass and epoxy and it was painted when built, didn't come out of a mold.

Re: How do you repair deep cracks in the Roof

Reply #17 – May 05, 2011, 12:08:51 pm

The primary issue with using epoxy as a finish is that it will yellow over time. Both epoxy and polyesters will chalk as they age. In the early days of fiberglass boats they made epoxy gel coat stable by adding copious amounts of opaque filler such as titanium dioxide. Same thing with polyester fiberglass. Much of the chalking is the sloughing off the fillers as the surface degrades from UV and abrasion.

The best coating for a fiberglass finish like our coaches is a cyclo aliphatic urethane. Coatings formulated for fiberglass boats and aircraft are a good example. It is expensive but will maintain its gloss the longest and is very chemical resistant. I am not aware of an after market gel coat. Gel coat typically has to be installed as the first coat in a layup mold.

The main reason a manufacturer would use epoxy resin over polyester is that epoxy can be modified for specific uses without loosing physical properties. If the esters are modified for better flexibility, heat resistance etc, they also loose some other physical properties. Also, many of the cataylsts for esters are very dangerous. Most of the dangerous polyester resin catalysts are not sold for consumer use but always use an appropriate respirator if working in an enclosed space.

Polyester resin is perfectly good for most polyester fiberglass repairs if one can handle the catalytic reaction time and the styrene odor. Neither epoxy or polyester resins should be used a an exterior finish. The repair should always be painted to prevent UV degradation.

Re: How do you repair deep cracks in the Roof

Reply #18 – May 05, 2011, 01:45:30 pm

Kent,

Good explanation. Do you have any brand names for the cyclo aliphatic urethane to recommend? Are these found in automotive clear coats? I did a quick search but have not found anything to match.

P&G
93' U300/36

Re: How do you repair deep cracks in the Roof

Reply #19 – May 05, 2011, 03:02:34 pm

Quote from: Pierce & Gaylie Stewart – May 05, 2011, 01:45:30 pm

Kent,

Good explanation. Do you have any brand names for the cyclo aliphatic urethane to recommend? Are these found in automotive clear coats? I did a quick search but have not found anything to match.

P&G
93' U300/36

I have been out of the business for several years but at that time most of the automotive urethane finishes were at least aliphatic urethane and all of the higher end products were cyclo aliphatic. Dupont, Sherwin Williams Automotive Finishes, Bayer and Kirker were some of the names. I also purchased white urethane from International Coatings for my aluminum boat deck. To my knowledge all automotive clear coats are aliphatic or cyclo aliphtic urethane. Keep in mind even a UV stabilized clear urethane will allow UV to penetrate to the base color. Chalking can then occur at the bond line between the paint and the clear coat causing interlaminary failure. The color coat also has to be UV resistant. You do not want to clear coat directly over gel coat, epoxy or polyester, if you want long term performance.

Re: How do you repair deep cracks in the Roof

Reply #20 – May 05, 2011, 03:20:10 pm

Pierce & Gaylie Stewart wrote:

Quote

I has been my experience that GV gel coats could be better quality. I have been reading about chalking on forum posts and have experienced it on mine. Every morning I have to clean off the white powder off the windshield. The gel coat also seems to be very thin and easily damaged by the sun. When I have attempted to buff it with a 1400 RPM professional buffer, I can never get any kind of high gloss as a finished product. When I have removed a decal, the gel coat underneath looks great and buffs out nicely. I have worked with older Fiberglas sailboats that have been in the sun and have been able to restore a high gloss with a good buffer and machine rubbing compound.

It's my understanding that when gelcoats are formulated the designer has to balance between a soft formulation that has a dull finish but is very resistant to cracks and a harder formulation that will create a nice shine but might be more prone to cracking. On my '91 (same year as John Cooper who started this post) my roof doesn't chalk but does seem to develop cracks and is quite thick -I would guess about .030". I also heard that too thick of a gelcoat will make it prone to cracking. I think .015" is ideal.
So, it makes me wonder if Foretravel switched formulations and went with thinner coats by the time Pierce & Gaylie's '93 was built to avoid cracking problems? Do you think there's any truth to this Kent?

Re: How do you repair deep cracks in the Roof

Reply #21 – May 05, 2011, 04:49:04 pm

John,

The first Foretravel we looked at was a '89 U280. It had two large cracks in the roof that were visible from the ground. It had been stored outside in the West at fairly high altitude. Guess I will take another look at mine.

Re: How do you repair deep cracks in the Roof

Reply #22 – May 05, 2011, 07:46:09 pm

Quote from: JohnFitz – May 05, 2011, 03:20:10 pm

Pierce & Gaylie Stewart wrote:
Quote
I has been my experience that GV gel coats could be better quality. I have been reading about chalking on forum posts and have experienced it on mine. Every morning I have to clean off the white powder off the windshield. The gel coat also seems to be very thin and easily damaged by the sun. When I have attempted to buff it with a 1400 RPM professional buffer, I can never get any kind of high gloss as a finished product. When I have removed a decal, the gel coat underneath looks great and buffs out nicely. I have worked with older Fiberglas sailboats that have been in the sun and have been able to restore a high gloss with a good buffer and machine rubbing compound.

It's my understanding that when gelcoats are formulated the designer has to balance between a soft formulation that has a dull finish but is very resistant to cracks and a harder formulation that will create a nice shine but might be more prone to cracking. On my '91 (same year as John Cooper who started this post) my roof doesn't chalk but does seem to develop cracks and is quite thick -I would guess about .030". I also heard that too thick of a gelcoat will make it prone to cracking. I think .015" is ideal.
So, it makes me wonder if Foretravel switched formulations and went with thinner coats by the time Pierce & Gaylie's '93 was built to avoid cracking problems? Do you think there's any truth to this Kent?

I'm not sure about the hard vs. soft formulation idea. Certainly with more filler and less resin, the coating would be more brittle and inclined to crack, but I'm not sure how that would affect gloss. You are correct that gel coat which has nothing to reinforce the resin like glass strands in fiberglass will be more inclined to surface cracking if it is too thick. I don't think there is a direct correlation between chalking and cracking. Gel coated fiberglass will always chalk when exposed to UV but it should not crack when properly formulated and properly installed.

Re: How do you repair deep cracks in the Roof

Reply #23 – May 05, 2011, 10:00:24 pm

Wow! There is an amazing amount of knowledge out there. I, too, have the white streaks from the chalking. It was so bad on the front cap that buffing did not do any good. I ended up wet sanding it with 800 grit and then buffing it as suggested by Associated PBE, my local body shop supplier. Then of course I could not do anything on it for a year and a half and so now I have to start over again. The roof definitely needs painting and the rest of the coach could use it as well. I just don't think I can afford to have some one do it.

Tomorrow I'll take a close look at the cracks and see if I can tell how deep they are. I will be drilling a hole at the end of them as suggested by Merle.

Re: How do you repair deep cracks in the Roof

Reply #24 – May 06, 2011, 08:44:07 am

Merlre, painting the roof is probably the best approach and can be done by yourself. Just sand to remove any chalking so that the new paint will bond to the fiberglass itself. A simple approach would be to buy a marine urethane deck paint and either brush or roll it on. A small amount of non-skid (Shark Grip) wouldn't hurt. Remember, a small amount of non-skid. Too much will make it hold dirt.

I would mask off the area to be painted so the paint can't be seen from the ground. Since you have a Grand Villa, you might want to get the sloped front roof spray painted by a body shop that can color match to the gel coat.

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