Jump to content
arpetrone

Mold Making & Casting Slip Mixing Questions

Recommended Posts

Hello everyone,

I am hopefully going to be embarking on a journey soon enough of selling some log cabins. I am hoping that I can figure out a way to make a mold of the design so that I will have an easier time producing them.

Here is a LINK to some pictures of one.

I am wondering if, with some modifications, a mold is able to be made of a complex shape such as this? The roof is separate and I would be making a separate mold for it. Are the amount of details added, such as the window panes and door frames too much detail for a mold master and would be better added afterward? The windows themselves would not be cut out yet of the mold master but is the hollow inside a problem? I am thinking since it is hollow than it would have to be a slip cast mold but since there are so many over hangs I am guessing it would not just slide out easily?

Would a two piece slip cast mold work though - that is split horizontally? This way it just pops off?

 

As for my slip cast mixing question. I've been doing some research and see that sometimes people say it has to be mixed for hours while other instructions only mix for 10-30 minutes maybe. Are hand drills with say a jiffy mixer used often and successfully in mixing slip or do industrial mixers need to be used?

Thanks in advance for any advice and I hope this makes sense.

Share this post


Link to post
Share on other sites

I will pass on the mold making- not my area.

slip however: 30 minutes with a low RPM (500) mixer is necessary to disperse the suspension agent, and to properly distribute particles. (Homogenous) if you are using sodium silicate, you have a short window (20-30) minutes before the negarptive ionic charges begin to diminish, with larger particles falling out of suspension. Darvan makes a short and long chain polymer; if you are going to store it; use the long chain. Long chain= long term suspension.

Tom

Share this post


Link to post
Share on other sites

Plaster moulds can be very detailed, you might just have to replace moulds more regularly to keep those details sharp. 

The shape of the house will probably have to be tweaked to make it easier to take out of the mould. Did you want the mould for the outside shape and texture or inside AND outside? 

I wonder if is might be easier to cast a textured rectangular shape and then add the windows and frames made in separate moulds?

Share this post


Link to post
Share on other sites

The inside is not very important. The textures on the outside don't even necessarily have to be there. But it would be helpful if I can have the door frames and window frames already in place. This way all I really have to do is cut out the windows and scratch in the textures.

So the two piece slip cast mold is totally do able? For both the cabin and roof?

Thanks for both of your replies.

Share this post


Link to post
Share on other sites

You could press mold some sections and then join them together. 

As to regualr slip molds you will need a 4 piece mold per side after you remove some under cuts.

I feel it would be easier to make a single or two piece press mold per side -Then join the walls together.

 

Share this post


Link to post
Share on other sites

Hmm thanks for the reply Mark. I wonder if that'd even be faster or take me just about the same time as just putting it together from scratch.

I guess the only way to find out would be to try both!

Share this post


Link to post
Share on other sites

if you would like to see a variety of clay houses, check out Windy Meadows Pottery.   jan richardson started this business in the 1970s and there are many of them out there.  she created plaster forms for the separate sections of each house and then had them constructed by others.  the work was done in people's homes so they could take care of children and housework while still making money.

buyers could choose the type of roof from shingle, thatch, tin, etc.  so every house could be custom made.  check out the possibilities of using something similar to make your log cabin from slabs rather than try the complicated mold method.

 

Share this post


Link to post
Share on other sites

You could make a  press mold of the components like the logs or the roof /tiles-press those and cut them and assemble.

Oldladys pots above on Windy Meadows pottery's looks like this has been all done well for a long time

Share this post


Link to post
Share on other sites

Thank you @oldlady for showing me that. It definitely gives me some ideas and upon further thinking, I think the press molds of each section is not such a bad idea.

When you say she created plaster forms for each section, you mean she carved them from plaster and then used a slab of clay to lay over the top and press into it to create the textures in the clay?

Edited by arpetrone

Share this post


Link to post
Share on other sites

that is the result.  you might contact her and ask.   she is a lovely lady and might have some suggestions to get you started.  see the website.

i made some small houses years ago and used various things to create texture.  one was a brick wall made with several different wood blocks.  i pressed them into clay and bisque fired a piece about 6x8 inches.  the roof was made with a couple of popsicle sticks that had straight ends.   i used a rubber mat like the kind you find just inside a store for keeping the floor dry when it rains.  that made clapboard walls.   stone walls were  made with many different tiny pebbles.  windows were cut with copper tubes found in model shops.  several sizes with the smaller ones pushing out the clay from the larger tubes.   many,many things were used.

look around you at all times to see the potential of everything you see for making texture.

Share this post


Link to post
Share on other sites

If you've not made a mould before, I'd suggest looking on ebay and other sites, and buy a multi-part mould.  Anything, just to get one and take it apart and put it back together, so you can see how they're made.  I don't have many moulds,  only mugs and bonsai dishes, but an old friend had hundreds.  Some need two or three separate castings and then stuck together while leather-hard.

 

For me, the hardest part of mould-making is knowing where to make the joins so there are no undercuts.  

