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How to Make an Easy Wood Soap Mold: Loaf, Slab, & Block

One of the most costly parts of soapmaking is the molds and cutters you use as you grow from making small single batches to wanting to make tons of soap all at once. If the investment of larger molds or silicone molds is off your pocketbook’s radar, you can DIY and build your own wood soap molds very inexpensively.

ANYONE can build these wood soap molds, you don’t have to be a woodworker to do it! I love making these wooden soap molds for many reasons:

  • they come almost completely apart, which makes storing them easy
  • they are hugely versatile, because you can change both the width and length easily
  • they are relatively inexpensive to build, many of the extra costs in building them are optional (like washers and wood glue)
  • they can grow with you, if made properly
Adjustable Width Wooden Soap Molds
What these wood soap molds look like when built and assembled

It is cheaper per mold to build multiple wood soap molds at one time. If you are planning on only making one, you will likely spend upwards of $20 to $30 on supplies as smaller wood boards at hardware stores are more expensive and you will have leftover wood. I recently made ten of these wooden soap molds and the total bill was $55, making each mold a nice and cheap $5.50 each (and a couple hours of time!)

I’ve stuffed as much information in here that I can! I’ve included tips and tricks I’ve learned over the many times of making these. I have also tried to explain the steps in the most approachable way possible. Ready to get started on your own wood soap molds? Let’s go.

(Not into DIY? Here are the best molds you can buy for every level of soapmaking.)

Supplies Needed to Build Your Wooden Soap Molds

Wood Needed to Build Your Adjustable Width Wooden Soap Molds

You can use any kind of wood you desire. I personally preferred using poplar because it’s a hardwood and it didn’t dent, get scratched, etc. It also seemed to insulate the soap better than other woods I had tried. A couple of common (and affordable) choices for wood soap molds are Baltic birch plywood or pine. My pine molds were made and used when I was a hobbyist, and held up fine, but there are others who have reported that they warp over time.

Another soapmaker who has built their own wooden soap molds also mentioned to watch out for woods that are either glued together or treated, especially if you CPOP (cold process oven process.) Woods that contain glue or are chemically treated should NOT be used in the oven as they could fall apart or may off-gas toxic chemicals.

If you don’t have a saw at home, many home improvement stores will cut your wood for you, if you ask, so keep that in mind! Just figure out your dimensions, and bring them along with you when you purchase your supplies!

How to Determine the Dimensions of Your Boards for Your Wood Soap Mold

For the end boards of your wood soap mold, the height should match the side boards, and clear 1″ taller than any fill capacity of the mold. The length of the end board should match the desired width of the soap loaf you wish to make. Changing out your end boards for new ones will adjust the width of the mold cavity, so you may choose to make multiple sets! Then you can customize your wooden soap mold for the job at hand.

Example end board dimensions for a soap mold that is used to create a 3.5″ wide, 2.5″ tall, and 10″ long loaf of soap: 3.5″ wide x 3.5″ tall

For your side boards, the height should match the end boards, and clear 1″ taller than any fill capacity of the mold. The length of the side boards should be calculated by adding the thickness of the end board pieces, the length of the soap loaf desired, plus an additional three inches.

Example side board dimensions for a wood soap mold that is used to create a 3.5″ wide, 2.5″ tall, and 10″ long loaf of soap: 10″ (length of soap) + 0.75″ (thickness of end board 1) + 0.75″ (thickness of end board 2) + 3″ (additional length) = 14.50″ long x 3.5″ tall (same height as end boards and 1″ taller than soap loaf height)

For your base board, the length should match the side boards and the width should accommodate the largest width of soap loaf you will make in this mold, plus the width of the side board pieces and an additional inch or so. I tend to default to making the width the same as the length of the steel bolts I’m using so that the bolts don’t stick out awkwardly past the base of the mold.

Example base board dimensions for a soap mold that is used to create a 3.5″ wide, 2.5″ tall, and 10″ long loaf of soap: 14.50″ long (matches side boards) x 6″ width (same width as 6″ bolts, must be wider than 5″ = 3.5″ width of soap + 0.75″ thickness of side board 1 + 0.75″ thickness of side board 2)

Tips on Deciding What Size of Wood Soap Mold To Make

How big your wooden soap mold is will affect the cost of supplies needed. Opting for any width of soap mold cavity beyond 12″ wide will greatly affect the cost, as the bolts needed greatly increase in price. Obviously, you will also need larger pieces of wood to make a larger mold.

