Hardwall on thermalites

[paul_v]

Just looking for some advice before I plaster a new bit of wall that has been built with thermalite blocks.

If I use hard wall how should I control the suction, I've seen lots of conflicting advice on this after looking around various forums. What would be the best option?

1. Pva the wall
2. sbr
3. Wickes bonding agent
4. Soak the wall the water

I will be skimming the wall with multi finish after.

There is also a concrete lintel in amongst all this, does it need different treatment?

Thanks for your help

 

[clive12345]

on sites we always used Thistle GypPrime ,for high suction backgrounds
before GypPrime we used to get the hose out
the lintel should be ThistleBond-it then bonding coat ,if it is a small lintel you might get away with neither
perhaps exrmet over where blocks and lintel meet
you have very high suction ,next to very low suction a bad combination
dabbing would be a lot easier

 

[Micilin]

SBR rolled on is good, but must be done the day before.

 

[NickB_99]

3. Wickes bonding agent

I've not used SBR, but my experience with WBA is that it is good for providing a good physical key (especially on 'shiny' surfaces) and provides an adequate level of suction control.
However, if you put it on too thin, I've found you can get suction problems in local areas. With something like thermalites underneath, I would be concerned you have to put the stuff on quite thick to stop this - and it's expensive!
I think I would be leaning away from the WBA on these and towards a combination of your other cheaper options - give it a good spraying down with water, and a couple of coats of diluted PVA.

 

[paul_v]

Thanks for your help guys

 

[Micilin]

3. Wickes bonding agent

I've not used SBR, but my experience with WBA is that it is good for providing a good physical key (especially on 'shiny' surfaces) and provides an adequate level of suction control.
However, if you put it on too thin, I've found you can get suction problems in local areas. With something like thermalites underneath, I would be concerned you have to put the stuff on quite thick to stop this - and it's expensive!
I think I would be leaning away from the WBA on these and towards a combination of your other cheaper options - give it a good spraying down with water, and a couple of coats of diluted PVA.

Spot on with the SBR needing to have good coverage and it is pricey.
However, if going with pva it is not as good.
Make sure whatever you use, that it is sealed up the day before. Unless the wall has stopped sucking badly, even a wall that looks well finished can crack and turtle in the hours afterwards as the wall sucks more moisture before the plaster is cured.

Perhaps a coat on successive days of pva is better ? If just soaking, then soak the night before then again in the morning.

Whatever is the case, I would rather plaster with ease than firefight afterwards.

OP, what areas are we talking? This may have a bearing.

Don't worry about the lintel unless it is smooth

 

[joe-90]

Perhaps a coat on successive days of pva is better ? If just soaking, then soak the night before then again in the morning.

I'd be going with that.