Flat roof sealant

[ross163103]

I've got a section of my house that has a concrete flat roof. It was great for around twenty years but has recently started to leak. An inspection up top doesn't revel any structural problems but water tends to seep thru and drip on the porch underneath. Does anyone know a good sealant to use for this issue? I've tried a few different acrylic sealers that last for a few years but I'm looking for something long term, possibly a membrane type of sealer. I've seen many in the various DIY stores, just not sure which one would be the best. Of course all the salespeople aren't much help. Anybody out there have any experience with this? Thanks in advance for any suggestions.  

[CharlieH]

Moved to DIY Forum

[kiteman9]

I applied this product called crocodile roof shield to my flat concrete roof 4 years ago and it still looks good, no leaks. It is best to use a membrane or just pour it on thick and spread it around to let it self level. I purchased it from Thaiwatsadu.   https://www.jorakay.co.th/en/repairing/waterproofing/crocodile-roof-shield

[Cake Monster]

Look into Roof Sealants from a Company called " Sista "

Did the job for me.

[3STTW]

I have a large flat concrete roof which has been leaking since the day I bought the property. I had it resealed (Bht 40,000) in March and, with the recent rain, it has leaked again - though not nearly as badly as before.

 

A couple of things to consider; firstly, if you have a small amount of water leaking in this is usually an indication of a much worse problem and the water may be damaging the concrete structure where you can't see it, if it gets into the rebar then it can lead to 'concrete cancer' and a very expensive repair job. So don't patch up the areas where you think the water may be getting in - do the whole surface.

 

Secondly, as always, success lies in the preparation. Start by removing as much of the previous coating as possible, this will reveal any cracks which were not visible before. Chase out any cracks with a grinder and fill them with roof filler, apply fabric roofing tape over the filler, and paint over with your chosen roof seal. Lay roofing fabric over the entire roof and paint over with the roof seal, then apply a second coat as directed. There are plenty of demo videos on Youtube.

 

I had a contractor use the Crocodile paint on the first attempt and the water came in again after about a month but I'm pretty sure this was lack of prep (I wasn't around to oversee the work). Second time around, a different contractor did all the prep but didn't lay the fabric - he told me his roof seal didn't need it. The roof seal turned out to be TOA and a bunch of people have since told me that it's okay but doesn't last long - which it didn't. And ALL roof seals need the fabric regardless of what the contractor tells you, without fabric the seal will disbond and shrivel up under the summer sun.

 

Apparently, the stuff you need is Sika Sikalastic 5 and you can get it from Hardware House or Thaiwatsadu. It ain't cheap but I'm told it's the only worthwhile solution in TH.

[The Theory]

Flat roof could become a real headache in Thailand, if you don't find what is needed as a true long life seal. I never looked for such since I never had a flat roof. 
look for something like in the photo. It is a real long term solution. 
 

Edited September 24, 2022 by The Theory

[Tropposurfer]

1 hour ago, 3STTW said:

I have a large flat concrete roof which has been leaking since the day I bought the property. I had it resealed (Bht 40,000) in March and, with the recent rain, it has leaked again - though not nearly as badly as before.

 

A couple of things to consider; firstly, if you have a small amount of water leaking in this is usually an indication of a much worse problem and the water may be damaging the concrete structure where you can't see it, if it gets into the rebar then it can lead to 'concrete cancer' and a very expensive repair job. So don't patch up the areas where you think the water may be getting in - do the whole surface.

 

Secondly, as always, success lies in the preparation. Start by removing as much of the previous coating as possible, this will reveal any cracks which were not visible before. Chase out any cracks with a grinder and fill them with roof filler, apply fabric roofing tape over the filler, and paint over with your chosen roof seal. Lay roofing fabric over the entire roof and paint over with the roof seal, then apply a second coat as directed. There are plenty of demo videos on Youtube.

 

I had a contractor use the Crocodile paint on the first attempt and the water came in again after about a month but I'm pretty sure this was lack of prep (I wasn't around to oversee the work). Second time around, a different contractor did all the prep but didn't lay the fabric - he told me his roof seal didn't need it. The roof seal turned out to be TOA and a bunch of people have since told me that it's okay but doesn't last long - which it didn't. And ALL roof seals need the fabric regardless of what the contractor tells you, without fabric the seal will disbond and shrivel up under the summer sun.

 

Apparently, the stuff you need is Sika Sikalastic 5 and you can get it from Hardware House or Thaiwatsadu. It ain't cheap but I'm told it's the only worthwhile solution in TH.

