masonary paint - number of coats?

[rubble2]

We have just had the outside of our house painted with Sandtex smooth white masonary paint.

The render looks fine but the stonework around the windows is showing signs of discolouration (yellow). We had problems in the past with these areas of stone so the paint was stripped right back to the bare stonework prior to repainting.

The decorator says he has applied five coats of masonary paint to these areas but there is still s faint trace of discolouration in certain parts, he has said it is due to painting onto the bare sandstone and if we consider it a problem he will return and recoat it again.

Just wondered how many coats the experts on here would consider necessary to completely cover bare sandstone?

 

[Robbie uk]

Where it is going yellow it really needs a coat of sealer to stop the yellow prior to the emulsion going on. Its a bit like a water stain which will keep coming through. Oil based undercoat or some alkali resisting primer over the yellow patches then touch this up with the emulsion.

 

[TheDec]

The sandstone should have been sealed\stabilised prior to your masonry paint.

Dec

 

[rubble2]

The sandstone should have been sealed\stabilised prior to your masonry paint.

Dec

Thanks but I understood that stabiliser should only be used if the surface is flaking/powdery. In this case although back to bare stone the surface was fine

 

[TheDec]

Sandstone is both soft and porous and needs to be sealed prior to the application of masonry paint, you can purchase a sandstone sealer or you can apply a stabilising solution.

Dec

 

[rubble2]

Sandstone is both soft and porous and needs to be sealed prior to the application of masonry paint, you can purchase a sandstone sealer or you can apply a stabilising solution.

Dec

Thanks for the extra information, given that the sandstone now has about five coats of masonry paint on it is there anything that can be done to overcome this or will adding more coats eventually resolve the situation?

 

[TheDec]

Follow the advice that was offered by Robbie, this will stop the staining.

Dec

 

[Robbie uk]

Like TheDec says, if the sandstone was unpainted first then a coat of stabiliser could have been used at that point or a specific sandstone sealer. Now that it has been painted a few times you might as well use the oil based undercoat, then apply another coat or two of emulsion on top.

 

[rubble2]

This is now becoming more noticeable, I have a tin of Zinsser Clear binding primer, would this be effective or should I stick to oil based undercoat?

Thanks

 

[TheDec]

Have you applied the undercoat yet?

Dec

 

[rubble2]

Have you applied the undercoat yet?

Dec

No not yet, I just wondered if the zinsser would be as good/better than the undercoat.

 

[TheDec]

Have you applied the undercoat yet?

Dec

No not yet, I just wondered if the zinsser would be as good/better than the undercoat.

I would doubt that it would, the oil based undercoat will hold back/****** the staining. I think that what you have to realise here is the fact that your Decorator is at fault, no self respecting P&D would have applied a masonry paint system without first sealing the sandstone, the application over the staining will i'm afraid only offer you a cosmetic cure. The sandstone is rejecting the masonry paint because the correct prep was not undertaken, and it will win in the end.

The only cure here would be the removal of the masonry paint and the correct procedure followed, for this, you should appproach your Decorator.

Dec