Help!: Mortar or adhesive? pointing or grouting? - terracotta tiles on gypsum screed.

[piggy]

Hi again

we were last in touch around Christmas last year about laying terracotta tiles on a gypsum screed. We established that we needed to install the GSHP and dry out the screed before tiling. UFH has been running since mid March and is now at 25 degrees C so conclude it should be dry.???!!!
We'll seal the screed before laying the tiles.

The tiles are handmade and quite uneven so will need atleast a 10mm bed.
Options

• 15mm-20mm sand/cement mortar with SBR latex additive to add flexibility. Pointed with same.
• 10mm PCI thick bed adhesive which we can either grout with risk of staining very porous tiles or could we point them up with mortar as above?

The first option is the cheapest and prefered option but we'd like feedback from anyone who has tried it or can point to the pitfalls.

Grouting terracotta rather than pointing, even after sealing them, seems a bit risky.

Many regards
Piggy

[Brinkley]

you will nee to seal terracotta about 7 times

[Dave]

Which brand of screed was it again.?

[timeless john]

A hand made Terracotta - who from.
Even with the roughest stuff a fast set flexible thick bed adhesive will do for most terracotta.
Personally I dust down and seal all terracotta and stack on edge to dry when they are unloaded.
The depth of colour usually depends on the type of tile and make of sealer - again I use a mixture of boiled linseed oil and white spirit.
Keep the face clean when fixing with a damp sponge and when completely dry give another coat of seal.
Before they introduced sandstone grouts we used to use a soft sand/cement mix to grout and by doing a small but decent area at any time, we never had a problem removing the grouted mix.
One of the nicest tile finishes around.
This is of course a brief outline and the correct seal mix/ drying times/etc are all just a small part of gaining a reduced maintenance floor which should improve with age.
(might change my handle to Terracottajohn.)

[piggy]

Hi Dave

Thanks for coming online. Floscreed pumped gypsum screed.

[Dave]

Not one i know.. is it a low laitence screed..? you might need to sand it first to remove the thin unstable top layer or ig low laitence then a quick sand to remove surface contamination before priming.. I would if i was you think about an epoxy primer as this will give better protection against calcium reaction with your choice of adhesive bed.... as for the rest then follow TJ's advice.. but please do make sure the pre of the screed is done right.. this is paramount for a trouble free installation.

[piggy]

Thanks John . That's really useful information. The tiles are York Handmade and we really want to keep the natural colour and finish rather than linseeding and polishing them.

what sealer/impregnator would you use and how many coats? Any tips you might have on the process would be greatly appreciated.

[doug boardley]

LTP Mattstone will have minimal impact on the finished look of your terracotta, but will give a good impregnating protection. Amount of coats will depend on porosity

[piggy]

It is low laitance. We intend sanding & prepping it thoroughly - how much sanding do low laitance screeds need? From reading old threads & what you say, an epoxy sealer would be better than the acrylic based one Floscreed supplied us with.

[piggy]

Thanks Doug - is that a better product than hg impregnator?

[doug boardley]

Thanks Doug - is that a better product than hg impregnator?

without a doubt piggy, and I speak from experience with both

[Dave]

Do a test seal on a spare tile/off cut.. Mattstone can darken slighty... so check before you go ahead on all of the tiles and you seal to the point of saturation..

[piggy]

Thanks for that - would you seal them to saturation before laying or before grouting?