to prime or not to prime!!!

[kilty55]

hi all i recently done a post regarding which substrates to prime and which i dont have to prime...im a bit lost im gettin different answers.. i was told plasterboard i dont have to prime and fresh plaster yes i do have to prime but other people are saying i must prime plasterboard??? basically ive almost completed a job with plasterboard which i didnt prime but i did use a self priming adhesive which im now being informed on doesnt mean i donnt have to use primer...there sems to be different veiws on these things can anyone clarify please? also im laying a glazed matt porcelain floor,,,,not polished shiny porcelain which im getting conflicting points on some guys are telling me to seal it whilst others advise me i dont have to seal porcelain unless its polished..can anyone clarify this also please..much appreciated and thats my moan for the day

[grumpygrouter]

Hi Kilty, if you are using tubbed adhesive, you don't normally have to prime plasterboard. The problem that arises normally is when using powder adhesive (cement based) it can have a reaction with gypsum based materials like plaster, and therefore plasterboard. There is a saying that crops up on the forum a lot which is - if in doubt, prime! - it won't hurt to prime.

As far as I am aware, it is only polished porcelain that needs sealing but usually the tile manufacturer will say on the box if it needs sealing

[Fekin]

Priming plasterboard slows down the drying time of the adhesive a bit for you as plasterboard can suck the moisture out of the adhesive a bit quickly.

For polished porcelalin I always seal.

[cornish dave]

hi green grade plaster board is moisture resistant so do you still have to prime

[smokey1234x]

been tiling for years and i never hav primed anything and never had any come backs i think as long as the surfaces r dust free the addy will stick,
if the porcelan is glazed u do not hav 2 seal it

[Dave]

Originally Posted by smokey1234x

been tiling for years and i never hav primed anything and never had any come backs i think as long as the surfaces r dust free the addy will stick,
if the porcelan is glazed u do not hav 2 seal it

So would you use a cement based adhesive straight on to gypsum plaster then...?..( no primer )......

[CJ]

If in doubt............slap it on.


Primer that is

[Fekin]

Originally Posted by Dave

So would you use a cement based adhesive straight on to gypsum plaster then...?..( no primer )......

Was thinking that myself, but he said he's never had come backs

[smokey1234x]

Originally Posted by Dave

So would you use a cement based adhesive straight on to gypsum plaster then...?..( no primer )......

well that is a different matter u hav 2 prime ther as gypsun plaster and cement based addy r not compatible.in that situation i would pva
but sure isnt that wrong 2

i change my post now from i never prime 2 i only prime in that situation

[grumpygrouter]

Originally Posted by smokey1234x

well that is a different matter u hav 2 prime ther as gypsun plaster and cement based addy r not compatible.in that situation i would pva
but sure isnt that wrong 2

i change my post now from i never prime 2 i only prime in that situation

Much has been written in the forums about priming with PVA. It is not recommended by adhesive manufacturers because of potential for failure and as such the appropriate Acrylic primer such as BAL APD or Adrex P51(other acrylic primers are available!) should be used instead.

[smokey1234x]

pva is and has been used for years in plastering and tiling,dont use it much myself,but i know of older tilers than myself who hav been tiling for 30-35 years who only hav ever used pva with no probs

[bigandy]

i got to admit i have always used pva (old school i suppose) and never had any come backs but i read on another thread that if not used correct primer then it can invalidate my insurance so pva no more!!!!!!