Hi All,

I have just de-molded a couple of panels and they have failed completely.

On the day the temp climbed from 79F to 90F degrees over the time of the spray and pour with it hitting 97F degrees by the time we had the covers on. 

The mold release is water-based and we have not had any problems with it before.

I am using Trinic admix, plasticizer, hydration and hardeners, all within recommended dosages.

The process we followed was:
Mold prep was completed the day before.
  1. Mold release sprayed 30-60 minutes before face coat spray.
  2. Face coat sprayed in 2 batches. One immediately after the other.
  3. First backing coat (same recipe) with 13mm fibers poured in (self-consolidating)
  4. Foam block outs placed and second backing coat poured in (City Mix and fibers). 
  5. Scrim added.
  6. Final backing coat (City Mix and fibers)
  7. Black builders plastic covering, electric blankets, painters coth drop sheet for 24 hours. Electric blankets turned off after 12 hours.

We have seen the patching in the middle of the slabs before. They were caused by the cement interacting with the satin board (from Laminex Industries). We find this is more likely to happen when we order larger sheets in 18mm thickness. 
We have never seen the cracks/crazing around the edges before and have no real idea what has gone wrong. 
If we were to hazard a guess we think the slab has dried too quickly but we had used this exact process before without problems. Any clues as to what we should be changing? 
Is there a way to repair the cracks? (I'm hoping some grouting work may bring the slab surfaces back up to an acceptable state).
Cheers.

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If it was 97 degrees there is no need to put a heating blanket on it. In the summer I just put  plastic over it. Definitely looks like a moisture problem. How long did you wait before you put your backer coat over your facecoat?? May be that your facecoat dried out before you put your backer coat on it.

Hi Guido,

We often need to wait up to 20 minutes before we apply the first backer coat. In this case, the wait was only about half of that. The temp was still below 30 degrees (Celsius). We also sprayed the face coat with mist before applying the self-consolidating backer. We also used about 40% ice in both the face and backer coats to help retard the set time.

Having said all that, I agree with you that the most likely cause of the cracking/crazing is that the face coat dried out too soon. Unfortunately, we have had very high temps over the past week and I think the slabs are beyond repair as far as the customer is concerned. It is a very high-end kitchen and these slabs were for a stand-alone island that is the focal point of the kitchen.

It looks like we will have to start all over again for this job.

Cheers.

Sounds like wet mud baking/cooking/frying in the hot dry sun and cracking/fissuring on a huge pervasive scale.

aka it seems like theres wayyyy too much heat too fast. I'm pretty novice with concrete though with a huge love for phsyics.
With that much heat that quickly you better have that think submerged :P

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