Box screed sand and cement - internal

[EdTurtle]

Looking to try and improve my plastering - slowly getting there. Next job is to fill in a doorway bricked up with celcon blocks. I'm using sand and cement - to a mix of 5:1. I've done some chase filling and other large holes with this mix, seems to work and i can get it flat.

I've been reading up on the dot screed/box screed (Like this for example https://www.adrianwest.org/plastering/dots.html). This might be a silly question, and i do understand why they use bits of plasterboard/plywood, but i also don't?! Why wouldn't you just put a dab of mortar on the wall, and press it flat, then screed off that? And, if you do use the p/b squares, do they stay in the wall forever more? How would you get them out once you've screeded?

I've bought a featheredge - 6foot, do i need a darby as well? Unrelated as well, but can i use the feather edge on the first coat on multifinish on a dished wall to get it a bit flatter, before the second coat? This isn't a wall that i've floated either, it was already like that.

Thanks

 

[stevethespreader]

The wood is taken out before it sets , why are they used ? thats a good question if you did not have them it would be easy to loose how thick the origonal dots were once you start screeding, i suppose they become a reference point and something to put your straight edge to thats my explanation anyway

 

[Deleted member 292770]

but can i use the feather edge on the first coat on multifinish

no. use a longer/ finishing trowel to close it in before your 2nd coat.

 

[Deleted member 292770]

I've been reading up on the dot screed/box screed (Like this for example https://www.adrianwest.org/plastering/dots.html). This might be a silly question, and i do understand why they use bits of plasterboard/plywood, but i also don't?! Why wouldn't you just put a dab of mortar on the wall, and press it flat, then screed off that?

There’s no point. if you start at the top right corner (if your’e right handed) , and follow the same mortar thickness through there shouldn’t be much screeding .
what chemicals are you adding to your 5:1?

 

[EdTurtle]

The wood is taken out before it sets , why are they used ? thats a good question if you did not have them it would be easy to loose how thick the origonal dots were once you start screeding, i suppose they become a reference point and something to put your straight edge to thats my explanation anyway

Ok, makes sense, so basically once finished all the screeding there would be four low spots where the four bits of wood/pb were, which would then be topped up with a little mortar?

no. use a longer/ finishing trowel to close it in before your 2nd coat.

Can I ask why? My trowel is 14inches i think.

There’s no point. if you start at the top right corner (if your’e right handed) , and follow the same mortar thickness through there shouldn’t be much screeding .
what chemicals are you adding to your 5:1?

I'm not certain i quite follow, which bit is there not much point in? I'm adding plasticiser, or admix. Is that ok?

Thanks

 

[EdTurtle]

Oh, one more.... Is it worth getting a cheap trowel to do sand and cement render, so as not to scratch my nice one for top coat?

Thanks

 

[Deleted member 292770]

Can I ask why? My trowel is 14inches i think.

good for laying on but a 20 or 22” is much better for flattening /closing in .more likely to keep it nice and flat .

 

[stevethespreader]

Ok, makes sense, so basically once finished all the screeding there would be four low spots where the four bits of wood/pb were, which would then be topped up with a little mortar?

yes

 

[stevethespreader]

Oh, one more.... Is it worth getting a cheap trowel to do sand and cement render, so as not to scratch my nice one for top coat?

Thanks

sand & cement work helps break the trowel in, once a trowel is broken in some spreads then call that their finishing trowel and will get another trowel to lay on since your trowel is new i would use it on the sand & cement

 

[EdTurtle]

yes

Thanks

good for laying on but a 20 or 22” is much better for flattening /closing in .more likely to keep it nice and flat .

