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Wood stripping by hand using chemical stripper and hand held sanders
Here I concentrate on the stripping and preparing of previously coated wood for restoration to it’s original clear finished or clear dye stained state. I will concentrate on methods used by wood restorers to preserve as much of the original patination of old timbers as possible.
The art of wood finishing is a complex and fascinating subject. Because of the breadth of information on this important subject it would be impossible to cover all topics in depth so I will constrain myself to what appears to be one of the main areas of interest to many period property owners, the stripping of paint and varnish from wood. My aim is give an impartial, professional and comprehensive overview. Be realistic. It is important to be realistic in what you can accomplish confidently and safely and what is best left to a skilled craftsman, stripping is almost always messy, arduous and offers ample opportunity to injure yourself.
If you feel confident then you are likely to do a decent job, if however you have nagging doubts it is all too easy for a project to go ‘pear shaped’ and cause more problems than it solves. Realising what you can safely accomplish is a skill in itself although sometimes the only way to find out is the hard way! Stripping and sanding are probably the most physically demanding and time consuming aspects of any wood restoration project, so plan your time carefully and as my Grandfather used to say, “Steady Eddie wins the race”.
There are two main ways of removing an applied finish from a wooden substrate: Chemical means, including applied solvents in thixotropic binder and caustic chemicals acids or (most commonly) alkalis and mechanical means, including rubbing, scraping and sanding. Heat can only really be used for the removal of paint and not varnish therefore is best reserved for exterior work where the wood is not left in its natural state. Within mechanical means you can scrape and sand by hand alone, by hand-held sanding machines or the more familiar walk around sanding machines. Some older properties with older more uneven floors or floors in which you wish to preserve as much of the original colour and three dimensional patination (the dips, the cupping, the rise and fall of individual boards much like the ripples in hand flattened sheet glass) can only be accomplished by hand sanding either by hand or more usually by large hand-held machines, which is the method I use in such circumstances.
In reality a combination of both mechanical and chemical methods are required when stripping wood because when you remove chemical stripper you will be using mechanical methods such as rubbing, scraping and digging. Remember sandpaper and wire wool are in themselves tools and in the wrong hands can do more damage than a power sander. It is also important to stress that you should not be put off using quality professional power tools per se, the reality is modern professional tools can sand far smoother than most humans and are surprisingly versatile. When used appropriately they can be of great assistance, although ultimately there is no substitute for the sensitivity and dexterity of the human hand, especially as old wood is very rarely flat. Listed below are all the main modern day methods used to remove applied finishes from wood. Some are more appropriate than others. The advantages and disadvantages of each method are shown plus a wood finishing professional’s perspective.
VERY IMPORTANT INFORMATION Please read before proceeding
As of 6 June 2012 it is now illegal, within the EU (which still applies! and will continue to apply after Brexit, European wide safety standards are unlikely to be downgraded in the UK seeing as our superseded BSI Kitemark is far more rigorous than the CE mark which has very low certification levels with notified body involvement) to sell DCM containing paint strippers for DIY use to the general public.
I am sure this product will continue to be manufactured for years to come until they develop a real viable alternative, if that is even possible, whether you will be able to purchase and use it in your home, is another matter.
Edit: Summer 2016. Please see http://www.hse.gov.uk/pubns/wis19.pdf of which below is the salient point.
“DCM evaporates easily producing high concentrations of vapour, particularly in confined spaces or where ventilation is inadequate.
DCM has been classified as a Category 3 carcinogen in the European Community. Under the Chemicals (Hazard Information and Packaging) (CHIP) Regulations it has the risk phrase R40 ‘Possible risk of irreversible effects’.
Note: Category 3 substances under the CHIP Regulations are those which give cause for concern, owing to possible carcinogenic effects, but in respect of which the information available is not adequate for making a satisfactory assessment.”
Dichloromethane (DCM) Restriction
A new ban on some supply and use of paint strippers containing the hazardous substance ‘dichloromethane’ (DCM, and also known as methylene chloride) is coming into force. For the purposes of this ban, the term ‘paint stripper’ is taken to mean DCM (or mixtures containing it) intended for stripping paint, varnish or lacquer. Pure DCM (or mixtures containing it) sold and used for other purposes (e.g. degreasing) aren’t banned and can continue to be sold and used (although not for stripping paint).
The new ban makes a distinction between three types of use:
‘Industrial’ use of paint strippers in ‘industrial installations’ (i.e. facilities where paint stripping takes place) – this is allowed to continue as long as certain safe working practices are followed.
