Waterproofing additive for mortar

Discussion in 'Builders' Talk' started by KayTen, Jul 4, 2011.

  1. KayTen

    KayTen Guest

    Hi! I'm renovating the kitchen and for starters I'm taking off the plaster and redoing it, this time with a decent mortar backing (bonding was used previously).  There's been a bit of damp showing here and there occasionally and I want to sort it out (might just be condensation, not sure, but a couple of the walls are exterior).  I want to put something in the mortar to repel damp (keep it from creeping through the brickwork to the inside, if that's where it's coming from), but I'm having trouble finding what's the best additive to use.  I was aiming to paint on a layer of a bitumen paint before I put the mortar on (or on a thin layer of it first, to save applying it to a rough brick surface), but apparently that's not a good idea.

    I came across mention of SBR waterproofer and bonding additive, but I'm not certain it's the best thing for this particular job. It made me think maybe even PVA would do the job just as well, but I don't know.

    Anyone use it before and can let me know if it's any good?  Or even if it's suitable for the job?  Or can anyone suggest a better product?

    Any advice would be helpful, thanks.
  2. blertsville

    blertsville Member

    You should find out what the problem is , it may be coming from outside , blocked cavity , etc. I have used black bitumen before and it was fine . Remove as much dust as you can and apply a decent coat , you may want to apply a second , then throw sand over the area of bitumen this will help key the render , the next day apply a scratch coat over area and leave until dry , apply top coat of render and set to finish
  3. KayTen

    KayTen Guest

    Thanks for your reply.  You've reinforced what I originally thought.  I think what put me off the idea was getting in touch with a manufacturer (by email)  and asking was their bitumen paint suitable for the job I had in mind - they advised against it.  Looking back now, I think that might be due to them being ultra-careful to give only what they see as the 'safest' advice, sticking closely to the precise product instructions.  But I suppose in this day and age, when kids are warned against playing conkers without safety goggles, companies are going to be frightened to use a bit of common sense and leeway.

    If anyone knows a sensible reason why bitumen paint wouldn't be suitable as a brick waterproofer, I'd like to hear it.  I guess since over 60 people have viewed this question so far and no-one's pointed out a reason why it wouldn't work, it's safe to assume it's okay.

    Thanks for your help.  I value the opinion of the contributors to this forum more than the product manufacturers.
  4. KayTen

    KayTen Guest

    About this problem I've got with what to add to the mortar to make it a more effective barrier against any possible damp ...

    I was virtually convinced that using a bitumen paint would be a fine old idea, specially since nobody seems to see anything wrong with it, but then, the more I thought about it, I started wondering would I actually be creating a problem.  If it does in fact make an effective barrier against damp, would it not also create damp conditions in the kitchen, since moisture in the air wouldn't be able to get out (through the brickwork, I mean)?  But then, if you have the walls painted, and (in parts at least) tiled, the damp in the atmosphere isn't going to get out anyway, right?  Thing is, to keep the kitchen well ventilated, I suppose.  Yeah, I know, obvious really.  But will using a bitumen paint on the brickwork before applying sand-and-cement make things worse by creating a damp-barrier, that's the question.

    Is there someone who knows about this type of thing and could advise me before I do something stupid.  I keep thinking about this and I'm talking myself into a corner!
  5. Tricky Bricky

    Tricky Bricky New Member

    I think Bitumen is fine as long as it is keyed properly. You can easily get waterproofer for render. If you are that worried you can use a breathable membrane and plaster over with bonding but I don't think there is too much of a problem with using bitumen. The only reason against using it I can think of is if it softens in heat as it is the kitchen but in reality I wouldn't have thought it would.
  6. blertsville

    blertsville Member

    As I said and brickie has said , its fine it will the the job, waterproof in the render , why , the problem is solved with the bitumen , don't think about it to much and get it done
  7. KayTen

    KayTen Guest

    Thanks, guys, I needed to hear it from someone qualified.  I'm actually quite a handy plasterer (for a pathetic DIYer!), but I'd hate to do the job, it looks all nice and smart and (almost) professional, and then a few weeks/months later, damp starts showing through, I was just nervous of that happening.  To hell with it though, I'll use the bitumen paint and render and plaster over it, I'm sure it'll be okay.  And the first thin coat of render (on the bare brick, before the bitumen) I'll leave it very uneven to help give it a better key, followed by a smoother coat.

    Thanks again, both of you, for taking the time to reply, it's much appreciated.:)

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