Waterproofing Masonry

[berty3000]

Hi all,

I want to put treatment on my outside walls, particularly on an extension, to make the masonry more waterproof to driving rain. House is 1960s brick.

My concern is that I want to find a product that is genuinely breathable to prevent causing internal damp problems. I am struggling to understand how any product could prevent water getting in whilst also allowing moisture out. Several companies claim their product achieves this (cream type products that get absorbed into the masonry). I don't want to go through with this though and I find out the hard way that they were talking a load of cobblers.

What are your thoughts and experiences with waterproofing masonry and which product would you recommend?

 

[George_engineer]

If it is 1960s then it should be a cavity wall. i would ensure you have eliminated alternative reasons why a cavity wall is experiencing damp. A well built cavity wall will not allow moisture to get to the inner leaf, since the external leaf + ventilated cavity is acts as am effective rain screen.

You need to eliminate the following
- internal condensation / high humidity
- leaks
- gutter / roof problems
- high ground level / penetrating damp
- blocked cavity / failed cavity insulation

If it is an issue that the external leaf is getting saturated and being frost damaged then increasing eaves or a layer of cladding would be a more effective solution than paint.

 

[^woody^]

Masonry water repellents don't work like paint or varnish with a layer on the surface, but work by lining the pores of the masonry to prevent capillarity and moisture movement. The masonry remains breathable.

Use a silane siloxane based product.

 

[jeds]

I am struggling to understand how any product could prevent water getting in whilst also allowing moisture out.

It's all about molecules. Water molecules big. Vapour molecules small.

I've worked extensively on commercial solid masonry buildings in the past where we used Liquid Plastics K501. It has its uses but even than has to be specified carefully. In your case, check all the stuff that George listed first.

 

[Ivor Windybottom]

I used one of the modern products on a house wall, but only because I was DIY repointing it and wanted to make it wipe-clean.

It worked great. But years later it's still beading the rain off, they're very good products.

It will end up a bit darker and shinier looking, basically like it's a bit wet. Not varnished looking, but you will be able to tell.

I also used similar on some stone paving. That wore away in a couple of years but, again, my purpose was to protect it against the muppet that was pointing it (me!), so it did the job.

 

[berty3000]

Thanks for the great responses chaps!

I don't have any particular issues with damp inside the house, except humidity is perhaps a little higher than I'd like, but I take care to ensure good ventilation and use a dehumidifer during the winter months. It is a bungalow. I just want to give a some extra protection against the elements.

The extension I am particularly intetested in using it on has a flat roof (no eaves protection) and so certain parts of its outer skin can get wet patches when we have very heavy rain. I've also noticed that woodlice and slugs seem to specifically like walking around the outside walls of the extension after dark in the winter - leads me to think the outer bricks are holding moisture. They don't seem to go on the other walls of the house.

The house had cavity wall insulation done by previous owners so this potentially undermines the cavity. And down one side of the house there is a concrete drive that is only 1 brick below DPC. Whilst that side of the house is pretty well sheltered from rain below the eaves, I am not able to remove this driveway for time being so would like to add some of this waterproofing a few bricks up as a precaution against splashing. No damp issues inside, as mentioned.

Long story short, seems sensible to add protection - providing it won't make problems I don't currently have!

Can this treatment be put on the masonry below DPC?

What do you guys think about render? Are there genuinely water proof but breathable versions of that?

 

[Ivor Windybottom]

I wouldn't use it below the DPC. While it will allow water vapour out, I'd suggest it's likely it may slow its evaporation. You don't want to trap water in the bricks any more than already happens, this is what makes them pop in the winter when it freezes. As you can't paint the underside of the bricks, you can't give any resistance against rising damp so you could be at risk of making them wetter than they currently are, if the amount of water coming up is greater than that getting in from the outside.

Do you have a suspended or solid floor? Our previous house had suspended and high humidity, and previous owners had been waterproofing the walls. In fact it was getting in under the floor from dodgy drains, it was like a lake when it rained then stayed wet for weeks after. Drains fixed, problem solved.

You should be aiming for 60% humidity. If it's much higher then you have much bigger issues than a coat of liquid is going to solve.

I wouldn't render anything unless it's necessary. It will just be a new maintenance issue and may devalue your house - people will wonder what you're hiding.

 

[berty3000]

Sounds sensible Ivor regarding the DPC. The bricks below do get visibly saturated, probably from rising moisture more so than splashing on exterior so I will leave them as they are and as unencumbered as possible.

There's nothing wrong with the drains. The house has concrete floors but mostly pre proper DPM, apart from those thermoplastic tiles. Tend to be able to maintain it at 60% humidity, falls a lot lower on a warm, dry day, more of a challenge in winter and this is a damp part of the country, especially when gas prices are high and I was too tight to have heating on (so moisture holding capacity of the air would be less)... I haven't had any problems with mold, rising damp, damp patches indoors.

I just want to help the house be as dry as possible. As mentioned in an edit, the extension is a particular beast, having a flat roof with nothing much in the way of eaves, and woodlice n slugs seem to like hanging out on the outer bricks in winter at night. I suspect the bricks are an especially absorbant type and get more water on them than rest of the house.

 

[Ivor Windybottom]

I've got the same floors in the current house, our experience with humidity is identical to yours. 1950s built, cloth and bitumen DPC in the walls, which appears to work well, but nothing in the floor. In our case it's painted with bitumen then lino or parquet stuck on top. I'd assume this is much less effective than a modern polythene sheet. I've seen under the parquet, it's more of a paint than a coating - matt black concrete basically.

I've also got some 70 year old water supply pipes built into the floor. I'm going to replace and abandon these before I look at other potential issues, it's perfectly possible that these are porous so are continually injecting water into the concrete. I've seen one, it was a green crusty blob. They didn't seem to know that concrete reacts with copper in the olden days.

I'll probably look at putting an epoxy coating over the floors in the future, room-by-room as they're refurbished. It's definitely not worth digging them up and replacing, you'd never get the time or money back.

Something I've been meaning to do is to try putting a polythene dust sheet over the entire floor in an unused room, taped to the skirting boards. I reckon this will cause a drop in humidity, proving that it's coming up from the floor rather than the walls. Perhaps I might even get some visible moisture under it.

All in all, it wouldn't harm to seal the bricks but it might not make any difference. If you've got a cavity then it should be irrelevant if the outer wall gets wet. Any decent cavity wall insulation shouldn't transmit it across the cavity.

 

[berty3000]

Thanks Ivor!

There will be humidity coming through the floor to some extent, but what I found when I renovated this place was that there was no mould or rotten skirting boards after the last 60 years in this damp climate, so I can only assume if you don't find any significant problems not to worry too much. And that's assuming issues can easily be diagnosed. E.g. is damp on the floor from penetrating moisture or moisture that condensed there from the air? There are always multiple factors.

Apparently these brick creams do reduce breathability by up to 10% so in my case I will have to consider whether the amount of moisture on the outside of this flat roofed extension, and protecting against that, would outweigh the reduction in breathability. I suspect it will be worthwhile since I'm not aware of damp problems inside.