Hi,
Preface:
We are having a large extension front and back to a small brick built cavity wall 1956 detached house. Architect plans and planning permission, build control involved. Basingstoke, Hants. Had a lot of trouble with builders. First builder gave up and left less than half finished, owing money, court case in progress. New builder who we had seen work quickly on neighbour's house hired, steamed along for a few weeks, we moved out and he's got to plasterboard stage. Whole house done, old ext walls, new ext walls, int solid walls and new studs. Builder said everything had to be done as plaster beginning to blow. Everything done except existing kitchen which has been stripped but has to wait until we have a kitchen plan.

Now, too late, I have just read your warnings about dot and dab, tony's advice about drafts from plug sckets etc.

I have a nasty feeling the dot and dab man didn't seal round the boards properly if it all.

I thought of buying some foam and going round sealing wall/floor join before skirting board done as the new section is on a beam and block floor. Is there anything else I can do at this stage? The new walls have been cavity insulated, standard 3" cavity and 3" insulation. The old ones could be insulated in the future but we have run out of money right now.

The builder is better than the last one and hard working and effective, but still not cheap and not the easiest to deal with and any more delay will drive us crazy, living with in-law at present. In other words I don't think I can bring myself to challenge builder to do the plastering over again, even if I am entitled to if he is in breach of regs.

But the main reason for posting is to ask if there's anything I can do now to remedy if even just slightly?

Thanks. 2 storey, ground floor is suspended block and beam. The screed was laid before wall boarding and came pretty close to the inner skin walls as I remember but don't think that guarantees a tight seal.

I plan to have cavity injected walls, if approved by a surveyor, and existing cavities are closed at the top. If the exterior brickwork is sound, exterior wall vents are closed off and all pipes and cables going through are properly sealed, is that enough to minimise the problem, apart from the seal between suspended floor to wall?

You mean foam seal from inside the loft? Otherwise wouldn't the wall board have to be pulled away?

Yes, I have seen a warning about expanding foam and I am googling up fixing foam now.

First floor void: You mean I have to get under the floorboards: Which bits do I seal?

The plasterboard gap probably does continue into the internal studwork.

I reckon I should also go around all the window reveals from the outside before the new windows are put in, and seal gaps between the plasterboard reveal linings and the inner skin

So generally even in a tidy looking brick house with CWI, (in the new parts and maybe if we get the old part done) wind p ressure can get through small cracks in brickwork and through the insulation?

Posted By: benawhileYou mean foam seal from inside the loft? Otherwise wouldn't the wall board have to be pulled away?

From inside the loft is the most reliable as you can see the gap being filled but access can be an issue to get 100% fill. If you leave even a few inches unfilled it will allow external air in.

To seal from inside, you dont need to take the wall board off. Drill a line of holes next to the gap you want to fill and squirt foam into the gap through the hole. Personally, so long as you dont get carried away with excess foam and your boards are properly fixed, I think the risk of pushing a board off is low. If youre concerned about pushing a board off, fix a batten across the board next to the row of holes- fix into the wall not the board! There was a thread a couple of months back covering this way of sealing

Posted By: RobLThe one-off cans with bendy straws are best for getting into awkward gaps, but the "guns" and cartridges are a lot more controllable.

I tape some pvc tubing to the end of my foam gun to access tricky areas. I'd definitely recommend foam gun and cartidges above the one - offs. With a decent quality gun you can leave it attached to the cartridge for up to a month between uses and it'll still work.

I am still repairing my dot and dab plaster boarded 2003 extension - double height side extension. I had in my spec for traditional wet plaster but they were so slow and behind I allowed them to make a plasterboard tent that has air sinking from the loft.

Do what you can as soon as you can before it is decorated and covered over.
Do you have any pictures of windows and how they were sealed - large source of pain for us.
RobL comment about tin and straw is a good one and wetting. Straws can get in 1 mm gaps as they squash flat.
See Tonys draught buster website

Let us know how you get on.

Posted By: philedgedouble check youre not being unreasonable in your requests

And that you haven't paid him in advance :)

I think a really useful document would be to list out the standard working practice v good practice, and make that available for everyone free to download.
Most people have little experience of building practice and specifications - experience is usually painfully gained.

If a document could be created and used at the start of projects to discuss with builders who are not familiar, along with advice on how to be sure those things are planned for, specified, paid for, testable (or other proof of existence) then all parties should have similar expectations.

Is this something this forum could create for the benefit of all? I know it is much much easier to say than do.
Maybe it already exists?

Posted By: HollyBushI think a really useful document would be to list out the standard working practice v good practice, and make that available for everyone free to download...
...Maybe it already exists?

There are two main sources of easily accessible information on 'required practice' for many products & systems:

1) The manufacturer's website, which will often provide installation guides - such as the British Gypsum Site Book, which includes dry lining (https://www.british-gypsum.com/literature/site-book-and-good-practice-guide/wall-lining-systems)

2) The British Board of Agrément (BBA) certificate for products & systems that have them (https://www.bbacerts.co.uk/)

'Standard working practice' depends on who carries out the work. Good contractors will (mostly) follow the above and stick to the plans - they do exist (I've worked for some as a manager). Poor contractors will cut corners, particularly those that cost them time or money, and may deviate from the plans to make (their) life easier or cheaper. The worst aren't aware that they're cutting corners as they don't have adequate skills or knowledge.

Of course there are dozens (or hundreds) of products in many buildings. And your contractor may substitute alternative products, though the substitute will frequently have very similar requirements. So not an easy task.

For maximum coverage, get yourself a building surveyor or architect to properly specify everything, to contract the work under an appropriate contract, and to monitor quality on site.

Thank you all, great link from philedge, anf the thread is only 3 months old! I hadn't realised on first glance how busy this forum is.
I am going to be busy once (if?) we ever move back in. The foam I purchased for future use was soudafoam low expansion
https://www.screwfix.com/p/soudal-soudafoam-expanding-foam-gun-grade-750ml/5026d

Posted By: philedgeBe careful using low expansion foam behind plasterboard where you cant see. If theres a gap in a blockwork joint or a chunk of block missing you may not fully fill the void at the back of the board. If that happens youll still have an air path !

Never done it but would using a camera endoscope through another hole help in those situations?