Liquid Screed Options

CPS84

I’m currently looking at options for the different types of liquid screeds and would appreciate opinions on which type would suit my new house best.

On the GF I will have a 60mm screed and on the FF a 55mm screed. Heating will be supplied via UFH from a GSHP which is due to be installed shortly. The GF has 100mm of insulation (2no. 50mm boards over lapping each other) and the FF has 25mm. The house will have good levels of thermal insulation and air tightness.

The liquid screeds options are as follows:

1. Cement based liquid screed (slow conductivity, cheapest)
2. Anhydrate (faster conductivity, mid range price, produces laitance and requires sanding)
3. Alpha Hemi Hydrate (faster conductivity, most expensive)

I’m fairly familiar with the pros and cons of each of these types, but I’m trying to decide which one would suit my house best. As I’m planning to do a lot of tiling throughout the house, I’m inclined at this stage to disregard anhydrate due to the amount of laitance it produces and therefore will require sanding. I know suppliers claim Hemi Hydrate doesn’t produce laitance and does not need sanding before tiling (just priming) – can anyone confirm this from experience?

Therefore based on my screed sizes, heating system and thermal environment conditions would a faster conductivity (Hemi Hydrate) screed or a slower conductivity (cement based) screed be more suitable? The UFH will be kept at a constant temperature i.e. no 'heating up, cooling down', so not really concerned about cheaper night time electricity prices, anyways I plan on installing PV in the long run.

So the big question really boils down to, do I need a slow or fast thermal conductivity in my screed?

CPS84

Bump

BarneyMc

My understanding is with Heat Pumps and UFH a slow conductivity/release floor is best. It means your HP will not go through as many cycles. That's why I'm tending to go with sand/cement on the GF but your cement based liquid screed looks interesting. If anyone has any additional info on this (option 1) then I'd be interested.

CPS84

BarneyMc wrote: »

My understanding is with Heat Pumps and UFH a slow conductivity/release floor is best. It means your HP will not go through as many cycles. That's why I'm tending to go with sand/cement on the GF but your cement based liquid screed looks interesting. If anyone has any additional info on this (option 1) then I'd be interested.

Here is some info on the cement based liquid screed:
mcgrathquarries.com/product_items/flo-screed/

PROJECT K

looking at spec sheet for cement based state min.60mm cover on pipework - therefore you would need min. 80mm if using u/f heating...?

CPS84

PROJECT K wrote: »

looking at spec sheet for cement based state min.60mm cover on pipework - therefore you would need min. 80mm if using u/f heating...?

60mm seems a lot of cover alright for a liquid screed.

BarneyMc

PROJECT K wrote: »

looking at spec sheet for cement based state min.60mm cover on pipework - therefore you would need min. 80mm if using u/f heating...?

Do you mean if pipes are 20mm then add 60mm on top of that which = 80mm in total? In that case 75mm sand/cement might be just as good.

PROJECT K

That's my understanding of the datasheet but might be worth speaking with the manufacturer (not installer) for confirmation. Cement based liquid screed would be a little more prone to cracking therefore requires additional depth, so I wouldn't be surprised if this is the case. Due to poor subfloor installation my screed downstairs (sand/cement) will vary between 60-110mm depth(!!!) therefore I went with reinforcing fibres to give it a little extra resistance against cracking. Whatever about using cement based liquid screed over a thin insulation layer at first floor I wouldn't recommend it over thicker layers on the ground floor - a little too much movement!

BarneyMc

What did you go with in the end CPS84?

My plasterers are finishing up tomorrow (thank God) so will be putting in floors soon.

BarneyMc

What did you go with in the end CPS84?

My plasterers will be finished up tomorrow (thankfully) so will need to make a decision soon. I was initially going to go with a sand/cement based floor but now veering towards a liquid screed. I hope to use my stove a lot and therefore might want a more responsive floor. I'll have an A2W HP, 250mm cavity, block build.

BarneyMc

What did you go with in the end CPS84?

My plasterers will be finished up tomorrow (thankfully) so will need to make a decision soon. I was initially going to go with a sand/cement based floor but now veering towards a liquid screed. I hope to use my stove a lot and therefore might want a more responsive floor. I'll have an A2W HP, 250mm cavity, block build.

CPS84

BarneyMc wrote: »

What did you go with in the end CPS84?

My plasterers will be finished up tomorrow (thankfully) so will need to make a decision soon. I was initially going to go with a sand/cement based floor but now veering towards a liquid screed. I hope to use my stove a lot and therefore might want a more responsive floor. I'll have an A2W HP, 250mm cavity, block build.