‘Professional’ use by workers where this takes place away from an industrial installation. This will be banned, but UK can choose to allow continued safe use by specifically trained professionals (which it has, although there is no regulation or testing of professionals to ensure safe practice and no enforcement of guidelines and so in reality ‘professionals’ denote anyone who can get their hands on the material)
‘Consumer’ use by the general public, such as DIY. Supply to consumers is banned (all paint stripper you buy from the DIY market on the high street is likely to be quite or very ineffective as it will contain no DCM, even though some may still be solvent based)
In reality, for responsible professionals like myself who have used respirators, allowed adequate ventilation and employ the use of portable fume extractors for many years it may be the case that responsible use in specific situations may still be possible for years to come. Professional certification for accredited professionals would seem to be a logical and safe route out of the grey area but for now anyone can buy DCM based strippers with a little investigation on the internet.
Having spoken to a few people in the industry sales of professional versions of the product have curiously gone up around 1000%. Hmmm. You work it out. Stripping work hasn’t suddenly gone up that much if at all, so the conclusion is, if you are clever you can, at time of writing this article, still purchase this if you do your homework, just not from B&Q anymore. If you do, perchance get your builder for example to ring up and order it from Mylands, Jenkins or Morrells just be a little sensible. Ventilate. Wear gloves. Goggles. Organic vapour respirator. Do not bathe the children or family pets in it. And please don’t go drinking it or anything and die and get the actual manufacturing of it stopped as then we would really be in trouble.
Use in a well ventilated area and wear a suitable respirator rated EN141 for organic vapours (always check with the supplier as safety regulations and standards change all the time)
You can still buy and use the trusty ‘Nitromors’ from the DIY sheds but may find it doesn’t work half as well as it used to, probably due to the fact that it doesn’t in fact contain any ‘Nitromors’ anymore ie no DCM. Nitromors ‘light’. I’m not a fan of either decaf or alcohol free drinks. Either give me full strength or nothing at all thanks.
I am afraid if you cannot obtain a DCM based stripper then you will have to use whatever you can get. I cannot comment widely on how to adjust your stripping technique to use the new strippers that are being sold as I have little experience of using them, only really using a handful of products to test them out, by comparison they were all fairly poor. And when I say ‘poor’ I actually mean pretty bad.
I try very hard to make my articles and advice relevant and accurate and I only rely on my direct real world day to day personal experience of many months or years of a particular material, product or method. Instead of blithely repeating a combined summary of manufacturer’s instructions, like many ‘expert’ articles. I can not and will not advise on areas I feel I do not have enough experience in. At present no one can say they have years of experience using these new products as they have just only recently become widely available.
I would suspect you can still achieve similar results on the easier stripping finishes but that it will take much, much longer as, at present non DCM strippers and the Bio-based strippers which use water as a solvent are much weaker. They are also more likely to potentially damage veneered work (for example many plywood veneered oak panels popular from the early 1900’s in many houses especially for staircases) and lead to iron staining especially on oak due to the reaction of water, iron from the steel wire wool and tannins in the wood releasing tannic acid. Whilst soda stripping, using hot water has been around for over a hundred years the hot soda is washed off quickly, modern strippers are designed for ease of use and normally contain a thixotropic agent for clinging to vertical surfaces and an evaporation retardant to keep the surface wetted for long enough for the stripping agent to work, in affect this means that the veneered panel may be wetted for an extended period, this is what can cause potential swelling and loss of adhesion. I would not walk into the same room as a period veneered antique with the new water-based strippers, honestly it’s not worth the risk, call a professional French polisher. He may not just save your life, but he may save your furniture.
Steel wool and wire brushes need to be used for stripping much of the time therefore however good the stripper is water is going to react and leave marks. If you are using this new water-based stripper be aware of this simple chemistry and watch carefully for iron stains on oak, try and clean off any wire wool fragments if you can and if possible use nylon or copper based coarse mesh scouring pads and strong nylon floor and washing up brushes.
For high quality wood finishing and restoration, to remove modern finishes (lacquers and varnishes produced since the 1950’s) DCM based strippers are still really the only option, which is why they were developed in the 1960’s. Before that old varnishes and French polish etc (which become brittle when they perish and so flake off easier, unlike modern finishes that remain softer and thus are harder to scrape) were mostly removed by scraping first with sharpenable cabinet type scrapers, then the application of an alkaline soda solution (less caustic than modern type caustic strippers) was applied by a skilled operative, this was applied hot and cleaned off quickly so the wood was not wetted for an extended period.
