Hi there and thank you for your question.
Well, like mentioned in the first post you will achieve best results with the paint removed and aggregate exposed.
And on the side note I also know that not always possible to. Been there.
Can you use compound right over what you've right now depends on the couple factors;
First your patch job is going to last as long as the paint does.
This said if your paint is flaking and coming off you should get rid of it before patching.
Second make sure wall is thoroughly clean before you start with the compound. If dealing with glossy and smooth finishes rough it up with the coarse sand paper prior to application.
Remove as many high spots as you can- this will reduce amount of mudding.
And finally check the mortar before all of this.Simply tap on it with the hammer and listen for the hollow sound. Sometimes is easier to chip all of the mortar off that to mud over it.
Hope this helps and good luck with your project.
My question is, I have an interior wall that was once an exterior wall. It is rather rough morter over cinderblock, and then it has been painted with a horrendously ugly lilac latex paint. Can I use joint compound over the paint to smooth out the surface and then paint again? Or am I going to have to chip all the mortar off and start from scratch?
Answer to your question can be found here;
My situation is a bit different, we have a block home, and would like to smooth out our interior block surfaces. Last summer we insulated all of our exterior walls with XPS, and then sided it. Therefore, we would like the wall to breathe (whatever moisture may get into it) toward the interior. I have read that the quickwall (or surface bonding cement) product seals and waterproofs the wall, which is what we DONT want. Half of our exterior walls are bare, unpainted block, but the other half have been painted (the paint has been scraped and wire brushed and is well secured) What would be the best options for us? Firstly, I am confused about when someone refers to "plastering" a wall whether they are using plaster of paris, cement based product, or simple drywall spackle. So, We have access to a drywall texture sprayer/gun... For the half that is not painted, what if we filled all the joints with mortar (very thin layer) and then threw the texture on it and painted, would that work? For the part that is painted we would add the step of painting "plaster weld" on the walls first, then mortaring the joints and then spraying the texture on. Am I crazy for thinking this would work?
In order to be able to give you a real and sensible answer i would need to know little bit more about the surface you are going to work on.
Is this surface on the exterior or on the interior wall?
Having said that you have a similar situation I’m going to assume that you are talking about the interior wall surface.
To prepare the surface for the Plaster of Paris you would first need to apply a scratch coat-base coat.
In addition if plastering over an interior smooth surface such a concrete or cinder block wall you can also use a plaster bonder to improve adhesion of the base coat.
Once the base coat cures (not dries) you can apply a finish coat of plaster.
I do not recommend using a Plaster of Paris over a large surface, this product sets in 20-30 minutes and the working time is only about 10-15 minutes depending on the humidity levels.
For the large surface area I recommend using a slow setting finish plasters that set in 60-75 minutes allowing for extra time for troweling and use over conventional sanded basecoats.
Hope that helps and welcome to the community.
I have a simular situation I plan to use plaster of paris on my project. Is this as easy? And what steps should I prepare the surface.
Welcome to the community.
Plastering or resurfacing concrete walls takes time and patience.
First in order to successfully plaster a concrete or cinder block wall you need to have aggregate exposed in other words your walls need to be clean and any type of coating removed. The main reason for that is that portland cement needs exposed portland aggregate to grab to. Once your walls are clean and prepared for work you can go ahead and apply a bonding primer. Some contractors’ use bonding adhesive or bonding primer in every application, I use bonding primer only when plastering smooth concrete walls, in my opinion there is no need to apply this product if surface is rough and aggregate exposed.
I always tell my friends that in order to do something right you need to understand how it works first. And in order to understand plastering you need to imagine two different surfaces; smooth and rough. Trying to stick something that is similar to plaster consistency to smooth vertical surface is very hard, so you need to create something for that same plaster to grab to; you need something that will create a rough surface.
That “something “is a mixture of portland cement water and fine sand. The mixture consists of 1 part portland cement 1 part of sand and enough water to create a slush consistency. Before you decide to apply this mixture protect the surfaces around the work area with painters plastic, this is a messy job and this mixture will bond very well to concrete floors. Also portland cement is very abrasive and absorbs moisture so please wear safety glasses and gloves.
The technique I use to apply this mixture is with something that is called a “mortar holder” (see attached picture).This is a specialty tool and you are probably better of improvising with something similar that you have in your home. Start off your application standing about 3’to 4’ away from the surface area, grab “mixture” with mortar holder and gently splash against the wall. To learn this technique takes patience and alternative solution would be to use a brush; this is a slower application but cleaner.
Once the mixture sets, and it will take anywhere from 12 to 24 hours to set ,you can go ahead and start applying your first coat of surface bonding cement. For the fist coat you can use few different product ,you can use a regular mortar mix, mason mix, stucco first coat mix or surface bonding cement “Quikwall”. The Rapid Set Mortar mix it is a great product but is more intended for fast repairs rather than continuous plastering. I recommend using a “Quikwall” for this application, the main use of this product is for a dry-stack application but I find this product easy to work with and ideal for first coat.
This product will give you a longer working time; it is alkali resistant, fiberglass reinforced and surface bonding. To use this product you only need to add water but when it comes to mixing I recommend mixing this with a concrete paddle (see attached picture) to create a uniform consistency. When working on large wall areas you need to create “runners” every 4’, runners are narrow vertical sections of material that are plum and smoothed out. Once these sections are dry you can go ahead and fill between them and use a straight piece of 1x4 lumber or level to remove excess material.
Like I've said at the beginning of this post plastering takes time and patience so again you need to wait for the filled sections to dry. You second coat of surface bonding cement needs to be little thinner consistency, apply this second coat with a trowel and wait for about 30 minutes to dry. To smooth out second coat you need to have a brush and a bucket of water handy, using brush spread only enough water for bonding concrete to change color and using a rectangular piece of white polystyrene foam smooth the bonding cement out working in circular motion. And finally In order to achieve ideally smooth surface apply finish coat of Durabond.
Hope that helps and good luck with your project.