After a lot of research and ringing around suppliers I ended up going with Alpha Hemihydrate flowing screed by Fast Floor Screed. One of the main advantages they have is they mix the screed onsite on their own mobile mixing unit (have a look at the video on their website). Other suppliers I spoke with mix the screed at their factories and then deliver to site in a concrete mixer type lorry, issue being that most suppliers of Hemihydrate screeds are based up in the midlands and to keep the product workable while delivering West Clare 2 or 3 hours away would need to be adding additional water on route which could compromise the quality of the screed. To be honest most of them other suppliers weren't too keen to take on the job anyways due to the distance.

Anyways the screeds have turned out excellent, could play billiards on them. In some areas upstairs where the screed was thinner due to slight bows in the structural slab they applied reinforcement mesh. Tradesmen working in the house have passed comment on the quality of them.

Regards

CPS84

BarneyMc

CPS84 wrote: »

In some areas upstairs where the screed was thinner due to slight bows in the structural slab they applied reinforcement mesh.

Thanks so much for your swift reply and glad to hear it worked out so well. Regarding the 'thin' areas you mention, some areas got less than 50mm? Can I also ask are you using a heat pump for your UFH?

CPS84

BarneyMc wrote: »

Thanks so much for your swift reply and glad to hear it worked out so well. Regarding the 'thin' areas you mention, some areas got less than 50mm? Can I also ask are you using a heat pump for your UFH?

There were two pinch points on the first floor that were below 50mm and they placed a reinforcement nylon mesh on these areas.

Yes, I'm using a GSHP with UFH.

Regards

CPS84

Charlie Charolais

BarneyMc wrote: »

What did you go with in the end CPS84?

My plasterers will be finished up tomorrow (thankfully) so will need to make a decision soon. I was initially going to go with a sand/cement based floor but now veering towards a liquid screed. I hope to use my stove a lot and therefore might want a more responsive floor. I'll have an A2W HP, 250mm cavity, block build.

hey barney,
have you considered footpath mix, concrete with 10mm chip, we were told this was ideal for UFH?
is there a reason to plaster walls or lay screed first?

BarneyMc

Charlie Charolais wrote: »

hey barney,
have you considered footpath mix, concrete with 10mm chip, we were told this was ideal for UFH?
is there a reason to plaster walls or lay screed first?

I assume this is a sand/cement mix? Yes considering this at 75mm also. It heats up slowly and releases heat slowly.

I hope to use my stove a lot and am a bit weary of overheating. I'm therefore veering towards the liquid screed now as it's more reactive. On the down side it might mean my HP 'firing up' more frequently which is not great. Hard to know so it is!

Charlie Charolais

BarneyMc wrote: »

I assume this is a sand/cement mix? Yes considering this at 75mm also. It heats up slowly and releases heat slowly.

I hope to use my stove a lot and am a bit weary of overheating. I'm therefore veering towards the liquid screed now as it's more reactive. On the down side it might mean my HP 'firing up' more frequently which is not great. Hard to know so it is!

hey, ya, it's a sand cement & aggregate mix; concrete
the heating is all a balancing act

THE DON FANUCCI

BarneyMc wrote: »

What did you go with in the end CPS84?

My plasterers will be finished up tomorrow (thankfully) so will need to make a decision soon. I was initially going to go with a sand/cement based floor but now veering towards a liquid screed. I hope to use my stove a lot and therefore might want a more responsive floor. I'll have an A2W HP, 250mm cavity, block build.

does your upstairs and downstairs screeds get poured on same day? whats the set up of your ground floor? insulation, concrete, smaller insulation, pipework, screed. sorry for the question if it seems stupid

BarneyMc

THE DON FANUCCI wrote: »

does your upstairs and downstairs screeds get poured on same day? whats the set up of your ground floor? insulation, concrete, smaller insulation, pipework, screed. sorry for the question if it seems stupid

Pour on same day - not sure, didn't ask the installer but I assume yes.
GF makeup from bottom up will be something like:

160mm PIR insulation
50mm liquid screed
15mm tile/laminate
25mm gap to bottom of door

or

150mm PIR insulation
75mm sand/cement
15mm tile/laminate
10mm gap to bottom of door

THE DON FANUCCI

BarneyMc wrote: »

Pour on same day - not sure, didn't ask the installer but I assume yes.
GF makeup from bottom up will be something like:

160mm PIR insulation
50mm liquid screed
15mm tile/laminate
25mm gap to bottom of door

or

150mm PIR insulation
75mm sand/cement
15mm tile/laminate
10mm gap to bottom of door

are your walls plastered and skimmed before the ground floor / first floor screeds are poured?

BarneyMc

THE DON FANUCCI wrote: »

are your walls plastered and skimmed before the ground floor / first floor screeds are poured?

Yip. I've another post here with full details.