Internal Hardwall and Sand/Cement

Members online

beader

Private Member
Ok, so how many on here skim s&c next day? I always have done.
When I was working for a damp firm we always skimmed the next day and guess what .....yes it always cracked but damp firms don't give a fook just get in and get out.
 

Squarehead

Well-Known Member
I can guarantee that loads of your skim won't be attached to the S&C backing within days of you finishing. I witnessed it plenty of times where the skim has just stood there shelled for years and years before it gets noticed. I've also seen it where it has been noticed almost straight away.
S&C shrinks, fact, and no amount of devil floating will make the gypsum finish plaster, which is rigid and brittle, move with it.
I always pva or SBR before skim as I don't trust it even when cured. Last substantial job I skimmed onto s& c was probably getting on for 10 years ago anyway. Bonding or hardwall and finish same day is the norm.
 

essexandy

The Lake Governor
I always pva or SBR before skim as I don't trust it even when cured. Last substantial job I skimmed onto s& c was probably getting on for 10 years ago anyway. Bonding or hardwall and finish same day is the norm.
What exactly don't you trust about cured S&C?
As a company I've done around 800 houses in S&C, always allowed to cure and never sealed prior to skimming.
 

Squarehead

Well-Known Member
What exactly don't you trust about cured S&C?
As a company I've done around 800 houses in S&C, always allowed to cure and never sealed prior to skimming.
I just don't believe that after 5 days s&c is fully cured. It may have set and changed colour but the curing will go on longer than that. It's probably enough for a reasonable bond but I just don't trust it, multi could sit there for years and then suddenly shell, seen it too often. I just like to be sure, which is why I mesh the lot too.
 

beader

Private Member
I just don't believe that after 5 days s&c is fully cured. It may have set and changed colour but the curing will go on longer than that. It's probably enough for a reasonable bond but I just don't trust it, multi could sit there for years and then suddenly shell, seen it too often. I just like to be sure, which is why I mesh the lot too.
Shelling of the finish happens because of shrinking as in the evaporation of the moisture from the mix which should be done in a 4 to5 day period depending on conditions . Curing means that the mix just keeps getting harder which will take much longer but the mix no longer contains water so the shrinking will stop .
 

Squarehead

Well-Known Member
Shelling of the finish happens because of shrinking as in the evaporation of the moisture from the mix which should be done in a 4 to5 day period depending on conditions . Curing means that the mix just keeps getting harder which will take much longer but the mix no longer contains water so the shrinking will stop .
Ok, shrinkage is one thing. But when cured the finish will have no chemical bond with s&c, you are then relying solely on key and in my book that makes me nervous. When using bonding or hardwall you have a gypsum chemical bond which is more reassuring. Don't just rely on key alone with s&c
 

McBentLegs

Well-Known Member
I prefer sand and cement if floating indoors but it's a pain in the arse if working upstairs or no where for mixer, for some reason I really enjoy using it and it's cleaner as doesn't stick to everything like Hardwall/Bonding.. just sweep up anything you drop. I work alone though, no labourer so often dabbing or Hardwall is easier.
 

McBentLegs

Well-Known Member
What exactly don't you trust about cured S&C?
As a company I've done around 800 houses in S&C, always allowed to cure and never sealed prior to skimming.

I trust you on this for sure but I'm the same as above, I worry the finish is going to shell off so will glue up also! Probably as I've scraped finish off rendered walls a few times where it hadn't took to the scratched surface very well! Infact I have one to do this week.. do I PVA or not.. lol

Brand new mixer too, fed up hiring!
15438321997006842725719835533384.jpg
 

Retired Spread

Well-Known Member
can't quite believe what I've seen on here..........I thought it was in the 'plasterers bible' when sand & cement should be skimmed over.

I've always skimmed over s&c when completely dry....same as Dri-coat and Renovating then just dampen down with water before skim.


