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Knotting under Demidekk?


(Nick Featherstone) #1

I think I already know the answer to this, now I’ve found Zinsser BIN (thanks for that!), but it’d be interesting to have it clarified. We’ve got new windows coated in Demidekk by the joiner who made them, and doors painted from bare timber by me. I was advised verbally (paint2go) to use knotting under the Jotun Visir primer, which I did, only to find it bleeds through and dries sticky. Maybe it wasn’t too bright to use brown knotting but anything fancy is hard/expensive to get on an island. I wiped the stickiness off with white spirit and carried on.
I don’t know whether the joiner used primer OR knotting on the windows, but there are brown stains now over the knots (but no blistering) I’ve had terrible trouble in the past in the south of England with [Dulux] blistering over knots, but I now think BIN is the way to go. Questions-(1) does anyone know whether knotting is needed under Visir? The technical fact sheets are strangely silent about this. (2) Do I need to strip the browned Demidekk over the knots, or can I just BIN over the top of it, whilst patch priming?
PS On the bare wood I warmed the knots up and bled as much resin as I could before knotting.


(Puma) #2

Make sure the knotting fluid / Bin is in date - it does go off quickly. Some knots cannot be blocked they bubble up resin which forces its way through any primer.

If it hasn’t bubbled you are probably fine to Bin over the brown staining. I am not sure about the Visir, but the vast majority of primers don’t block knots.

If there are just a few you can drill and fill to save buying another product.


(Andy Crichton) #3

I have contacted Jotun and asked if they could address the Visir question.


(Nick Featherstone) #4

Thanks Puma, the recent knotting was almost brand new, but there’s no sell-by date on it so it could have been in the shop for years! The knots in Dorset were obviously pretty potent as that window was about 20 years old at the time! The sun’s hotter there, too. That’s a clever idea, drilling; it wouldn’t work in this case as there are too many, but I’ll bear it in mind for the future. I’m sure BIN is the way forward!


(Nick Featherstone) #5

Thanks Andy, that’s above the call of duty!