How to effectively seal a flat concrete roof?

[Encid]

Our architect has finally issued us with a preliminary copy of our house design detailed construction drawings, and although the concrete roofs look flat, they actually have a 1:100 slope on them to corner drains to let rain water out.

 

Sample below:

 

 

 

He has specified a product called "Beger Cool Roof" to provide a heat-reflective and waterproofing coating.

 

See below:

 

 

 

When I look at the Beger Thailand web page to learn more about this product it does sound like a fantastic product.

 

Depending on whether you want the 7 year product or the 15 year product the price is not so expensive for a quality roof paint.

 

The prices below are from Global House:

 

 

They recommend applying an elastomeric primer such as Beger Cool Super Ceramic Shield No. 8000 for new concrete surfaces, and recommend that the cement surface should be left to dry completely for one month and the moisture content is less than 14%.

 

Does anyone have any experience with this particular product or can recommend any other concrete roof sealant?

 

[Kwasaki]

The important thing is that as long as the concrete roof is laid correctly that product is as good or better than others. 

If the architect specified it why question it. 

 

My question would be why a flat roof on a house. 

[Encid]

1 minute ago, Kwasaki said:

My question would be why a flat roof on a house. 

Because we like the appearance of a modern style U-shaped house and that is what we commissioned our architect to design for us.

 

We are very happy with the result.

 

[Encid]

Actually after finding the detail of the spoon drain/gutter on the roof edge and the PVC drain outlet pipes, it appears that the heat-reflective and waterproofing coating is to be applied to the flat RC roof before the sloping sand mortar finish is applied.

 

 

Any comments?

 

[IvorBiggun2]

When pouring concrete to make it basically watertight you need to pour it all in one pour. I made that error when we built the cellar in my house.

 

"Cold joints occur when the first layer of concrete sets up before the next layer is placed. This prevents the two layers from intermixing and opens the concrete up to honeycombing and water seepage."

 

[Kwasaki]

42 minutes ago, Encid said:

Actually after finding the detail of the spoon drain/gutter on the roof edge and the PVC drain outlet pipes, it appears that the heat-reflective and waterproofing coating is to be applied to the flat RC roof before the sloping sand mortar finish is applied.

 

 

Any comments?

 

Would prefer low pitched panel roofing over the construction of concrete flat roof areas which take water out over the edge.

 

Nice design house a cool design in both meanings of the word,  especially facing North. 

[Encid]

1 hour ago, Kwasaki said:

Nice design house a cool design in both meanings of the word,  especially facing North. 

Thank you... we are really pleased with it and are really looking forward to building it hopefully later this year.

It is a relatively passive design and energy consumption should be low (except for the pool pump).

It faces East.

 

But back to the main subject... does anyone have any experience with this particular product or can recommend any other concrete roof sealant?

[Kwasaki]

15 minutes ago, Encid said:

Thank you... we are really pleased with it and are really looking forward to building it hopefully later this year.

It is a relatively passive design and energy consumption should be low (except for the pool pump).

It faces East.

 

But back to the main subject... does anyone have any experience with this particular product or can recommend any other concrete roof sealant?

The only knowledgeable thing i can say is your roof design will need a maintenance scheduling or in my experience it will be a future misery.

[Don Chance]

I doubt that product will work very long. You need thick tar  or rubber sealant not acrylic. As other have mentioned a real sloped roof that over hangs the house would be much preferred.

You also need to seal the exterior walls and any ledges or patios that over hang and get wet. Water will penetrate any tiles and wick into house through the subfloor and under the tiles and cause mold.

The slab foundation should also have a rubber membrane to keep water out or better to raise the entire building up. You know like the Thai's have been doing for centuries?

 

 

 

[Kwasaki]

42 minutes ago, Don Chance said:

I doubt that product will work very long. You need thick tar  or rubber sealant not acrylic. As other have mentioned a real sloped roof that over hangs the house would be much preferred.

You also need to seal the exterior walls and any ledges or patios that over hang and get wet. Water will penetrate any tiles and wick into house through the subfloor and under the tiles and cause mold.

The slab foundation should also have a rubber membrane to keep water out or better to raise the entire building up. You know like the Thai's have been doing for centuries?

 

 

 

Your just get a laugh, I think OP knows only what architect tells him.  ????

