SBR screed - PVA instead ?
sm_jamieson
can be used intead. That may well be cheaper.
Certainly when you pour dilute PVA onto plaster / loose screed it
turns it almost plasticky like SBR does.
Anyone heard of this ?
Simon.
Jim K
depends what you're trying to achieve...any clues? :>)
Jim K
sm_jamieson
Well, compared to sand / cement ...
To cure a bit quicker.
Be a bit stronger.
Cope with depths down to 30mm (a bonded screed).
Simon.
Jim K
I think SBR would be overkill and it ain;t (wasn't) cheap when I last
bought.
IIRC SBR's mainly used to make waterproof screeds, concretes etc -
(google for a SBR datasheet - easy enough)
I'd bung some PVA in if you really fancy it.
Tho at 30mm even a decent sand & cement mix should be hard enough
under normal household floor situations.
Don;t kow if either will make the screed cure any quicker? you've got
to give the cement and sand grains time to interlock and carbonise
whatever else you bung in there..
Cheers
Jim K
sm_jamieson
It appears that SBR is more flexible than PVA (being a rubber),
and that PVA can re-emulsify in damp conditions. Not sure about
waterproof PVA / EVA. SBR is more waterproof.
So it appears, SBR is like a "better" PVA.
I am screeding on top of a slab with DPM underneath, so do not require
waterproofing.
I want good adhesion so I can screed in several bays / sections over a
period of time.
So I think PVA may be fine for my application.
I'll have to cost up the job and see what the difference in price is.
Simon.
Tim Watts
> I think SBR would be overkill and it ain;t (wasn't) cheap when I last
> bought.
80 quid or so from Permagard for 25l.
> IIRC SBR's mainly used to make waterproof screeds, concretes etc -
> (google for a SBR datasheet - easy enough)
>
> I'd bung some PVA in if you really fancy it.
> Tho at 30mm even a decent sand& cement mix should be hard enough
> under normal household floor situations.
>
> Don;t kow if either will make the screed cure any quicker? you've got
> to give the cement and sand grains time to interlock and carbonise
> whatever else you bung in there..
>
Personally, for the OP's application I'd stick to the SBR. I wouldn't
substitute PVA to save 80 quid. SBR I can vouch for personally in
screed. *If* the screed gets damp, SBR will not fail and it's tougher
than PVA IME, and penetrates better (it is very fluid). This gives an
excellent bond to old concrete, provided you apply the initial coat of
SBR/water. PVA can have a tendency to not penetrate well, which is fine
on hard concrete, but if it is friable in any way, the bond will be weak.
As to setting: The screed will set faster due to the SBR, but the curing
phase of the cement remains similar to normal. Oh, I forgot to mention
last time, after lating the screed, it should be covered by plastic for
48 hours to allow the moisture to remain in and start th cement cure.
Takes about a further week for 30mm to dry out after that.
--
Tim Watts
Hung parliament? Rather have a hanged parliament.
sm_jamieson
I have about 25m^2 of floor to do, average depth, lets say 50mm.
How much SBR would I need for that area ?
(Sorry for being lazy, I could calculate it myself) !!
Simon.
Tim Watts
> On 02/06/10 09:56, Jim K wrote:
>
>> I think SBR would be overkill and it ain;t (wasn't) cheap when I last
>> bought.
>
> 80 quid or so from Permagard for 25l.
>
>> IIRC SBR's mainly used to make waterproof screeds, concretes etc -
>> (google for a SBR datasheet - easy enough)
>>
>> I'd bung some PVA in if you really fancy it.
>> Tho at 30mm even a decent sand& cement mix should be hard enough
>> under normal household floor situations.
>>
>> Don;t kow if either will make the screed cure any quicker? you've got
>> to give the cement and sand grains time to interlock and carbonise
>> whatever else you bung in there..
