Working with Foamboard - Joining Basics Part 1

In the last tutorial I covered some basic foamboard principles. Namely how to mark and cut your board. As a quick addition to that, there are a number of potentially useful tools which can help you to cut clean straight lines and avoid mis-angled cuts... I have not used these tools before so will be doing some more research before providing you with more information. In the mean time though, I thought that it would be good for me to talk a little bit about ways that you can join pieces of foamboard.

If you're familiar with woodwork joinery techniques then you'll probably spot some similarities here!


Gluing
Whilst it is possible to create cuts to allow boards to be joined without needing glue, Foamboard (AKA Foam core) can normally be easily glued together. This can be augmented in a number of ways, some of which I will cover in future posts.

Superglues can actually melt away the foam and so should be avoided. You can use superglue to stick other things to the board, such as card, or other details, but just don't get any on the foam!

So what's the answer? General purpose PVA glue... it really is that simple! Well... yes and no. You can also use Hot Glue from a glue gun to strengthen some connections, but if you don't have access to this then there are a number of alternative options; aside from joint strengthening you can use a "No more nails" type product. Incidentally, these come in very handy when you are looking to glue things like plastic details to the board!

Whilst you now know the glue you should use you still need to know HOW to join pieces. The tips below will help you learn how to make strong and neat connections.

Simple Rabbet Joint
A Rabbet Joint can be used to neatly connect two pieces of foamboard together into a corner. It is a much better join than a simple Butt Joint because it looks much neater whilst also being much stronger. The reason it is stronger is because there is more surface area between the two pieces for your glue!

To make a simple Rabbet Joint is easy. All you need to do is mark a line in from the edge of one of your pieces which the thickness of your material (1). Here, I have marked 5mm in because I am using 5mm Foamboard. Then you can cut through the first layer of card, before carefully cutting through the foam. Avoid cutting (or even scoring) the second layer of card. You can then use your blade to trim away the foam, or alternatively use your ruler to scrape it out! (2) You will then be able to fix the two pieces together and you won't see any of the foam filler!

A point to note is that you need to take account of the thickness of the card when using this joining technique or you will end up with off measurements. The piece that sits within the Rabbet should be the desired length minus the thickness of the card (3). Remember to double this if you will be sandwiching the piece between two Rabbets!

You will still need to cover the foam at the top & bottom to hide it, but you won't need to do the edge!

Simple Housed Joint
A Housed Joint is similar in principle to the Simple Rabbet Joint except that it is used away from the edge of a section. It is great because it offers strength, saves on cutting out independent panels and even gives you a way of retro-fitting additional pieces! What's more, is this type of join can be adapted to allow you to join foamboard with other materials at right angles, such as card or plasticard. Be aware of the principles for the Simple Rabbet Joint by marking the correct position for your foam board piece, remembering it has a thickness (1).

Again, cut through the top layer, and the foam, but avoid putting pressure on the bottom layer of card. Removing the foam filler is more difficult with a Housed Joint (2). Depending on the blade you are using you may be able to turn it on its side, otherwise a narrow chisel can do the trick.

As with the Rabbet Joint, be aware of how the junction affects overall dimensions. You can see that the added surface area with this type of joint means it will be MUCH stronger than a simple Butt Joint (3), as such, it is usually well worth the extra time and effort.

Summary
I've covered all of the above joints together because they are all made using simple cutting techniques. There are a range of more difficult junctions which involve angled cuts. Whilst they can be more difficult to achieve, they offer some of the neatest junctions. So next time I will cover angled cutting and joining.

Hopefully these diagrams have been useful and easy to understand, they are definitely clearer than trying to take clear pictures of white foamboard!