a technical question ??

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gooner59

gooner59

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with ewi systems a lot of them stipulate that the cloth mesh is fixed just under the surface of the base coat !! ,is it technically going to make a much difference if it is put -on then rendered over ? as is the case with scrims, if you think about it the holes in the mesh should be the correct size to let the render make good contact with the insulation and bond anyway !!! what do you think guys ??.

if there was a failure can the manufactures use this as a get-out ??.
 
In theory it would be weaker, but in the real world it might still be strong enough.

You can bet your arse that they would jump all over that if it failed.
 
Never put mesh on first it should be troweled in the base coat . Then a tight coat to cover on top , job done !
 
Mickyboy said:
Never put mesh on first it should be troweled in the base coat . Then a tight coat to cover on top , job done !
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i know that ! but why should it make a difference? as i said it should not interfere with the bond ! anyway why is EPS deemed a suitable sub straight to render-onto ,it should have some mechanical key on the face to be rendered ?
 
If you put the base coat directly onto the substrate it will have 100% contact Gooner, but if you were to put the mesh on first, the base coat would be maybe 80-85% onto the substrate with the remainder sitting on the mesh. Probably a negligable difference in strength of 'anchorage', but enough for a get-out by the suppliers :RpS_thumbup:
 
Hi gooner it depends on the mesh, if your using a mesh with small holes eg 4mm u must bed the mesh into the render as the render will not push through the holes enough to ensure a good bond to the background but if your using a mesh with 10mm holes eg Parex tv10 mesh it should be fine because the render will get in and behind the mesh ,but I always bed my mesh it just to make sure .
 
I would think that the mesh needs to be bedded in as it going to make the render coat a lot stronger, I don't think it would do naff all just laid onto the insulation. Some render systems using mesh are fibrous also, especially on thincoat.
 
bubbles65 said:
If you put the base coat directly onto the substrate it will have 100% contact Gooner, but if you were to put the mesh on first, the base coat would be maybe 80-85% onto the substrate with the remainder sitting on the mesh. Probably a negligable difference in strength of 'anchorage', but enough for a get-out by the suppliers :RpS_thumbup:
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yep.
 
10mm mesh is for mono due to the size of aggregate, 5mm for thin base coats, although ive used it with rend aid or hp12 in the past with no issues when weve been short, or with parmurex as a base coat for dpr.
 
Hi Guys

I suggest you get advise from the render system supplier you are looking at using...... but with most thin coat renders, the mesh is not applied to the substraight, but should be in the outer third of the basecoat / finished render - in the basecoat......

Most thin coat systems state you msut use their mesh - and in thin coat systems they are almost always 5mm holes!

Best advise - choose a system supplier, get a formal spec and stick to it!
 
drove past a house this morning just been boared came past it later in afternoon all finished dashed .dont think anyone on these councils knows what there looking at
 
Well some great points, and advice here tonight ! thanks lads, this is the way we can all learn from each others experience's :-D
 
ye possible just wondering how many other house they got away with . every house looks **** ,no beads on bottom mesh hanging out over all edges and throwing dash upwards some of them look like ficking windmills when there throwing,
 
on a permaroc system ,we used a very heavy weight scrim on the ground foor of a block of flats to stop the locals from kicking the render in.
 
you need full 100% coverage onto the background of the adhesive mortar placing mesh first would drastically reduce the coverage and therefore bond/long term integrity - NEVER DO THIS.
ALWAYS embed the mesh within the adhesive mortar.
Mesh will provide its best crack resistance the closer to the finished surface it is - mesh that is fully back near the substrate can allow the depth of render in front of it to still crack and show through to the surface. it is technically proven yes.

hope this helps
 
mayti said:
drove past a house this morning just been boared came past it later in afternoon all finished dashed .dont think anyone on these councils knows what there looking at
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Same up here. I have a subby wanting to help him dash some council houses on insulation and there are some being done near me the last 3 days.

