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Knot seal

Started by colly56, Apr 08, 2016, 10:36 pm

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Apr 08, 2016, 10:36 pm Last Edit: Apr 08, 2016, 10:40 pm by colly56
Thankfully too soon for wood rot.

The rain.

I noticed a paint blister on the door, when I went to look at it I saw another on the other door, so I had a full check around and saw two very large ones on the corner flank of the roof. "Oh no , if I leave it in a few weeks it'll be all blisters," so I dismantled her and took her back in the garage. I did some internet research and found it to be caused by unsealed wood knots. In very wet weather (i.e. Britain) wood knots, if unsealed will release resinous gasses and cause these bubbles (quite large, some)

These knots could be handled as and when they appear by scalpelling them off, sanding the edges and then treating the area before painting over. But I decided that along with water ingress where the roof sits and crap varnish that speckles white when it rains this called for a full recall so to speak.

I'm going to strip her of paint completely, no half measures here, she took me 18 months to build, a couple more weeks, no prob. I had the doors stripped in a day with a Black and Decker heat gun.

I can't be doing this all the time. I've really got to do it properly this time. All advice much appreciated.


No advice, I'm afraid.  Only empathy.  If you figure it out, let me know. 
"My dear Litefoot, I've got a lantern and a pair of waders, and possibly the most fearsome piece of hand artillery in all England. What could possibly go wrong?"
-The Doctor.


Apr 09, 2016, 06:01 am #2 Last Edit: Apr 09, 2016, 06:02 am by galacticprobe
Colly, did your internet research give any indication on what to treat those knots with once they've been scalpelled out? My first thought would be fiberglass or epoxy resin; almost nothing gets through that stuff.

"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"


Specifically made "knot sealing solution" look it up, I've already bought some off amazon. I'm then going to cover it with Dulux timber sealant undercoat instead of just ordinary undercoat as before, I'll then paint it again and I'm looking for a better finishing varnish, I don't recommend Rustins, it leaves white speckles. And how the hell did moisture get into the paint and knots if the exterior varnish was so good. I know Ronseal yacht varnish is really tough and impermeable, I've got it on lots of outside furniture but after a couple of coats it turns yellow, so anyway I'm still working on that one.

It'll take me another couple of weeks (of my spare time) to strip her completely so unless better advice or new ideas come in, that's the plan at the moment.

Also when setting the roof down I plan to use waterproof expanding foam to fill the join completely (silicone sealant was a mess)

I'm not pissed about having to dismantle her, I'm still keen, I just see the 3 weeks outside as a test flight, she's just not finished yet.

Sorry I didn't keep a build diary but I'll try and help future builds by cataloging any problems.


Quote from: colly56 on Apr 09, 2016, 10:55 pm
And how the hell did moisture get into the paint and knots if the exterior varnish was so good.

It was probably there when you started and your varnish sealed it in. You can have the same problem with wood floors. Wood takes time to dry. In the States moving wood flooring from  Florida to  Arizona,  requires weeks of drying time. Your wood had a high moisture content when you started, then it came out under the different conditions.
Yeah I sympathize and I am happy to be living  in a climate where wood can be left out for years without rotting away ( In Colorado you can go still see the remains of log cabins built 100 years ago...)   


God, if I'd been on here earlier I'd have immediately suggested "Knotting solution", it does what it says on the tin. Put it on the bare wood, leave it to dry and paint over. It's an old carpenter/boatbuilders product that really should be more well known about.
Sad really, isn't it? People spend all their time making nice things, and other people come along and break them.~The 2nd Doctor


Would it be OK to cover the whole thing in knotting solution? the expense doesn't bother me, wouldn't that protect it completely?