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Lesson 4: All About Glue
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For woodworking there's a few types of glue that are used, but by far the most common is carpenter's glue. This type of glue is called polyvinyl acetate adhesive, or PVA for short. PVA glues are inexpensive and have great holding ability, making it an ideal woodworking adhesive.

There's lots of different types of PVA glue to chose from, but I like to use Titebond III which is waterproof, has great adhesion, and accepts paints and finishes.

Some other choices for woodworking glue include CA glue (cyanoacrylate or Super Glue), hot glue, or polyurethane construction adhesive (used with a caulking gun); each has its own performance abilities and limitations, but for the scope of this course we're going to cover common carpenter's glue (PVA).


Glues and Grains

Gluing two pieces of wood together is fairly straightforward, but you do have to pay attention to the pieces you are gluing.

You'll hear the term "wood grain" used in the workshop. Wood grain is the longitudinal arrangement of the wood fibers and is an important attribute to understand for woodworking. Different types of wood have different grain structure, but all wood has a "direction", this can be categorized as straight grain (parallel along the direction of the grain) or cross grain (perpendicular to the direction of the grain).

When gluing it's important to know that the two aspects that make a good joint are surface area, and grain direction. Surface area is the amount of surface that will be glued together, so a butt joint connection will have less surface area than a finger joint connection.


Butt joints have low surface area


Finger joints have much more surface area between each finger

The grain direction means that a joint along the direction (straight grain) of the grain will be stronger than one that is against the grain (cross grain).


Straight Grain


End Grain

This is easily seen if you look at the end grain if a piece of wood, the porous end grain doesn't have the same strength as gluing along the grain. While end grain glue joints can work, they will probably fail eventually or will require some other method to help support the joint. A good everyday example of this is a picture frame, which has mitred corners which are end grain - if you look you'll probably see a nail or some other supporting joinery which holds the joint together. We'll tackle this exact problem in Lesson 8 - Bevels and Mitres when we build our own custom picture frame.


Clamps

With almost every woodworking project you make you're going to need a clamp somewhere along the way. Clamps allow you to hold things together while glue dries, or just hold a piece in place temporarily while you work on another part. There's loads of different types of clamps out there, and you can never have too many of them!

Shown above there's a band clamp, a bar clamp, a spring clamp (also called an A-clamp), and a ratcheting bar clamp. There's plenty more types of clamps out there, and they all have a variety of uses.

When using glue you're going to want to use clamps to keep your work securely in place while the glue dries. Invest in a few clamps of different types and sizes to start off to find the type that works best for you, it's one of the best tools in the shop.


Cover Work Area Before Gluing

A common mistake is to start a glue up without covering your work area before you start, at best this makes a big mess to clean up but at worst it can result in gluing your project to your workbench! Rolls of "builder's paper" are inexpensive, but old newspapers serve the same function and are free.

When your glue dries to the paper it'll be much easier to remove with a knife, scraper, or sanding than trying to repair damage from having it stuck to your workbench.


Glue Application

There's nothing special about applying carpenter's glue, but it's important to take care when applying and to use the right amount.

Before starting any glue up consider first what you're going to need to hold your piece together, maybe it's a few clamps, or maybe it's tape. Make sure you have your supplies close at hand before starting anything, it's a real pain to scramble afterwards for that last clamp.

When you're ready to glue apply a bead along your work surface, then drag your finger along the bead to evenly spread out the glue.

Since glue can cause wood to swell where it's applied it's important to joint the pieces quickly after glue application, this is especially true for joints that have tight tolerances.


Clamping + Cauls

Once the surfaces are glued together you can clamp your work until the glue has set. When clamping it's good to apply pressure to the pieces being glued, but over-tightening can cause too much glue to squeeze out the pieces may not bond.

For some pieces you may need clamping pressure on the top and bottom to keep your pieces level or aligned. Adding straight scrap pieces to the top and bottom of your glue up, and then clamping them in place, can help keep your work stable and level. These wood pieces that transverse the glue-up on the top and bottom are called cauls.

Cauls added to top and bottom of clamped piece

To make things even easier for cleanup you can add a barrier of paper between the cauls and your work so you don't accidentally glue them together.

When tightening your clamps make sure not to over-tighten, which not only squeezes out all the glue, but can also dent and damage your work.

Dent in wood caused from over-tightening


Glue Cleanup From Wood

One of the best methods to remove excess glue from your work piece is to rub sawdust all over the joint. The sawdust will mix with the glue and clump together, making cleanup a breeze. You should avoid using a wet towel or sponge as moisture causes wood to swell and too much might deform your work. Sawdust is an easy and readily available solution to glue cleanup.

It is important to clean up the extra glue as soon as possible since wood that absorbs glue will stain differently than the rest of the wood.

A putty knife makes a great tool for both glue application and clean up

Another great method for applying and cleaning glue is a putty knife, the flat surface does a great job of evenly spreading glue over your surface and the sharp edge makes cleaning up excess glue easy.


Glue Cleanup From Hands

If you get any glue on your hands after your piece is secure you can easily remove it by just rubbing your hands together. Wet or still damp glue should just flake off.


Project Time - House Numbers Made With a Glueup

Now it's time to put the glue theory into practice. We'll combine the skills of cutting wood from lesson 1 with glue to make scrap wood house numbers.

Tools + Supplies:

Using scrap wood, we'll trim up the ends so they're square and the right length, then glue them together into a plank which your house numbers can be mounted to. I started by sketching up the idea, and the dimensions to suit the house numbers I bought from the store.

With the idea all planned out we can get started.


