How to seal a piece of wood before painting?

[DIY_Duncan]

Hi there, I am replacing a piece of wood outside which will need to be sealed prior to painting - see pic. It's a relatively small piece. 

Looking for your just the one piece needs sealingsuggestions on a suitable product.

Cheers,

DIY Duncan

[MitchellMc]

Hi @DIY_Duncan,

That looks suspiciously like untreated Pine, which isn't suitable for external use. Sure, you can seal or paint it, but it's still going to have a very limited lifespan once moisture eventually finds its way in. At a minimum you should be starting with H3-treated Pine, which you'll also need to paint.

If you wanted to proceed with the untreated Pine, you'd use either exterior varnish or paint to seal it. I am not aware of any sealer designed to be used before painting. There are timber treatments, but those are designed as supplementary coatings to seal cut ends on already treated timber.

Please let me know if you have any questions.

Mitchell