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Filling In Rooftop Screw Holes

April 30, 2017, 08:21:27 pm

Question for any of you who have experience with fiberglass:  is it sufficient to simply fill unused screw holes with one of the gelcoat repair mixes or does something need to be put into the screw hole to take up the vacated space? 

I will be removing the large kitchen fan assembly and replacing it with one of the Maxxair units that has a smaller exterior flange that would leave those screw holes exposed.

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Re: Filling In Rooftop Screw Holes

Reply #1 – April 30, 2017, 08:50:53 pm

Robert,

I'd like to purchase your old assembly if it is a Kool-o-Matic model. Thanks. Paul

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Reply #2 – April 30, 2017, 09:23:31 pm

I would go to a boat repair place and get some non-woven fiberglass mat, the smallest amount they will sell you and a two part polyester resin. Maybe a half pint or so. And some gel coat repair material, usually a two part mix.  You will need a small brush for the gel coat repair kit.  See what is recommended, maybe a 1/2" brush.  Polyester foam brushes will likely not work. The resin will disolve them.

Practice the following steps dry to make sure you have the tools you need.

Clean out all of the holes you want to fill. Blow them out with compressed air or vacuum them clean. No loose bits.
Mix up a small quantity of resin. Check the working time. Mix only what you can use in that time. Use a small stick like a tongue depressor or a popsicle stick.
Put some resin in the hole with the mixing stick. tear off a small bit of mat and press it into the hole with a small dowel or something small enough to push it into the hole.  It doesn't need to be very much and it can stick out of the hole.  It is just there to reinforce the patch.
Add a bit more resin so that the fiberglass in the hole is wet and the hole is full.  Let it cure according to the directions. 
When it has begun to set up and is pretty stiff you can do a knife trim.  It will be like hard rubber at this stage. Use a safety razor blade and carefully cut off everything that sticks up from the roof. 
Let it cure completely.
Tape off the spot maybe leaving an inch diameter showing
Use a disc sander and grind off a bit of the new material and some if the surrounding existing gel coat.  Clean up the repaired spot with toluene or acetone.
Mix up a bit of gel coat repair material and cover the repaired spot. This might take two coats.

A bit fussy but the holes will be filled and reinforced and sealed with new gel coat.

Or call Rance at Xtreme and ask him.
Or take it to Rance.  I think he would do the same thing.

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Reply #3 – April 30, 2017, 09:31:43 pm

Thanks Roger.

It is all yours, Paul.  I'll contact you when I get it removed.

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Reply #4 – April 30, 2017, 10:03:47 pm

Here's another option.  I think I'd put the new fan on and then use 5" Eternabond tape around the whole.  Cover the new holes and the old.  Then let Rance at Xtreme fix it the next time I was in Nac.

Much easier for someone who has never done fiberglas.

Rich

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Reply #5 – April 30, 2017, 10:05:09 pm

Or, use Eternabond to cover the holes filled with a good polysulfide  such as 3M 4000.

This does NOT need to be structural.

The above for just waterproofing holes.

But if replacing a through-roof fan with a smaller one, I would use some 1/8" thick aluminum the same size as the old one and mount the new fan on the aluminum.  Paint the top side white. Drill holes in the aluminum using the old fan as a template and use the original screw holes and polysulfide to bed it.

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Reply #6 – April 30, 2017, 10:10:08 pm

Roger,
 
Thank you very much for the detailed fiberglass repair instructions. Would these instructions also work if the hole was a little bit bigger?
 
In addition to holes, I have a couple of places where the edge of the wheel openings received damage. The material is still intact, but there is definitely a crack in the fiberglass. What would be the proper procedure for that?
 
Something happened to my lower ladder section, that forced the bottom mounts to push the mounting surface enough to break the fiberglass, causing that section to recess a little bit below the fiberglass surface. Should I try to use a clamp to force the depressed piece back to the surface, or just try to fill the damaged section? How would you handle that type of repair?
 
While I have your attention, I have a corner of a wheel opening (about 2" x 3") that has broken off. How would you go about trying to reattach that piece?
 
Thanks, again,
 
Trent

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Reply #7 – April 30, 2017, 10:12:32 pm

For small holes, I like white Marine Tex.

