Bonding Coat

[peterhurley]

Hi,

I'm using Thistle Bonding coat to put on to breeze block prior to skimming. As the wall isn't even its going on in places at up to 15mm. But whats happenig all over is cracking like mud on a hot day.

Is this normal or have I put it on too thickly? The packaging says 11mm max. Any leeway in this do you know?

Can i just carry on an put the skim or should I do something about it, and if so what?

Thanks,
Peter

 

[dazdel]

Hi pete
Are you sure they are breeze blocks ?, and not a thermalite blocks ?

 

[peterhurley]

Not too sure. The house was built around 1965, does it affect things in different ways?

 

[roughcaster]

It's crazing because the water in the bonding coat is drying out too quickly. You've to be careful with high suction backgrounds. Giving the blocks a good soaking with water as you go, is always advisable, but not always possible because of the mess. You can PVA high suction backgrounds, let it dry, then PVA again and coat onto it while wet/tacky. Don't overload the coat as you put it on. Put the plaster on around the advised thickness, but don't worry about the odd area that might be a bit thicker. Just leave it to steady up,, don't play with it or it'll slump. The crazed plaster you have on already,,, how big an area have you done, and does it sound hollow underneath when you tap it. If it does, i'd take it off and start again,,, as per above.

 

[dazdel]

Agree with the above

 

[peterhurley]

Thanks guys, we'd already pva'd the area but I'm going to do a second coat for the rest. Doesn't look like the other will be a problem but its still drying at the moment, so fingers crossed theres no hollow sound.

Thanks again,

Peter