Dry greensand for lost foam...?

I was thinking about attempting my first lost foam pour this mother's day weekend. ...and yes as you may have guess the end result will be a mother's day present.

The idea is to make a little plaque that will incorporate artistic details done by the kids. I was thinking the easiest way for me to pull this off is to get them to draw something, tape it to a piece of the pink foam board, and then router it out.

My only real problem, beyond not ever attempting lost foam before, is the sand I need to bury the pattern into. I don't have anything on hand other than my greensand. The bonus here is I haven't used it in about 1-1/2yrs so any moisture content will be from climate exposure.

Can I get away with using greensand for a lost foam pour..?

All hand holding on presented on this will be greatly appreciated...lol

 

If it runs and pours it should be fine. Vibrating a plastic bucket with a hammer works well, I'd put the flat side mostly down to make sure sand falls into the details. Are you planning to mud it? (I highly recommend that, thin it down to thick latex paint consistency) My first big mistake was not making a ring groove around the sprue opening to catch any over fill and it ran across the sand and caught the bucket on fire. A little trough in the sand fixes that.

Waiting for the pictures!!

 

I was doing some quick research on our forums and found mention of "mudding" the foam form. I have a box of drywall mud that's gone crispy on the outside which means it's too annoying to bother with for it's original purpose. May as well coat the foam with it.

I'm going to assume that if I do cover it with mud, I'll have to make venting efforts...?

 

Your sand should be OK, especially if you mud the plaque. Some lost foam has been done in rammed greensand, but I think that is overkill.
Depending on the size and thickness, I prefer a vertical or slanted orientation. Gravity is your friend and the angle eliminates voids in the underside where the detail is. Vibrate or settle the sand to be sure it fills any undercuts.
I don't add any venting or risers.
If this is your first time I would make a dummy piece about the same dimension as the project and pour it first. The initial fill action is not something we are used to with a conventional mold. I use Kush head made from a soup can, but a taped cone works too.
Pour hot for the first test.

 

Thin your drywall mud. Think really soupy milkshake consistency. Let it dry and do it once more. It's 2 really thin coatings you are looking for then you can bury it in catpoop and it should come out fine. Here was my first casting.... This was done with foam, dry wall mud and a bucket of rocks. I was destined to screw with ceramic shell right from the beginning.
AWWW... The good ol days.

 

I'm getting good results with one coating of mud. Thin milkshake is a good description.



I let it vent back through the sprue. I just use an aluminum foil pouring cup. I don't pour particularly fast but you have to keep pouring because after you think you've got it full it will feed and need more material. This is one of my cones today, doubled aluminum foil, mashed and formed around a 1/2" square sprue.



Then I finish filling the bucket with sand and lay a piece of sheetmetal on the edge of the bucket to shield the bucket from the crucible radiant heat.

 

Thanks for the advice guys... All will be applied over the next few days.

I was hoping to have an overall thickness of nothing more than .5", but I couldn't find any of that pink foam board any thinner than 1". I don't have anything to slice it thinner, but depending on the size (undetermined) I might be able to rip it in two passes on the table saw...lol

I'll be sure to make at least two "foamies" for sake of having a back up. ...and drywall mud will be used.

There's a sand pit a few minutes walk down the street from me. I'm thinking I'll embrace my inner cheap self and grab a few buckets rather than pony up for play sand at HD.

 

It rained last night