Edited February 16, 2023 by Kwasaki

[Muhendis]

14 hours ago, Encid said:

Actually after finding the detail of the spoon drain/gutter on the roof edge and the PVC drain outlet pipes, it appears that the heat-reflective and waterproofing coating is to be applied to the flat RC roof before the sloping sand mortar finish is applied.

 

 

Any comments?

 

That is a reasonable enough way to seal the roof.

It will be like having a dpm (damp proof membrane) which, if done right and made thick enough, should last the life of the house. Another way would be to do the same thing but using an hdpe (high density polyolefin) sheet which would be a bit better but more expensive..

[Dante99]

I think there are additives that should be mixed into the wet concrete that will help waterproof it.  Thais have been using such additives on bathroom floors particularly on upper levels for many years.  New products for this purpose have of course become available.  Check it out, probably can have concrete delivered with additive already mixed into it.

[Don Chance]

13 hours ago, Kwasaki said:

Your just get a laugh, I think OP knows only what architect tells him.  ????

His design is flashy but impractical for Thailand better for a desert climate somewhere. When there are heavy rains water will penetrate everywhere, roll off of the flat roof, over the exterior walls, flood the slab foundation. You can see buildings everywhere in Thailand that are covered in mold inside and out, this weakens the strength of the concrete, it takes years for concrete to properly dry out and reach max strength.

 

Lots of glass windows will maximize heat.  I stayed in a GH in Kampot like this with a big glass windows infront. Had the blinds always closed and still it was too hot for the AC to work properly.

[farmerjo]

16 hours ago, Encid said:

Actually after finding the detail of the spoon drain/gutter on the roof edge and the PVC drain outlet pipes, it appears that the heat-reflective and waterproofing coating is to be applied to the flat RC roof before the sloping sand mortar finish is applied.

 

 

Any comments?

 

What product is the sand mortar,an adhesive type?

Also will the roof area be scabbelled for the paint to stick.

Edited February 17, 2023 by farmerjo

[sometimewoodworker]

1 hour ago, Dante99 said:

Check it out, probably can have concrete delivered with additive already mixed into it.

You certainly can CPac has a verity of additives available.

[Kwasaki]

2 hours ago, Don Chance said:

His design is flashy but impractical for Thailand better for a desert climate somewhere. When there are heavy rains water will penetrate everywhere, roll off of the flat roof, over the exterior walls, flood the slab foundation. You can see buildings everywhere in Thailand that are covered in mold inside and out, this weakens the strength of the concrete, it takes years for concrete to properly dry out and reach max strength.

 

Lots of glass windows will maximize heat.  I stayed in a GH in Kampot like this with a big glass windows infront. Had the blinds always closed and still it was too hot for the AC to work properly.

The 'U' shape design is a good one for a hot climates.

 

From my quick look and observations just trying to help, there are too many junctions, boundary wall details for flat roof construction with a internal water gulley system for liking but if OP is happy with it, up to him. 

[Encid]

17 hours ago, Kwasaki said:

Your just get a laugh, I think OP knows only what architect tells him.  ????

That's exactly why I am asking for opinions on this forum from members with real experience.

I have never had a flat roofed house before.

 

BTW, our architect specializes in flat-roofed U-shaped houses, and has designed and built many across the country... he is highly recommended and respected amongst Thai builders and other architects.

 

I am not questioning his advice, just asking if others have used similar or recommend other sealants.

[Encid]

18 hours ago, Don Chance said:

You also need to seal the exterior walls and any ledges or patios that over hang and get wet. Water will penetrate any tiles and wick into house through the subfloor and under the tiles and cause mold.

The walls are designed as cavity walls with 7.5cm AAC blocks on the inside and outside with a 5cm air gap between.

Both inside and outside will be rendered and painted with appropriate paint to ensure they are waterproof.

 

18 hours ago, Don Chance said:

The slab foundation should also have a rubber membrane to keep water out or better to raise the entire building up. You know like the Thai's have been doing for centuries?

If you looked at the images I posted before you will see that the entire house is raised off the ground... by 90cm actually.

The external decking will be 80cm above grade level... just like the Thais have been doing for centuries.

And the whole building site has also been raised some 1.8-2m above the highest recorded flood level in the province.