Oil and wax based finishes were removed with turpentine and shellac sometimes by meths or pure alcohol before that. These solvents can still be used on the appropriate finishes if the person can correctly identify the applied finish and has the extra skills and patience required to use the techniques involved.
At the moment the situation is in flux and if you cannot procure the ‘proper stuff’ you will just have to experiment. In general you should follow the manufacturers instructions although common sense and a little wisdom from a professional should still be followed ie. apply stripper generously, do not let it dry out, use lots of wire wool and cloths, apply a final coat after you think it is clean and restrip to make sure. Wash off and neutralise effectively. With ‘end user’ based products (non professional) manufacturers will often over hype their products (modern marketing, ugh) and this has to be continued to a certain extent on the tin via the instructions or people will just smell a rat, so in general be prepared for the job to take slightly longer and for you to apply slightly more coats of stripper, slightly thicker, for slightly longer than the instructions state. End user products typically found in the DIY stores may, more or less, do what they ‘say on the tin’ but frequently not in the way and using the methods they say. A combination of prior knowledge, common sense and often a little experimentation is required for best results in conjunction with the manufacturers instructions. Professional products do not normally come with instructions, if they do they are likely to be far more accurate, if they don’t you can try asking the supplier or manufacturer directly for advice or for a ‘technical data sheet’ which often contains site / application instructions.
Stripping via solvent or water-based strippers is still preferable to sanding alone. If I am forced to use them and develop revised techniques in the future (in the mean time most of the themes and techniques employed for DCM type strippers will be applicable to newer non-DCM products.
Chemical stripping Solvent (DCM) based
Gives the best possible result, quicker at removing finishes than sanding alone, can be the most gentle on the wood. Will remove all finishes eventually, even modern ones. Very gentle, will not in itself damage the wood, the only stripper used in antique restoration for example. No discolouration. Nothing gets the wood as clean, even in the grain.
Chemical strippers are hazardous, care must be taken at all times and respirators may need to be worn. May prove more expensive to use than caustic strippers as you may use a greater volume of product. Can cause burns, gives off strong fumes, good ventilation required. Can be messy. Harder work to remove heavy paint build up than caustic strippers.
There are two basic forms of chemical stripper: Caustic (alkaline, sodium or potassium hydroxide) normally thixotropic (viscous so they stick to vertical surfaces) paste and Solvent based (usually methylene chloride based) non-caustic, may also be thixotropic.
You will need
Dust sheets; thick polyethylene or cotton plus newspaper for protection. Masking tape. Sharp cabinet scraper or modified decorators scraper (see SUMMARY) Stanley 1992 heavy-duty knife blades or equivalent. Coarse, (number 5 or 6 Trollul) (oak, ash, pine) or number 4 or 5 grade (fruit woods, maple, cherry etc) wire wool. Lint-free rags for washing, wiping and neutralising. Stripping chemical. Suitable container for decanting stripper into. Brush and/or spatula for applying stripper. Brass wire brushes and/or nylon brushes for cleaning. Newspaper/small cardboard box/bin bags for disposing of stripped finish safely. Gloves, goggles, overalls/apron dust mask/respirator as appropriate. Bucket of clean water. Methylated spirits/white spirits/acetic acid as appropriate for neutralising.
1. Always read the label and follow the safety instructions.
2. If you have poor ventilation or are stripping large areas consider a respirator with a filter for organic vapours (EN. 141)
3. Mask up adjoining areas and sheet up with thick polythene and/or cotton dust sheets. Keep a rag that has been dampened in white spirits handy to remove any spills or splatters.
4. Pour some stripper into a metal paint kettle or large glass jar (beware it will melt some plastic jars) apply to surface with a grass brush or an old paintbrush.
5. Leave for five minutes. The surface should start to bubble. You may need to apply another two, three or four coats, work it in with your brush, be generous, the more stripper you use the better.
6. Do not let the stripper dry out. When the finish starts to bubble and just before it starts to dry remove residue with a sharp cabinet scraper.
7. Apply another coat of stripper, let it soak in for five minutes then remove with number 4 or number 5 grade wire wool, you can work quite hard with the wool, always with the grain direction.
8. You should start to see the wood get completely clean; it should feel bare and not waxy.
9. You may need to repeat this process several times. Neutralise with methylated spirits (my choice) or white spirits (the manufacturers choice) by rubbing over with a rag wetted with the respective solvent.
