# Forum Home Renovation Bathrooms  Cement bedding under bathtub??

## Brettus

Just about to install a bath and after some advice / experience on what people have used to bed the base of the bath tub into.  Its an acrylic bathtub. 
Last bath I installed I made a bed of sand / cement (4-1 mix) underneath as per manufacturers specs, then fitted the bath into the mix, jiggled it in, then set some medium weights in it with the intention of holding it to the mix and hopefully bonding.
That didnt really work because now when you stand in the bath you can hear some crackling which is evidence there is space between the base and cement.  It is very solid though, so not a disaster. 
Anyone got any good methods of bonding the base of the bath to the sand / cement, or is it better to use mortar as that would bond a bit better?? 
Any suggestions will be much appreciated.
Cheers

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## Bedford

Hi Brettus, I would do what you did last time but without the weights, I think this probably slightly distorted the bath shape which sprang back and left a gap between the bath and mortar. 
When ever I've installed them, I get it set up, put the mud in place, gently wriggle into place and when it's used, no movement or squeaks. :Smilie:

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## r3nov8or

Yeah, you're on the right track. Make sure the cement is a slurry (i.e very wet - pretty sure the instructions will say that - mine did) so the bath can easily make its way into the mix. Built a box to hold the slurry until it went off (again, as in my bath's instructions)

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## Brettus

Cheers guys I reckon both your points are spot on, and yes the manufacturers install guide did say a wet mix.  All good Im sure this one will work out a treat, I will let you know, not that it will be quick because I still havent got the bath or tiles yet.

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## Oldsaltoz

This is normally done with bath fully installed so not possible to wrigle it into position. 
This means that in most cases you will only have access from one side; the following may help. 
Look around for some old bricks or blocks and use them to retain the wet mix, untreated timber should never be left in this area. 
Start by pushing the mix to the far side of the bath and establish a slight overhang along the far edge, work back towards the front making sure no voids are left under the bath, leave a small lip at the front as well. 
No weight is needed in the bath and you are not looking to stick the bottom of the bath to the support fill. 
Hope this helps.

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## Vernonv

I actually think a wet (or overly wet) mix is a bad idea. The more water in a mix the weaker it is and the more is shrinks.  
I've only done one bath and used a fairly dry mix (i.e. it was "self supporting" and didn't need any form-work. After raking it to get roughly right level, I squished the bath into the mix and then just let it dry (no weights or anything).  
It doesn't make any cracking or sand crunching noises and feels very solid.

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## r3nov8or

> I actually think a wet (or overly wet) mix is a bad idea. The more water in a mix the weaker it is and the more is shrinks...

  Well, you know, I'd rather trust the bath manufacturer on this one.

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## jago

Bondcrete (check manuf. instructions) the area of bath you want to set ... should help stick like @@@@ to a blanket! :Biggrin:  
Or save your self  the hassle and buy a freestanding bath.

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## Vernonv

> Well, you know, I'd rather trust the bath manufacturer on this one.

  So would I ... and I did ... and it worked very well. 
Funny thing is, I checked out a lot of different install inststructions for baths from different manufacturers (to get an idea how other manufacturers install theirs) and I don't recall any of them mentioning using an overly wet mix or form work.

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## Vernonv

Here's a couple - 
From Decina  

> Mix the mortar to a dryish consistency tominimise shrinkage and droop

  From Lannark  

> ... a minimum 50mm thick (wet enough to be pliable)

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## plucka32

hey guys, when i did my bath the plumber told me that a good way to support the bath is to use expander foam in a can. just spray heaps all under the bath and let rise into position. also told to half fill the bath so it sits nice and even. i followed this and have had no probs with the bath. hope this gives u another idea on how to do it. cheers :Biggrin:

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## Brettus

Hey all, there is a few opions around.  One thing I have heard (cant remember where from) is that exandable foam is not a good idea. 
Just reading Lanark instructions now, and yes it does say "wet enough to be pliable" I reckon people confuse this with "make a wet mix". 
It also says 6:1 sand / cement mix which seems a bit too much sand, everything ive done is about 3:1. 
And I agree boncrete or an agent like isolastic would work well. 
Cheers

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## intertd6

expanda foam under bath is a no no, will gradually fail, ok for insulating around the bath though, 3:1 mix is ok if its a dry mix, but its really for packing under high stressed structural base plates where high strength is needed, dry packed (moist) 6;1 would be fine.
regards inter

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## r3nov8or

> So would I ... and I did ... and it worked very well. 
> ...

  Mine worked very well too. Yay for us  :Smilie:

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## multiblade

lol i just did a medium mix... and half filled the bath, which provides a perfectly even weight down.
Dont knoe if that was needed but no pro*blems*

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## autogenous

Mix a screed mix which is like bread crumbs damp.  That prevents shrinkage.   
Have the bath set in place where you want it prior to packing.   
Use bricks if you want help with slump prevention but keep them at least down 50mm from the underside of the bath that's if the bath sits that high off the ground you are packing. You need to get your hands right through under the bath. 
Start pushing in the damp cement crumble with rubber gloves on till you are packed even across the base the manufacturer specifies as the place of support. 
Packing a bath is only to stop the bath from cracking or moving under extra heavy load. 
Packing is not to hold the bath down.   The bath should be solidly set prior to packing underneath. 
3 buckets of sand, 1 bucket of Portland Cement 
Expanda foam is expander which can pop the bath or warp it.  It can break down over the longer term too, especially if exposed to water under load.   
That goes the same for many aspects when using foam.  The expansion can blow or crack lots of objects.

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## ScroozAdmin

Mine is sat quite high in a hob so I put it on besser blocks with a 2" fairly wettish screed as it had to be bedded so the weight of the edges was supported on the frame, it took a fair amount of adjusting to get it right but seems OK.  
The whole thing was a major faff tbh and next time I'll definately get a more expensive bath with a metal frame and adjustable feet.

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