Keep thinking of a speedskim, about 900mm, would that be a good shout? Lay on with the 14, then flatten with the 900mm, then polish/flatten again with the 14?

sand & cement work helps break the trowel in, once a trowel is broken in some spreads then call that their finishing trowel and will get another trowel to lay on since your trowel is new i would use it on the sand & cement

The trowel i'm using isn't new, i've used a fair few times, quite possibly not fully in worn in yet though, as i only do a little bit of plastering here and there - as should be obvious by my questions . Anyway, if the trowel was broken in, would you use it on s&c, or steer clear?

Thanks

 

[Deleted member 292770]

i’ve got a 600 and 900 speedskim and only use them on huge ceilings tbh. I have a 20” marshalltown , 600 refina spat and 600 plaziflex for normal finishing.

 

[stevethespreader]

Thanks

Keep thinking of a speedskim, about 900mm, would that be a good shout? Lay on with the 14, then flatten with the 900mm, then polish/flatten again with the 14?

The trowel i'm using isn't new, i've used a fair few times, quite possibly not fully in worn in yet though, as i only do a little bit of plastering here and there - as should be obvious by my questions . Anyway, if the trowel was broken in, would you use it on s&c, or steer clear?

Thanks

If its proper worn in i would steer clear

 

[EdTurtle]

i’ve got a 600 and 900 speedskim and only use them on huge ceilings tbh. I have a 20” marshalltown , 600 refina spat and 600 plaziflex for normal finishing.

How is a 600 plaziflex different to a 600 speedskim - genuine question, am i missing something?! I'm only looking at screwfix atm and i can see this - https://www.screwfix.com/p/refina-plaziflex-trowel-18-x-5/487hj - quite a bit smaller than 600 though. Is this good for finishing? Why is plastic better than stainless, and is this a flexi plastic? I do have a v stiff plastic trowel (unsure of intended function) - could i use this for the s&c? Other options are https://www.screwfix.com/p/ragni-r425-16-cement-flooring-trowel-16-x-4/881kh or https://www.toolstation.com/marshalltown-qlt-soft-grip-finishing-trowel/p63126. I'm really struggling with the different options! My current trowel is a marshaltown, one of the preworn stainless steel ones, cost a lot more than that last one i linked, and isn't as big?! Think its this one. though slightly different to whats pictured https://www.toolstation.com/marshalltown-pre-worn-finishing-trowel/p46608. https://www.toolstation.com/marshalltown-pre-worn-plastering-float/p56640 Would this be a good buy, lay on the s&c with it, then in future use it to polish the top coat?

Thanks

If its proper worn in i would steer clear

Thanks, good to know. Just to decide on another one then....

 

[Deleted member 292770]

the plazi has one interchangeable handle for all size blades.
you can’t fit a pole to it.
speedskim has interchangeable steel and plastic blades. you can use an extendable pole to it - or not.

Why is plastic better than stainless

not better just different.

I do have a v stiff plastic trowel (unsure of intended function)

sounds like a polyeurethane float. you can use it to rub up.
The last one would be ideal for finishing but it’s carbon steel so will rust for fun.
As for cement work I prefer a narrower blade 4”. x 14 or 16”.

 

[stevethespreader]

the plazi has one interchangeable handle for all size blades.
you can’t fit a pole to it.
speedskim has interchangeable steel and plastic blades. you can use an extendable pole to it - or not.

not better just different.

sounds like a polyeurethane float. you can use it to rub up.
The last one would be ideal for finishing but it’s carbon steel so will rust for fun.
As for cement work I prefer a narrower blade 4”. x 14 or 16”.

im retired now but i was one of the fore runners of plastic trowels i used to lay on with steel flatten with a plazi and finish with a barton which they stopped making so i made my own i use to sell them on e bay and to the lads on here, with the barton blade you can leave a finish before the plasters set saving you about 30 mins a set they are nothing like the float you use to rub up if you go to my profile and albums you can see the plastic trowels i made the Scousers were the first to use them they used to take the exit sign onsite and used to trowel up with it anyway ask @roughcaster or @Alastairreid they have used my trowels along with a few others on here plastic trowels are a game changer