Roof painting –be patient, work quickly

Sounds like an oxymoron doesn’t it?  Let me explain. 

The paint on a boat roof has a hard time, sun, rain, frost, lying snow, poles, planks, solar panels etc all take their toll.  I reckon the paint on the roof is lucky to last half as long as that on the cabin sides.  Herbie’s roof is no exception, suffering particularly where it comes into contact with roof “furniture”  Even a bag of coal left on the roof over the winter caused a lot of paint damage and resultant rusting because of the film of rain water that lingered under the bag.  Repairing and painting the whole roof in one go is nigh on impossible unless the boat can be taken indoors for a week, so I’ve been doing it in sections.  Learning more and more as I go.

I’ve talked to a few people who “mean to get round to doing their roof one of these days, but it all seems a bit daunting”.  I also spoke to someone who was quoted £1000 for having it done professionally. So for the record and in case it helps or inspires anyone to have a go, here is how I’ve been doing it. 

I suppose the first thing to say is that just patching over little bits of damage is only a stop gap at best.  New paint never matches the old. In an ideal world you would take the whole roof back to bare metal and start again, but I don’t think you can do that out of doors unless you have loads of time and fantastically lucky weather. The better way is to repair/ make good  damaged patches and then repaint a whole section of the roof at one go.  Then it’ll look OK.  Two years ago(?) I repaired and repainted a 20cm wide strip along either side of the roof  to fix a lot of small scars and wotnot  caused by boat hooks, gangplank, autumn leaves etc.  You can just make it out in the second photo below. Then last autumn I repaired the section where the coal bag had lain.  I wish now I had done that better because the repaint still bears the unevenness caused by pitting in the rust.  Then a couple of months ago I had a go at the central section of the roof, around the stove chimney, where there was a fair bit of corrosion.  That time I used filler to even the surface and got a much better finish.

So now I move on to a ten foot section towards the rear of the roof which includes where the solar panel has lain.  The magnetic feet of my fancy titling panel frame are the main culprits here.  Ordinary magnets rust like crazy and attack the roof at the same time.  A lesson learned!

This is the point where I should show you a photo of the damage, but stupidly I forgot to take one.  Sorry folks I’ll do that next time when I attack similar damage under the feet of the roof box.  By the way, another big lesson is revealing itself here.  The best way to keep your roof in good nick is not to store anything on it!

So, to the process.  This is where the patience comes in.  Even if you are repairing and repainting a tiny area, you need several days to do it, because of paint drying times.  Yes you can claim to be working whilst spending twenty three hours a day watching paint dry. That means at least four consecutive days with suitable weather, no rain (especially in the mornings), not too hot, not too cold, not too windy, not too dusty.  Flippin’ ‘eck!  Does that exist? Well last weekend it looked promising so I had a go.

If you already know how to suck eggs, you can either stop here or read on and tell me what I’m doing wrong

Day one. Sand off the rusty patches, feathering them out as best you can so as to help with a smooth finish later. Your patches will now be twice the size of the original damaged area. I used a nice little palm sander, only thirteen quid from Wickes, and ideal for this job. While you’re at it lightly sand over the whole area to be repainted, I expect you’ll find little nicks in the paint here and there.  Treat them just the same as the bigger patches.The sanding also helps get rid of any accumulated grime etc. on the “sound” paint. Wash it all off with clean water and over the exposed metal patches  brush a coat of Fertan rust converter, which is easy to apply and is happy in the wet.  Total time taken, about a couple minutes per patch.  No more than an hour for the whole day’s work.

Day two.  Areas of rust converted by the Fertan will have turned black. Wash off them off, lightly sand the patches again and when the roof has dried, mix up some filler.  I used Isopon which sets really fast so you have to mix smallish bits at a time. Smooth the filler over the pitted area and beyond the edges of the exposed area.  Each patch will now be three times the area of the original damage!  You can sand the Isopon after only an hour drying out.  It sands very easily.  You should end up with a smooth surface right across the patch, extending it still further to blend in with the roof surface.  Sand harder at the edges to feather out. At this point I brought out the little hand held Dyson and sucked up what dust I could before washing the whole area off again. If the weather is right, the roof dries in minutes. (If it steams, stop right there, it’s too hot to paint). When dry, brush on some good metal primer, again extending beyond the prepared patch and feathering out as best you can. That’s all you can do today, most paints need sixteen hours between coats. Again only about an hours work.

Day three.  This depends a bit on how many days you can spare in total.  Another coat of primer would be good.  I didn’t have that much time, so after sanding down and washing yet again, it was on with a coat of some high build undercoat.  By now the patches over smallish areas of damage seem enormous.  Here I do have a couple of photos.

Some of those smaller patches cover an area where the damage was only a few millimetres across.  Yet again, less than an hours work today.

Day four. Another undercoat would be a very good idea, but I didn’t have any days left.  Now you might say just leave it for another time then, but undercoats and primers are pretty porous and it’s not a great idea to leave them exposed to the weather for long for the damp will get in. So I pressed on. Out comes the old sander again – last chance to get a smooth surface before the top coats. Feathering out still further.  It can seem a bit daft slapping on all that paint then sanding half it it back off, but that’s what you have to do.  Then, a final light sanding over the whole area to get it clean and smooth, a quick vacuum if you have one, and a good rinse with clean water.  When that is dry, a final wash with a white spirit soaked rag to remove any grease and you’re ready for the top coat. Getting it all really clean is vital. Work so far today, about an half hour. 

Now the first top coat of, in my case, raddle paint.  Four inch brush, well stirred paint and work as fast as you can to keep a wet edge, working the paint in then quickly laying off the paint side to side right across the roof. I was cursing the met office because half way down we got a short light shower of rain. I stopped and waited for an hour.  It dried off and looked ok.  Better to start off against a touch dry edge than a half dry sticky one.  That ten foot section took about twenty minutes. Here and there the paint “grinned” a bit (showed through). Ignore that and keep going, never go back over sticky paint, the second coat will sort out all that.

So that’s where I stopped because we had to go home.  That single top coat will hold out the weather till I resume sometime soon, but I will have to sand and wash again first.

So that’s four days to do less than five hours work.  Each time I chose to do the work mid morning, after any dew has gone and leaving plenty of drying time before the evening damp descends, and  hopefully before any sun makes the roof too hot to work on.

On the other hand, also this weekend I went from this:

to this:

in about five minutes.  Yes I just screwed on the front panel I had painted indoors at home.  I think it has worked out OK.  Herbie looks instantly smarter.