Ripples in plaster

Hi paul. I have a question on troweling up after I put
the second coat on, let it take for a bit then give it the first trowel it
begins to show ripples in the plaster and they never trowel out, even when its
on the final trowel they just never seem to come. There not noticable when
painted unless direct sunlight hits the wall. Would if you had any advice on
this?

Answer
The plaster tends to ripple if it is being applied too thick. Following the step below should help:

1. Make sure the plaster is not mixed up too thick - when you pull the whisk out it wants to have soft peaks of about 25mm or so in height.
2. If the plaster is thin, it may be a bit harder to control on your hawk but does ensure that a thin coat can be applied.
3. Make sure the plaster is not being applied too thick - 2mm is ideal.
4. Let the 1st coat firm up quite a bit and then flatten any ridges or ripples. If when you do this you are finding you are solving one problem and creating another then let it firm up more. It is ready when if you touch it with your fingers it is tacky but does not all come away on your fingers.
5. Wait until it has firmed up enough to remove the ripples in the 1st coat then they will not be transferred through to the 2nd.
6. Make sure the 2nd coat is the thinnest smear to cover the whole wall - 0.5 to 1mm thick. Mixing up a small amount of thin fresh plaster may enable this to happen more easily.
7. Apply firm pressure when troweling.

Paul

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skimming problems

When skimming old walls do I have to do a backing coat (bonding?) make that flat? Totally flat? What happens if it goes off before I have covered the whole wall? I have a big
problem is doing big areas. It’s gone off by the time I have finished
applying the first coat of finish. I have found that I get holes and ‘cats
faces?’ and shudder lines which are impossible to remove after a million
trowelling’s. Can I fill these holes and shudder lines with very thin layer
of 3rd coat of plaster?
Regards
Angie

Answer
Hi Angie
To summarise and help answer your questions:
An existing plastered wall can be skimmed over with 2 coats of multi-finish.
If there are any undulations or unevenness that are more than about 5mm it may be best to flatten these areas out with some bonding coat where needed.
Then apply PVA over the whole wall. If it is a large area 2 or 3 coats will seal the wall and make it less so porous so that it doesn't dry too quickly.
Then apply 1 coat of finsh plaster, quickly flatten before applying the 2nd coat (stage 3). To give you longer working time - mix up a fresh batch for the 2nd coat.
To avoid the shallow holes - apply more pressure and flatten your trowel slightly to ensure plaster is pushed along the whole length of your trowel and into these areas.
The judder marks can happen as a result of flicking the trowel off the wall - turn the trowel into the next section and pull away from the wall. If a trowel mark is left behind it will be smoothed out when completing the next section as shown on : http://www.diyplastering.co.uk/application.html.

Larger areas mean you have to just do what is needed as you have no time to 'play around' with just one areas - always view the wall as whole. If it cannot be done all in one go then there is some info regarding this at:http://www.diyplastering.co.uk/walls.html

Hope this all makes sense - let me know how it goes!

Paul

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Tiny cracks in finish coat

by Travis
(Nong Hong Thailand)

Hello. I am working on a house with lime plaster walls. The first two coats are up. It we are having a real hard time with many tiny cracks on the finish coat. We wet the wall and use a 1 to 1 sand to lime putty ratio but still cracks! What should we do?

Answer

The plaster needs compressing more with the float or trowel to compensate for the shrinkage that is taking place.

Paul

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Ceiling slight bulges or bumps only noticeable when painted

by David
(West mids)

Hi, Paul
I've done fair bit of plastering self taught and have achieved some great finishes but one thing I struggle on is ceilings for some reason it looks all great when done no blemishes or craters etc but when painted when the light casts across ceiling it show bumps only slightly where am I going wrong I lay the plaster on nicely just puzzled is it I'm not applying enough pressure on trowel ? any advice would be much appreciated thank you

Dave.

Answer
Hi Dave,
Could be a few different things:

As you say pressure on your trowel at all stages - but make sure you have the correct angle (the leading edge of the trowel will be 10-15mm away from the ceiling) This pushes the plaster flat rather than following any contours.

Make sure the plaster is not going on too thick - each coat should ideally be no more than 2-3mm. Any thicker than this and the plaster will be difficult to keep flat. Make sure the consistency of the plaster that you mix up is not too thick.

When you are applying the first coat make sure flatness is your priority.

When this 1st coat has firmed up a little then make sure you flatten all ridges out so that your 2nd coat doesn't have to be too thick to cover them and only needs to be a very thin skim of less than 1mm.

The longest trowel stroke you can manage will help to keep it flat.

Lights are not always a plasterer's best friend! Strip lights can be very unforgiving and always pay a bit more attention around these areas.

Paul

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Star cracks when plaster dried.

by Alan
(East Anglia)

I've watched the video and skimmed 4 walls, The results are not too bad for a beginner but, On the last wall near the ceiling the plaster has cracks in a star pattern. What could cause this.

Many thanks.

answer

Hi Alan

Most likely that the plaster may not have adhered properly to the background or excessive suction. Either way can be prevented next time by applying another coat of PVA.

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