>>
>
> Personally, for the OP's application I'd stick to the SBR. I wouldn't
> substitute PVA to save 80 quid. SBR I can vouch for personally in
> screed. *If* the screed gets damp, SBR will not fail and it's tougher
> than PVA IME, and penetrates better (it is very fluid). This gives an
> excellent bond to old concrete, provided you apply the initial coat of
> SBR/water. PVA can have a tendency to not penetrate well, which is fine
> on hard concrete, but if it is friable in any way, the bond will be weak.
>
> As to setting: The screed will set faster due to the SBR, but the curing
> phase of the cement remains similar to normal. Oh, I forgot to mention
> last time, after lating the screed, it should be covered by plastic for
sm_jamieson
I need just over 1m^3 of screed.
The proportions are done by weight.
cement 50kg
sand 200kg
SBR 10kg
water 11kg
So question is, what is the density of the cement/sand.
Anyone know ?
Simon.
sm_jamieson
Well, on the basis of the density of sand being approx 1500kg/m3, and
assuming the cement disappears between the sand grains, I reckon you
need about 75 litres of SBR per cubic metre.
So SBR would cost me around 250 quid.
Equiv volume PVA would be around 150 quid.
Hmmmm.
Simon.
Jim K
well 75 litres PVA even in 5 litre jugs from Wickes is £135
Shurely you can google for a bigger drum.....
Jim K
Bruce
PVA has its uses, and it would be better than no additive in a screed,
but that's about all.
PVA is not the "poor man's SBR". It isn't remotely as good, or
anywhere near as durable.
I have been using SBR in specialist concrete applications since the
early 1980s, when it was new, exotic and extremely expensive. It has
since become a standard building product and is (relatively speaking)
much cheaper than it was then. I cannot praise it highly enough.
Perhaps one day someone will develop an alternative to SBR at
something nearer the price of PVA. But that seems a long way off.
sm_jamieson
Interestingly on permguard site it says for screed over 25mm thick,
reduce SBR quantity by half and top up with water. Well that seems
reasonable.
Simon.
Tim Watts
> On Jun 2, 11:33 am, sm_jamieson<sm_jamie...@hotmail.com> wrote:
>> On 2 June, 11:14, sm_jamieson<sm_jamie...@hotmail.com> wrote:
>>
>>
>>
>>> On 2 June, 10:54, sm_jamieson<sm_jamie...@hotmail.com> wrote:
Sorry, I have lost the start of this thread, so out of band reply...
>>> I need just over 1m^3 of screed.
>>
I missed that last time.
>>> The proportions are done by weight.
>>> cement 50kg
>>> sand 200kg
>>> SBR 10kg
>>> water 11kg
So 1m3 according to
http://www.source4me.co.uk/calculate_floor_screed.htm
would need
1m3 sand, around 1250 kg according to them
425kg cement, so 17 bags
So that's 62.5kg or litres of SBR
If this is 10m2 of floor, you'll need about 10 litres to give it a very
good soaking or 5l should be adequate for a not too mouldy base. Say a
couple of extra litres for cement slurry.
So, for 1x25l + 2x5l from permagard.co.uk, that is 119 including VAT and
delivery (always have a little extra SBR handy for enevitable
misestimates and wastage).
stuart noble
I think the single pack screed mixes are pva based because that can be
incorporated as a powder, whereas SBR is supplied as a liquid additive.
It's also to do with the minerals used. The aggregate in flooring
screeds produces a smoother finish than sand.
I agree SBR is overkill unless you're tanking a cellar or something.
Jim K
Maybe a readymix screed would use Lytag or some other sh1te but IME a
mix-yourself-screed is sand and cement 4:1 or thereabouts.
Ar you thinking "self" levelling compounds per chance?
Cheers
Jim K
sm_jamieson
I found the following mix (all based on "pro" 48% solids SBR)
cement 50kg
sand 175kg
SBR 5kg
water 15kg
It seems a general rule for screeds over 25mm or "medium duty", to use
half the normal amount of SBR, or SBR = cement / 10.
A few sources agree on this, some also saying 1:3 SBR:water in the
mix.
If I use that mix, its not quite so bad. I'm not after a fully
waterproof screed.
Thanks,
Simon.