Bonding

[liteweight]

Have searched the forum but can't find an answer to my question.

Years ago a builder covered a wall in our house with a product called PlasterBond (?), I think. It's a thick pink, plaster look-a-like with shiny bits. Sorry that's the only way I can describe it. He smoothed it over and skimmed it. The building inspector came along and told me to remove it as it was an outside wall and if water penetrated the brick then this substance acts like blotting paper drawing the moisture into the room. He said it could only be used on internal walls and never where the wall met the outside (if that makes sense). It was like trying to remove pink cement. The builder called it Bonding and it was applied about three inches thick.

We have a leaking pipe (slow leak, didn't notice it) at the back of our house and it wasn't until we stripped the wallpaper that we noticed this Bonding was used on that wall also. Its saturated but is still rock hard and refuses to come off the wall!! We put a de-humudifier into the room but the bloody thing refuses to dry out! Now we're noticing a touch of mould.

Any idea if the building inspector was correct? We've gotten a quote from a builder and it says 'to apply Bonding to the wall'...is he talking about the same product??

 

[Carpenter]

I haven't got my Gypsum Manual to hand (seriously!) but what your referring to is commonly known as bonding but is probably a Gypsum Basecoat. This is basically a gypsum based alternative to a traditional sand/ cement undercoat. Gypsum basecoat is a modern plastering product, often used where a plasterer doesn't want to (or can't) get in bulk sand to mix up a traditional sand/ cement basecoat. It's also used for small jobs or repairs (patching in) because of its convenience. Now to answer your question: it is perfectly acceptable as a basecoat (undercoat) on any wall- internal or external. But that said, conventional sand/ cement renders and undercoats are certainly more impermeable to moisture and a good deal harder too. The only instance where I could see a gypsum based undercoat being a problem is where it is used on a solid masonry , concrete or brickwork wall, i.e. where there is no cavity- in this instance the basecoat could act like a blotting paper.

 

[liteweight]

Thanks for that Carpenter, very informative. At least I'll have some idea of what I'm talking about now when I see the builder.

It is a red brick wall, over a hundred years old so I doubt it's cavity. Also the Victorians used to use wood blocks in patches in the wall so I suppose that doesn't help where moisture is concerned.

Thanks again.

 

[Carpenter]

Any buildings over 80 years old are liable to have wooden grounds or plugs built into the walls, these allowed the carpenters of the time to fix their timber trim in position- well before the advent of hardened masonry nails or hammer drills. Your wall is most likely 1 and a half bricks thick, say 325mm or so, plus plaster. You should probably consider drylining such a wall, allowing you to incorporate some insulation into the structure.

 

[liteweight]

The OH tells me it is a cavity wall but it has been breached over time due to dirt etc. It's 2 bricks deep (not that I know what I'm talking about). We can't dry line the walls, unfortunately because we would have to remove the ornate decorative mouldings to do so. These would cost an arm and a leg to replace and there's nothing like the originals.

 

[Lak]

The product is indeed bonding and is perfectly acceptable as a backing coat internally. Under absolutely no circumstances whatsoever however should this material be applied to an external area....Never, never, never!!!!!
Bonding is however not strictly designed for use generally as a backing coat, it has many various uses but generally speaking what was used was browning and still is though for high suction backgrounds they now use hardwall. This was all before the advent of drylining which while in the uk is almost 100% the preffered practice is still not widely accepted in Ireland. The old fashioned methods of sand cement float and set (rendering and skimming are still the best) unfortunately there is a saturation of plasterers, so called, out there who dont know their a**e from their elbow!
Liteweight, anyone suggests using bonding to an external wall send em packing "tuite suite"

 

[liteweight]

Thanks for that legs-akimbo (think your name is gas, always gives me a laugh!!). When the building inspector came (20 years ago mind you), he didn't insist we take it down but we figured he knew what he was talking about so we removed it all, or so we thought! At least now I feel more sure of my ground when talking to the builder. Thanks again for all the help.