Scratchcoat before drylining

murphyep

Hi Folks,
Getting ready to put up the insulated slab in my new build.
Has anyone applied a scratchcoat to the walls before putting up the slabs?

Are there advantages to this?


Regards,
Eddie

ninjaBob

I've been told that it helps with AirTightness by our engineer, but my Builder wass a bit confused by what I was saying.

sydthebeat

ninjaBob wrote: »

I've been told that it helps with AirTightness by our engineer, but my Builder wass a bit confused by what I was saying.

the scratch coat is only a sand and cement based mix and cannot help with air tightness... its only when the wet plaster is applied that the airtight layer is formed.

If you are drylining i would treat it the same as a timber frame build. Seal all the openings back to the blockwork with proprietory tapes and membranes. Seal junctions of walls and floors, and walls and other walls. Seal junction of roof with wall.
Do all this before starting the drylining...

iamlegend2008

Hi

Both my BER assessor and air tightness installer recommended the sand/cement skim on all the external walls before the drylining was applied but this could well be because I was only applying the airtight membrane to the dormer (although all windows downstairs were tape sealed etc).

If the house is a dormer then remember that you are talking about the skim going up as far as where the blocks meet the edge of the roof and on the gables I did right up to the apex.

It gets a bit subjective but Im very happy with the results and people have actually commented on how warm the house feels (and I have yet to put in subfloor downstairs)

Cheers

sydthebeat

iamlegend2008 wrote: »

Hi

Both my BER assessor and air tightness installer recommended the sand/cement skim on all the external walls before the drylining was applied but this could well be because I was only applying the airtight membrane to the dormer (although all windows downstairs were tape sealed etc).

If the house is a dormer then remember that you are talking about the skim going up as far as where the blocks meet the edge of the roof and on the gables I did right up to the apex.

It gets a bit subjective but Im very happy with the results and people have actually commented on how warm the house feels (and I have yet to put in subfloor downstairs)

Cheers

theres a difference between a full skim and a scratchcoat.... perhaps the op can clarify what they are referring to.

legend, have you had a blower door test carried out yet?

iamlegend2008

Hi Syd

I had never planned to do the blower door test. I do understand that this is a measure of how well the air tightness is performing but in the end I felt that the money could be better utilised as I was with the installer for the whole duration of the membrane install and was happy with the quality of the work.

I realise that many will argue against this approach but budgets are tight at this stage.

Cheers

sinnerboy

If you are not completed the works as of 30 June 09 - as defined by TGDL 08 -meaning structure of external walls is complete - you MUST test . If not you do not comply .

sydthebeat

iamlegend2008 wrote: »

Hi Syd

I had never planned to do the blower door test. I do understand that this is a measure of how well the air tightness is performing but in the end I felt that the money could be better utilised as I was with the installer for the whole duration of the membrane install and was happy with the quality of the work.

I realise that many will argue against this approach but budgets are tight at this stage.

Cheers

in all respect, thats like standing over a chef making a cake (which youve ordered and paid for!)... and not getting to taste the results....!!!

unless you have years of experience in air tightness membrane fixing, why are you happy with his work??

iamlegend2008

Hi

Sorry for the delay in replying.

Sinnerboy: My understanding is that a test is not required for my property as the majority of the works (roof on etc) were completed before July 2007:

Sydthebeat: I understand what you are saying but I dont need to play the guitar to appreciate a great guitarist

I understand that the door test is both desirable from a consumers point of view and now manadatory. All I can say is I have spent the money on the BER spec report, airtight insulation etc, and dont have enough remaining funds to cover the blower door test.

The road washed away 3 days ago due to torrential rain so Im currently having to fork out for this and these all eat into the contingency fund.

Cheers

sydthebeat

iamlegend2008 wrote: »

Sydthebeat: I understand what you are saying but I dont need to play the guitar to appreciate a great guitarist

i understand what your trying to say, but thats not a great analogy....

with a guitarist you can physically hear the results...

what you are doing is a kin to saying "well, he has the long hair, the flying v strat, the gold rimmed pick, the snake skin boots... so he MUST be a great guitarist"....

judge... book.... cover..... etc...

murphyep

sooo....scratch or skim before drylining???

sinnerboy

Unless you can afford time for a plaster coat to fully dry out - don't do it . The dry lining board will trap constructcion moisture - which will collect at elec points causing injuries or worse . Mould "pizzas" will thrive out site behind the dry lining

Internal plasters need to be applied at min 20mm thickness for them to have integrity ( not crack ) . Min 1mm per day drying out + " 1 week to be sure" - minimum .

There is a product under development which will be called a parge coat plaster - may be applied 6mm thick and retain integrity - but not aesthetic . i.e. purpose made for this application . But it ain't available yet .

( I don't work for the company and can't issue updates )

Technophobe

Pardon my lack of understanding on this and for jumpin in but...!!