I agree with you 3S.

 

The old materials need to be scraped cut and perhaps even ground away using a grinder attachment wheel for concrete example image

Be careful and try to source a  complete waterproofing system not just an individual product and try not to mix different brand products as the sealant 'systems' types are nano tech designed to meld together.

I.e. corner and joint sealer tapes, floor-pan collars marry (no layering and thus no ingress point between same is possible with this tech) to the paint-on membranes.

I would suggest to buy only the best e.g Sika, Gripset, Gorilla make stuff but I don't know about their gear.

 

We used Aussie Gripset in all our wet areas and flat area roof sealing's. I used this stuff for many years in OZ as a builder and it is superb stuff.

It is highly UV stable and will handle Thai sunlight with ease for many decades and it is pure nano-tech genius stuff.

 

Don't let someone tell you to use a tar based sealer on the roof (hot or cold pour) as it will eventually shrink and crack. I know in some countries this is still used but in Oz no way! Its old tech and obsolete.

 

Must use a long life (average 50 years) flexible membrane.

 

Codes in Oz require a minimum of 2 membrane layers in such types of areas as you've got.

e.g

1. Liquid membrane
2. Flexible sheeting membrane on top of that
3. These two membranes marry together even after the liquid membrane has dried
4. *** If you have any drainage floor-pans then you should pull them up and install the same 'system' pan-seals to ensure no ingress around the rims and joint of these pans (vey common point of water ingress into the sub-floor). Simply painting over the pan rim edges with the new membrane is not advised.

• Clean down entire area with sealant company recommended cleaner
• Scrape, chisel or impact hammer with spade-bit if need be any old and 'other sealing product' till you have the original mortar showing
• For all cracks clean out as 3S advised and fill with same brand crack sealer.
• It might pay to check the structural integrity of walls and joints - if there are cracks in places that might be indicating subsidence of footings being transferred to walls and roof slabs. 
  • If this is a problem then seal the crack with a concrete epoxy until overflow, wiping away excess before it dries. This will prevent these crack opening any further whereas flexible sealant will only expand and as the gap grows simple separate after their max elasticity point is reached.
• Tap all around the roof and listen for hollow sounds -Remove any and all loose mortar to where the mortar is tight and strong. 
• Re-screed/float any such areas with new mortar with a waterproofing agent in the mud mix Silasec (e.g. Aussie brand cement concrete water-proofing compound)
• If you want to be super sure re-float the entire roof with a Silasec type mix then apply membranes as I advise below.
• clean area thoroughly again - vacuum 
• paint on new liquid membrane as instructed
• Then lay membrane sheeting

I'd stick with the 2 membrane spec if I were you (we did) the builder was perplexed (even though he builds for a developer who has extensive experience and builds Western spec homes here) and didn't understand why but my structural engineer (build manager) and I simply smiled and helped, hands on, with the work (I've done tonnes of this in my past life).

We congratulated all workers with cold beers and some nice food when the waterproofing was done, all good ... lol????

 

If you suspect moisture might be entering through the sides of any roof buttresses/side-retaining/safety or nib walls then paint the liquid membrane right up and over the top of these side walls and down the outside too for maybe 300 mm ( you can paint straight over the membranes so don't worry about that.

 

Hope this helps with 3S's good advise.

[BritManToo]

16 hours ago, ross163103 said:

An inspection up top doesn't revel any structural problems but water tends to seep thru and drip on the porch underneath. Does anyone know a good sealant to use for this issue?

TOA Roofseal,

Works a treat, apply with a paint roller.

Don't know how long it lasts as I only used it at the start of this year.

[ross163103]

Thanks for all the suggestions. Will definitely go with a  membrane type system as I've tried coatings on their own and they didn't last. 

[HighPriority]

Mostly good advice given above.

I will add that yes you have a “ flat” roof but you need to have fall to an edge, probably a minimum of 8mm per metre, 10mm is better.

If you have any ponding after rain that is your problem right there, so you need to correct that first and foremost.

Then you can look to a membrane system, crack preparation, priming, and likely 2-3 coats of membrane.

There are membranes that are rated uv stable, I can’t vouch for their real lifespan though.

There are many membranes designed to be protected by tiles, Astro turf etc.

Im a tiler, I’d be checking out companies like Ardex,
Latticrete, Mapei, or whoever is “strong” in your area.