Cut Scraps to Length

Using the techniques from lesson 1 on how to make straight cuts, collect and cut your scraps to the approximate length for your house number sign. I like the random length stacked style, so these scraps are between 6"-8".

I had these scraps left over from some other projects, but you can easily find scraps at any lumber store. In this example we have a mix of pine, maple, walnut, purple heart, and zebrawood.

Since this is a scrap wood project it doesn't really matter what condition the wood is in, so chip out, nail holes, and rough edges are all acceptable. The important part is to have clean and straight edges for the glue to bond to.

Try a few orders of your stack to get the style you like.


Glue

Apply a bead of glue to each piece of wood, smear the bead with your finger to get even coverage, then clamp wood together. Remember to add cauls so the glue up stays together perpendicularly.

Clean up any excess glue and squeeze out by rubbing sawdust into the glue until it clumps together and falls away. Allow the glue up to dry overnight.


Sanding

Once the glue has dried you can remove the clamps and inspect your work. Sometimes there's dried glue that you didn't catch while it was still wet, this can easily be removed now by either scraping or by using a sharp knife to get under the glue and pry it off (careful not to damage your work!).

Another method for getting off small amount of dried glue is to use sandpaper. We'll cover sanding in much more detail in the Sanding part of Lesson 7, for now we'll just start with a coarse grit to clean up the edges and surface.

Start with a rough grit (80 grit) to remove any blemishes and dried glue, rub the sandpaper all over the wood until each section of wood is smoothed. Switch over to a finer grit sandpaper (120 grit) and rub over the piece again until the rough abrasion marks from the 80 grit are gone. Step up again to an even finer grit of sandpaper (180 grit) and rub over the wood pieces until they are nice and smooth. You can continue moving to finer sandpaper if you like, but for this outdoor project 180 grit is fine.

After sanding wipe down your work with a dry rag to remove any fine sawdust from sanding.


Exterior Finish

This project is destined for outdoor use and will need to be protected with a finish to prevent the wood from rotting or discoloring. Finishes in Lesson 9goes into more detail on types of finishes, but for now we can just apply any clear exterior polyurethane coating to achieve protection.

Apply the finish with either a foam brush, a chip brush, or lint-free rag. Make sure the polyurethane gets onto all parts of your piece, especially the uneven portions where the wood is glued together. After application wait a few hours until the surface is dry and apply a second coat, then allow to dry completely overnight.


Apply House Numbers

Once the finish has dried the house numbers can be attached. I used 4" high numbers, but yours can be based on whatever width your glue-up was.

Arrange the house numbers on your scrap wood to determine the best location for each number, take care to place the screw holes as your scrap wood glue up may have some uneven areas.

With a pencil mark the screw hole locations, then drill a hole with a drill bit smaller than the diameter of the screws the house numbers came with - this small hole is called a pilot hole. Drill down as far as the screws are long.

Place the numbers back onto the scrap wood and tighten the screws down using a screwdriver.


Mounting Hooks

Choose a mounting method that suits your needs. I wanted to have my house numbers removable and have minimal impact to where they were mounted (since I rent), so I used keyhole hangers which only require a 2 screws into wherever I mount.


Mount Your Masterpiece!

All that's left is to mount your masterpiece near your front door, showing people where you live while showing off your new woodworking skills.

There's really not much to gluing, but does take a little time to prepare your area and work pieces before starting and taking care not to use too much glue. Throughout the rest of this course you'll have plenty of opportunity to apply this knowledge and gain confidence.


Quiz - All About Glue

{
    "id": "quiz-1",
    "question": "PVA glue stands for Pliable Very Adhesive glue",
    "answers": [
        {
            "title": "True",
            "correct": false
        },
        {
            "title": "False",
            "correct": true
        }
    ],
    "correctNotice": "Correct! PVA glue stands for polyvinyl acetate.",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-2",
    "question": "End grain glue ups are just as strong as straight grain glue ups",
    "answers": [
        {
            "title": "True",
            "correct": false
        },
        {
            "title": "False",
            "correct": true
        }
    ],
    "correctNotice": "Correct! End grain glue ups are much weaker and require a special joint or mechanical fastener to make a good connection.",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-3",
    "question": "When clamping a glue up it's best to squeeze the pieces together very tightly until almost all the glue seeps out.",
    "answers": [
        {
            "title": "Clamp until you can't aply any more pressure.",
            "correct": false
        },
        {
            "title": "Clamp firmly, but not so tight as to remove all glue from joint.",
            "correct": true
        }
    ],
    "correctNotice": "Correct! Squeezing a glue up too tightly will remove all the glue in the glue up and prevent adhesion, and very tight clamping can cause indents to the wood.",
    "incorrectNotice": "That's incorrect"
}
{
    "id": "quiz-4",
    "question": "Why should you avoid using a damp sponge or towel to clean up excess PVA glue after it's been applied?",
    "answers": [
        {
            "title": "Moisture from the damp sponge or towel can cause the wood to swell and deform.",
            "correct": true
        },
      {
            "title": "Water can splash around and make a big mess.",
            "correct": false
        },
        {
            "title": "PVA glue is not water soluble.",
            "correct": false
        }
    ],
    "correctNotice": "Correct! When introduced to water wood can swell and deform. While this isn't terrible, it can represent more finishing work later.",
    "incorrectNotice": "That's incorrect"
}

Class Project!

Share your glue-up House Numbers in the Class Project box below. Did you do anything differently than my example? I'd love to see your version!

Next up we'll learn all about how to make perfect drilled openings in the next lesson, and make a fun project that applies all we're learned so far.

CLASS PROJECT

Share a photo of your finished project with the class!

Nice work! You've completed the class project