Log in
Article search:

Q & A

Sealing fibreglass roof.

I have a 50-year-old narrowboat with a fibreglass roof. In recent years it staretd to leak more and more, in different places, particularly after heavy rain. I can't find the actual cracks, and more will probably appear, so I was wondering if I can seal all of it somehow, for instance using glass fibre resin or epoxy. Is it feasible? Would it make the roof texture very uneven? It doesn't have to be perfect and shiny, but I'd rather avoid thick smudges and such.
Thanks a lot,

Asked by: Jedrek Burakiewicz  | 2.09pm, Monday 20 August

WW says:

Epoxy resin is certainly a possibility- many GRP boatbuilders use West System epoxy resins, and a flow-coating resin may do the trick! It can be a pain to apply though (the pot life can be around 30 minutes or less once made up) and may require painting after.
Another option might be to use a water-based polymer solution, which can find its way into any cracks, sealing them as the water evaporates. Once such product is the interestingly titled "Captain Tolleys Creeping Crack Cure"... however, this might be better for small areas of seepage, rather than a whole coating of the roof.
Often it is where the cabin sections are joined, or where a wooden handrail is screwed to the superstructure, that leaking occurs- so just treating these areas might work. A combination of resin, filler and matting (CSM- chopped strand mat, or woven rovings) around weak points could easily be covered with a suitable textured deckpaint.
You could also remove all the exterior fittingss and then apply one or two layers of glass fibre mat, wetted out with resin, then topped with a filled resin as a final flow coat to give a smooth(ish) surface to paint over- though this again can be a pain to do on a large scale.
If you go down the glassfibre/polyester resin or the epoxy resin route, surface preparation is key to ensure that the resin keys well to the surface- good mechanical abrasion is importants, as well as degreasing thoroughly with a good quality detergent (sugar soap is good, washing up liquid bad (!) due to the silicones which can prevent adhesion).
Hope that gives you a starting point- if we can be more specific, please ask away!

Mark Langley  | 3.34PM, Monday 20 August

http://www.westsystem.com/ss/ is a good place to start with advice...
They are usually very good in answering specific queries as well. You might want to to a surface test (using acetone (propanone)- or specific recommended solvent) to ensure that any previous coatings are not going to fail.
There is a good handbook available as a free download on the site, which will give you probably more detail than you ever need!
Best of luck- and do let us know how you go on!

Mark Langley  | 4.20PM, Monday 20 August

Readers say:

That was quick and thorough, thanks a lot! I need to repaint the roof anyway, so I might go for the epoxy. I did the joints a few years ago and they still seem to be in good condition, and the railings are screwed down fairly high up. The roof in general seems to be in a bad condition, so I think epoxy resin it is. Thank you again.

Jedrek Burakiewicz  | 3.48PM, Monday 20 August

I was going to write up the outcome for future generations, and somehow didn't get round to doing it for a long time. At least now I had almost a year to see how it worked. So, here goes.
In short - it works, and very well so. For my 45 foot narrowboat I used a West Systems B-pack 105 resin (6kg) with 205 hardener (fast), and it was a bit more than enough to cover all of the top surface of the roof 3 times. I also got a pump set to measure it out evenly, and I guess it was a good idea, since the whole process is messy enough as it is and you don't want to end up spilling this stuff around.
To prepare the roof, I sanded it down and filled in any holes with your average silicone sealant, then gave it a good soapy scrub. I mixed the resin as I went along (10-15 hits on each pump). There are 2 ways to apply the sealant it seems: either put one layer, let it dry for 24 hours, then sand it down before putting on another one, or put the next layer on the first one after about 8 hours (details are in the instructions). I put the first two layers together, then sanded them down and put the third one on separately. Then I sanded down the final layer and painted it - one layer of undercoat and two layers of overcoat.
The results were really great. Before I wasn't able to walk on the roof much, as it bended in wherever I stepped and I was worried it might crack. Now the whole section of the roof bends instead (as opposed to one spot), and only mildly so. And we had several leaks in the roof that we couldn't track - all gone, not a single leak this winter, even when the snow was melting (usually that was when we got most water). So on that front it was definitely worth it. From an aesthetical point of view - the surface is pretty smooth, and it was quite easy to paint over. It's not perfect, but I wasn't going for that anyway.
Things to consider and remember:
- I was doing the work outdoors, at the end of August, in nice weather. The resin is very sensitive to humidity, so unless you're working in the hangar, I reccomend you put on one layer in the morning, leave it to dry, sand it down and then put a new one on. The two layers I put on first did not set correctly because of the humidity overnight and I think it compromised the quality in a few places (I got some bubbles in a few areas. Sanding this stuff is very easy, much easier than with the paint, it took me maybe 30-40 minutes to sand down the whole roof, so it's not worth risking the whole project just for that.
- Wear gloves and general protective clothing. This stuff is terrible, and sticks to everything.
- If you're using a paint roller like I did, leave it to hang somewhere safe after you're finished. The reaction that sets the resin seems to give out a lot of heat, the roller was burning to the touch after about 15 minutes and started smoking. I'm not sure if it was enough to set fire to the newspapers I wrapped it in originally, but I didn't want to find out.
- If you want to reuse the handle, take the roller off it as soon as you finish. When the resin sets you won't be able to. I tried with a hammer, a very sharp knife and a few other tools and failed.
- Don't put it next to the chimney. It's not heat resistant, and some of it leaked down the outside of the chimney in the winter, into our sitting room, then burnt there merrily, producing a rather unpleasant smell.
- Don't try to fill any larger holes with it, do it beforehand with a sealant or something else (I mean screw-sized holes or bigger, obviously it works for cracks and stuff).
- If the resin comes onto anything, clean it immediately - once it sets it's really hard to remove.
I hope someone finds all this useful at one point. Good luck!

Jedrek Burakiewicz  | 3.10PM, Thursday 6 June

Hi Jedrek,
Thanks so much for this update. I am about to redo my GRP top and looking for all the advice I can get as is fairly daunting when you're new to it.
Kind regards,

David  | 4.08PM, Monday 13 August

Hi David, thanks, it's good to know this stuff still helps people. The site doesn't post the year - I actually posted this in... 2012 I think? But your post made my day.
I hope the works went well, happy cruising!

Jedrek Burakiewicz  | 11.31AM, Sunday 9 September

You must log in to post an answer.