 

But none of this has anything to do with sealing a flat concrete roof...

[Encid]

4 hours ago, Don Chance said:

Lots of glass windows will maximize heat.  I stayed in a GH in Kampot like this with a big glass windows infront. Had the blinds always closed and still it was too hot for the AC to work properly.

All the glass doors and windows will be uPVC framed double glazed with tint low-E glass... very little thermal transmission will happen.

All of the glass will also be fully shaded from about 9-10am on the East side, and until 4-5pm on the West side.

There are no windows on the South side. 

 

But again, none of this has anything to do with sealing a flat concrete roof...

[HighPriority]

AS mentioned above there are sheet membranes that can be applied and various versions of the liquid applied product suggested by your Architect.

I assume the sand/cement topping over the membrane is primarily to protect from UV.

The concrete roof itself should have a fall of 1/100 prior to the membrane being applied.

[Encid]

1 hour ago, Kwasaki said:

From my quick look and observations just trying to help, there are too many junctions, boundary wall details for flat roof construction with a internal water gulley system for liking but if OP is happy with it, up to him. 

The roof plan is quite simple really... there are three different levels, each sloping towards a spoon drain/gutter, which in turn is drained via 2" PVC pipes onto the lower levels.

 

The bottom level will be conventionally guttered in order to catch the rain water for domestic use.

 

We are off the grid wrt government water supply, so our bore/well water will be supplemented by collected rain water, after the first heavy rains have cleaned the roof of course. 

 

[sometimewoodworker]

14 minutes ago, Encid said:

All the glass doors and windows will be uPVC framed double glazed with tint low-E glass... very little thermal transmission will happen.

That is an interesting theory, not correct but interesting.
 

I have uPVC framed double glazed with tint low-E glass and laminated outer panels and I can assure you that when you have sunshine hitting the windows you will get thermal transmission. The supervisor, who is more sensitive, agrees 

Only if you never have sunshine hitting the windows will you have little thermal transmission. We have one wall, where despite 2.5 meter overhangs on the roof and trees shading much of it there is sunshine from about 6am to roughly 9:30. The way to combat this is reflective blinds that are semitransparent (they have holes that are probably around 10% of the material)

 

All the other windows are shaded until about 5:30, they allow a little heat through 

[HighPriority]

This is one eg of a sheet membrane system:

https://ardexaustralia.com/product/ardex-wpm-1000/

 

This is an eg of a liquid applied membrane system:

https://ardexaustralia.com/product/ardex-wpm-908/

 

The entire Ardex roof and deck waterproofing range can be found here:

https://ardexaustralia.com/products_category/waterproofing-roofing-membranes/

 

Ardex are a premium company, good products but they make you pay !

 

I've used the liquid applied membrane once, about 20 years ago but I've never used the sheet style membranes. I found the liquid applied product was difficult to apply neatly in the heat in Darwin Australia.

The sheet style membranes seem to have become the "go to" product for commercial projects from what I can gather.

The skillset and experience of the applicators should be your guide  in my opinion...

 

PS I'm surprised that you're only getting 50mm outlets to drain the roofs, I can see theres multiple of them but personally I'd be looking at more like 100mm, will take more volume and be more resistant to blocking with leaves etc.

Edited February 17, 2023 by HighPriority
PS

[Kwasaki]

6 minutes ago, Encid said:

The roof plan is quite simple really... there are three different levels, each sloping towards a spoon drain/gutter, which in turn is drained via 2" PVC pipes onto the lower levels.

 

The bottom level will be conventionally guttered in order to catch the rain water for domestic use.

 

We are off the grid wrt government water supply, so our bore/well water will be supplemented by collected rain water, after the first heavy rains have cleaned the roof of course. 

 

As i said if your happy all good. 

 

Another suggestion would be the rendered wall facing the south will get the most sun so make sure a proper workman like job is carried out with good quality sealants at the proper dried out stage and use white is what I've found the best.

 

Knowing what I know now my outer face walls facing sun would of been brick to save on maintenance. 

[Kwasaki]

12 minutes ago, sometimewoodworker said:

That is an interesting theory, not correct but interesting.
 

