Blisters!!!

[Lew's Canoes]

After 8 or 9 successful new/restoration projects, I thought I was immune from the dreaded paint blisters that I have read about here in the forum. Silly me!!! I am nearly complete with the restoration of a 45 year old Chestnut, and guess what is showing up all over my nice smooth hull and paint job - they look like goose bumps and feel like someone threw a handful of sand into the paint just before I dipped my brush into the can!! HELP!! First I need to understand why this is happening - the sequence of events leading up to now is as follows: Aug 27-sand interior, apply sealer coat of 1/3 varnish, 1/3 mineral spirits, 1/3 linseed oil. Aug 31 - sand exterior and apply coat of warmed linseed oil. Sept 6- canvas. Sept17- apply filler. Nov12 (7+weeks later-canoe cured indoors)- wet sand filler and first oat of paint. Nov 13 - wet sand, second coat of paint. Nov 16 - dry sand, third coat of paint. After outwales and keel...Nov 20 - sand interior and varnish. Nov 22-sand and varnish interior. Nov 26 - sand and varnish. Nov 28-sand and varnish. Initial varnish coat was about 50% cut with MS, final coat only cut about 5%. When I turned the hull over to finish the painting job, there they were! Not everywhere, but several places. So...... I gave the hull another thorough wet sanding and applied coat number 4. Within 2-3 days they were back, and they are still growing. Paint is Benjamin Moore Impervo Alkyld Enamel, with small amount of Penetrol added for brushing. So....... can anyone tell me what is going on here? What is pushing it's way up through the paint - varnish,thinner,linseed oil, filler components, water from wet sanding?? Second question is what are my choices as to what to do about this? Tear off and start over? How about a super sanding right down to the filler level, let the boat sit for a month or so, then repaint? Another approach? Finally, it occurs to me that there may be something in the sequence of my steps that is a contributing factor - perhaps I should have completed all of the interior varnishing before canvasing, filling, painting on the outside. All comments are welcome and greatly appreciated!! There has to be a good lesson here all builders...

 

[Dave Wermuth]

HI Lew,

I just rubbed in a second coat of Wm Clements filler and blisters are something I fear. So far in my limited experience I have not had blisters and I have no clue why not. One of my boats sits outside the entire season on sawhorses. So far so good but it's only been 4 years. I checked some past posts and it seems there are several reasons for blisters.
1) water infiltration from the inside. usually goes away.
2) oil coming out of the filler.
3) water infiltration from the outside. peel and repaint.
4) filler/paint incompatibility.
5) your guess is as good as mine.
I also read an interesting post on boiled linseed oil and have since, for the most part quit using it. For this boat I 'sealed' the outside with thinned spar varnish after two thinned coats on the inside. I'll give another 2-3 coats inside of varnish at some point in the future after the filler has cured. Maybe this'll be the one that blisters, who knows? I am using Wm Clements filler, and Kirby's paint. I am going to use a primer this time. Kirby's. So, for what's it's worth, that's my story.
regards, Dave.

 

[Dave Wermuth]

ONe more quick thought

If you were able to sand and repaint to get a good finish after the first visit from the blisters, perhaps if you let the thing cure a bit more the next time you sand and paint it'll be ok? Worth a try?

 

[Dan Miller]

First thing I think I would do is to pop a blister and try to determine what is in it. That could go a long way towards figuring out your problem.

To speculate a little, because you apparently gave enough time for the filler to cure (though I wouldn't rule it out entirely), and the canoe hasn't been used yet, I would look into the wet-sanding for the problem. Oil and water don't mix, and you are alternating a water step with an oil step... I question this method of wet-sanding on canoes in general - it usually means you are sanding with finer grit than 150, and I think that leads to problems. (For the record, old cans in the basement from Interlux and Petit specify to sand with 100-120 grit paper...) Paint needs some tooth to adhere to...

Like Dave, I've been fortunate, so far, to have (knowingly) avoided blistering problems. Knowing my time is coming, I keep knocking on wood (why does my head hurt so?) I do all the interior varnish work prior to canvassing and painting, so maybe that's part of it, but I know other builders who swear by varnising after canvassing. So, Dave probably is on the right track with suggestion number 5.

 

[Lew's Canoes]

Thanks for all comments and empathy. After much thought I have concluded (guessed?) that the problem in this particular case is varnish that seeped between the rather wide spaces between the old planking, spread along the canvas, and is now curing by releasing solvents which are finding their way through the filler and blistering the paint. So...... I sanded most of the paint off of the hull, which really opened up the blisters. Most have not reappeared - just one spot about 12 inches in diameter in the middle of the bottom. Have a 100 watt worklight with a conical reflector suspended about 8 inches above the bad spot to attempt to draw out the solvents. Seems to be working so far - I will sand and wait, sand and wait, etc. and hopefully the cycle will end with a permanently smooth hull which I can then start to repaint. Stay tuned.........

 

[Blue Viking]

I need to jump in here for a question!....Did you oil the planking before you canvassed?....I did a Sebago boat and it had spaces between the planking due to its age and varnished the interior completely before canvassing. Prior to doing the canvas..I removed any drips that came thru the spaces. Canvassed, filled with Bill C's filler, left it alone for 8 weeks, sanded a little, then 4 coats (2 then 2 more-sanding in between) and it has survived perfectly and got a pretty good work out this summer...It is now sitting out in the snow,covered off course and off the ground, and it looks the same as when I finished it............Sooooo........I wonder if you oiled the planking!...that process bothers me to put canvas on oiled wood!.....Well thats my concern and will be doing 2 more once the snow disappears!

 

[Dan Miller]

that process bothers me to put canvas on oiled wood!.

If you are using traditional filler (which has lots of linseed oil in it), then oiling the hull prioir to canvassing shouldn't be of any worry. It's when you don't allow the filler to cure fully that is one of the causes of blistering.

 

[Blue Viking]

Thanks Dan......Will make sure I continue to allow sufficient time for the filler to completely cure....Bill C. suggested that 8 weeks was a good time to wait and I will continue to do that![/B]

 

[Lew's Canoes]

Follow up on Blisters

Just to bring this thread to a close, I think I have arrived at a successful finish to the blister problem. I followed the steps outlined in my post of 12/27/06, sanding off any new blisters every few days and keeping the work light in place to mildly heat the areas that continued to bubble up. After a couple of weeks, no new blisters appeared, so I repainted - 5 new coats in the usual fashion, with sanding in between coats. Seems to have solved the problem, as the hull is smooth as can be with no blisters to be found. Seems reasonable, since it now has about 9 coats of paint applied ( with 4 having been almost completely sanded off). For the future, I think I am in the camp of varnishing the interior before canvasing/filling, especially on a restoration which has wide spaces between old planking. Perhaps on a new boat with nice tight planking joints this would not be necessary. I really feel my problem in this case was varnish coming through from the interior, spreading along the canvas and finding its way out through the filler and paint. It will be interesting to check back on this hull in a year or so.............