Hey ! So the title basicaly says it all ... but how can I do a strong and re-usable cardboard mold for a concrete obstacle? Need some tips !
I have already heard I need to use some sort of protection to the inside like duck tape (or that adhesive layers you use to protect your school books) in terms of protecting the cardboard from the water and make the concrete surface smooth
Some people also use an anti adherent spray to prevent the concrete from sticking up but I'm not sure if that applies to the case since it's cardboard ...

Anyway , SHARE YOUR KNOWLEDGE !

I too would be interested in an answer for this, looking to make a barrier with a cardboard mold.

Vizq wrote:

I too would be interested in an answer for this, looking to make a barrier with a cardboard mold.

same here

I've used Vaseline to avoid the concrete sticking, works great but it's not 100% smooth. Might just be how I apply it, though, you can probably get it smoother.

I use PAM cooking spray to help prevent sticking in my molds...
Not sure how that would work for cardboard...

When I used to make molds from wood.. I would clear coat the inside of the mold to help make a smooth surface...
This might help with your cardboard... just not sure about the strength of cardboard...

Thanks for the tips ! I'm still doing some research about all this ... And ofc the cardboard needs to be super strong!
But yeah , I will experiment some stuff and If everything goes out as I planned I will make a tutorial and post it here !

More opinions are welcome

I have been trying out concrete molds, have had some success. I spray lacquer in the mold to make it smooth and then once that's nice and dry I spray pam. here is a pic of a mold I did. I doodled on it so don't judge me on my lack of artisticness

i just tape the cardboard with many layers so it wont get wet from the crete also makes it stronger!

I have a friend who did both of them , tape and some kind of oil ! Good to know I can only use tape

Alright ! And what about the amount of cement and water?
It's X amount of concrete + X/2 amount of water , right?

I just add cement to the bucket and then add water, mix, repeat. till the mix is right. I always make it a little runny so the bubbles cam get out and also it fills the mold easier. im sure some of the other guys have it dialed to a ratio

Ohh yeah ! So if the concrete "paste" is too consistent (too much concrete per water) it will create those air bubbles in the obstacle?
Besides that what can I do to prevent bubbles?

didi.kid wrote:

Ohh yeah ! So if the concrete "paste" is too consistent (too much concrete per water) it will create those air bubbles in the obstacle?
Besides that what can I do to prevent bubbles?

first off I have only with in the last month been trying out concrete.
but am pruty sure that the bubbles will be there no matter what. I tap against the side of the mold with a screw driver handle and bubbles come up every time. another thing you may or may not have thought of is to make some sort of rebar to make it stronger. I made a few parking blocks that just broke cause I didn't use rebar. chicken wire works good. ive even used paper clips.

But usually the bubbles dont come to the surface of the ledge, right? They won't affect the ledge performance unless they come to the surface (I think)

I actually thought about that too ! But I was thinking of making one without it first to work on the mold and re-check the measures and then experiment to do a parking block with a metal bar... Chicken wire? u wrap it or something like that ? make a role of wire , maybe ?

i just cut sections out and stick it in the concrete to act like rebar. chicken wire is like fence so sections of it work as rebar perfectly. paper clips is what i used first and a box of those are cheaper than a roll of chicken wire. im sure some one with better advice will be lurking around here sooner or later. i found out that the cret brakes easy without rebar