I've said it before on this forum and I'll say it again....do some people on here actually know what the f**k they are talking about?
 

beader

Private Member
Ok, shrinkage is one thing. But when cured the finish will have no chemical bond with s&c, you are then relying solely on key and in my book that makes me nervous. When using bonding or hardwall you have a gypsum chemical bond which is more reassuring. Don't just rely on key alone with s&c
You are wrong my friend. skimming does not need a chemical bond how do you think it sticks to plasterboard . when the skim drys on sand and cement it goes through a shrinking process also, and when this happens it grabs into the groves left in the rubbing up process .If your skimming is not adhering to the floating then you may want to re asses you rubbing up of the backing coat .IMO.
 

Squarehead

Well-Known Member
You are wrong my friend. skimming does not need a chemical bond how do you think it sticks to plasterboard . when the skim drys on sand and cement it goes through a shrinking process also, and when this happens it grabs into the groves left in the rubbing up process .If your skimming is not adhering to the floating then you may want to re asses you rubbing up of the backing coat .IMO.
I can probably count on one hand the number of s&c I've done. I've nearly always used bonding and hardwall. I came into plastering just after I'd heard about multi shelling and it put me off. The plasterer may have skimmed it too early, who knows, but I will never trust relying solely on key, hey I'm probably wrong. Paranoid?.... definitely.
 

malc

TPF Special Forces
OK to skim after a couple of hours then?

with hardwall and browning it depends on the background suction when you can skim. on very high suction we may float and set twice a day. on very low suction we may leave it over night. if it looks to dry we would mist it with water.
 

malc

TPF Special Forces
You are wrong my friend. skimming does not need a chemical bond how do you think it sticks to plasterboard . when the skim drys on sand and cement it goes through a shrinking process also, and when this happens it grabs into the groves left in the rubbing up process .If your skimming is not adhering to the floating then you may want to re asses you rubbing up of the backing coat .IMO.

i have noticed that some gangs rub the sand and cement up smooth ,no scratch. as they think that multi is able to adhere better then the old sirapite and does not need a scratch.
these gangs float slow but can skim quickly.
 
D

Deleted member 32554

Guest
Do you skim sand and cement without a bonding agent?
I've been shot down before about using PVA on sand and cement Being told to skim too early (as far as I was concerned) and when I started floating s/c on my own always left for a week at least ,used PVA , no scratching ( devil ), don't think I'd use SBR as would act too much as a moisture barrier but each to their own,
 

Vincey

Private Member
Do you skim sand and cement without a bonding agent?
Yes mate I wouldn’t use a bonding agent but hey do what ever feels best I’ve enjoyed reading this thread everyone has there ways
It’s been good to read a half decent thread on here instead of the typical diy ones of late
 

beader

Private Member
I trust you on this for sure but I'm the same as above, I worry the finish is going to shell off so will glue up also! Probably as I've scraped finish off rendered walls a few times where it hadn't took to the scratched surface very well! Infact I have one to do this week.. do I PVA or not.. lol

Brand new mixer too, fed up hiring! View attachment 29404
How long is your mixer going to stay that clean and shiny?. Smile face.
 

ChrispyUK

Well-Known Member
with hardwall and browning it depends on the background suction when you can skim. on very high suction we may float and set twice a day. on very low suction we may leave it over night. if it looks to dry we would mist it with water.

Cheers Malc
 

essexandy

The Lake Governor
I just don't believe that after 5 days s&c is fully cured. It may have set and changed colour but the curing will go on longer than that. It's probably enough for a reasonable bond but I just don't trust it, multi could sit there for years and then suddenly shell, seen it too often. I just like to be sure, which is why I mesh the lot too.
Even if not 100% cured I definitely couldn't measure any further shrinkage after the fourth day at 18mm thickness on Celcon blocks in early summer.
In case you're wondering, yes I was sad enough to do lots of checking/testing. I've always been genuinely interested in the how's, why's and wherefores of our trade.
 

Densel

Member
Float and set all the way. Boardwork is far more prone to cracking than solid walls. If the solid walls are cracking its due to movement in one way or another. And as for people chasing themselves going over hardwall its due to improper wall preperation.
 
Top