Thread: Caustic Soda used as paint stripper?

Not used it myself but a quick Google found that there could be issues which may not suit what you want.

http://www.woodweb.com/knowledge_bas...ng_Fiasco.html

Originally Posted by Bob38S

Not used it myself but a quick Google found that there could be issues which may not suit what you want.

http://www.woodweb.com/knowledge_bas...ng_Fiasco.html

Not clear whether that one is user error or product. Helpful link though,
cheers.

You are welcome, enjoy the forum.

We had Oregon doors in our old house that were covered with many layers of paint over a very old sticky varnish - same as you described on your cabinet.
We tried to strip them ourselves and we could not get all the paint out of the cracks so we sent them off to be dipped in caustic soda.
We made a big deal to the stripper that we wanted every last bit of paint removed

When we got them back they were clean as a whistle but had gone a dull grey colour (weathered look) as the caustic had leached the colour out of the wood.
The stripper had probably over leached them to remove all the paint.

So we had to stain them back and this was problematic because different sections of wood took up the stain differently. In the end we settled for a jarrah type colour because the wood seemed to take up this stain better than others.

The other thing we noticed was that a couple of the doors had ply panels which delaminated after the stripping process.
The caustic will also eat any fixings like nails or screws so watch out for that.

Originally Posted by BobL

We had Oregon doors in our old house that were covered with many layers of paint over a very old sticky varnish - same as you described on your cabinet.
We tried to strip them ourselves and we could not get all the paint out of the cracks so we sent them off to be dipped in caustic soda.
We made a big deal to the stripper that we wanted every last bit of paint removed

When we got them back they were clean as a whistle but had gone a dull grey colour (weathered look) as the caustic had leached the colour out of the wood.
The stripper had probably over leached them to remove all the paint.

So we had to stain them back and this was problematic because different sections of wood took up the stain differently. In the end we settled for a jarrah type colour because the wood seemed to take up this stain better than others.

The other thing we noticed was that a couple of the doors had ply panels which delaminated after the stripping process.
The caustic will also eat any fixings like nails or screws so watch out for that.

Very similar experience to the link above, you guys got out of it better though. I always try to steer clear of the industrial guys, as good as some are, I find you dont get the type of attention to detail that we as restorers, furniture makers and renovators put in. Thanks for the reply, Dave

Wood bleach (the oxalic acid kind) can be used to lighten some types of stains.

http://www.antiquerestorers.com/Arti...ood_bleach.htm

Just to add some thoughts to all of this on the use of strippers and sanding based on my experience gained over 20 + years of restoring antiques and antique joinery.

First off, paint stripper (eg. selleys etc) works perfectly well when combined with coarse grade steel wool. My normal approach is to heat gun off the main layers of paint, carefully not to burn the wood below and then use paint stripper to cleanup the residual. In using paint stripper and before applying a new finish, be it shellac or whatever, always give the finished timber surface a good clean to neutralize any residual stripper. I use warm water and soap with steel wool and dry off. Oxalic acid or even metho can also be used.

Next, in regards to caustic (solution or a paste) yes this can be highly effective if doing by hand but it can darken the timber (eg pines like Baltic etc), but should remove all traces of paint or previous stains used. So perhaps test trial first. Commercial dipping is effective in removing paint, but as noted it will bleach the timber, especially pines, and never use with cedar. It splits cedar badly and can badly grey the wood. It also affects old glues, but effectively cleans up any metal work, eg. hinges etc

If commercially dipped, you will need to sand as it affects the grain and will make the surface furry. Basically you will need to sand the timber.

If handstripping using paint strippers and/or even caustic, from my experience you still generally will need to sand, using various grades, 120, 240, 400 and beyond if you wish. If you are careful you won't loose the patina through sanding. This concern IMHO is overstated. If you wish hop over onto the restoration threads to have a look at projects done by myself or Thumbthumper to see what I mean.

Originally Posted by 1MansTrash

G'day all,
I was told that caustic soda can be used as a "last resort" paint stripper. I am restoring a cabinet that is 100 years old at least, and had quite a few layers of lead/linseed oil based paint on it. Because of the beautiful petina that has built up, I dont want to sand it at all, so have been using paint stripper, metho and steel wool to remove the paint. There is a horrible stain that has been left in the grain (maybe 2mm) that i was told to use caustic soda as a paste to remove. Has anyone done this before or heard of this method? Any doubts?
Thanks heaps!

Caustic works well on the right timber and poorly on the wrong ones. Suggest you try a small patch first to see if you get any adverse reactions.
Has anyone suggested using a heat gun to remove the bulk of it first? On a timber that is sensitive to caustic you can use smaller amounts of commercial paint stripper.

