Bubbles - Bubbles on the ready products face

[areks]

Hello

I have been trying to produce imitations of stone since some time. I have a problem. On the surface of the ready products wholes appear. They are produced in poliurethane moulds and made of cocnrete. I use vibrating table. I have tried diffrent types of cocrete (dense, thick) as well as plasticise. But the bubbles still appear.
I would like to ask to give me some advice how to minimazie or get rid of the problem at all. Maybe I am doing something incorrectly.

Greetings

Arek

[Tony McC]

There are dozens of possible causes and all you can do is play around with all the variables until you find a combination that gives better results.

Amongst the usual contributers to this problem are...
<ul>
<li> improperly cleaned moulds
<li> poor quality mould release oil
<li> insufficient vibration
<li> vibration at wrong frequency
<li> poor quality plasticisers
<li> poor mix design
</ul>

...and probably a dozen more!

[mouldmaker]

One of the most common culprits (other than those mentioned by Tony) is too much mould oil. This will cause blow-holes, discoloration and make the surface friable and prone to dusting.

[WETCAST]

how long do you mix your concrete for the longer you mix it the more air it gets