Airtight advice selfbuild

Robert Allen

Just wondering if anybody might offer advice if possible. ( apart from - ask your engineer.... engage an airtight professional...you shouldve thought of this sooner... etc etc if thats ok ...)

We have hollowcore slabs, ends wrapped in 1200 gauge polly sheet. ( architect/ engineer/ assigned certifier said that would be grand, it didnt need to be airtight membrane - too late now to change that). Screed poured upstairs and down stairs, no airtight tape in place yet, we are putting in MHRV. Block walls upstairs and downstairs. Anyway..

The questions are:

1. Does the top and bottom of every wall, upstairs and downstairs , where it meets the floor/screed/slab/ceiling, regardless of being internal or external need to be made airtight with tape or membrane etc?

2. Anybody hear of nailing expanding metal and plastering after to hold down / seal membrane to wall instead of tape? Plaster said he did a house like this - sounds dodgy enough though.

3. Hope im not breaking rules, apologies if so but anyone familiar with any less costly alternatives for an airtight type fleece tape you can plaster over? Ones in local hardware cost about €100 for 25-30m.

Thanks to all who take time to get back to me. ..i honestly think ill need councilling before its built!!

Cheers lads ðŸ‘is

MicktheMan

What's your target?

listermint

Don't buy tape in local hardware for one.

Look to contiga is very good value in tj o Mahoney's. Also try goodwins

mfceiling

What I'm seeing now is external walls are fully sand and cement down as far as the bottom of my ceiling installation.

Majority are wrapping the hollowcore and letting the membrane down (sand and cement over this).

BryanF

1. No. Just the external walls and first floor ceiling.
2. No.
3. I spec and have just used intello.

If you can’t afford professional advice, or the price of good tapes, why not reduce the houses footprint.

Robert Allen

listermint wrote: »

Don't buy tape in local hardware for one.

Look to contiga is very good value in tj o Mahoney's. Also try goodwins

Thanks for that, i did price a few bits from membrane to airtight sealant here, it came to about €1200. The exact same products and shopping list from a German website came in at €690 delivered. Its some difference. Thanks again.

Robert Allen

mfceiling wrote: »

What I'm seeing now is external walls are fully sand and cement down as far as the bottom of my ceiling installation.

Majority are wrapping the hollowcore and letting the membrane down (sand and cement over this).

Thanks for that, i did hear somepeople didnt plaster the block under slab/in the ceiling area for some reason. Cheers for getting back to me.

Robert Allen

BryanF wrote: »

1. No. Just the external walls and first floor ceiling.
2. No.
3. I spec and have just used intello.

If you can’t afford professional advice, or the price of good tapes, why not reduce the houses footprint.

Thanks for the to the point answers, its appreciated.

As for reducing the footprint - i cant as foundations were poured lastyear and now the house has a roof.

Cheers.

Robert Allen

MicktheMan wrote: »

What's your target?

The target is to get the 3 questions answered.

After that ill be good to go, thankfully a few users are taking time from their day to point me in right direction. Cheers.

Gumbo

Robert Allen wrote: »

The target is to get the 3 questions answered.

After that ill be good to go, thankfully a few users are taking time from their day to point me in right direction. Cheers.

Mick means what’s your target with regards to air tightness result. You really should read the posts and understand what your been asked before being snarky.

You’ll quickly run out of posters offering help on here with that attitude and to be honest, Mick would probably be one of, if not the best person on this site to give you advice in this field.

Robert Allen

kceire wrote: »

Mick means what’s your target with regards to air tightness result. You really should read the posts and understand what your been asked before being snarky.

You’ll quickly run out of posters offering help on here with that attitude and to be honest, Mick would probably be one of, if not the best person on this site to give you advice in this field.

Snarky? That attitude? Relax.

I didnt ask about ACH, Pa, or M3/hr/m2. I dont want to be told to get an assessors opinion, and in fairness answering 3 questions with a question hasnt helped - though i know where you were going with the question Mick so thank you.

Im a simpleton. Ive 3 simple questions i need general opinion /advice on. In fairness the info has been provided by the above users who got back to me.

Apologies to Mick if you read this, i know you provide valuable advice for many people here and sorry if i caused you offence.

893bet

Robert Allen wrote: »

2. Anybody hear of nailing expanding metal and plastering after to hold down / seal membrane to wall instead of tape? Plaster said he did a house like this - sounds dodgy enough though.



Cheers lads ðŸ‘is

Yes but you also use a mastic (comes in a tube like silicone) to seal the membrane to the wall. Then cover with expanding metal and plaster as normal.

Robert Allen

893bet wrote: »

Yes but you also use a mastic (comes in a tube like silicone) to seal the membrane to the wall. Then cover with expanding metal and plaster as normal.

Ah yes it make more sense with the mastic. Thanks for that , might look into it. Good few euro could be saved on tape that way i guess. Cheers & thanks again.

BryanF

Robert Allen wrote: »

Ah yes it make more sense with the mastic. Thanks for that , might look into it. Good few euro could be saved on tape that way i guess. Cheers & thanks again.

This is the problem with asking specific questions and taking what you choose to understand from them.

asking questions outside of the scope of an OP’s questions tends to be because the question screams that there are other factors not being addressed/considered.

For example, Mastic is not nessecarily a suitable for air-tightness. a flexible air-tight adhesive has specific properties not often known by a hardware shop.

BryanF

893bet wrote: »

Yes but you also use a mastic (comes in a tube like silicone) to seal the membrane to the wall. Then cover with expanding metal and plaster as normal.

Wall needs to be made air-tight with smooth plaster key first, before taking sealant/membrane

893bet

BryanF wrote: »

This is the problem with asking specific questions and taking what you choose to understand from them.

asking questions outside of the scope of an OP’s questions tends to be because the question screams that there are other factors not being addressed/considered.

For example, Mastic is not nessecarily a suitable for air-tightness. a flexible air-tight adhesive has specific properties not often known by a hardware shop.

When I said mastic I did mean the special Airtightness one for clarity. Was just using a terminology that would be familiar.

Mokeydope

Bit of a noob question

How are the electrical boxes and electrical pipes made airtight on a external block wall with insulated slab?

sydthebeat

Mokeydope wrote: »

Bit of a noob question

How are the electrical boxes and electrical pipes made airtight on a external block wall with insulated slab?

With great difficulty

The problem is with using the insulated slab

Mokeydope

sydthebeat wrote: »

With great difficulty

The problem is with using the insulated slab

Ok thanks how does.that differ from cavity or external insulation fitting

Robert Allen

Mokeydope wrote: »

Bit of a noob question

How are the electrical boxes and electrical pipes made airtight on a external block wall with insulated slab?

1.You can buy an airtight type of sealant you apply with a brush to the wall chase before the conduit is in place to improve airtightness.

2. You can apply a specialised airtight render to the wall and over the conduit. (Not sure how it compares to a normal sand cement coat)

3. If its too late for 1& 2 then you can apply mastic to seal the ends of conduits, that will help you out too.

Best of luck with it.

BryanF

Mokeydope wrote: »

Ok thanks how does.that differ from cavity or external insulation fitting

The internal concrete leaf is your air-tightness layer - it’s the easiest line to achieve air-tightness