repointing - what material to use? + damp issues

ih8stress

Got damp issues in my hallway. Had some rotten skirting board removed about a year ago (told it was rising damp causing it). Walls still feel cold and smell damp at times.

The wall outside has stone cladding on it and am planning on getting this repointed (along with other options) to see if this helps, so I need to know exactly what material should be used, please.

keystone

ih8stress wrote: »

The wall outside has stone cladding on it......

Does it bridge the DPC? If so no amount of repointing will help in reality. Sand/cement mortar mix for repointing BTW A classic mix is 1 part cement, 3 parts bldg sand and 1/4 hydrated lime. You can get the existing mortar tested to determine the exact ratio to match.

Cheers.

Fire_Fox

Have you rectified the rising damp?

keystone

Not if the cladding bridges the DPC he hasn't!

Cheers

ih8stress

keystone wrote: »

Does it bridge the DPC?

I'm not sure. How would I check this out?

ih8stress

keystone wrote: »

sand/cement mortar mix for repointing btw a classic mix is 1 part cement, 3 parts bldg sand and 1/4 hydrated lime.


Thanks for this. Since asking, i've seen another post that suggested using mortar plasticiser instead of lime. Trying not to sound like harry hill .......... Which is better?:p


you can get the existing mortar tested to determine the exact ratio to match.

I wouldn't know where to start, and am more concerned with getting the damp issue sorted than 'colour matching':)

..............................

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ih8stress

Fire_Fox wrote: »

Have you rectified the rising damp?

I don't know the exact cause of this, so am trying the repointing. The plaster behind the rotten skirting board went to floor level so this was chipped out and new skirting fitted, which I hoped would solve the problem but it still seems to be there unfortunately.

iamcornholio

Don't get hung up on plasticiser/lime. This is only really needed if you are laying bricks.

You need building sand, not sharp or any other sand. Building sand mortar will be a bit sticky and will stick to the trowel when pointing. Other sands will slide off and end up on the floor

If you find that the mortar is not very sticky, then you could add a bit of plasticiser (fairy liquid) to the whole mix to liven it up. But thats the only time you need it for pointing

Better to add some PVA (glue) to the mix and wet the joints with a PVA solution, as this helps everything stick and the mortar not dry out too quick (which causes shrinkage cracks)

Use a 1:5 (cement:building sand) mix. Anything stronger will be inflexible and more likely to crack.

The most important thing with pointing, and the factor which determines if the repointing lasts or not, is the compression of the joint and the finish applied to the face - this is what gives it it's weathering abilities.

Mix the mortar not too wet (like you would for bricklaying) but not too dry either. And when you repoint the joints make sure to completly fill the joint, leave it for a while to dry, then press hard with the trowel or jointer to compress the joint and give a smooth surface. Rub it back and forth with the tool one or two times for this. After it's all dried, give it a brush with a soft broom

To check for a DPC bridge, just find the DPC level (normally a thick 30mm or so) joint near the floor level, and check that the cladding stops above this joint.

With damp and cladding, often the rain is getting in way above where it is showing. So don't assume that you just need to point on the outside wall opposite the damp patch. Check the whole wall above right up to the roof for an signs of gaps or cracks

ih8stress

Wow, thank you for the detailed explanation! I won't actually be doing the job myself, just wanted to check that the person doing it has the right mix as I know this is important and I wasn't sure about the lime/plasticiser/fairy liquid issue.

I'll have to check the dpc tomorrow now. I know there are 2 rows of bricks before the cladding begins but cannot remember offhand where the dpc starts. (It was redone 2 years ago when I moved here). The cladding under the window has a dark, dirty looking section. Last year there were ants going 'inside' near the front door and I think there are a couple of gaps in the mortar. This is part of a single storey flat roof extension - don't know if that is relevant. The roof appears to be okay.

ukmaggie45

Search for posts by David Aldred to find out more about causes of damp.

Canucklehead

Hi

Have a rummage around here. And find the appropriate materials to use.


GSR