Plywood concrete mold, what to coat it with? - Page 1

[ARCHIVED THREAD] - Plywood concrete mold, what to coat it with?

Posted: 5/24/2015 3:37:54 PM EDT

I want to make a reusable mold for concrete out of plywood. What is a good thing to coat the plywood with so the concrete comes out smooth and the mold itself doesn't get beat up? I thought of using melamine to make the mold until I realized it was made of particle board.

Posted: 5/24/2015 3:50:50 PM EDT

[#1]

We always used form oil on plywood, you can roll or spray it on.

Posted: 5/24/2015 5:42:46 PM EDT

[#2]

Use a decent grade of plywood and build up a layer or two of Johnson's paste wax. What shape are you wanting to cast and how many pours are you hoping to achieve?

Posted: 5/25/2015 9:14:21 AM EDT

[#3]

It will be hexagonal, flat bottom and straight sides, I would expect to do 30-40 pours in it.

Posted: 5/25/2015 9:41:51 AM EDT

[#4]

We used to use diesel fuel for forms but it is verboten now on state and federal jobs.

Posted: 5/25/2015 9:43:12 AM EDT

[#5]

Form oil.

Pretty much any type of oil will work if you don't mind discoloration.

Posted: 5/25/2015 6:14:51 PM EDT

[#6]

Melamine coated in olive oil (cooking spray or brushed on) works great. Yes it's particle board but it works fine as long as your considerate with screw placement each time you reassemble it.

Posted: 5/25/2015 6:41:58 PM EDT

[#7]

Diesel, corn oil, Pam

. Whatever is handy.

Posted: 5/25/2015 8:05:36 PM EDT

[#8]

Quoted:
I want to make a reusable mold for concrete out of plywood. What is a good thing to coat the plywood with so the concrete comes out smooth and the mold itself doesn't get beat up? I thought of using melamine to make the mold until I realized it was made of particle board.

View Quote

we always used to use transmission fluid on forms.

J-

Posted: 5/25/2015 8:06:24 PM EDT

[#9]

The second time I poured a concrete shooting bench top, I used used veggie oil. Had a ton of it that was old and just poured it into the mold and then wiped it with a paper towel leaving a pretty good coating. Tabletop came out looking pretty good except for some minor honeycombing.

Posted: 5/25/2015 9:34:50 PM EDT

[#10]

50/50 diesel fuel and motor oil don't get caught with it on state jobs though.

Posted: 5/25/2015 10:30:44 PM EDT

[#11]

Maybe use UHMW?

Posted: 5/25/2015 10:39:02 PM EDT

[#12]

If you want 50 pours, use something like this to build the form. Coat it with diesel fuel as stated above.

This stuff will hold up to the vibrator and hammering out the bubbles. It is pricey though.

Posted: 5/25/2015 10:47:37 PM EDT

[#13]

If you want it really smooth use melamine ( plywood coated with plastic ) this will give you a smooth product over and over , just make sure you "puddle" the form well as you pour ( tap on form with rubber mallet to reduce air pockets )

Any regular plywood that has a rough surface will produce a rough finish on your product. Also the rough plywood forms tend to stick more to the concrete thus making the forms harder to strip off and reuse

Posted: 5/26/2015 1:03:10 AM EDT

[#14]

Quote History

Quoted:
Maybe use UHMW?

View Quote

that would be the way to go on a small, reoccuring job. Kinda expensive for bigger stuff.

J-

Posted: 5/26/2015 1:43:09 AM EDT

[#15]

I believe Symons uses a phenolic resin coated plywood. You could probably do just fine with melamine or even an epoxy resin over baltic birch plywood. You would still probably do well to use some sort of form release agent. In the good old days we used form oil cut 50/50 with diesel. The stuff stinks.

Posted: 5/26/2015 6:52:42 AM EDT

[#16]

Quote History

Quoted:
I believe Symons uses a phenolic resin coated plywood. You could probably do just fine with melamine or even an epoxy resin over baltic birch plywood. You would still probably do well to use some sort of form release agent. In the good old days we used form oil cut 50/50 with diesel. The stuff stinks.

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this. Phenolic plywood.

If you do a search, it can be found at contractor's yards that sell to those who work in the trade.

Posted: 5/26/2015 6:58:07 AM EDT

[#17]

Quote History

Quoted:
The second time I poured a concrete shooting bench top, I used used veggie oil. Had a ton of it that was old and just poured it into the mold and then wiped it with a paper towel leaving a pretty good coating. Tabletop came out looking pretty good except for some minor honeycombing.

http://i126.photobucket.com/albums/p111/Albinator/Shooting%20bench%20pics/IMG_20150214_102926863Large_zpse109e304.jpg

View Quote

If/When you do another pour, use a palm sander to vibrate the concrete after you've filled the mold.
It will help pack the concrete and should alleviate or minimize any bubbles.

Posted: 5/26/2015 9:34:17 AM EDT

[#18]

Quote History

Quoted:

If/When you do another pour, use a palm sander to vibrate the concrete after you've filled the mold.
It will help pack the concrete and should alleviate or minimize any bubbles.

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
The second time I poured a concrete shooting bench top, I used used veggie oil. Had a ton of it that was old and just poured it into the mold and then wiped it with a paper towel leaving a pretty good coating. Tabletop came out looking pretty good except for some minor honeycombing.

http://i126.photobucket.com/albums/p111/Albinator/Shooting%20bench%20pics/IMG_20150214_102926863Large_zpse109e304.jpg

If/When you do another pour, use a palm sander to vibrate the concrete after you've filled the mold.
It will help pack the concrete and should alleviate or minimize any bubbles.

How exactly do you get this to work?

Posted: 5/26/2015 10:53:08 AM EDT

[#19]

Hold the sander against the outside of the form using the rubber backing pad only, no sandpaper. The vibration causes the concrete to settle, and the air bubbles in the concrete to break loose and rise to the top. It's not going to be perfect, but it will likely help. The bigger the form, the more vibration you need. Also, I don't think a true random orbital sander will work, it ought to be one of the cheap 1/4 sheet style sanders.

Do a youtube search on making concrete countertops. I'd post a video link, for you, but I don't think I can as a non-member.

Posted: 5/26/2015 1:17:42 PM EDT

[#20]

Quote History

Quoted:
If/When you do another pour, use a palm sander to vibrate the concrete after you've filled the mold.

It will help pack the concrete and should alleviate or minimize any bubbles.

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:

The second time I poured a concrete shooting bench top, I used used veggie oil. Had a ton of it that was old and just poured it into the mold and then wiped it with a paper towel leaving a pretty good coating. Tabletop came out looking pretty good except for some minor honeycombing.

http://i126.photobucket.com/albums/p111/Albinator/Shooting%20bench%20pics/IMG_20150214_102926863Large_zpse109e304.jpg

If/When you do another pour, use a palm sander to vibrate the concrete after you've filled the mold.

It will help pack the concrete and should alleviate or minimize any bubbles.

Well I'll be go to heck! That's a great idea! And I do have a Bosch palm sander, never thought about using it. On the first pour, I did try my Dillon case cleaner vibrator, but it didn't seem to put any vibration into the mold at all, so I quit using it.

Thanks!

Posted: 5/26/2015 6:00:33 PM EDT

[#21]

Is it possible to slope the side walls even 1/8"? If you are able to build draft into your form you could stripped it without removing the sides.it is pretty difficult to do this many pours on one form and keep your dimensions and appearance good.

Posted: 5/27/2015 3:39:00 PM EDT

[#22]

We used to get used fryer oil.

[ARCHIVED THREAD] - Plywood concrete mold, what to coat it with?

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