I have uPVC framed double glazed with tint low-E glass and laminated outer panels and I can assure you that when you have sunshine hitting the windows you will get thermal transmission. The supervisor, who is more sensitive, agrees 

Only if you never have sunshine hitting the windows will you have little thermal transmission. We have one wall, where despite 2.5 meter overhangs on the roof and trees shading much of it there is sunshine from about 6am to roughly 9:30. The way to combat this is reflective blinds that are semitransparent (they have holes that are probably around 10% of the material)

 

All the other windows are shaded until about 5:30, they allow a little heat through 

I've been meaning to hang bamboo roller blinds from the window overhang at certain areas of my house as a bit more of a sun barrier.

 

Edited February 17, 2023 by Kwasaki

[Encid]

12 minutes ago, sometimewoodworker said:

I have uPVC framed double glazed with tint low-E glass and laminated outer panels and I can assure you that when you have sunshine hitting the windows you will get thermal transmission.

This is the type of glass we are intending to use.

 

As it will be in direct sun only for a few hours in the early morning on the East side, and only for a few hours in the late afternoon on the West side, we are not anticipating a lot of thermal transmission.

 

Sure, there will be some... but it should be negligible (we hope).

 

[Encid]

16 minutes ago, HighPriority said:

This is one eg of a sheet membrane:

https://ardexaustralia.com/product/ardex-wpm-1000/

 

This is an eg of a liquid applied membrane:

https://ardexaustralia.com/product/ardex-wpm-908/

 

The entire Ardex roof and deck waterproofing range can be found here:

https://ardexaustralia.com/products_category/waterproofing-roofing-membranes/

 

Ardex are a premium company, good products but they make you pay !

 

I've used the liquid applied membrane once, about 20 years ago but I've never used the sheet style membranes. I found the liquid applied product was difficult to apply neatly in the heat in Darwin Australia.

The sheet style membranes seem to have become the "go to" product for commercial projects from what I can gather.

The skillset and experience of the applicators should be your guide  in my opinion...

Thanks for those links. 

 

I will have a look around for a similar product here.

 

Having worked in Darwin previously myself I know what you mean about applying liquid products in the heat... it's very similar to here.

[Encid]

19 minutes ago, Kwasaki said:

Another suggestion would be the rendered wall facing the south will get the most sun so make sure a proper workman like job is carried out with good quality sealants at the proper dried out stage and use white is what I've found the best.

I do plan on being on-site for every day of the build to try to keep the workmanship at a high quality with no shortcuts.

Yes, white will be the colour for all the external walls.

 

I have already had the discussion with my builder that if I see anyone watering down any paint, they will be removed (by him) from my project.

He (insert nervous laughing) has agreed!

 

[Kwasaki]

5 minutes ago, Encid said:

I do plan on being on-site for every day of the build to try to keep the workmanship at a high quality with no shortcuts.

Yes, white will be the colour for all the external walls.

 

I have already had the discussion with my builder that if I see anyone watering down any paint, they will be removed (by him) from my project.

He (insert nervous laughing) has agreed!

 

Okay just a few hints. 

 

Does the architect know the builder. ?  

Have you seen any of the builders recent completed constructions.?

 

Keep an eye on what quantities of materials that are ordered. 

[Encid]

27 minutes ago, sometimewoodworker said:

We have one wall, where despite 2.5 meter overhangs on the roof and trees shading much of it there is sunshine from about 6am to roughly 9:30. The way to combat this is reflective blinds that are semitransparent (they have holes that are probably around 10% of the material)

I vaguely remember you talking about that in another topic...

 

I think we will take the "suck-it-and-see" approach first... the East facing wings on the LHS and RHS of the pool are both bedrooms, so will have floor to ceiling curtains with the silver reflective "backout" material, as there will be occasions that we do not want to wake up when the sun rises at 6am. Our current house master bedroom windows face East and those curtains do a good job of blocking out the light and stopping the heat from entering the room, although the glass is very hot to the touch. Having said that we are both usually up and about well before 7am so if it becomes a problem we might have to keep those bedroom curtains closed a little bit longer until they are not in direct sunlight.

 

The West facing windows and doors will be in the external Thai kitchen (which does not matter heat-wise, therefor only single glazed tinted low-E glass there) and the living/dining area which has an overhanging eave of 2.5m. We may have to look at planting some shade trees on that side if it becomes uncomfortable.