Flex Grout or Sand Cement for Grouting?

[g cambrensis]

Have laid flagstones throughout house and needed advice.
UFH needs to be considered and the adhesive was flexibe. I understand that a flexible grout is the product to be used but the size of the joints are quite big and the flags are between 300x300 and 900x600.
Wanted to know if there was any flexible additive that could be included in a sand cement mix to allow for thermal variation.

Thanks

 

[Terry Cottar]

There are loads of flexible additives for sand and cement but there is a specialist on here who deals specifically with that sort of thing

tel

 

[jimbob]

How big are the joints??

 

[g cambrensis]

Biggest joints are about 20mm
So in principle can sand cement be used?
Thanks

 

[jimbob]

Don't know! You can get flexi grouts though which should be able to deal with those joint sizes - Mapei Ultracolour plus can be used for joints 2-20mm.....

 

[david campbell]

if you have used flexible adhesive over ufh then it will need to be a flexible grout,what you are saying is grouting with mortar and it won't work because it has minimal amount of movent if any!

 

[dock]

The beauty of using a proprietary grout is that the minor additives that help control shrinkage particularly important when grouting a wide joint are already incorporated throughout the mix so there are no batching issues, worries about particle size of the sand and also particle size distribution, the sand is washed dried and graded.
The polymers/co-polymers that provide flexibility are evenly distributed and responsible manufacturers will give a guarantee that their products are free from manufacturing defects.

Weigh this up against the hundreds of polymers/co-polymers that are available most of which have never been properly tested to ascertain if the adhesion of the sand:cement is enhanced enough nor the flexibility/deformability or cement compatibility confirmed. The parcle size and distribution is uncertain as is salt content of the sand because it probably isn't washed

 

[Diamond Pool Finishers]

use SBR mate it's very good in this application