10. If using the modern DIY water-based strippers then you should restrict the use of metal scrapers, steel wire brushes and instead use copper-nylon or nylon scourers, nylon brushes, brass wire brushes and plastic scrapers to reduce the incidence of black staining caused by the reaction of iron and water, especially on woods like oak whose high tannin content can exacerbate this problem by the production of tannic acid during the stripping process.
When specialist wood finishers talk about stripping, this is what they mean. For the professional 99% of the time this is the only way, it is hard work but gives a far superior finish and if done with care will not damage the wood.
Chemical stripping Caustic based
Will remove most finishes. Especially good on thick paint build up. Less fumes than solvent based. Cheaper. Quicker.
The main ingredient, a very powerful alkaline chemical normally sodium or potassium hydroxide (as found in most oven cleaners) stains the wood by reacting with natural wood acids in the same way as fuming. It also attacks all living tissues slowly breaking down wood at a molecular level so can cause cracking and peeling of surface on damaged and old worm eaten timbers such as beams, especially if left in contact with the bare wood for extended periods. Beware, companies have to advertise such strippers as gentle on the wood or some people would not buy them, ask for a technical or COSHH data sheet (they have to supply them on demand by law) read the ingredients and make up your own mind. Can cause severe burns if not used properly.
1. Always read the label and follow the safety instructions.
2. Sheet up with dust sheets and polythene, mask adjoining areas and keep a damp cloth handy to remove splatters and drips.
3. Apply stripper as per manufacturers instructions, they are made in differing strengths but as a rule work best overnight on deep paint build ups, covering up with grease proof paper or polythene will stop it drying out and keep the stripper active for longer, applying more water can reactivate old stripper.
4. Remove with cabinet scraper, large chunks should peel away. May need to reapply.
5. Better method is to apply solvent stripper as advised above to remove last residue along with wire wool.
6. Remember to neutralise the remaining alkali with acetic acid (or white vinegar) really give it a good scrub.
7. After a few days a white powder may form, this salt is the reaction by product of neutralisation and can be removed by washing with clean water or by gentle sanding.
French polishers and wood finishers rarely, if ever, use this method. Any stripper in direct contact with the wood will cause staining and may actually damage the surface. Depending on the exposure time pine will go brown then dark brown; mahogany and oak will go dark brown to black. Even using powerful modern bleaches (which will further damage the wood) you may not be able to remove all of the staining and anyway the original patination will have been lost. I would therefore not recommend this stripper on wood that is to be left natural or where the original patination and colour is to be left intact, I would never use it on very old (over 200 years) worm damaged oak beams. On the other hand it is superior to solvent strippers at removing thick paint layers on relatively new and undamaged (e.g. 100 year old pine) artifacts where the wood is to be repainted or stained dark as the discolouration effect will not be so apparent. Also ideal for removing heavy paint build up on old floors before machine sanding as the aggressive floor machines should remove any staining.
All the solvent (DCM) strippers do much the same job. Good ones include Paramose, Parimova (from Jenkins) and Perfecta Stripper (from Mylands). The new water-based strippers from Nitromors et al for sale to the general public at the time of writing are quite inefficient and will require a lot of extra effort to remove light paint and shellac / wax finishes. Currently the water-based strippers are not able to effectively remove modern water-based lacquers and two part solvent finishes like AC lacquer or moisture cured polyurethane, if you have to remove one of these tough chemical resistant modern finishes and you cannot (or wish not to) procure a solvent-based DCM stripper you are best advised to contact a French polisher for assistance.
Chemical Stripping Summary
Caustic strippers are good at removing heavy paint build-ups and for complex mouldings but may stain the wood and damage old friable timber surfaces. Best reserved for stripping pine doors etc that are to be stained dark or painted (it actually works best on plaster, stone and metal which are better able to withstand its caustic nature)
Solvent (DCM) strippers, if you can manage to source them are more expensive and messy to use and worse on heavy paint but will not damage or stain the wood and generally give a cleaner, finer finish especially if going for the natural look. Along with scraping and sanding the only safe method to use on old oak and damaged beams. If in doubt, buy a limited quantity of different strippers and test them on small inconspicuous areas to see which you best prefer. A final sand either by hand or machine or by both will remove the final vestiges of residue. Use brass and heavy nylon brushes in corners and mouldings, stiff denture tooth brushes and heavy duty Stanley 1992 razor blades are handy for removing build up from awkward areas. Do not use shave hooks, they will dig into the wood. If you cannot get a quality cabinet scraper (which is really worth seeking out) then round off the corners of a decorators stripping knife with a file to avoid digs and scratches.