You also want to consider how heavy the wood soap mold will be when filled with soap. I recommend a maximum length of 18″ for a single loaf configuration, as beyond that, it will become unwieldy to move and/or store when not in use. A single loaf at 18″ in length will range in weight from approximately 6 to 8 lbs of soap.

The largest mold that I’d recommend with this method of building molds is 18″ long and 12″ wide. Keep in mind that you can control the height, too, which means you can make a block mold! If you were to build a mold that is 12″ square inside, that’s a whopping 40 lbs of soap or so.

To configure your wooden soap mold to your bar size, think about the dimensions of your bars and how many bars of soap you want to make. If you make 2.5″ tall, 3.5″ wide, and 1″ thick soap, you will want to:

  • Use a width of the mold in multiples of your bar width (3.5″ for a single loaf, 7″ for a double loaf slab, 10.5″ for a triple loaf slab)
  • Use a height of the mold that is 1″ taller than the bar height for a loaf or slab configuration (3.5″ tall) -OR- you can also double up/triple up the height to create a block mold (6″ tall for two loaves on top of each other, 8.5″ tall for three loaves tall, etc.)
  • Use a length of the mold that is multiples of your bar thickness (10″ for instance makes 10 bars)

You may also want to consider what silicone liners are available from soapmaking suppliers. It’s almost always cheaper to build your own supporting mold box for silicone liners than it is to buy the accompanying mold from the supplier. If you build your molds to fit a silicone liner, remember that your mold cavity will actually be the exterior dimensions of your silicone liner.

(Need to scale up all of your soapmaking equipment for production? We’ve rounded up budget and high-end soapmaking tools for big batches.

Keep in mind that you can make multiple sets of end boards to change the width of the wood soap mold, from a single loaf to a double or triple slab! You can also create an extra end board of each dimension to use as a dam, creating a shorter loaf of soap than the intended mold cavity you make.

This article discusses how to calculate your recipe and mold size, and it’s helpful for deciding what size of mold you’d like to use.

Other Supplies Needed to Make Your Wooden Soap Molds

You’ll need wood glue (optional) and at least 2″ long wood screws to securely fasten one side board to the base board. The number of wood screws depends on the length of your mold, I tend to use one screw for every two inches of length.

You’ll also need four sets of steel bolts and accompanying nuts, two sets for each end of the mold. You can use hex bolts or tap bolts, or even carriage bolts, if you wish. You don’t have to use stainless steel or any high grade steel, the standard zinc plated steel is fine. There are also bronze bolts, that you can use if you want. You just want to make sure to avoid aluminum.

I like to use 5/8″ diameter bolts, as they feel substantial enough without being gigantic, but again, it’s entirely up to you. The length of your bolts will be determined by the width of your mold cavity and thickness of your side boards. To determine the minimum length of the bolts, take the width of the soap loaf, add the thickness of your two side boards, and an additional inch.

Example bolt size for a soap mold that is used to create a 3.5″ wide, 2.5″ tall, and 10″ long loaf of soap: 5/8″ diameter 6″ long zinc plated steel bolts (must be wider than 5″ = 3.5″ width of soap + 0.75″ thickness of side board 1 + 0.75″ thickness of side board 2)

Bolts tend to run anywhere from $1.00 to $3.00 each  up to 12″ lengths, which is long enough for a slab that is three loaves of 3.5″ width soap. After 12″ of length, the bolts tend to get much more expensive. It’s usually cheaper to buy a box of bolts instead of individual bolts, so it’s more economical to build multiple molds at one time. If you are unable to find the length of bolt you need at a local hardware store, there are several online specialty suppliers for fasteners.

Washers are totally optional, I like to use them so that the bolt head and the nut don’t dig into the wood.