Makes you wonder why the contractor allows the subcontractor to work and the labour only subby is allowed to work by their boss? Who takes the can for this when it goes wrong?
 
gooner59 said:
probably the lads that are on the tools in the courts
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It could be contested. All the lads? they could always say they was told to work in the cold. I would say the blame is on the rendering contractor for not managing his workforce.

It's one of those you are damned if you do and damned if you don't! The contractor is on a time penalty clause and if the rendering isn't getting done (quite rightly) then the main contractor is going to get in a flap and put the rendering contractor in an awkward position to catch up on time. Not that easy at this time of year.
 
is this right to bed mesh in
3-4mm coat rule with notched rule bed mesh gently on top flatten with trowel to base coat gently then top with 1-2 mm base coat
or coat up with base coat bed mesh in press with trowel into adhesive so it comes through lightly then tight coat over top?
 
I would have thought being virtually on the top is as bad as being on the bottom? Halfway to 2/3rds through sounds more like it to me.
 
Rigsby said:
I would have thought being virtually on the top is as bad as being on the bottom? Halfway to 2/3rds through sounds more like it to me.
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not really, but of course not right next to the surface - mesh must be covered until no longer visible in the basecoat even before any top coat but...
the mesh of course is specified in the front third of the systems but cracks can and do still occur in the deep part of the render and this can sometimes be in front of the mesh if it is too far back. The mesh layer can stop a crack coming through and what we don't want is the crack to make it to the surface where it becomes visible and can then allow water ingress. In addition any mechanical damage from the outside can be dealt with better when the mesh is in the final third or even closer (but of course not "virtually on the top" your words Jonny boy not mine:RpS_lol:)

anyway your mesh is in the front third you have nothing to worry about because you did everything you shouldv done maaaaan
 
spunky said:
is this right to bed mesh in
3-4mm coat rule with notched rule bed mesh gently on top flatten with trowel to base coat gently then top with 1-2 mm base coat
or coat up with base coat bed mesh in press with trowel into adhesive so it comes through lightly then tight coat over top?
Click to expand...

the method that i was taught at tellings was apply a base coat , lay on scrim, scrape back access material on top of scrim, second fix then dash.
then when we went to do externals in rotterdam, they wanted a 10mm coat on top of the scrim. they even wanted widgets to make sure they got a 10mm thick for the dashing coat
 
Just been reading through all these points, I thought I would add in what is shown on the Knauf EWI and JUB systems and included in the training.

If the base coat is meant to be 5mm - a 10mm notched trowel can be used to spread this out. - On top of the base coat lay the mesh on, you then trowel the mesh in so it is in the outer third of the base coat. No skim coat is required after, however maybe required occasionally. With a spatula like the Excalibur / s*p*r*lex or EZE Spat you should be able to get the basecoat flat enough to top coat over

The mesh being in the outer 3rd helps prevent the surface cracking.

Rule of thumb is then to leave the basecoat a mm per day for drying

Hope that helps
 
use of a notched trowel (not to be confused with serrated rule for mono) is a great help imo using thin coat base products. the depth is more even across the whole wall and allows to keep the mesh in the front third too.

some product will finish mint without a second 1-2 mm pass but some benefit a skim over after the first has firmed up and some systems specify two coats for the warranty.....
 
If the insulation or boards (or whatever backing sub structure) is flat and level - the use of the notched trowel means that you have an equal and level amount of basecoat applied to the surface........ lay in the mesh and the skim over it and smooth out.

yes it adds a bit of time to a job, but it means you don't end up with high spots or hollows in the think coat - which with light at the right, or wrong, angle can really be seen with a thin coat!


See I do listen when I have the training sessions........... LOL

some basecoats dry faster that others - read the data sheets - but a rule of thumb is as Ryan stated - 1day / mm thickness......
 
the mesh should be inthe top third of base coat rule base coat with serrated rule then spat the mesh in top third of surface
 
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