PVA

[Tabby]

I PVAed several bits of gripperrod to dry cement screed, left them overnight and not one stuck. But why? I thought pva liked both wood & cement/sand.

Lots of undiluted pva used, items all weighted down overnight. One I'm not confident on though, I used No Nonsense brand pva - I normally steer well clear of that brand, but figured 48% pva is 48% pva whoever its from.

Where did I do wrong? Unfotunately its too late to see which surface the pva failed to stick to.

NT

[Adam Aglionby]

Guessing problem is partly there, dry, reallly wan`t to seal surfaces abit to stop them soaking it straight in.

Really want a no nails or stronger type adhesive would think, some gap filling ability, PVA only good for very close joints.

Cheers Adam

[Spamlet]

Have to say I'm not at all surprised that PVA wouldn't stick to cement - assuming you had a reasonably smooth and sound surface even - but when I think of it I can't put my finger on exactly why it shouldn't. Possibly the chemical processes that are continually taking place in cement, just don't give it a stable enough environment to adhere in. Possibly it just dries out too quick.

S

[pete]

Yes, presuming (tho' it's not a certainty) that it was the PVA-cement bond that failed, it could be that the cement was too friable so all you were gluing to was a layer of surface dust. It could be that the cement wicked all the solvent out of the PVA so (as Spamlet says) it dried too quickly. It could even be a contaminated surface (grease, oil ?) somewhere. The only way to know for sure would be to inspect the work, which isn't possible.

[Vortex7]

Ironically I think you need to (dilute) PVA the strip of cement concerned then have another go....but would hold better with Pinkgrip or similar grab adhesive.

D

[stuart noble]

Weird stuff, pva. I've noticed it goes from thick to thin with very little water added, suggesting that the viscosity is not related to the solids content. Same as gel paints I suppose, which seem thick on the brush, but soak in to the surface as they dry. Grab adhesives are formulated differently, and are so cheap there seems little point in using anything else.

[Tabby]

Thanks for the explain everyone.

Masonry nails just broke the screed every time, and PVA was what I had on the shelf, and thought would work. It got done with PU in the end.

NT

[Tim Watts]

Yep - good on wood and paper, not so good elsewhere.

PU or epoxy are better for non absorbent surfaces where some gap filling may be required.

For the gripperrod use, I would have gone with epoxy.

[Peter Johnson]

When I had a carpet fitted last week the fitters used an aerosol adhesive to seal the concrete and followed it with something akin to no-nails - the carpet was fitted as soon as they'd finished putting the grippers down.