Deck Building – Setting the Posts: Using Fast-Setting Concrete Mix and a Construction Laser Level

Michelle Tether
Written by Michelle Tether

If you’re looking for a guide to get your decking on track, and an easy way to follow along and get things accurate, this is the article for you. We will discuss all the short cuts and tips the professionals use to get it done. Setting posts doesn’t have to be difficult, with the job broken into a nice simple order, you’ll be surprised just how quickly this can be done with relatively little experience of building or DIY.

Deck Building – Setting the Posts

There’s a few steps that you’ll of taken to get to this stage and they’ll include deck design fundamentals, deck framing concepts,  timber support sizes and spacers, and then the layout of the posts themselves. This article will deal with actually setting posts in concrete. Some of this involves the question of the geographical location where the deck will be built – some latitudes are colder than others and demand deeper post holes. The most important thing is getting each simple part right. If you do, your deck will look something like this too.

Very stylish decking

Image source. Very stylish decking

Install the Ledger Board

If the deck is going to be attached to your home, we need to install the ledger board first. The ledger must be fastened to the home’s exterior wall studs with lag screws – if you don’t know what these are simply make a quick search for them on Google and then head into your local hardware shop for them. On flat siding, keep the ledger off the siding using ½” exterior plywood spacers where the screws penetrate. They should be 3” wide and pointed at the top for water run-off. For good measure, soak them in wood preservative and wrap them with roofing felt, it should give you a fair amount of use before any rot and rust can set in.

For lap siding, the siding must be cut away prior to attaching the ledger. Then, slide metal flashing up under the siding, attach the ledger, and bend the flashing over it.It’s imperative that the ledger is level.

Dig the Footings for the Posts

Use a shovel or post-hole digger to dig the holes where you’ve previously marked out. The holes should be roughly a foot wide at the top and then spread out underneath to 16” at the bottom. The depth is important you need to get under the frostline so that concrete isn’t damaged. For areas that don’t freeze, 24” deep is sufficient. Otherwise, the hole should be 8” below the frost line. This makes for sturdy footing posts, you want to do a lasting job that’ll add value to your property when you sell. Here’s a good idea of what your footings should look like.

Decking footings

Image source. Decking footings

Set the posts

Start by pouring a base of pea gravel into each hole; this is for proper drainage and it’s also a good base for the quit setting concrete. Use the string lines from the post hole layout article as guides to make the poles line up. So go corner to corner and then run a line, it’ll help keep things in pretty good shape. Set a post in each hole. Use a 4’ level to get them plumb in both directions and stake them. The posts should be taller than finish height.

Fill the holes with fast setting concrete mix. This mix is easy to work with because the water is added to it right in the hole – no wheelbarrow required and very clean job considering. There are plenty of good concretes that soak well but Quick set concrete makes a good one and it’s available at most builders yards.

Building a Level Deck

This is where it matters, getting a level deck is actually very easy if you follow simple instruction and it’s super important, you can’t make any quality flooring job without a level base. This guide will ensure that the finished deck will be level. There are three ways to do this. The preferred method is to use a construction laser level from the top of the ledger and mark each post with a pencil and then cut them flush, it’s not required though if you don’t want to spend out on one. Old school builders use far simpler methods.

Building the deck framework

Image source. Building the deck framework

When determining the post height, keep in mind that the joists will butt into the ledger, but ride on top of the beams. The next best method to transfer level marks is to use a water level – and still preferred by many older builders. This is simply clear plastic tubing filled about 90% with water. The water level on one end will be the same as on the other end (as long as there are no bubbles in the tube).The third (and least accurate) method is to use the string line with a line level.

About the author

Michelle Tether

Michelle Tether

I love everything home. I write as a passion for non profit about the things I love.

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