Is doughlas fir (4x4) stronger than yellow pine? Is it as weather resistance as pressure treated wood? If it sit( bare)outdoor would mildew grown on it, would kilz keep off the mildew? Thanks

No, no and yes. And then no

To recap, yellow pine is much stronger and is using in framing structural members, if you put fir outside untreated it will rott. And mildrew will grow on it as it rotts, kilz will stop the mold but for only so long, it will come back again and again,

Quote:

---

Originally Posted by caibuadday

Is doughlas fir (4x4) stronger than yellow pine? Is it as weather resistance as pressure treated wood? if it sit( bare)outdoor would mildew grown on it, would kilz keep off the mildew? thanks

---

I saw it at HD in the middle of pressure treated section, so I thought it was weather proof. It cost 50% more than the pressure treated wood.

This user is talking about Douglas-fir, not true fir. "True" fir is weak, mold-susceptable, and unsuitable for structure. Douglas-fir, which is not a member of the "fir" family, is the strongest of the western softwoods, and is indeed stronger than yellow pine.

Oh, and because douglas-fir is so dense, it is generally resistant to moisture and mold penetration. So treating it is a) pointless and b) difficult, as the density of its grain makes it difficult to penetrate.