Cement advice

sillygoose

Hi,
I never seem to have much luck with cements so avoid the stuff!

I need to make some for bedding down a shower tray to a plinth I have built. Google suggested 4 to 1 mix.

Made some up yesterday as a test, 4 scoops building sand, 1 scoop rapid setting cement. It started to go off as expected after 30 minutes. Looked at it this morning and its set hard and gone light colour but is disappointingly brittle, can snap bits off with my fingers - this is always the problem when I try to make cements (Compared to the stuff the builder made when he did some garden landscaping his is as solid as stone!)

Its a high quality resin tray with upstands that I have rebated into the 3 sides and I will be tiling down into so I want it set as solid as a rock so the overlapping tiles are not stressed by any flexing.

Any advice where I am going wrong?

Thanks.

crazyguy

did you put this down on a wooden floor, if so best to put a pva glue and water mix down first,
you should lay this onto marine ply board,
paint with pva and water mix
The base should idealy be 5-8mm
Allow to set, then add a silicone seal around the cement base and wall area below the tray.

I think a 5 to 1 mix is better here,

sillygoose

crazyguy wrote: »

did you put this down on a wooden floor, if so best to put a pva glue and water mix down first,
you should lay this onto marine ply board,
paint with pva and water mix
The base should idealy be 5-8mm
Allow to set, then add a silicone seal around the cement base and wall area below the tray.

I think a 5 to 1 mix is better here,

Hi,
No not laid it yet, it will go onto a sturdy wood plinth topped with marine ply when I'm ready.

Having had trouble with cement before I made up a test batch and left it to set just to see how it turned out.

So you think its the cement that makes it brittle and increasing the sand to 5-1 wil make it tougher?
Cheers

DVardysShadow

sillygoose wrote: »

Made some up yesterday as a test, 4 scoops building sand, 1 scoop rapid setting cement. It started to go off as expected after 30 minutes. Looked at it this morning and its set hard and gone light colour but is disappointingly brittle, can snap bits off with my fingers ...

Any advice where I am going wrong?

Thanks.

Wrong? It's your expectations.

Cement takes time to come to strength. Currently it is set, but not cured. Concrete is only tested for strength at 28 days and gets stronger over decades. It does not really come to useful strength until 1 to 3 days.

If you want to accelerate the process, leave your set cement in a bucket of water for half an hour and try its strength again after about 6 hours.

crazyguy

5-1 mix is fine for this but as per DVardysShadow comment it does take time to set properly, I would if you can leave it for a few days before setting the tray down at least 2 if poss,

sillygoose

DVardysShadow wrote: »

If you want to accelerate the process, leave your set cement in a bucket of water for half an hour and try its strength again after about 6 hours.

Curious! will give it a go.. .tis' witchcraft this cement stuff!

Actually it does seem to be going tougher by the hour.

ormus

normally takes anything up to 30 days to reach its real strength.
certainly itll be very green for the first few days.

MX5huggy

Are you using any plasticiser? A drop a Fairy is the old trick, seems to work, would not use this outside.

tpt

if your onto wood get a bag of single part flexible tile adhesive instead -as long as the bed isnt much thicker than 15mm

sillygoose

tpt wrote: »

if your onto wood get a bag of single part flexible tile adhesive instead -as long as the bed isnt much thicker than 15mm

Hadn't thought of that! (been following the instructions) but I can do tile adhesive OK, would be 'stickier' too I suppose. Thanks, may have some knocking around come to think of it..

anotherbaldrick

Are you using cement from a bag that has been opened some time previously (week ) If so cement will be DEAD .ie moisture in air will have initiared chemical setting preocess.