Query on Masonry Paint

[Belboz]

Before you ask why this is in this section, my query revolves around bricks so I though I would get the best answer here.

I have just purchased a couple of 5L tubs of Sandtex Smooth Masonry Paint. I bought them from Screwfix after reading good reviews on the paint.

When the tubs arrived, as usual, I read the instructions on the tub. It clearly states what it is suitable for but also states:

NOT SUITABLE : Common, Fletton or Engineering type bricks

Apart from the fact that this non-suitability is not mentioned anywhere on the Screwfix website, can anyone tell me why it isn't suitable for these surfaces please?

Reason for asking is that the paint was purchased mainly for a rendered external area (so all good) but did plan to use some of it on an external wall between my house and next door (this is not part of either dwelling - just a 'standalone' wall made up of common brick)

Thanks in advance.

 

[^woody^]

It's because of the properties of the clay, moisture and spalling come to mind.

I did not think that it mentioned engineering bricks, just commons and flettons.

 

[Belboz]

Thanks Woody. Not sure I understand that though. If the bricks are fully dry (or new) then sealed with the paint, surely moisture (and thus spalling) would be prevented?

As for the mention of engineering bricks, that category is not shown on the Sandtex website but it is on the rear of the tub (see picture below) Their pdf is evidently out of date. Sorry for the lack of focus!

 

[Denis-Painting]

Thanks Woody. Not sure I understand that though. If the bricks are fully dry (or new) then sealed with the paint, surely moisture (and thus spalling) would be prevented?

As for the mention of engineering bricks, that category is not shown on the Sandtex website but it is on the rear of the tub (see picture below) Their pdf is evidently out of date. Sorry for the lack of focus!

View attachment 82046

 

[Denis-Painting]

Impermeable or low permeability coatings trap moisture. Large pressure can build up if there is any internal moisture such as from humans which are mostly water anyway. Suns heat does this. Freezing conditions also bad.best solution is to use paint with no polymers such as snowcemplus. It's only cement white or colour shade. Brush, paint trowel or spray.

 

[JohnD]

why no gutters?

 

[tony1851]

Before you ask why this is in this section, my query revolves around bricks so I though I would get the best answer here.

I have just purchased a couple of 5L tubs of Sandtex Smooth Masonry Paint. I bought them from Screwfix after reading good reviews on the paint.

When the tubs arrived, as usual, I read the instructions on the tub. It clearly states what it is suitable for but also states:

NOT SUITABLE : Common, Fletton or Engineering type bricks

Apart from the fact that this non-suitability is not mentioned anywhere on the Screwfix website, can anyone tell me why it isn't suitable for these surfaces please?

Reason for asking is that the paint was purchased mainly for a rendered external area (so all good) but did plan to use some of it on an external wall between my house and next door (this is not part of either dwelling - just a 'standalone' wall made up of common brick)

Thanks in advance.

Rising damp from the ground is trapped in the bricks by the paint. In the winter, the damp freezes and expands, thereby forcing the outer face of the brick off.
Trapped moisture can also cause sulphate attack, which breaks down the mortar.

 

[tony1851]

Thanks Woody. Not sure I understand that though. If the bricks are fully dry (or new) then sealed with the paint, surely moisture (and thus spalling) would be prevented?

As for the mention of engineering bricks, that category is not shown on the Sandtex website but it is on the rear of the tub (see picture below) Their pdf is evidently out of date. Sorry for the lack of focus!

View attachment 82046

The problem may be that many engineering bricks are very smooth. Although they won't be damaged, the paint may not adhere very well.

 

[Denis-Painting]

Thanks Woody. Not sure I understand that though. If the bricks are fully dry (or new) then sealed with the paint, surely moisture (and thus spalling) would be prevented?

As for the mention of engineering bricks, that category is not shown on the Sandtex website but it is on the rear of the tub (see picture below) Their pdf is evidently out of date. Sorry for the lack of focus!

View attachment 82046

 

[Denis-Painting]

Re paint on Fleton bricks, the manufacturers are probably protecting themselves against potential failures due to excess moisture content. These bricks are especially porous with potentially high moisture content eg left outside in rain for long periods. I use snowcem for this reason because the water content can be adjusted to suit conditions when mixing eg a little less water added to the powder. I used to use the old Sandtex 365 a lot until I read the safety data sheet and discovered how Toxic is was. The new sandtex look a lot safer but have not used it yet.

 

[Denis-Painting]

why no gutters?

Did not see where that came from JohnD. I must have missed the point re 'no gutters'

 

[Denis-Painting]

Thanks Woody. Not sure I understand that though. If the bricks are fully dry (or new) then sealed with the paint, surely moisture (and thus spalling) would be prevented?

As for the mention of engineering bricks, that category is not shown on the Sandtex website but it is on the rear of the tub (see picture below) Their pdf is evidently out of date. Sorry for the lack of focus!

View attachment 82046

The problem may be that many engineering bricks are very smooth. Although they won't be damaged, the paint may not adhere very well.

 

[Denis-Painting]

Engineering bricks give little adhesion for any type of paint, they have hard, dense and impervious. At the same time, they seem okay with cement because how would you be able to build a wall otherwise. Obviously should not have glazed face. There are many primers out there, which should help with engineering bricks, sika, cemprover etc.

 

[JohnD]

"Gutters" was my mistake, wrong thread.