V-bit choice for MDF concrete mold?

[Shane]

I've got a job and they require some MDF letters cut to create a mold for a concrete slab pour. But am needing some advice on the best angle for mold release.

The 100-150mm high letters will made using 18mm thick MDF. I know the MDF would swell up if placed into the wet concrete but I'll be coating the MDF in Lanolin which should repel any water.

I'd like to know would a 22.5 deg V-bit be the best choice or does it need a bigger angle on it? I was going to use a 45 or 60 degree bit and not have it extend all the way through the 18mm but I think there needs to be a angle on the whole 18mm thickness otherwise it will not release from the concrete.

Shane.

[gc3]

i've done this but we used the prism function in vcp...from experience let me say you'd be better off sealing the mdf letters...we used epoxy

[kevin]

Gene is right the smother the finish the concrete will copy .I use oil based plastic paint never water based it stick to the concrete i found out the hard way

I just finished my most complicated form to date .The angle is unimportant it about the concrete and that takes practice .I think there is huge market for this type of work

[kevin]

Here a recent form the suck was incredible i have to use the form twice .You make it out of rubber but I'am okay with mdf painted