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Reply #8 – April 30, 2017, 10:45:19 pm

The repair process for a few holes is a bit over the top but it would reinforce the holes and the space around them against cracking.  Caulking and tape would prevent leaks. 

When rance repairs a crack or a broken piece he will grind a shallow recess on either side of the crack, maybe. An inch on either side and into the underlying resin.  Clean it up paint on a coat or resin, press in a layer of mat maybe an inch and a half wigemand then brush on more resin to thoroughly wet out the mat.  He probably has a roller that helps make sure the mat is pressed in and wet and there are no air bubbles.  Then when it is cured he grinds it smooth and slightly loew than the finished surface.  He sprays on gel coat, lets it cure and then sands that out with finer and finer paper and them polishes it out.

He uses a structural urethane adhesive to put pieces together and then grinds and glasses and gel coats and polishes.  Perfect

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Reply #9 – April 30, 2017, 11:13:41 pm

I used this 18 years ago on my '87 and it's still there. In fact, I use if for everything.

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Reply #10 – April 30, 2017, 11:34:00 pm

For holes that pass all the way through the roof to the interior I use two different products:  Wood-Epox, and Marine-Tex.

Parts of the interior structure of the roof are wood.  Where the hole goes through wood I use Wood-Epox by Abatron to fill the hole level with the wood.  Wood-Epox is a wood epoxy/filler that is certified for use on buildings on the National Historic Register.  It bonds to the wood and when cured can be screwed into, nailed, sawed, carved, routed, etc.  When cured this layer will act as a structural backer for fiberglass filler, polysulfide caulks like Brett mentioned, etc.

For the top layer above the Wood-Epox I also used Marine-Tex like Twig.  It does not include a gelcoat/gloss finish.

Chris

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Reply #11 – May 01, 2017, 01:58:05 am

Make sure the screw is out of the hole b/4 you cover and seal it.  Don't ask me how I know. 

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Reply #12 – May 01, 2017, 06:09:38 am

White Marine-Tex would be my choice also.
Not that you need to on the roof, but I have filled voids in white boat hulls, tooled and sanded them smooth, then buffed.  The repairs were invisible.

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Reply #13 – May 01, 2017, 07:39:43 am

Robert,

I haven't looked at how the fan was caulked but my tv roll up was done with 5200 or similar.  Screw holes weren't as big an issue as peeling gel coat.  I don't know where you are based but if there is a West Marine store nearby you can pick up a West patch kit for your small job.  It comes with excellent instructions.  Marinetex is also available.  I like Marinetex for small or temporary patches and carry it with us.  In the past, with my boats, I preferred the kits and gel coat.  The link below takes you to their site and offerings in this area.  Videos are available as well. 

I will be using the West System to repair the black non skid area at the ladder when I remove it in a couple of weeks.

5200 for the holes alone is a good approach but if you have a bigger area after removal you might want the kit.

WEST MARINE Gelcoat Repair Kit | West Marine

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Reply #14 – May 01, 2017, 07:57:31 am

Obviously there are many ways to fix a screw hole in the roof.  I think the choices are based on permanent or temporary life expectancy.  If you were going to have your roof painted how would you want old holes repaired?  Many of the short term fixes are good ones.

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Reply #15 – May 01, 2017, 12:47:58 pm

I fill lots of holes on boats and am going to do the same on my RV Roof. It's not that complicated. Get some epoxy resin. Get some high density "micro balloons" (west system makes both that are easy to use, but a slight premium).  I sometimes use chop fiberglass as well in the mix.

Make sure the hole is plugged in the bottom so resin doesn't just flow through. Countersink the top of the hole. Mix up a batch of resin and thicken it...this also adds strength (if high density), and get small syringes to fill the hole from bottom up (west system has good ones). You must use a syringe otherwise you'll get air in the repair.  If you want, add some coloring agent to the resin and match it to gelcoat color.  Fill it slightly above the level of roof as resin may shrink some. Once cures, hit it with a whiz-wheel sander and level it.

If you want spray some paint on it or gelcoat and blend. Gelcoat is porous and not good to fill holes with.

Do it right with epoxy and it will be almost as strong as new and take screws in the future if needed. Sealer 5200, etc is just a patch.  If doing that, though, use 5000UV as 5200 won't handle the sun UV

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