Making foam armrests on the cheap!
November 27th, 2015, 06:08 AM
#1
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Join Date: Sep 2015
Posts: 32
Making foam armrests on the cheap!
Hello all,
If you read my earlier post about foam arm rests you will know that I had little luck finding replacements. After a lot of research I decided a mold was going to be expensive. I got to thinking why not cast from a plaster mold? I decided to give it a try.
The attached photos show the results. I started with an $11.00 Bag of Plaster of Paris from Home Depot. I made a small mold box from some scrap plywood and then went at it. My first attempt was to try to do it fast so I mixed a batch of plaster and tried to bed the arm rest into the plaster to the original mold line. This resulted in a lot of porosity and a poor mold.
I decided not to attempt any more short cuts, so armed with an A C Moore 50% off coupon I purchased a 10 lb box of water based clay for $7.00. I used a throwaway chip brush and applied some Carnuba wax to the armrest and placed it in the mold box. I then put clay around the foam arm rest being careful not to compress or distort it. Once I had a reasonably level application to the mold line I put some acorn nuts around it for keys in the joint line. I calculated the volume and mixed and poured the plaster on top. Then vibrated the box to remove the air bubbles and left it to set.
After about an hour I removed the mold box, re waxed it and flipped the mold over. I removed all the clay and wrapped the mold box around it. The first photo shows the result. I repeated the process for the other half of the mold. Once the mold was set I separated the half's and removed the foam armrest. A few small bits stuck to the mold but thank God there was no real damage to my good armrest!
I had some small metal modeling picks I used to scrape the soft plaster. There were some areas of foam missing from the original so I carved out the plaster so the new rest would be complete. I was growing impatient with the process so there are not a lot of photos here. There was an area of the mold that broke when I removed the foam rest and it had to be repaired. I made a clay dam and added some plaster to make the repair. I then stood the mold on end in front of a small fan forced ceramic heater. Placed a cardboard shield on three sides and let it dry overnight.
I had seen a you tube where a guy coated a plaster mold with Mod Podge so I thought I would give it a try. It sticks to the surface of the plaster but did not soak in. As a result it stuck to the foam and made it very difficult to remove. I will tell more about that in a moment. The next one will be sealed with shellac.
I filled a container with water and put the old armrest in the container. Then marked the level of water with a sharpie. I removed the armrest and then added water to the line measuring the amount it took to get to the line (22 oz). Knowing the volume of displacement I weighed the rest and went to the internet to fine a formula to convert to density (17.5 lb per cubic foot).
I settled on a company called Smooth ON for the foam. They sell a product called Flex Foam-it 17 which is 17 lb flexible foam. It was $29.00 plus shipping. I calculated the required amount and dispensed it into some solo cups. I decided to coat the mold with Vasoline and then heat it with the heat gun so it would smooth out the brush marks. Next time wax!
Well I drilled six 1/4" vent holes in the top of the mold where the originals were and set up to pour. After mixing the two component urethane and pouring into the mold, I clamped the half's together and waited 40 minutes. When I went to de-mold the part stuck to the Mod Podge and was very difficult to remove. I ended up breaking the mold! However the foam part came out fine.
You can see in the photos the end result. Though the density is correct the foam is much stiffer then the original. I should have picked a less dense formula from Smooth On for something a little less stiff. Overall I am happy with the results and not willing to spend another $40.00 on different foam. I have enough to make several more and may try to fix the broken mold. For now I need to make a mold of the other side and at least have enough to finish my project before I make any extras.
Hope you found something of interest in this adventure. It was a true learning experience for me. I only wish I had the time and money to try some other materials to get it closer to the original. I know that no one else but me will know the difference.
This Thanksgiving I have one more thing to be thankful for...Foam armrests!!
Jeff K.
If you read my earlier post about foam arm rests you will know that I had little luck finding replacements. After a lot of research I decided a mold was going to be expensive. I got to thinking why not cast from a plaster mold? I decided to give it a try.
The attached photos show the results. I started with an $11.00 Bag of Plaster of Paris from Home Depot. I made a small mold box from some scrap plywood and then went at it. My first attempt was to try to do it fast so I mixed a batch of plaster and tried to bed the arm rest into the plaster to the original mold line. This resulted in a lot of porosity and a poor mold.