I am not condoning or explicitly suggesting you should try and obtain these ‘restricted’ solvent strippers. I just supply the facts that they work and the replacement water-based strippers to a large extent do not. I am simply pointing out that if you try you can, at the time of writing, still practically obtain them. If in doubt then please seek expert help and advice via the assistance of a trained French polisher, the legislation was enacted precisely to restrict their use to trained professionals who are better acquainted with them and are able to take appropriate measures to ensure safe usage. Their restriction is, in my opinion a perfectly sensible and reasonable idea as they are powerful and unpleasant products and if used incorrectly, harmful to your health. If in doubt always seek advice.
Very cheap, quick, very efficient at removing all finishes.
Very messy, unfortunately also very efficient at removing the underlying wood, destroying patination and damaging worm eaten areas. Can lead timber resembling driftwood. Likely to require listed building planning consent if used to remove surface finishes in a listed property.
Abrasive particle bombardment accelerated by high air pressures and volumes. Contact sandblasting company, or hire equipment.
Personally I think there should be a law against its use because it completely destroys fragile timbers, patination, colour and form and has no place in wood finishing.
Water / Sand (WSB) Blasting
More expensive, otherwise as above. Slightly gentler, less messy.
Still damages fragile and worm eaten areas leading to damaged patination.
Abrasive particle in high power water/air vortex. Same principle as sand blasting but much more efficient therefore requires lower volumes of air and abrasive thus reducing damage. Contact specialist company.
Fine for sound roof timbers in large barn conversions where surface finish is not critical and other methods not economically viable, also economically advisable for large items like boats where surface will be repainted heavily. Not recommended for fine finishes or where patination and / or historical markings are important. Will require further sanding afterwards to obtain smooth finish.
Power sanding small hand held sander
Low skill level required to achieve reasonable finish, can be fairly clean.
Can be very messy if no dust extraction available, can damage patination if not done with care, can take a lot longer than chemical stripping on heavily soiled areas due to abrasive clogging up.
You will need
Sander (possibly extension cable) and appropriate abrasives. Sharp cabinet scraper, damp rags or tack rags for wiping down. Dusting brush. Dust sheets and masking tape for dust traps. Dust mask (essential if you are not using a dust extractor) goggles, kneepads, earplugs or ear defenders (optional). Vacuum cleaner and/or dust extractor.
1. Start off with coarse grit paper (as low as 36 grit on floors, 60 grit on everything else) and work your way through the grades up to the finer grits finishing with 120 for floors (finer may impair adhesion of floor finishes) or finer 240 for other woodwork.
2. Dust down, wipe and vacuum in between, a dust extractor prolongs the abrasive life and makes the job far less messy (you can connect your normal vacuum extension tube with masking tape but you may need to clean the filter regularly.
3. Finish by hand sanding with 240 or 320 grit paper on beams and doors.
4. For uneven floors with deep scratches or reclaimed wood with planing/sawing marks it may be quicker to use a sharp cabinet scraper to scrape out some of the damage before sanding.
5. Get the right tools for the job, belt sander for floors, a good orbital or random orbital, cheap machines are next to no use and can be slower and more tiring than by hand alone.
6. Use sanders in combination i.e. Belt, roughing orbital, random orbital getting a progressively finer finish. The idea is to clean the wood with the first pass using the coarsest grit, the subsequent passes are purely designed to remove the scratches from the previous pass until you cannot see or feel the scratches.
7. Finishing with 400 grit on a random orbital should feel like silk.
Power sanding with small portable sanding machines alone is not always the smartest method to remove applied finishes, it is okay for nearly bare, discoloured or rough timber or timber that has already had most of the finish removed by other means or for stained and thin film finishes or for finishes that are old and perished and therefore brittle. It is probably the slowest of all methods for stripping multiple paint layers and other thick film finishes like heavy oil, wax finish or varnish build up as the friction of the moving abrasive will just heat up, melt the finish and clog up the abrasive quickly and repeatedly, for these thicker coatings either a solvent based DCM or poultice based caustic type stripper would prove more efficient at removing the bulk of the coating.
Subsequent power sanding after the stripper has been neutralised and allowed to fully dry will help remove any residue, even up any residual colour differences from penetrative dye stains and remove any mechanical marks from the stripping process ie from scrapers and / or wire wool. A professional random orbital sander coupled with a good dust extractor provides probably the cleanest stripping method of all and done with care can give the cleanest and most pleasing result whilst preserving much of the original patination.