Old buildings need to allow for moisture exchange, internally and externally. Damp problems can often be exacerbated, or at least influenced, by using the wrong paint. This can hold moisture in to a surface and prevent it from naturally evaporating. The consequences can be timber decay, beetle damage, damaged plaster/render and generally unsightly surface appearance.
At some stage, most homeowners face the dilemma of needing to remove modern paint but they can struggle to understand the options or whether any additional damage will be caused to the surface. The risk is that an aggressive approach could not only remove the paint but also remove part of the fragile surface underneath. This can be particularly damaging on historic timbers and it is irreparable when the damage has been done.
The use of aggressive techniques such as nitromors paint stripper, sand-blasting and a heat-gun with scrapers should not be used as they will most likely cause irreverisble damage. The use of cosmetic paint-on products which simple colour the timber rather than remove the paint does not help the objective either. These products may lead to the colour being acceptable, but they simply add further paint on the top which increases the lack of permeability of the timber to allow for natural moisture evaporation.
Whatever technique you might choose, always do a small sample test first in a less obvious and discreet location, just to see if it is going to work. Do not assume that the end result will be what you thought it might.
For the purposes of this demonstration, five techniques were used, side by side, to learn which option performed most appropriately and without causing any damage. The chosen options were..:
- benzyl alcohol paint thinners
- DOFF – superheated water, with and without water recovery
- Soda blasting – using bicarbonate of soda
The building is a Grade II* timber frame, part C15 and C16, which requires repairs and removal of inappropriate cement fillers. There is also some 1930’s internal timber work that requires paint removal. An application for Listed Building Consent will be submitted for the paint removal, prior to essential repairs being done, and the purpose of this experiment was to learn which option is most suited to this building. This evidence will be used for the justification as part of the Listed Building Consent application.
The test started by choosing a small area and then applying the poultice. We used Klingstrip, which is available from https://www.stripperspaintremovers.com
The poultice was applied quite thick, using a trowel, and was then covered in plastic. The length of time to leave the poultice to activate is entirely dependent on the specific circumstances, thickness and type of paint, weather, air temperature and, to some extent, to professional judgement. It could be anything from a few hours to overnight to a couple of days. In the case of this demonstration, we only had a relatively short period of time and the result showed that wasn’t long enough and it will need longer, or will require more than one attempt.
The result of this test sample was that the poultice did start to work and that no damage was caused to the timber work at all. Clearly it needed longer time though and will need to be done again.
While the poultice was activating, the adjacent section of timber was coated with the benzyl alcohol paint thinners. A generous amount was painted on and left and later washed off.
In this test, the paint thinners made no impact at all and did not work.
Next, the DOFF system was tried. This was better with the water recovery option as otherwise the water spray would have been very messy. The DOFF system uses super-heated water sprayed under pressure and as the water vaporises it can lift the paint at the same time. This was done in short bursts and with considerable care as we did not want to cause damage to the historic timber frame. In this test, the DOFF system clearly worked but it showed that at even the lowest pressure setting that the spray did start to eat into the oak and removed some of the softer timber in between the grain. As soon as we saw this, the test was stopped immediately. The DOFF system is not suitable for this particular use. However, it was tried on a small area of painted cement render and it did work perfectly there. So, this is a good example that one option will not work for every situation.
The next demonstration was for soda blasting. This uses bi-carbonate of soda which is directed under pressure and can be simply brushed off or washed off. In our experiment, the soda was effective and seemed to work better than the DOFF but it still showed some subtle loss of the historic timber. This is not appropriate so the test was stopped.
Dry-ice was tried next. The use of dry-ice is the complete opposite of the DOFF system. Dry-ice granules are ground up under pressure in the nozzle of the hand-held spray and then ‘fired’ on to the timber under pressure. As with the DOFF system, we could immediately see some evidence of loss of timber. The softer timber in between the grain started to disintegrate, so the experiment was stopped immediately. The experiment showed that, in this case, the dry-ice is totally unsuitable and that it has the potential to cause even more damage than the DOFF system.
Each of the spray options was incredibly fast. The sequence of photos shown above for the DOFF, soda-blasting and dry-ice was from only about 30 seconds of use in each case. These techniques are very quick and from a consumer point of view this might be a persuasive sales aspect. However, as we have shown, they have the potential to cause irreversible damage and on a whole wall the result would be very disappointing and probably disfiguring too. For this building they have all been shown to be unsuitable. The best option was shown to be the tried and tested poultice method. The demonstration showed that the poultice should be left longer to allow for more time to activate. This is valuable information to go forward with for the project. Of course, time is money. While the poultice does work best, in this case, it will also be the most expensive option in terms of time and the volume of the product required. There is also the environmental factor to be considered of the waste disposal of the product and the dissolved paint afterwards. Of course each of the options has an environmental impact it is simply that the spray options create substantial ‘dust’ particles that can be breathed in and will settle over the subsequent weeks after the work is done. None of the options are totally without an environmental impact.
With this new knowledge and information, we then moved inside and tried the same methods. On the arched-brace under the crown-post we only used tried the poultice and the benzyl alcohol paint thinners. The result showed that the benzyl alcohol paint thinners had no impact or success at all. The poultice did start to work but, as with outside, it would need to be left much longer to fully activate. When the plastic was removed, the poultice had started to work but more time is required.
On the 1930’s staircase, each of the options was tried. Here, we found that the dry-ice did work on the splat balusters quite successfully but that was not suitable for anything else. Again we found most success with the poultice. The DOFF system was not successful, nor was the soda-blasting – both causing some ingress into the grain. The benzyl paint thinners also work to some degree of success.
The result from this has been shown to be straightforward. Externally, none of the options that use a pressure spray – even on a very low pressure setting – were suitable. The poultice was the best option and showed no sign of any damage. The dry-ice was the most damaging option tried. The benzyl alcohol had no success at all. Perhaps on a different building the result might be different but on this building the poultice would be the choice to go with, even though it will end up being by far the most expensive and the most time-consuming.
Internally, the dry-ice did work successfully on the balustrade without any obvious sign of damage. However it was not successful on the other timber work. The most successful option is a combination of the poultice and the benzyl alcohol paint thinner.
What did we learn from this..?
The demonstration highlighted the importance for trying different options first as a test and that previous success does not automatically mean that it will be successful in all cases. Protection of the building and avoiding unnecessary damage must remain the prime importance and objective of whatever method is chosen. None of the methods have no environmental impact at all. All of the methods have a time and cost implication. The poultice is clearly a much more time-consuming method and will use a large volume of the product. It will thus be the most expensive. However, the result will be the most desired.