You’ll also need a power drill to predrill holes for the wood screws, holes for the bolts, and to drill the screws in place. A simple handheld cordless power drill set tends to come with the standard drill bits you’ll need. If you don’t already have one, this Black & Decker Drill and Project Kit will have everything you need. (Besides, I think everyone should have such a kit on hand for basic maintenance work around the house. Plus, you can use the drill to stir large batches of soap with a paint mixer when you start doing production size batches of 20 lbs or more.)

Directions to Build Your Wood Soap Molds

Drill the holes in your side boards for the bolts
Drill the holes in your side boards for the bolts

GET STARTED: Start off by drilling the holes for your bolts in your side boards. You’ll want to use a drill bit that accommodates the diameter of your bolt.

The placement here is important, as you need to ensure that you place the bolts with enough room for the soap mold cavity and the end boards. I like to mark the center of the board, and then measure and mark where the end of the soap cavity should be on either end. And then place the end boards in place and trace a light pencil line on the outside edge of each end board. This gives me a clear indication of where I should place the holes for the bolts.

It’s easiest to stack your side boards on top of each other, clamp them together, and then drill the four holes into the side boards together at one time. Doing that will make sure that your drilled holes are perfectly lined up so that the bolts are level.

Why two holes in each end instead of one, you ask? The first time I built these molds, I only put one bolt in each end. It was a horrible mistake that resulted in leaky messes. When I poured soap in the mold, the soap pushed the end board’s bottom out under the bolt if the bolts weren’t tight enough. Using two bolts prevents the end boards from moving at all – perfection. Your two holes (and thus the bolts) should be evenly spaced across the height of the mold.

Attach one side board to the base board.
Attach one side board to the base board.

CREATE THE BASE: On the bottom of your base board, line up a side board similar to what is shown in the illustration except do so on the bottom of the base board. Trace the inside edge of the side board using a pencil, this will help you line up the placement of the wood screws to secure your side board to the base.

Pre-drill holes for your wood screws along the edge of the base board within the section you outlined. I like to place a wood screw every two inches or so. You can mark the placement of the holes prior to drilling if you wish.

Optional: After you pre-drill the holes, apply a thin line of wood glue to the top edge of your base board and clamp your side board to the base. This will secure the side board in place and allow the glue to dry. Gluing the side board to the base is optional, but recommended. If you CPOP your soap, you will want to skip this step.

Use your power drill to fasten your wood screws into the pre-drilled holes from the bottom of the base board, as shown in the illustration above.

Assemble your new wooden soap molds!
Assemble your new wood soap molds!

ASSEMBLE & ROCK YOUR SOAP POT: Hurray! No more scary power tools!

Thread your steel bolts through the secured side board, and your loose side board. Place the end boards in between the two side boards to create the soap mold cavity. Like I mentioned before, you can place washers between the bolt and the wood, as well as the nut and the wood, but this is entirely optional. Tighten the nuts onto the bolts, and voila! You’re ready to line your new wooden soap molds and rock your soap pot.

If you want to change the width of your wood soap mold, just change out your end boards for a different size!

Using Your New Wooden Soap Molds

If you did not build your wood soap molds to fit a silicone liner, you will need to line your mold. I personally use the same method as Amy at Great Cakes Soapworks, you can view her video tutorial about how to line soap molds with freezer paper here. If you build block molds, you will want to use a trash bag liner or a silicone liner. Freezer paper will likely leak when used for a block mold. These trash can liners are the ones I prefer.

If putting them together or taking them apart seems confusing, here are some “live action” photographs of using these molds:

Wondering how to fill your new molds efficiently? In 27 pages, Efficiency in Scaling: Introduction to Masterbatching covers how to scale production for soapmaking, how to move to big batch sizes, procedures for master batch soap making, various equipment setups, tips, tricks, safety information, and so much more.

And there you have it! Wood soap molds that are so versatile, you can truly tailor them to your own needs. Yesssss. If you happen to build these molds, I’d love to hear from you in the comments below!

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41 Responses

  1. Hi,

    In the example side board length calculation, should the thickness of the end board be doubled? Or does the .75″ include the thickness of both the end boards?

