Does this outdoor screed spec sound okay? - TilersForums.com

[itidiot]

Hi All,

Been having a bit of a headache about tiling outdoors and posted a number of threads over the past few months.

The back story
When buying tiles for kitchen and bathroom I got suckered into buying some matching outdoor tiles to the kitchen ones. The idea was to open our bi-fold doors and that the inside & outside tiles would all match up, looking like it was one big open space. The tiles for outside are specific outdoor tiles before anyone asks!

So i asked the "builder" to lay a concrete base and type 1 hardcore etc. It all looked good, shiny and new until it started to rain and pool in locations. So i ran a laser across it and found it was 0mm to 40mm out and the so called gradient was totally wrong! :mad2::mad2:

Finally summer ending and i need to sort it, fast!

I have to get the lot releveled and have finally got a quote in from a decent floor screeding company, I hope. But want some advice, does this read okay (burnt once with this)?

To supply and lay a slurry primer (to adhere the screed to the existing concrete base) followed by 10-40mm of bonded 4:1 Isopol polymer modified screed incorporating PP fibre reinforcement for 28m[SUP]2 [/SUP]for the exterior patio area. Screed to be laid to falls. Screed to receive floor finishes.

Materials include jumbo bags of sharp sand, 25kg bags of cement, Isopol polymer additive and PP fibre reinforcement. Equipment to be supplied includes a Putzmeister screed pump and Topcon laser level.

As discussed I have quoted for a polymer modified screed which is a high strength screed capable of being laid to thin depths whilst retaining its strength and ideal for your situation. This type of screed has a high compressive strength, is water resistant

All our screeds are site mixed in our screed pumps for optimum results and normally are laid to a guaranteed flatness of ±1-3mm deviation as per SR1 which is the highest standard in screeding.

Questions
- Does all this sound okay?
- Should I get it laid to Sr1 or should i get a gradient/fall to stop further pooling?
- am i running the risk of having a really badly laid base if the gradient is wrong again!?
- Is it okay to tile on top of this screed?
- Also should i be get nervous about coming up too close to damp course

thanks

Chris

 

[White Room]

I laid a polymer screed externally for someones drive outside a garage with a slurry, that was for a guy who I worked for and he was a sika guy and qualifications coming out of his ears and it's still solid.

What distance is there from your existing patio to the damp course......

 

[itidiot]

Thanks good to know. well damp course is circa 10 cm now. So the screed will bring it up by another 1cm and then another 2 cm tiles and adhesive. However the bi fold doors are the majority of the wall just about 1meters worth. box drain in front

its tight?

 

[White Room]

The damp course should be about 150mm from the finished surface of the patio....

 

[itidiot]

i know ... big risk

 

[Spud]

I would get them to state what gradient of fall they will achieve away from the house apart from that the specification does sound okay

 

[Ajax123]

Based on the depth i would expect more rigorous surface prep to the concrete substrate i.e. scabbling to expose coarse aggregatetans to remove any laitance at the concretes surface thus to produce good mechanical interlock between the new screed and the existing concrete. The main issue I foresee is the screeds propensity to curl at very thin depths which could lead to it "peeling" and subsequently cracking. This risk would be minimised by producing a much more effective mechanical key. I would also be surprised if they actually acheive sr1 as most screeders do not ( although most firmly beleive they do). A gradient away from the house is essential and you should deffinitely worry about how they intend to deal with creating a potential damp bridge due to its proximity to the existing damp proof membrane. At just few centimetres below the existing damp proof level for the house could be a building regs issue and as this is a paved external area it should have planning consent anyway in order to meet the current SUDS regulations.

I am not familiar with this particular additive but am aware of many similar and the are generally good. It is a pretty standard SBR additive. You should check the spec of the pp fibres as these are generally specified differently for external use than for internal. The external fibres e.g. Fibrin XT allow for freeze thaw protection. Most screeders use the same fibres for internal and external which is a risk especially based on the depth. I am guessing the fibres will be from flowcrete also.

The minimum depth for bonded sand cement scrreed to meet bs8204:1:2003 is 40mm but as this is a polymer modified screed it becomes a proprietary material so falls outside of the remit of the British standards. My suggestions that you check your guarantees very carefully not in respect of the materials but in respect of the installation. You would also be wise to view the mixing and addition of admixtures as the amount of polymer is important. Also check how they intend to cure the screed post installation. It should generally be covered with polythene for 7 days following installation. If this is not done you could find that all manufacturer warranties will be void. Also you should satisfy yourself of its fitness for purpose. Most of these additives are fine outdoors but they are designed to go indoors and onto a topping which is dry to below 75%rh. You are unlikely to acheive this with an external concrete so if anything goes wrong the manufacturer has an immediate get out.

Lastly SR1 is NOT +or- 1 to 3mm deviation from flatness. (if you think about it this wold allow a flatness of -3mm to + 3mm against a given plane. I.e. it can vary by 6mm. Tis really is not very flat at all.

SR1 means no more than 3mm deviation a any point along a 2m long straight edge placed on the surface of the screed and allowed to rest under its own weight. This is much much flatter. Also bear in mind that flatness and levelness are different attributes. You want a nice flat screed i.e. SR3 that falls to a gradient so is not level if that makes sense.

Other than that it sounds ok.....;p

 

[itidiot]

this site continually amazes me with the amount of knowledge on here - thanks for all the help. Have been busy getting the surface prep'ed hence me dropping off radar for a couple of days.

Anyway, the screeders turned up yesterday and blew my socks off! Just witnessed a masterclass in screeding I think. I now have seen three screeding outfits and their results but these made all the others looked amateur. They turned up and nearly walked off site saying my box drain was too low as it was 2-3mm below where it should be. I have never seen someone so an*l!

After lots of discussion about falls and ratios they talked me through it all and the knowledge that you guys passed over to me help me understand absolutely everything. so many thanks. The only thing they did not do is do the mechanical prep but he assured me it was fine.

Just gone out today a peeled back the polythene (to help cure it) and have ran the spirit over it (against the fall if that makesense). Haven't found it out at all and must have checked it 10 times!

They wasn't happy about having to run the screed pump pipe through my house over my new wood floors and tiles either. But they left it spotless.

Think its going to save me a fortune in adhesive so well worth it plus its now going to be a doddle when i come to lay it... lets hope anyway.

 

[itidiot]

Cant seem to upload more photo's will have to try again.

 

[White Room]

Ali straight edges, finish as you go.....