During part one of our Bunk-alow series, I told you I'd talk a little bit about digging the post holes for the platform that acts as the floor for the bunk-alow. I think I probably did a lot of things wrong, but I know I did at least one thing right.
I used a post hole digger.
I'm telling you this because if it weren't for my husband telling me about post hole diggers I'd have no idea that this tool exists. And I wouldn't want you to try to dig a deep, narrow-ish hole without one. I tried to use a regular shovel at first, mostly to prove Scott wrong. Because he always says this is the best tool in our arsenal when it comes to digging. And he's right. He uses it for digging holes for perennials, for trees, for fence posts...it's worth the $19.00 to pick one up.
I'm not going to pretend I know how to get the post holes in the right location. I could give reasonably good directions for how to do that on a flat surface, but I was setting these posts on a hillside, where the back left corner of the deck would be sitting on ground that's about five feet higher than the front right corner. There must be a way to figure out where to dig the post holes. I just have no idea how. But I can tell you how to dig some mean holes.
Here's my first one. Once I knew where I wanted my first post (I started at the highest corner of the hill) I dug down to about 30" and about 7" wide. Some of the later holes were much wider than 7", because I had to keep re-digging them to get the posts in the right spot. Trial and error is probably not how the professionals do it.
Once the holes were dug, I put about 6" of gravel into the bottom of the hole. I hear this helps with drainage? Again, once we get beyond digging the actual holes I'm not an expert. But I can tell you what I did. Ask me again in five years and I'll tell you whether the deck is still standing.
After I'd pored the gravel into the bottom of the hole, I used my post to tamp it down. Then I set my post inside and added a few more inches of gravel just to hold the post in place while I poured in the concrete. (The posts I used are 4x4 pressure treated pine, reclaimed from the kids' fort I tore down to make room for the Bunk-alow. They were in great shape and I've even got enough to use for the front porch railing...if I ever get to that point.)
Here is the concrete mixture I used. I mixed half a bag at a time with water in a five gallon bucket until it was the consistency of sloppy mashed potatoes. If you're going to mix concrete this way, please grab yourself one of this mixers:
It turns your high speed drill into a super powerful mixer, good for mixing concrete, thinset, grout, mortar, and also gigantic batches of whipped cream.
Once my concrete was the right consistency, I poured it into the hole around each post hole. I probably should have used a whole bag of concrete per post hole, but I only had two bags so I used a half bag of concrete which almost filled the holes. Once it cured I topped off the holes with more gravel, tamped down around the post.
Concrete and gravel costs about the same per bag (around $3/bag) but I didn't realize I'd go through so much concrete. Next time I'd buy double.
Before my concrete cured, I made sure all of the posts were plumb.
|Sights like this make Scott very happy.|
Instead of trying to figure out how tall to make all of the posts before putting them into the ground, I stuck them in the ground extra long and then cut them off once I leveled the frame for the deck.
The next day, my concrete was cured well enough to continue building. More on the deck in part three!
Psst...I am not an expert on setting posts and even if I were, I make mistakes. This isn't a tutorial. It's more of a building diary. Click here for all of the Backyard Bunk-alow posts!
Edited to add: I just read in This Old House Magazine that posts set in concrete will eventually rot because of the moisture trapped against the post. Let's cross our fingers that these posts won't see that fate for a very long time.