Knotting after priming

[hondacrm]

Hi,

I have had a new set of garage doors installed and my builder was keen to give them some form of protection asap so 2 coats of water based primer have been applied. I have just noticed that the knots haven't been treated. My question is can I apply knotting compound over the primer?

 

[HERTS P&D]

No, you would have to sand down the primer and then apply the knotting.

Andy

 

[vibrobullit407]

I would apply an aluminum primer over the existing. This will ensure that no knotts are missed. I tend to apply aluminum primer to all exterior timber as it is self knotting and gives a great base to apply subsequent coats.

 

[misterhelpful]

I would apply an aluminum primer.....
...it is self knotting and gives a great base to apply subsequent coats.

True, but, as with all forms of knot sealers, even this should be applied directly to bare knots and resinous timber. It may work in this situation, but it will be the already applied primer that is acting as the first line of defence and could still allow sap/resin to blister beneath it and affect the finish, even if it doesn't stain through it.
Having said that, some extremely resinous knots can bleed through any knotting/paints for years if they are subjected to direct sunlight.

The choice is yours, but I would prefer to sand back and then knot.

 

[vibrobullit407]

You are correct in what you say misterhelpful in the fact that knotting should be applied directly onto the bare knots. And yes sanding down back to the bare knots would be preferable but as the door has had 2 coats of primer it will be quite easy to miss some due to not being able to see them through the primer. In this particular instance I would opt for applying an aluminum primer over the existing as sanding all the primer off could take some time. At the end of the day the builder should not of primed the doors without knotting them first but hey ho someone else thinking that painting is just slapping on the paint with no knowledge beforehand.

 

[misterhelpful]

I understand your point, vibrobullit, and have no problem with the OP going down that route, but was just making them aware that it's not a guaranteed remedy.

 

[vibrobullit407]