Cracks in SLC UFH layer

[hillhead]

Shrinkage in the SLC or gaps below for it to escape etc can all play a part in this.
Was the SLC mixed properly( right ratio of water/powder)?

 

[jshollick]

Yes. The ratio was 4.25 Litres water per 25 kg of SLC, mixed with mixer paddle on electric drill. The Wickes mix was more fluid than Ultra so where they met the Ultra may have thinned a little.

 

[Del W]

What primer did you use? Did it say on the SLC bag to prime ?

 

[Stewart]

Sounds to me like the insulation boards are compressing under foot traffic causing the slc to crack. If its the type of board I'm thinking, they don't like being point loaded and compress quite easily.


Created on iPhone.....

 

[Ajax123]

If it is hollow it is knackered....... When the same thing happened to me i overboarded with 6mm hardi backer screwed down. Be careful notto screwthe cables though

 

[jshollick]

Thanks Ajax123 that's really helpful and has cheered me up no end! Where can I get supplies of this board.
How would I screw it down as there is 8mm slc, 50mm foamboard and then concrete. Is there a special screw to attach it to the foamboards? Would not priming the surfaces and using good flexi tile adhesive be the only way to fix Hardieboard. I am not walking on the floor now except on boards on the top to prevent making things worse as cracks are now appearing in more places. I shall leave alone for now, let it dry more and see what happens and then use these boards, all being well.
Do you have any more tips that will get out of this situation?

Thanks again!

 

[jshollick]

Yes, they look like ice cream wafers and do compress easily. Walking over it to decorate could not have helped. The Hardie board on top looks a way out of the problem.

 

[jshollick]

The technical sheet says to prime on porous and wood surfaces only. The supplier of the boards said they did not need priming.

 

[jay]

NOTES
1. James Hardie Underlays are suited only as a substrate for tiles on
timber floors. For tiling of walls use Villaboard® lining.
2. James Hardie underlays must not to be used on concrete slabs. To
build up height of concrete, purpose-made concrete levelling
compounds are more suitable



http://jameshardie.com.au/products/...Underlay+&+Vinyl+and+Cork+Underlay+Jan+12.pdf