Shellac on Treated Wood

[Coop]

If that’s the route I decide to go with, treated for legs on a project, will shellac help curb the moisture on the treated 4x4’s for them as a primer for them be painted?

[Mark J]

I didn't think that shellac was much of a moisture barrier.  Isn't that why a wet glass will leave a ring?  

[pkinneb]

I agree with Mark that shelac won't provide much of a barrier. Also make sure you let that treated lumber sit for weeks to dry out before applying any finish on it. That stuff is basically soaking wet from the big box stores.

[gee-dub]

Many of your stain-blocker primers have shellac in them as the blocker.  This is to block visual stains or bleed through.  If I was going to paint I would consider something like Sherman Williams shellac primer or Zinsser BIN.  I used BIN on OSB for shop walls in my previous shop.  It is tinted white and I didn't even bother to paint over it.  I agree that treated lumber needs to dry for a long time before priming and painting.

[Coop]

On 3/9/2026 at 10:23 AM, pkinneb said:Also make sure you let that treated lumber sit for weeks to dry out before applying any finish on it. That stuff is basically soaking wet from the big box stores.

I knew that, just needed to be told!

I bought a 10’ treated 4x4 today and got it cut like I want it but don’t have weeks worth of patience for it to dry out. Will cedar be almost as good with the ends touching the ground if they are sealed with something? At my age, I’ll probably be sitting in a rocker watching cartoons and it won’t matter anyway. 

[Beechwood Chip]

Just a thought: Since it's going to be painted anyway, use whatever wood you want and paint the ends that will touch the ground with a penetrating epoxy like CPES.  That way it's essentially plastic and won't rot.

[Coop]

When setting treated fence post, I will cover the bottoms with black roofing puckey to about 10” above ground level with the exception of the bottom. My reasoning is that if the very bottom is covered with this stuff, it will trap moisture much like a saucer. Are my thoughts justified? 

[pkinneb]

On 3/9/2026 at 8:35 PM, Beechwood Chip said:

Just a thought: Since it's going to be painted anyway, use whatever wood you want and paint the ends that will touch the ground with a penetrating epoxy like CPES.  That way it's essentially plastic and won't rot.

x2

[Beechwood Chip]

On 3/9/2026 at 9:47 PM, Coop said:

My reasoning is that if the very bottom is covered with this stuff, it will trap moisture much like a saucer.

Disclaimer: I have no experience, I'm just blowing smoke.

I'd coat the bottom, since I'd be more concerned about ground water wicking up into the wood, than about water working it's way down from the sides or top.  I figure the upper parts are breathing moisture in and out, but the bottom is basically sitting in a puddle.

[Coop]

You’re prob right as I find from the past that most rot is at ground level. 

[Von]

On 3/9/2026 at 10:14 PM, Beechwood Chip said:

Disclaimer: I have no experience, I'm just blowing smoke.

I'd coat the bottom, since I'd be more concerned about ground water wicking up into the wood, than about water working it's way down from the sides or top.  I figure the upper parts are breathing moisture in and out, but the bottom is basically sitting in a puddle.

Same disclaimer but this has been my logic. I usually put a bunch of gravel under a post to allow drainage and avoid direct soil contact. Now that I'm used to using epoxy, I'd also seal the end grain with it.

[gee-dub]

We are wandering a bit off topic here but I will add some data.  I did the epoxy dip on the legs of my fire pit chairs made from white oak.  They have been outside (although under "Duck" covers when not in use) since the end of 2022 and are still fine.