block wall-sealing mortar and blocks- advise

Hi, The Room I am working on will to be the Drum tracking room in my Studio Dimentions Width 10' x Lenght 15' x height 9'-6". The room sits on a concrete slab 12" thick I will be building a room within a room employing the inside out wall and ceiling construction method, all of this sitting on a timber frame floated deck built to the specs outlined by john in this forum. My Question, All of the four perimeter walls which make up the outter leaf of the structure are constructed from 4" concrete blocks, two of which are plastered, 2 are just the bear block and mortar lines. I am happy that the plastered walls are sealed airtight but I am not so sure about the bear block walls, in fact i am sure there are little cracks rendering the walls not airtight... Does anyone have any suggestions for a quick and easy way to seal these 2 bear concrete block walls without having to render them with plaster....? My thoughts I thought i would just plaster the very obvious cracks with mortar but I'm not convinced this this is sufficient! Also, on the forum I have seen people use a tar like product to seal basement walls from moisture, do these products also make the walls airtight? Photos I don't have the usb lead to transfer photos to PC but if u need photos i can get it tonight and post photos tomorrow Look forward to your advise hally

Easiest is to paint them. Andre

Thanks Andre, Any particular type of paint, emulsion, water based, oil based, does it make a difference... I assume I would use a brush, dabbing the paint into any crevices or cracks One more thing - how many coats would u suggest? thanks hally

hally wrote:

Thanks Andre, Any particular type of paint, emulsion, water based, oil based, does it make a difference... I assume I would use a brush, dabbing the paint into any crevices or cracks One more thing - how many coats would u suggest?

The goal is to seal the surface. Any type that does that will work, taking into consideration if it on the outside or inside, etc. Brush application is fine, as you described it. As far coats go, what is recomemnded for the particular paint you choose. Good luck! Andre

hally wrote:

Any particular type of paint, emulsion, water based, oil based, does it make a difference...

Look into Sto- Stolastic. It's made buy a German company called of course Sto. They manufacture synthetic stucco products along with special coatings. It is a elastomeric paint that will bridge cracks. It runs $125 per 5 gal, so not that much more, for a top shelf product.

Thanks guye for the suggestions This product, Sto- Stolastic, will this give an airtight seal on the blockwork, some of these products give a breathable waterproof seal, please advise Thanks hally

Hally, I did a search for StoCorp in Ireland, and I couldn't see where they had this particular product. I would call them, they will be able to tell you, also other products they make. They make some cutting edge coatings.

Thanks gn87berner, I'll do a bit of research on it

hi gn87berner & Andre I got a product similar to the stuff u suggested, its a damp proof membrane black horrible stuff paint that I'm confident will do the trick, €22 for 5 litres which should be enough... It will seal the wall airtight and stop the damp, this is an exterior wall and its really damp here in Ireland, I've posted some pics of the work in progress...with a quick question to do with where the concrete floor slab meets the wall... thanks again Below is a pic of where the floor slab meets the wall and as u can c there is about a 2" - 3" deep cavity, is it ok to fill this in with cement or is it serving some purpose like seperating the exterior wall from the interior concrete slab. Where the black dirty horrible sticky paint stops is the block layer with the damp proof course if this is any help... Any thoughts, thanks hally

Hally, The issue with moisture and block walls is that it is just as often coming in from the outside. But since we tend to look at our rooms from the inside, we forget about that. You can attempt to slow the moisture down by coating the interior of the room, but my guess is that, especially with a porous product like concrete block is, it is migrating from the outside to the inside. The separation that you point to in the concrete, is most likely where a footer was placed for the block and then some where down the road in time, a floor was poured on the interior side of this room. Pointing it up with concrete is not as good a barrier as you would want so you should get a elastomeric type specific for concrete joints. You want to seal that up to ward off possible moisture creeping into your room and you do not want to add the rigidity of a hard connection that can stop the cycle of expansion/contraction.

Thanks xSpace for your input, so if I understand you correctly, I should leave the cavity alone, clean out all the dust and apply a damp proof membrane paint to the cavity... I have already checked the floor slab for moisture and its ok so am I correct in assuming I don't need to damp proof the floor slab? cheers hally :?:

Sorry Hally, ...what cavity and what paint did we discuss? Are you talking about the floor area with the crack concrete?

xSpace wrote:

Sorry Hally, ...what cavity and what paint did we discuss? Are you talking about the floor area with the crack concrete? Sorry Hally, ...what cavity and what paint did we discuss?

Hi xspace, the paint I refer to is a damp proof elastomeric type, I use the word paint because I paint it on the walls which have already been primed with a mixture of 6 parts water: 1 part elastomeric stuff. The cavity (my choice of word maybe not correct) is the space or rebate(not a crack) between the concrete floor slab and the block wall. Are u advising that this space also get treated with damp proof elastomeric type paint and should i also treat the entire floor slab (10' x 15') I hope this is a bit clearer thanks hally

hally wrote:

The cavity (my choice of word maybe not correct) is the space or rebate(not a crack) between the concrete floor slab and the block wall. Are u advising that this space also get treated with damp proof elastomeric type paint and should i also treat the entire floor slab (10' x 15') I hope this is a bit clearer thanks hally

No sir. Elastomeric grade >caulking< designed for concrete.

Do you have a link to such a product and i'll try and find it here in ireland cheers hally