On the wrong timber caustic can be disastrous as mentioned above cedar and pine don't react well, oak definitely doesn't react well and most ply wood will de-laminate and turn into a wavy, cracked up mess. Caustic can ruin glue joints and often deform timber if not used carefully. It also loves human skin.

If you are having a problem with paint stripper not removing the paint from mouldings, carvings, turned sections and some open grained timbers try applying it and letting it soften the paint then wash it down with warm water containing a heap of pure soap like Velvet laundry soap. It may hiss and bubble a bit but it should clean up pretty well. You will still need to give the entire thing a good wash down with metho and lots of clean rag and then in almost all instances sand to remove the last of the paint.

Washing down with metho and course steel wool to remove paint after stripping is also good but the steel wool can react with some timbers that are tannin rich like cedar, oak, walnut, mahogany and blackwood to name but a few. Also be careful where you leave the steel wool as it will oxidise and rust really quickly when used with metho and this can cause really bad stains if left in the wrong place. It is also a major fire hazard and extremely hard to extinguish unless immersed in water.

In a 100 year old piece you might find more problems with the grain filler than the paint itself especially if it's cedar, oak or another open grained timber.

Hope this is of some help or at least some interest.

Cheers - Neil

In case you decide to use some caustic, the recipe I've always used calls for a small amount of flour mixed with water to a runny consistency with the caustic flakes added later and stirred until the mix thickens evenly. Use a distemper paint brush and gloves to apply!!

Originally Posted by ubeaut

On the wrong timber caustic can be disastrous as mentioned above cedar and pine don't react well, oak definitely doesn't react well and most ply wood will de-laminate and turn into a wavy, cracked up mess. Caustic can ruin glue joints and often deform timber if not used carefully. It also loves human skin.

If you are having a problem with paint stripper not removing the paint from mouldings, carvings, turned sections and some open grained timbers try applying it and letting it soften the paint then wash it down with warm water containing a heap of pure soap like Velvet laundry soap. It may hiss and bubble a bit but it should clean up pretty well. You will still need to give the entire thing a good wash down with metho and lots of clean rag and then in almost all instances sand to remove the last of the paint.

Washing down with metho and course steel wool to remove paint after stripping is also good but the steel wool can react with some timbers that are tannin rich like cedar, oak, walnut, mahogany and blackwood to name but a few. Also be careful where you leave the steel wool as it will oxidise and rust really quickly when used with metho and this can cause really bad stains if left in the wrong place. It is also a major fire hazard and extremely hard to extinguish unless immersed in water.

In a 100 year old piece you might find more problems with the grain filler than the paint itself especially if it's cedar, oak or another open grained timber.

Hope this is of some help or at least some interest.

Cheers - Neil

Thanks Neil, for making these comments, for yes I totally agree with your views regarding the use of caustic. Thanks also re the tip in using velvet soap. Another element to add to my methods for cleaning and polishing old wood. My previous observations and experience have shown me exactly what you are talking of. I have a Baltic and Cedar door (1/2 glazed) and it was dipped (not by me) and the cedar panels and mouldings were terribly damaged. It took a lot of work to sort that out.

I am not clear on what strength solutions that commercial dippers use, though understand it is a caustic based solution. With Baltic pine it does seem to be very effective in removing paint but as I noted it does bleach the timber badly, hence the need thereafter to sand and apply stains when re-finishing with shellac. Unlike when one paint strips by hand, the need to add stains is not necessary and the colour of the timber being so much richer.

I do accept that dipping though not actually cheap, does save time and hard work, as well as exposure to fumes when heat gunning or paint stripping by hand.

In terms of using steel wool, either when stripping or cleaning up afterwards, I appreciate the risk of residual fibres becoming engrained and thereafter rusting. It is for this reason that I also sand. I appreciate some people have concern over the risk of sanding and/or removing patina, but then again, patina to me is about the bumps, scratches, marks etc, and as a rule unless you plane or hard sand a surface, in my experience this shouldn't really be a risk in loosing these characteristics.

To create a fine and lustrous surface when applying a finish in truth will require you to sand and/or use 0000 superfine steel wool. If going for the ultrafine finish of French polish, some people even go to the point of finishing off with 2000 grade wet and dry. It is not what I do, but I understand the method and results.

I used caustic soda once on a 100 year old fireplace carved panel. Not sure what the timber was, but suspected oak.

The timber came out all fuzzy, fibrous and unusable.

I would be hard pressed to use it again.

Originally Posted by cava

I used caustic soda once on a 100 year old fireplace carved panel. Not sure what the timber was, but suspected oak.

The timber came out all fuzzy, fibrous and unusable.

I would be hard pressed to use it again.

Always test a small piece first!

OH..and do ya selves a favour...buy Neil' book..."A Polishers handbook".....all this is covered in there...you will bless the day.

Available direct from our benevolent dictator or most good woodworking suppliers.

someone will put a link here

cheers