I decided not to attempt any more short cuts, so armed with an A C Moore 50% off coupon I purchased a 10 lb box of water based clay for $7.00. I used a throwaway chip brush and applied some Carnuba wax to the armrest and placed it in the mold box. I then put clay around the foam arm rest being careful not to compress or distort it. Once I had a reasonably level application to the mold line I put some acorn nuts around it for keys in the joint line. I calculated the volume and mixed and poured the plaster on top. Then vibrated the box to remove the air bubbles and left it to set.
After about an hour I removed the mold box, re waxed it and flipped the mold over. I removed all the clay and wrapped the mold box around it. The first photo shows the result. I repeated the process for the other half of the mold. Once the mold was set I separated the half's and removed the foam armrest. A few small bits stuck to the mold but thank God there was no real damage to my good armrest!
I had some small metal modeling picks I used to scrape the soft plaster. There were some areas of foam missing from the original so I carved out the plaster so the new rest would be complete. I was growing impatient with the process so there are not a lot of photos here. There was an area of the mold that broke when I removed the foam rest and it had to be repaired. I made a clay dam and added some plaster to make the repair. I then stood the mold on end in front of a small fan forced ceramic heater. Placed a cardboard shield on three sides and let it dry overnight.
I had seen a you tube where a guy coated a plaster mold with Mod Podge so I thought I would give it a try. It sticks to the surface of the plaster but did not soak in. As a result it stuck to the foam and made it very difficult to remove. I will tell more about that in a moment. The next one will be sealed with shellac.
I filled a container with water and put the old armrest in the container. Then marked the level of water with a sharpie. I removed the armrest and then added water to the line measuring the amount it took to get to the line (22 oz). Knowing the volume of displacement I weighed the rest and went to the internet to fine a formula to convert to density (17.5 lb per cubic foot).
I settled on a company called Smooth ON for the foam. They sell a product called Flex Foam-it 17 which is 17 lb flexible foam. It was $29.00 plus shipping. I calculated the required amount and dispensed it into some solo cups. I decided to coat the mold with Vasoline and then heat it with the heat gun so it would smooth out the brush marks. Next time wax!
Well I drilled six 1/4" vent holes in the top of the mold where the originals were and set up to pour. After mixing the two component urethane and pouring into the mold, I clamped the half's together and waited 40 minutes. When I went to de-mold the part stuck to the Mod Podge and was very difficult to remove. I ended up breaking the mold! However the foam part came out fine.
You can see in the photos the end result. Though the density is correct the foam is much stiffer then the original. I should have picked a less dense formula from Smooth On for something a little less stiff. Overall I am happy with the results and not willing to spend another $40.00 on different foam. I have enough to make several more and may try to fix the broken mold. For now I need to make a mold of the other side and at least have enough to finish my project before I make any extras.
Hope you found something of interest in this adventure. It was a true learning experience for me. I only wish I had the time and money to try some other materials to get it closer to the original. I know that no one else but me will know the difference.
This Thanksgiving I have one more thing to be thankful for...Foam armrests!!
Jeff K.
November 27th, 2015, 07:39 AM
#2
Registered User
Join Date: Dec 2011
Posts: 7,286
Very ambitious. I can see where the plaster lets you fix surface imperfections easily. I have used Smooth-on two part mold making compound in runny form to duplicate things.
One trick you may wish to employ- you can place strips and bits of screen into plaster or other mold material which will act like rebar in concrete and make it much more resistant to breakage.
One trick you may wish to employ- you can place strips and bits of screen into plaster or other mold material which will act like rebar in concrete and make it much more resistant to breakage.
November 28th, 2015, 04:24 PM
#5
Registered User
Join Date: Dec 2011
Posts: 7,286
I am making molds tonight and dropped pieces of screen into the runny mold compound.
As long as it does not sink all the way to the part down there, it makes a good strong mold.
http://imagizer.imageshack.com/img911/5913/AHGyv9.jpg
As long as it does not sink all the way to the part down there, it makes a good strong mold.
http://imagizer.imageshack.com/img911/5913/AHGyv9.jpg
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