Waterproofing mortar.

[soup]

Hi folks I want to waterproof some cement at the base of a greenhouse how would I go about this? There was a small gap between slabs and the aluminium base of a greenhouse I filled this gap with a 6:1 sand:cement mix now whenever it rains hard a small pool of water forms at the base and this water seaps through the S+C mix. I was thinking of painting it (the mortar), what kind of paint/mastic is recommended and is it easy enough to apply? The water used to lie for a while as I had "pointed" the gaps between the slabs but have now drilled holes in this "pointing" (neatly, it doesn't look as horrendous as it sounds) to allow water to drain away . I fully realise that greenhouses are NOT wind and water tight (although for most purposes...)but there is more influx than desirable (although this influx is not major I would still like to stop it).

[The Natural Philosopher]

Soak the mortar with PVA. This isn't water PROOF but its sufficiently pore filling to pretty much stop the water soaking through..

[Stuart Noble]

Why not just use a proprietary cement waterproofer? I think this is probably some kind of surfactant that packs the particles closer together

[The Natural Philosopher]

[mail]

Either rake out the mortar and fill it with the proper mix i.e. 3:1 sand: cement incorporating a pore blocker such as SIKA No 1 or a hydrophobic chemical "waterproofer" such as the Feb or Cementone brands ideally with SBR in mix and on surfaces or paint on what you have with SBR PVA may well re-emuslify in an external environment chris

[Mike P]

.. >Stuart Noble wrote: .. >> The Natural Philosopher wrote: .. >>> soup wrote: .. >>>> Hi folks I want to waterproof some cement at the base of a greenhouse .. >>>> how would I go about this? .. >>>> There was a small gap between slabs and the aluminium base of a .. >>>> greenhouse I filled this gap with a 6:1 sand:cement mix now whenever .. >>>> it rains hard a small pool of water forms at the base and this water .. >>>> seaps through the S+C mix. I was thinking of painting it (the .. >>>> mortar), what kind of paint/mastic is recommended and is it easy .. >>>> enough to apply? The water used to lie for a while as I had "pointed" .. >>>> the gaps between the slabs but have now drilled holes in this .. >>>> "pointing" (neatly, it doesn't look as horrendous as it sounds) to .. >>>> allow water to drain away . .. >>>> I fully realise that greenhouses are NOT wind and water tight .. >>>> (although for most purposes...)but there is more influx than .. >>>> desirable (although this influx is not major I would still like to .. >>>> stop it). .. >>>

.. >>> Soak the mortar with PVA. This isn't water PROOF but its sufficiently .. >>> pore filling to pretty much stop the water soaking through.. .. >> .. >> Why not just use a proprietary cement waterproofer? I think this is .. >> probably some kind of surfactant that packs the particles closer together .. >AKA 'PVA' :-)

But PVA can re-emulsify, can it not? Therefore perhaps slowly but surly letting water back into the render.

Mike P

[The Natural Philosopher]

It does a bit, but it still occupies the pores..

[Stuart Noble]

I don't think so. Last one I used was the same consistency as a plasticiser (which isn't PVA either :-) ) A drop of washing up liquid reduces the amount of water you need to make it workable by a huge amount, so I guess that would produce a denser, and therefore a more water resistant, mortar. SBR is certainly miles better than PVA but it doesn't incorporate itself into the mortar that well

[Andrew Gabriel]

I don't think so -- washing up liquid is a wetting agent (surfactant) and often salt.

The waterproofing agents have the opposite effect, causing water to be repelled from the internal surfaces in the mortar. You can buy combined plasticiser and waterproofer for mortar from a builders merchant (and on occasion from Wickes and B&Q too). These will prevent moisture wicking through mortar, but probably won't prevent moisture under pressure from penetrating.

[Stuart Noble]

Cement plasticisers are also wetting agents (often lignosulphonates). Supposedly they reduce the voids between the particles.