    “Example side board dimensions for a soap mold that is used to create a 3.5β€³ wide, 2.5β€³ tall, and 10β€³ long loaf of soap: 10β€³ (length of soap) + 0.75β€³ (thickness of end board) + 3β€³ (additional length) = 13.75β€³ long x 3.5β€³ tall (same height as end boards and 1β€³ taller than soap loaf height).”

    Thanks!

      1. This is a FABULOUS article! I love that it addresses scaling molds to wider widths and higher heights for so much versatility. I am now planning my next mold.

        Love your website…always Interesting and informative. Thanks for all you do!

  2. Kenna,

    Should this section be changed also to accommodate the correction above. 13.75 to corrected 14.50.

    Example base board dimensions for a soap mold that is used to create a 3.5β€³ wide, 2.5β€³ tall, and 10β€³ long loaf of soap: 13.75β€³ long (matches side boards) x 6β€³ width (same width as 6β€³ bolts, must be wider than 5β€³ = 3.5β€³ width of soap + 0.75β€³ thickness of side board 1 + 0.75β€³ thickness of side board 2)

  3. great tutorial. i keep ending up on your blog as i research soapmaking and am really liking your blog. thanks!

    p.s. for some reason this post didn’t come up when i did a google search. maybe change “build” in your title to “make”. just a thought. i did find you on pinterest though.

    1. As far as I’m aware, there are no glues you should be used for molds that are for CPOP. Just skip using wood glue, and make sure you aren’t using treated wood.

  4. Kenna,
    Thank you for providing instructions on how to make your own adjustable soap mold. I have purchased all the supplies needed up to the bolts. I looked at the bolts and they seem mighty thick and large at 5/8″ in comparison to your picture provided. The picture you provided looks more like 1/8″ rather than 5/8″. Could you confirm that we do need to use 5/8″ diameter bolts ( head and bolt body)? J

    1. The pictures of the molds in the post are my first molds I built using this method, my current molds use 5/8″ bolts. As mentioned in the article, you could use any diameter bolt you wish, it’s the length that matters. πŸ™‚ Typically, it’s going to be based on availability – not all home improvement stores or hardware stores carry a large variety, so get whatever you think will work. It just holds it together, it’s not like you’re going to sit on your molds or throw them around the room! πŸ˜‰

  5. Thanks so much! I built a couple similar and the one I like best has the long sides mounted to 1 x 2 on bottom and base board sits on the ledges created by the 1 x 2s. It seems a little easier this way, to store flat(-ish). I used scrap lumber so the only cost was the bolts, washers, and wing nuts. I commandeered a small ratchet wrench and socket for extra tightness and keep it with the mold. Sunniest regards, -Wendy

  6. Hi Kenna,

    I love your mold plans and will put them to use immediately! What is your favorite kind of loaf cutter and where do you get yours from? I’ve made my own loaf cutter box in the past which allows me to cut only one bar at a time, which used to be fine, but my business has really increased. My cutter also allowed for some unwanted slippage and made some bars thicker or thinner than others. Now, I need a larger scale cutter.

    Thanks,

    Lou

  7. Hello there
    Thanks for this wonderful sharing. (2.5 “tall, 3.5” wide, and 1 “thick soap) for how many grams of soap can you use?

  8. Hi,
    we made a few molds following this post! For now we made 2x 10″ long loaf molds. We used poplar .75″ thick but we kept the sides 4.5″ tall, so, by replacing the 3.5″ spacer with a 2.5″ end side we can transform the mold from the classic squat one to a tall and skinny form.
    Also, by using inside dimensions 9″ x 12″ we built, in the same way, a slab mold that can accomodate lots of different configurations: by using a divider we can make 18 2″ x 3″ inches bars (thickness can be anywhere from 1″ to 3″), or a flat slab design for elaborated swirls, or even for blocks of soaps up to 3.5″ thick.
    It was a fun project! And we got 3 “convertible” molds for a total of $ 75!
    Thanks!
    Lorenzo

  9. Great design, Kenna. I made molds a couple of years ago, and while they worked, they weren’t great…or the same. My design wasn’t as practical or easy as this one, either. I’ll give this a try. I really like the idea of making it double wide if I want. I’m not sure if I would do that exactly, but I will try making 2 loaves with three long boards. Better use of space and wood.

