screed

[andrew]

I understand that screed is a dryish mortar of cement and sharp sand but what advantage has it over a concrete with fine aggregate, possibly finished off with a self levelling latex finish?

AJH

[David P]

IME, durability. It wears far far less than other finishes esp. in a commercial environment.

[Tim Watts]

In this day and age, with the amazing range of SLC products - nothing wrong in principle AFAICS.

In fact, one of the F Ball Stopgap products has an application video showing:

a) A bloody big site (could be a hospital, could be anything - but big, like that) with concrete subfloors laid.

b) Then, starting at one end, a bloke walks backwards with a small (1-2" ?) dia hose from an SLC mixer/pump system outside, pouring a half inch or so on top of the concrete.

That would make a lot of sense as they could probably have a whole floor done in a day and it would be absolutely perfect[1] - how many men would that take to do the old way? And it would be walkable on in an hour.

[1] IME F Ball Stopgap 300 self levels nicely at even as little as 5mm thick provided you get it down quick and work it over with a spiked roller to keep it agile (and remove entrained air from crude bucket mixing). This assumes you follow the instructions and prime with the green stuff that prevents the substrate sucking the water out - and the day is not too hot.

But, to clarify the original question, I would choose Stopgap 300 for the application (can be mail ordered) and not use some crap from the sheds.

Also bear in mind that to put even 5mm over 15m2 (a medium room) in one hit (the best way) requires 5 25kg bags of the stuff. In a 60+litre megatub you can just mix 3 bags with a plaster's mixer (do not try 3 bags with an SDS whisk - those can only just do 2 bags).

You have 30 mins max from the powder touching the water to being out the room. That will be the shortest 30 mins of your life.

2 people, two tubs with teh correct amount of water in each, bags ready to go, tubs at the 1/3 and 2/3 marks in the room ready to go - mix the 3 bag mix for 3 minutes - the go over and mix the 2 bag mix for 3 minutes. Go back and give the 3 bag tub one more mix. Give assistent the mixer to clean (hose off). Kick both tubs over and drain. Pass to assistant for immediate hosing.

Quickly move round with an inverted wooden "tee" about 2' wide with a couple of roundhead screws in the crossbar to for a gap (of the desired SLC thickness) between the wooden bar and the concrete. This enables quick wetting to approximtely the right thicknes in the shortest time (few mins at most).

Then work the room with a spiked roller for 10 mins all over. Now walk backwards out of the room rollering over the footprints - they will disappear. Go out, clean wellies and roller. Wait 1 hour. Perfect floor.

I did something similar and I judged the above to be the limit for 2 people

- but to do 5+mm over a bigger floor (and that assumes your concrete is pretty level - within 3mm or so) would require either more people and mixers

- or doing it in dammed off sections.

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So in short, the only two reasons it's not done in the domestic setting so often is a) pumps are probably expensive and large floors are thus not practical unless building a road full of newbuilds; b) builders are mostly dinosaurs and have not heard of the good SLC products and stick to using crap for small repairs.

[Tim Watts]

There is that. Stopgap 300 warns it "is not a wear surface". It assumes you will cover it - but that could probably be floor paint, provided you keep the paint good. Sticking heavy lumps of steel on it would be a different matter...

[Bolted]

Concrete is way more durable than screed of either type (although the highly polymer modified bagged type exemplified in SG300 is truly wonderful)

A warehouse floor is likely to be power floated concrete and then epoxy or equivalent painted. Why introduce a second layer the adhesion of which might fail?

[Bolted]

Which was a long-winded way of saying that the real reason is cost and ease of use. It is simpler to use a semi-dry (and very weak, cement- wise) sharp sand mix and tamp to level than it is to shutter a concrete pour and then tweak with expensive slc.

[The Natural Philosopher]

wears far more. its cheaper than concrete, that's all. Less cement. And it shrinks less.

[John Rumm]

This one?:

That would make a lot of sense as they could probably have a whole floor

I would have thought concrete and a man with a power float might get a fair area done in a day as well...

[David P]

Andrew asked what the advantage of screed was over latex - I said durability ie that screed is more durable than latex.