Drycasting - topcoat sand ?

[simplesteve]

Hi guys,
I'm patching up a bit of blown roughcasting I've removed from a brick outhouse. I've got the scratchcoat on, ( 3:1 , sand being Sharp & Buildi g 50/50) and am about to do the topcoat before I hurl the stones on....
But getting very conflicting advice re what type of sand to use ???
I believe it's to be 5:1 this time, but Sharp or Building sand ?

 

[simplesteve]

Anyone ?

 

[noseall]

Hi guys,
I'm patching up a bit of blown roughcasting I've removed from a brick outhouse. I've got the scratchcoat on, ( 3:1 , sand being Sharp & Buildi g 50/50) and am about to do the topcoat before I hurl the stones on....
But getting very conflicting advice re what type of sand to use ???
I believe it's to be 5:1 this time, but Sharp or Building sand ?

Use plastering sand with additives (plasticiser etc). Wet the scratch coat. Sometimes helps in the summer if the gravel is damp too.

 

[simplesteve]

Thanks for the reply. Is there a ' going off ' time, between applying the topcoat and ' hurling' the stones at it ?

 

[ree]

OP,
No need for expense or journeys. For a bit of patching use whatever sand you have at hand - no need for additives or plasticiser.
Take up suction with water - could be there's no need to wait but its a judgement call, & then hurl the stones - use a straight edge to pull the patch in line with its edges - lightly tamp the stones into the coat with a bit of flat trowel pressure.

 

[Nige F]

so it's noseall or ree - which is right ?

 

[noseall]

Thanks for the reply. Is there a ' going off ' time, between applying the topcoat and ' hurling' the stones at it ?

Yes. It's rapid in the summer. You ned to be swift, otherwise the gravel will bounce off.

 

[simplesteve]

Oh dear, I was hoping no one was going to reply !! Lol
Well, I think I’ve met my limit for ‘trying anything’ :- This is the first job ive done that never went to plan…….. the top coat kept sliding/ slumping down.
The scratch coat was solid, well adhered and reasonably flat. Has dried over the last 3 weeks. I have it a quick fine hose down first, and when that was nearly dry I have it a coat of SBR. Applied the top coat then immediately put the stones on, and everything was sliding everywhere.
Guessing the mistake was either:-

SBR was too wet when I started.
Top coat put on too thick
Dashed it too early
Dash ( 10 mm pea gravel) was too heavy for it.

Probably a combination of a few of the above .

It’s drying with a few holes in it, I’ll assess the remedial action when I’m in a better mood