 

Think of a banana and an apple.   Both can be made with a two-part mould.  A straight banana could have it's seam line along the length, in almost any position.   The seam line on a curved banana needs more thought.  Same with an apple.   A box or sphere can have the seams in almost any position.  Same with your log cabin.  Every piece of plaster must be able to pull away from the casting, without any catches.

 

If this is something you want to make lots of, it might be worth getting a commercial mould maker to make the first one for you.  

Share this post


Link to post
Share on other sites

You might go to the library and look at some mold making books.   I would purchase your favorite one off of Amazon so you will have it for reference when you try making a mold.   I would make a small press mold as your first project.   You should also buy a bag of pottery plaster  a 25lb bag should be a good start,  I recently made a 14x14x5 press mold and used a half of bag.  Fortunately plaster is cheap.   Have fun and good luck.   Denice

Share this post


Link to post
Share on other sites

Thank you all for your help.

I have rebuilt the log cabin in Plasticine in sections with much more care and detail. My plan is to make a press mold or two from the various parts of the actual cabin and a tile mold for the two halves of the roof and then put it all together. It should still save me considerable time. I'm still trying to work out the best way to do the chimney though...

My plaster should be here later today so I will make the molds probably tomorrow and post the results here for anyone in the future.

Edited by arpetrone

Share this post


Link to post
Share on other sites

arpetrone-

Regarding the chimney:

Do you have access to an extruder? If so, a square hollow die would make quick work of it, especially if you can find method for applying the stone texture. 

Look at fabrics like netting or a potato bags. If you can find a sidewalk or paving stone that has raised/exposed pebbles you can make your own texture tile or mat. A 1/2” thick  slab of clay pressed against one of these should give you a “negative” of that surface, and then bisque fire it before using it on either an extrusion or slab. Dust the surface with dry clay powder before pressing it against you original texture  so it will release easily. Actually it doesn’t matter much what type of powder you use, as long as it doesn’t melt or flux in the bisque.

Alternately you can make your texture  “mold “ or mat by using  a silicone or latex mold compound, using an appropriate release agent.

Another possibility is to crush a bone dry slab of clay ( about 1/8 inch thick) with a rolling pin to make your own “rocks” which you can press into the soft clay and leave it embedded  in the chimney shape, dry that and fire it.

Lots of possibilities! And think - each one will be unique. Enjoy

BTW. How big are your cabins?

Regards,

Fred

Share this post


Link to post
Share on other sites

I don't have access to an extruder unfortunately, at least not one that would be large enough for the chimney anyway, I don't think. 

It's that the chimney is hollow that's giving me pause about how to go about it, otherwise I would just do a press mold. I'm thinking I could still do a two piece press mold, where it's split down vertically, but I would have to line each half of the mold with a thin slab or clay and push it in, scoop out the center and then shove them together??

Very interesting ideas for quicker and unique textures.

The outside dimensions of the cabins are roughly 6.5in x 6in x 7

Share this post


Link to post
Share on other sites

If I am understanding your design correctly you could make a separate press mold for the chimney and then attach it to the cabin.   Many molds are two or three pieces,  you can go back and add details and undercuts after it has come out of the mold also.   You can find the type of finessing in commercial pottery if you look closely.   Denice

Share this post


Link to post
Share on other sites

That's exactly my plan. So far I'm planning three separate press molds for the pieces of the cabin and the chimney and a tile mold for the two halves of the roof. It's that the chimney needs to be hollow and go through the roof to access the interior of the cabin that I have to think about how to do it differently.

I would like as much as possible of each section of the house to be reproduced within the molds, as it will still take me time to assemble, clean up everything, then add details to make each unique.

I could probably just make a single large press mold for all the parts that need pressing but I figure smaller molds would be easier to work..?

Edited by arpetrone

Share this post


Link to post
Share on other sites

Just poured the first batch of plaster...aye aye aye it took forever to get all the parts seated in the clay hopefully to the half way mark...

I also think my water was way too cold because the plaster is taking forever to set...I also hope it wasn't too liquid when I poured but I let it sit for at least 10-15min after mixing to try and let it thicken up.

Share this post


Link to post
Share on other sites

I'm wondering if it is only important that a mold be completely cured when slip casting? Can I use a press mold sooner? What would happen, it just might take longer to release the clay?

One other question, should I use a powder to help in the release of clay from press molds or just let it go naturally?

Share this post


Link to post
Share on other sites

Make sure mold is completly dry for press mold or any mold. Do not use powder or anything other than a dry mold.

It takes some time for a newly made mold to dry-blow air across it to speed drying

 

Share this post


Link to post
Share on other sites
On 4/7/2019 at 3:28 PM, arpetrone said:

I'm wondering if it is only important that a mold be completely cured when slip casting? Can I use a press mold sooner? What would happen, it just might take longer to release the clay?

One other question, should I use a powder to help in the release of clay from press molds or just let it go naturally?

Even for press-moulding, the mould should be properly dry.  If it's not, the pressed clay will take forever to release, and will release unevenly, with risk of cracking.  Ask me how I know this?

Share this post


Link to post
Share on other sites

Are you saying the clay will crack or the mold?

i waited until all the molds were dry (not cold) to the touch - today I was pressing some clay in one and it cracked right in half...Maybe I was pushing too hard? The mold is only about 12 inches long

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.