I had planned to do this: "The internal face of the external walls to be dry lined with 50mm composite plaster board/Polyiso (Xtratherm Thin-R XT/TL-MF) board fixed with screws/dabs and skimmed to a smooth finish".

So should I be considering a skim or scratchcoat finish to the block walls before this is done...??

Per Syd's quote: "If you are drylining i would treat it the same as a timber frame build. Seal all the openings back to the blockwork with proprietory tapes and membranes. Seal junctions of walls and floors, and walls and other walls. Seal junction of roof with wall.
Do all this before starting the drylining... "

By this do you mean tape directly onto the block around external openings and junctions? If so, what type/name of tape is most effective?

thanks

sinnerboy

Technophobe wrote: »

Pardon my lack of understanding on this and for jumpin in but...!!

I had planned to do this: "The internal face of the external walls to be dry lined with 50mm composite plaster board/Polyiso (Xtratherm Thin-R XT/TL-MF) board fixed with screws/dabs and skimmed to a smooth finish".

So should I be considering a skim or scratchcoat finish to the block walls before this is done...??

See post above yours

Technophobe wrote: »

Per Syd's quote: "If you are drylining i would treat it the same as a timber frame build. Seal all the openings back to the blockwork with proprietory tapes and membranes. Seal junctions of walls and floors, and walls and other walls. Seal junction of roof with wall.
Do all this before starting the drylining... "

By this do you mean tape directly onto the block around external openings and junctions? If so, what type/name of tape is most effective?

thanks

3 systems - Siga , Intello and Vario . Google for them

Technophobe

Hi Sinner,

sinnerboy wrote: »

See post above yours

I did see the post but am not sure if I am interpreting you right...
Are you saying that if you can afford the time to let it dry out, then it's ok?
If so, how long would I have to leave mine?

Or are you not a fan of this approach? Is the alternative then to put a wet cement plaster finish?


I will google these but wnated to know if they go directly onto your cement blocks?

thanks for the help

technophobe

sinnerboy

sinnerboy wrote: »

Internal plasters need to be applied at min 20mm thickness for them to have integrity ( not crack ) . Min 1mm per day drying out + " 1 week to be sure" - minimum .

I can't add any more . sorry

sydthebeat

Technophobe wrote: »

Hi Sinner,



I did see the post but am not sure if I am interpreting you right...
Are you saying that if you can afford the time to let it dry out, then it's ok?
If so, how long would I have to leave mine?

Or are you not a fan of this approach? Is the alternative then to put a wet cement plaster finish?


I will google these but wnated to know if they go directly onto your cement blocks?

thanks for the help

technophobe

according to SBs post "1mm per day + week over"...

so if you have 20mm plasterwork, thats 27 days....

wet sand and cement is not as air tight a barrier as plaster...

ardara1

Google it - a 'PARGE' Coat in UK (Scratch coat in good old Ireland) is seen as best practice - don't mention tapes of any kind as an option.

morning delight

sinnerboy wrote: »

There is a product under development which will be called a parge coat plaster - may be applied 6mm thick and retain integrity - but not aesthetic . i.e. purpose made for this application . But it ain't available yet .

I found it thanks to google - airtite plaster. It claims great results but can't find anything on it other than the manufacturer's website.

Anyone out there have any experience of it yet?

dunlopwellies

We have put on a coat of sand and cement plaster under the thermal board. The bottom line is it is not as air tight as the specific membranes. It does fill any gaps left in blockwork which will inivatible be left even after the best block layer. It also straightens poor blockwork to install thermal board onto.
F.Y.I. Skim coat is the finish coat applied to grey coated walls and plasterboard. Next layer after the skiming in paint!! Defiantly no skiming before plasterboards.
The current air tightness regulations are a joke anyway. I was having a house tested recently and the guy had left a bathroom window open. Out of interest he did the calculations and the house still passed. A bit mad but true.

No6

I am reccomending any of my clients who are drylining to give the blockwork a scrathcoat first, true its not a membrane but it is far beter than drylining on plain blockwork as it gives some element of a seal to the blockwork which lets face it is exceptional in term of air perimability, next stop is a sieve!!!

Technophobe

An Air tight plaster is now available from a well known company that supply this kind of thing..had a rep out to me and he stated it was company guaranteed....FWIW

morning delight

Technophobe wrote: »

An Air tight plaster is now available from a well known company that supply this kind of thing..had a rep out to me and he stated it was company guaranteed....FWIW

Hi Technophobe
Can you say who the company is? Has the product an form of certification/ guarantee? i.e. Agrement certified! Has an airtightness test been done on any house that has used it?
You can PM me details if you want.
Cheers;)

Technophobe

as requested

Lightning McQue

TechnoCan you pm those details please.Thanks.Lightning