  10. kindly send me a finished product of the mold with slabs. Thank you for the instructions on building my own mold.

  11. I want to make some 8 ounce bars, and am confused as to the size dimensions for a mold to build. Do I build a slab mold, and what size if I am using 10 pounds of soap?

    1. You need to decide on the dimensions of your bar before you can figure out the dimensions of the mold to build. As a general rule, a bar of soap contains 0.55 ounces per square inch. So, if you want an 8 ounce bar of soap, you need to have around 14.55 square inches (and also a huge bar of soap)! A 2.5″ square cube is pretty close – about 8.5 oz, a 4″ by 3″ by 1.25″ bar is close – about 8.25 oz, etc.

      You need to find your bar dimensions, and then you can figure out a slab mold mold size that would be 10 pounds of soap. For instance, if you go with 2.5″ cubes, you know you need your slab to evenly divide into 2.5″ sections and produce about 20 bars of soap (around 10 lbs of soap divided by 8 ounces each, obviously, it’ll be slightly more than 10 lbs if your bar size is 8.25 oz or 8.5 oz). You could do a slab that is 5″ by 20.5″ (two rows of ten 2.5″ cubes) or 10″ by 12.5″ (four rows of five 2.5″ cubes).

      Without your bar dimensions, it’s impossible to say what mold size you should use. Most soapmakers use a 2.5″ by 3.5″ by 1″ bar size, which is 4.8 oz on average pre-cure, and around 4.5 oz after cure – depending on textured tops, embeds, etc. That makes it easy to figure out molds, especially because that is what is widely available. When you deviate from that “standard”, you gotta figure it out!

  12. Hi I just found this tutorial and it looks quite easy. However, the mold I use now has flushed slots to fit the boards into and I still experience the odd leak that gets under the wood. How does this hold up for leaks?

    1. Hey, Sharie,
      Preventing leaks is going to depend more on the liner you choose than the mold. Silicone molds are going to have virtually no leaks. A trash liner won’t either if you are cautious about punctures. With careful lining, freezer paper probably won’t leak, but that’s definitely the method that gives me the most issues.

      I have wood molds I’ve used well over a decade. They hold up to occasional leaks and drips, but, clearly, you want to limit exposing wood to raw soap as much as possible.

  13. Hi Kenna, thanks for the tutorial. In Spring, I build 6 loaf molds using these plans and they’ve been wonderful. I decided to make another bigger mold using the same technique, but I find that the front board does not stay flush with the base when I tighten everything up. There’s a small gap about quarter inch. My mold is 21″ L x 9.25″ W a 5.5″ H. I guess the length is longer than you’ve recommended — could that be the problem? To overcome, I will add a couple hinges that connect the front board to the base. It’s not ideal because it locks me into one configuration, but not sure how to fix it. It seems like too much of a gap, though I will be using a silicone liner. Any advice?

  14. Hello πŸ™‚

    I read through this post and I am excited to make the smaller mold posted in your picture. Can you please give the EXACT measurements? I find that this will be easier for me if I have a list of what exactly I need. Thank you.

  15. I have built several of you forms and love them. Easy to build, and easy to use. I’m new into making soap and these really make it much easier.

  16. Hi, My son is can do this mold but he need direct measurements. My soap is 5 oz with 1 inch thicknesss. I want at least 10 bars . Can you just give me the measurements so I can give them to him. He works and he knows how to work with wood. He just needs the measurements. Thank you soooo much. I’m making soap for the first time.

    1. Cathy,
      You need to decide on the dimensions of your bar before you can figure out the dimensions of the mold to build. (A bar that is one inch thick could be square, a tall rectangle, a wide rectangle, etc.) As a general rule, a bar of soap contains 0.55 ounces per square inch.

      Most soapmakers use 2.5β€³ by 3.5β€³ by 1β€³ bar size, which is 4.8 oz on average pre-cure, and around 4.5 oz after cure. So, once you determine your own preference, follow the instructions in the article to determine mold size.

  17. Kenna sou iniciante no ramo da saboaria, e o melhor presente foi ter te encontrado nesse site!
    Amando todas as suas dicas!
    Aprendendo muito com vc!
    GratidΓ£o!!!

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