What Knotting Solution to use.

[niall Y]

I have some gates to to repaint because the knotting solution I used has failed and the paint has come away from all the underlying knots. I don't understand why, as this seems to be happening a lot recently. A friend, a few years back, was having similar problems, but in his case the knots were grinning through, rather than the paint falling off.
Looking at what is currently available ,I notice that some are not recommended for exterior use. Duh!....
Surely, shellac functions outside, just as well as inside?
I have not encountered problems before, so what could be going on here ?
It would be interesting to find out if any readers of this post. have come across this problem, and if so, - - what was your solution ?

 

[Jacob]

I have some gates to to repaint because the knotting solution I used has failed and the paint has come away from all the underlying knots. I don't understand why, as this seems to be happening a lot recently. A friend, a few years back, was having similar problems, but in his case the knots were grinning through, rather than the paint falling off.
Looking at what is currently available ,I notice that some are not recommended for exterior use. Duh!....
Surely, shellac functions outside, just as well as inside?
I have not encountered problems before, so what could be going on here ?
It would be interesting to find out if any readers of this post. have come across this problem, and if so, - - what was your solution ?

I blame the paint. Knotting is usually the last thing to go.
What paint did you use?

 

[niall Y]

I blame the paint. Knotting is usually the last thing to go.
What paint did you use?

Hi there,Jacob Yes, it was a conventional solvent based paint that was used- and I will be switching to a linseed-oil one to repaint it. In fact I'm having a go at making my own , when the pigment I have ordered, arrives.
There is a possibility that it is the paint, but since I have not encountered this problem until recently and the type of paint I use has remained fairly consistent, I would suspect that it is the knotting that is the problem here. Hence my interest in what other people have experienced
Niall

 

[GerryT]

Niall

As Jacob says, the paint may be the problem if it’s just coming away from the knotting solution but not if the knots are bleeding through well adhered paint.

I‘ve found most knotting products pretty poor when used with modern paints.
I started using a couple of thin coats of Titebond 3 over knots and that seems to hold up better than the many off the shelf knotting products.
I then sand the edges down very lightly without touching the glue that sits on the knots.
This is not something I discovered as its been on the net for a while now.

Another worth a try is an Aluminium Primer .
Ive used it plenty of times on a variety of problem timbers when painting and found it stops bleed through as good as any.

 

[johnnyb]

First off shellac and by extension knotting isn't at all flexible...never has been and never will. I like bin sealer for knots(2 coats as 1
isn't enough) I think that a patch of shellac with an overall ally primer is as good as you can get.
patch seal the knots the smaller the better. prior to painting heat the knots with a stripping gun and scrape the goo away.

 

[johnnyb]

I'm not commenting on linseed paint but flexibility is very important in a top coat. sandtex flexi gloss is my preferred oil gloss.
bedec use there own sealer for knots on there water based products which may be more flexible.

 

[okeydokey]

About aluminium primer - used it many years ago with my father very good and successful int and ext - must be something better nowadays, I think we did 2 coats letting it dry well between

 

[okeydokey]

Aluminium paint takes a good bit of stirring as there is nice bit of sludge in the bottom of the tin better known as finely powdered aluminium (maybe flakes) was a very small tin - good old solvent based

 

[gcusick]

No matter what paint system you use, if the resin from the knots expands under the paint, it will eventually break through. The only perm solution I’ve found - for anything but the smallest knots - is to drill a shallow recess into the knot and plug with clear timber. A bit tedious, admittedly, but the result is worth it.

 

[Bristol_Rob]

https://www.zinsseruk.com/howto/paint-knotted-resinous-timber/

 

[woodieallen]

First off shellac and by extension knotting isn't at all flexible...never has been and never will. I like bin sealer for knots(2 coats as 1
isn't enough) I think that a patch of shellac with an overall ally primer is as good as you can get.
patch seal the knots the smaller the better. prior to painting heat the knots with a stripping gun and scrape the goo away.

I'm assuming you mean BIN 123 ? I thought that was also shellac based ?

 

[johnnyb]

zinnser bin is white shellac. 123 is water based and 123 plus is pliolite based. cover stain is oil based.